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melchiro
Silver CB900F
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Joined: Aug 10, 2003
Posts: 1511
Location: Mill Creek, WA.

PostPosted: Mon Oct 14, 2013 4:35 am Reply with quote Back to top

Oh boy... Shocked .. This is what I did.... 1980 CB750-F with 900 cams and a Supertrapp 4-1 racing exhaust..

I bought these pods.

Image

Image

You MUST VERIFY that the "bump stop" inside, does NOT block off the carb inlet venting. If so, you must notch out or remove a portion of the stop. With my pods, the stops are 1/4" away from the edge of the carbs, so I left them alone..

Somewhere I read that Keihin jets are metric sizes, meaning that 110 jet are 1.10mm hole size. So I purchased a set of metric hobby drill bits, so that I could drill out the Primary & Secondary jets. I knew that I would have a bit of trial & error. Drill the jets, install & test ride.. Below pic..

Image

In my case, I was happy with size 80 Primary and size 120 Secondary, with the mixture screws at 2-1/2 turns out. It ran great.

And yes, the slides did open up.. I strapped my mini cam to verify.. Click the link below.. Pretty cool. ! Very Happy

Mel's Carb Video Link


Link


If you have pods or velocity stacks on now and did not do the "RSC CARB MODIFY", and your bike runs great, what is your jetting? Share your info and post it here..

.

_________________
1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project

Last edited by melchiro on Fri Nov 01, 2013 12:10 am; edited 2 times in total 
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JJam
Red CB1100F
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Joined: Nov 08, 2009
Posts: 3847
Location: Sandy OR

PostPosted: Mon Oct 14, 2013 4:44 am Reply with quote Back to top

Well the video takes too long to down load with the shitty internet that I have but I take your word for it.

I have used 900 slide springs in a set of 750 carbs to help the slides open faster. The 900 has the shortest and weakest springs of the 3 sizes of bikes. I don't remember the jetting as that was a long time ago but I did use the Dynajet stage 3 set up and K&N pods that didn't have the lip.

Thats all I know.

Peace, Jim
 
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Shawn_Mc
CB1100F
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Joined: Jul 30, 2012
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PostPosted: Mon Oct 14, 2013 5:31 am Reply with quote Back to top

Well, the slides seemed like they were pinned quite nicely to the top of the carbs and it didnt seem to miss at all. Nice job.

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Hondamax
Silver CB900F
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Joined: Feb 02, 2006
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PostPosted: Mon Oct 14, 2013 6:55 am Reply with quote Back to top

Smooth operation, no stuttering, swift movement ... sorted!

Regards,

Max

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1979 900Fz (from new) - NC30 Single-sided Swingarm, CBR1000F Forks, Tokico 4-Pot Callipers, Hindle 4:1, 985cc, RamAir Filters
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melchiro
Silver CB900F
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Joined: Aug 10, 2003
Posts: 1511
Location: Mill Creek, WA.

PostPosted: Tue Oct 15, 2013 3:02 pm Reply with quote Back to top

I guess some people could not get into my Photobucket, so I uploaded the video to YouTube.. Enjoy.

YouTube Video Link

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1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project 
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Jebbysan
Red CB1100F
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Joined: Dec 08, 2007
Posts: 7126
Location: New Braunfels,Texas

PostPosted: Thu Oct 31, 2013 9:40 pm Reply with quote Back to top

I don't know how I missed this but you rule Mel....always creative.....

My CBX uses 80/120 jetting as well with pods.....this may seem irrelevent until you realize that a CBX is
really based on a 750....and is a 175cc per cylinder motor.....
It pulls with zero hesitation as well....

Jebby

_________________
Ass, Grass or Gas....no one rides for free....
1979 CBX
1972 Corvette Stingray Coupe 406/4spd
1982 Z/28
2011 Silverado Crew Cab


"I don't do T and A...because I don't have much of either" Tea Leoni 
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melchiro
Silver CB900F
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Joined: Aug 10, 2003
Posts: 1511
Location: Mill Creek, WA.

PostPosted: Fri Nov 01, 2013 12:47 am Reply with quote Back to top

Yeah, I figured we were lacking on good info for Pod jetting for our stock carbs.. If you type "Pods" or "Jetting" in the SEARCH, you get a crap ton of posts. Most of them don't state what the jet sizes are and it would take hours of reading to find any good solid info. Though some posts are actually entertaining to read, bickering and cussing and name calling in a few of them.. Entertaining indeed!
So that's why I thought we could post our jet sizes here.. I think stating what modifications,if any, would be beneficial to.

If you have PODS and your bike runs good, tell us your jets..

_________________
1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project 
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JJam
Red CB1100F
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Joined: Nov 08, 2009
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PostPosted: Fri Nov 01, 2013 4:48 am Reply with quote Back to top

That was AWESOME Mel!! It would probably even open faster with the pod on giving it a bit more vacuum? Did you drill the slide holes also?

peace, Jim
 
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melchiro
Silver CB900F
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Joined: Aug 10, 2003
Posts: 1511
Location: Mill Creek, WA.

PostPosted: Fri Nov 01, 2013 9:59 pm Reply with quote Back to top

Hey Jim, no I did not drill out the slide holes.. These 750F carbs are as stock from honda, except my jet changes.. As for more vacuum with the pods on? I don't know..

_________________
1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project 
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genesound
Red CB1100F
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Joined: Feb 20, 2006
Posts: 11796
Location: Studio City, California

PostPosted: Fri Nov 01, 2013 11:34 pm Reply with quote Back to top

Yep, those look to be working just right! They seem to snap up for quick blips about as quickly as necessary, I can't see any faster actually being much more benefit. Is your crank lightened?

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melchiro
Silver CB900F
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Joined: Aug 10, 2003
Posts: 1511
Location: Mill Creek, WA.

PostPosted: Fri Nov 01, 2013 11:59 pm Reply with quote Back to top

No mods to the crank.. It's a CB750SC motor with 900 cams & a Supertrapp exhaust. My "Fixxer Upper" project bike.. Really, there is nothing fancy.

Image

_________________
1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project 
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Jebbysan
Red CB1100F
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Joined: Dec 08, 2007
Posts: 7126
Location: New Braunfels,Texas

PostPosted: Sat Nov 02, 2013 12:07 am Reply with quote Back to top

The more I think about the airbox....the more I think it was an air resonance plenum.....it could not induce a vacuum as that would be counter intuitive....I feel it had a "ram" effect......
When you remove the box....you have to jet up....as the carbs will lose signal due to not having a "third order resonance" similar to adjusting the length of stacks on a Hilborn injection unit for a V-8....
I also wholeheartedly believe that degreeing the intake cam to open sooner improves carb signal.....

Maybe we can dispell the myth forever.....maybe not......
Just my two cents and please comment on my thinking if you like!

Peace,
Jebby

_________________
Ass, Grass or Gas....no one rides for free....
1979 CBX
1972 Corvette Stingray Coupe 406/4spd
1982 Z/28
2011 Silverado Crew Cab


"I don't do T and A...because I don't have much of either" Tea Leoni 
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DrOlds
Silver CB900F
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Joined: Feb 23, 2008
Posts: 1237
Location: Watertown NY USA

PostPosted: Fri Nov 08, 2013 11:30 am Reply with quote Back to top

My bikes and bikes I helped people with run fine by increasing the primary (or slow speed) jets 1 number size and the mains 2 number sizes. Readjust the idle screws for peak idle and then in 1/8 turn. (These are sea level / up to about +1000 ft.) The best way to gauge the jetting is mileage moderate riding should yield about 40-50 mpg. These bikes will run ok excessively rich which is a waste of fuel & money and may damage the motor by washing the fuel off the cylinders and by contaminating the the oil with gas. I have ridden with guys that under moderate to frisky riding (street) have hit reserve at 100 miles. The only descernable (nitpicking for sure) symptom of poor CV lift on the stock Keihin carbs with pods & pipe is some low throttle opening / first gear hesitation or balky type feelings. As for me I only use first gear to get my bike moving. Once underway I could care less about using it. The engine losd created in any gear above first lifts the CV's just fine. Doc

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cbxdog
Rest in Peace



Joined: Mar 08, 2005
Posts: 12974
Location: The Sticks

PostPosted: Fri Nov 08, 2013 12:55 pm Reply with quote Back to top

Would swapping to the 900 slide springs be of any benefit?

_________________
1979 CBX
1979 CBX
1979 CBX
1980 CBX
1983 CB1100F
1980 CB1100RB Replica SC05 engine
1982 CB1100RC
1982 CB1100RC - basket case
1970 HD FLH
1976 HD FX
1983 HD FXRT
1988 FX 85th anniversary
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McNugget
Twinstar
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Joined: Sep 17, 2012
Posts: 69
Location: Kansas city

PostPosted: Mon Dec 02, 2013 3:55 pm Reply with quote Back to top

Forgive my ignorance, but you literally drilled out the stock jets with a drill bit? Also, did you shim the needles for this set-up?
 
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oldschoolcarbs
Hawk
Hawk



Joined: Jun 28, 2013
Posts: 311
Location: Santa Clara +CA

PostPosted: Mon Dec 02, 2013 5:36 pm Reply with quote Back to top

Jebbysan wrote:
The more I think about the airbox....the more I think it was an air resonance plenum.....it could not induce a vacuum as that would be counter intuitive....I feel it had a "ram" effect......
When you remove the box....you have to jet up....as the carbs will lose signal due to not having a "third order resonance" similar to adjusting the length of stacks on a Hilborn injection unit for a V-8....
I also wholeheartedly believe that degreeing the intake cam to open sooner improves carb signal.....

Maybe we can dispell the myth forever.....maybe not......
Just my two cents and please comment on my thinking if you like!

Peace,
Jebby


By all means, educate us further regarding "signal" and how it relates to performance dynamics in situations where various mods are made, beginning from inside the airbox and continuing all the way through to the exhaust tips. A chart would be lovely, or dyno printouts to compare with the ones we made last year.

We've had resounding success jetting for pods, historically speaking (150+ DOHC carb sets with perhaps 5% having pods and/or headers) and because we tend to stay in touch with customers I've accumulated a database of what has worked and what hasn't.

The one thing we're on the lookout for is lean running over time so we advise a few simple tests to ensure that were not slowly burning valves.

Techno-babble is all well and good but well-documented trial and error yields real-life results that are far superior to theory.

We add CBX slide needles to the mix, which in one notable case was the difference between an 1100 not running at all to purring like a tiger.

You can also acquire adjustable needles without the dynojet rapid step-down profile but they're pricey. You just have to know where to look.

As for drilling jets, this is an extremely common track-side procedure, but with one caveat: we don't want to go up more than a size or two because any more than that and we'll change the geometry of the conic cavity on the interior orifice of the jet, which will in turn vastly affect fuel flow.

Interesting to note: While both are indeed metric and thus have the same size orifice, a dynojet #98 main jet delivers more flow than a stock Keihin #98.

OSC
 
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melchiro
Silver CB900F
Silver CB900F



Joined: Aug 10, 2003
Posts: 1511
Location: Mill Creek, WA.

PostPosted: Mon Dec 02, 2013 7:46 pm Reply with quote Back to top

McNugget wrote:
Forgive my ignorance, but you literally drilled out the stock jets with a drill bit? Also, did you shim the needles for this set-up?


Yes... I drilled out the stock jets.. I have done this for years, on various types of bikes and carbs. I did not want to buy $100.00 worth of various jet sizes to do the, trial & error, to find that perfect setup.

As Oldschool states, I drill out one size at a time. Then install and test ride... Can you imagine the amount of time & labor spent here??

And no, I did not shim the needle...

For me, it really was as I stated.. No fancy trickiness, no black magic.. Just A LOT of trial & error..

_________________
1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project

Last edited by melchiro on Sun Dec 08, 2013 5:59 pm; edited 1 time in total 
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Jebbysan
Red CB1100F
Red CB1100F



Joined: Dec 08, 2007
Posts: 7126
Location: New Braunfels,Texas

PostPosted: Mon Dec 02, 2013 8:39 pm Reply with quote Back to top

oldschoolcarbs wrote:
Jebbysan wrote:
The more I think about the airbox....the more I think it was an air resonance plenum.....it could not induce a vacuum as that would be counter intuitive....I feel it had a "ram" effect......
When you remove the box....you have to jet up....as the carbs will lose signal due to not having a "third order resonance" similar to adjusting the length of stacks on a Hilborn injection unit for a V-8....
I also wholeheartedly believe that degreeing the intake cam to open sooner improves carb signal.....

Maybe we can dispell the myth forever.....maybe not......
Just my two cents and please comment on my thinking if you like!

Peace,
Jebby


By all means, educate us further regarding "signal" and how it relates to performance dynamics in situations where various mods are made, beginning from inside the airbox and continuing all the way through to the exhaust tips. A chart would be lovely, or dyno printouts to compare with the ones we made last year.

We've had resounding success jetting for pods, historically speaking (150+ DOHC carb sets with perhaps 5% having pods and/or headers) and because we tend to stay in touch with customers I've accumulated a database of what has worked and what hasn't.

The one thing we're on the lookout for is lean running over time so we advise a few simple tests to ensure that were not slowly burning valves.

Techno-babble is all well and good but well-documented trial and error yields real-life results that are far superior to theory.

We add CBX slide needles to the mix, which in one notable case was the difference between an 1100 not running at all to purring like a tiger.

You can also acquire adjustable needles without the dynojet rapid step-down profile but they're pricey. You just have to know where to look.

As for drilling jets, this is an extremely common track-side procedure, but with one caveat: we don't want to go up more than a size or two because any more than that and we'll change the geometry of the conic cavity on the interior orifice of the jet, which will in turn vastly affect fuel flow.

Interesting to note: While both are indeed metric and thus have the same size orifice, a dynojet #98 main jet delivers more flow than a stock Keihin #98.

OSC



You know what dude? You are just a dick.
WTF do you know about engine dynamics?
You can chart and graph yourself into a corner....but physics do not lie.
My theory has more often than not been correct......
So YOU tell us why you jet up when removing the airbox. Smartguy.

You know what else? Signal is everything....without it...the engine does not run. Vacuum signal is
#1 in the world of carburetors...I figured you would know that.....

Mel...sorry to crap on your thread.

Jebby

_________________
Ass, Grass or Gas....no one rides for free....
1979 CBX
1972 Corvette Stingray Coupe 406/4spd
1982 Z/28
2011 Silverado Crew Cab


"I don't do T and A...because I don't have much of either" Tea Leoni 
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Blainethemono
CB1100F
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Joined: Mar 03, 2004
Posts: 3278
Location: Seattle

PostPosted: Mon Dec 02, 2013 11:36 pm Reply with quote Back to top

Hay Mel. sent you a PM

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Blainethemono
CB1100F
CB1100F



Joined: Mar 03, 2004
Posts: 3278
Location: Seattle

PostPosted: Mon Dec 02, 2013 11:42 pm Reply with quote Back to top

melchiro wrote:
McNugget wrote:
Forgive my ignorance, but you literally drilled out the stock jets with a drill bit? Also, did you shim the needles for this set-up?


Yes... I drilled out the stock jets.. I have done this for years, on various types of bikes and carbs. I did not want to buy $100.00 worth of various jet sizes to do the, trial & error, to find that perfect setup.

As Oldschool states, I drill out one size at a time. Then install and test ride... Can you imagine the amount of time & labor spent here??

And no, I did not shim the needle...

For me, it really was as I stated.. No fancy trickiness, no black magic.. Just A LOT of trial & error..


Yeah, I do this as well. I use a Welding tip cleaner for very fine adjustments when needed. As Mel said, if I have some ole jets Im never going to use, why not "drill" them out. Lot cheaper then swapping expensive brass back and forth

_________________
You can't be a real country unless you have a beer and an airline - it helps if you have some kind of a football team, or some nuclear weapons, but at the very least you need a beer.

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Blainethemono
CB1100F
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Location: Seattle

PostPosted: Mon Dec 02, 2013 11:46 pm Reply with quote Back to top

Quote:
You can also acquire adjustable needles without the dynojet rapid step-down profile but they're pricey. You just have to know where to look.

You can also acquire adjustable needles without the dynojet rapid step-down profile but they're pricey. You just have to know where to look.



By that time, I just said FUCK Dyno jet and the horse they rode in on, and bought some VM33s.... carb issues solved.

Friends dont let Friends buy dyno jet crap...... we have the same discussion over on the ZX11 board. There, its Factory Pro jet kits or nothing.... I wonder if this board could talk them into making a jet fit for the vaunted F bikes.... stranger things have happend.

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You can't be a real country unless you have a beer and an airline - it helps if you have some kind of a football team, or some nuclear weapons, but at the very least you need a beer.

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McNugget
Twinstar
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Joined: Sep 17, 2012
Posts: 69
Location: Kansas city

PostPosted: Tue Dec 03, 2013 3:42 pm Reply with quote Back to top

Well, I drilled and tested all day yesterday, ended up with 80 and 120. It pulls clean, rev's nice. what a difference. I pulled the tape off my pods and now running with no choke. I'm still thinking about shimming my needles one or two washers to see if that will make any difference. Thanks, great mod!

BTW, my stock jets were 68 and 102, not no more Very Happy
 
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melchiro
Silver CB900F
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Joined: Aug 10, 2003
Posts: 1511
Location: Mill Creek, WA.

PostPosted: Tue Dec 03, 2013 5:06 pm Reply with quote Back to top

Awesome. I'm glad you followed through. Time for a new video showing you revving past redline. Just don't get caught by your local police for doing 120mph. Haha.

Others with good running F bikes using pods should share there jet sizes here. And I don't mind the few rants. Keeps things interesting.

_________________
1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project 
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Flip78
Twinstar
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Joined: Sep 12, 2013
Posts: 67
Location: Ontario, Canada

PostPosted: Wed Dec 04, 2013 3:10 am Reply with quote Back to top

I have a 1980 cb750f. Stock header with a hindle can, stock cams. Would the 80/120 work with my set up or would it be too much fuel? You guys rock!
 
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melchiro
Silver CB900F
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PostPosted: Wed Dec 04, 2013 4:35 am Reply with quote Back to top

Flip78 wrote:
I have a 1980 cb750f. Stock header with a hindle can, stock cams. Would the 80/120 work with my set up or would it be too much fuel? You guys rock!


I'm assuming you will be replacing the stock airbox with pod filters.. If so, I am not sure.. But this is where buying the metric "hobby" drill bits will be put to good use. Try a 75 primary with a 110 secondary, then continue increasing the size until it runs good. With each different setup on bikes, this will take a few trial and error test runs..

But before you start this "adventure", you must make sure that your idle port are fully clean, your idle mixture screws are set and all four butterflies are in synch.

_________________
1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project 
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Shawn_Mc
CB1100F
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Joined: Jul 30, 2012
Posts: 2819
Location: Anaheim Hills, Ca.

PostPosted: Wed Dec 04, 2013 6:58 am Reply with quote Back to top

melchiro wrote:
Flip78 wrote:
I have a 1980 cb750f. Stock header with a hindle can, stock cams. Would the 80/120 work with my set up or would it be too much fuel? You guys rock!


I'm assuming you will be replacing the stock airbox with pod filters.. If so, I am not sure.. But this is where buying the metric "hobby" drill bits will be put to good use. Try a 75 primary with a 110 secondary, then continue increasing the size until it runs good. With each different setup on bikes, this will take a few trial and error test runs..

But before you start this "adventure", you must make sure that your idle port are fully clean, your idle mixture screws are set and all four butterflies are in synch.


And only make one change at a time.

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oldschoolcarbs
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Posts: 311
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PostPosted: Wed Dec 04, 2013 6:02 pm Reply with quote Back to top

Jebbysan wrote:
oldschoolcarbs wrote:
Jebbysan wrote:
The more I think about the airbox....the more I think it was an air resonance plenum.....it could not induce a vacuum as that would be counter intuitive....I feel it had a "ram" effect......
When you remove the box....you have to jet up....as the carbs will lose signal due to not having a "third order resonance" similar to adjusting the length of stacks on a Hilborn injection unit for a V-8....
I also wholeheartedly believe that degreeing the intake cam to open sooner improves carb signal.....

Maybe we can dispell the myth forever.....maybe not......
Just my two cents and please comment on my thinking if you like!

Peace,
Jebby


By all means, educate us further regarding "signal" and how it relates to performance dynamics in situations where various mods are made, beginning from inside the airbox and continuing all the way through to the exhaust tips. A chart would be lovely, or dyno printouts to compare with the ones we made last year.

We've had resounding success jetting for pods, historically speaking (150+ DOHC carb sets with perhaps 5% having pods and/or headers) and because we tend to stay in touch with customers I've accumulated a database of what has worked and what hasn't.

The one thing we're on the lookout for is lean running over time so we advise a few simple tests to ensure that were not slowly burning valves.

Techno-babble is all well and good but well-documented trial and error yields real-life results that are far superior to theory.

We add CBX slide needles to the mix, which in one notable case was the difference between an 1100 not running at all to purring like a tiger.

You can also acquire adjustable needles without the dynojet rapid step-down profile but they're pricey. You just have to know where to look.

As for drilling jets, this is an extremely common track-side procedure, but with one caveat: we don't want to go up more than a size or two because any more than that and we'll change the geometry of the conic cavity on the interior orifice of the jet, which will in turn vastly affect fuel flow.

Interesting to note: While both are indeed metric and thus have the same size orifice, a dynojet #98 main jet delivers more flow than a stock Keihin #98.

OSC



You know what dude? You are just a dick.
WTF do you know about engine dynamics?
You can chart and graph yourself into a corner....but physics do not lie.
My theory has more often than not been correct......
So YOU tell us why you jet up when removing the airbox. Smartguy.

You know what else? Signal is everything....without it...the engine does not run. Vacuum signal is
#1 in the world of carburetors...I figured you would know that.....

Mel...sorry to crap on your thread.

Jebby


Don't get in a twist. I merely asked you to explain the term “signal.” I don't know what for about "third order resonance." A theory that cannot be definitively and repeatably verified is akin to voodoo.

I eschew jargon. Not that esoterica doesn't have its place but I prefer plain English. My customers appreciate it and they're the only ones whose opinions actually matter.

And of course it's all about real-life results so we put a bike on the dyno with EGA sniffer in the exhaust stream and diddle with the carbs to see what's actually going on. Charts indeed!

So anyway,

When the piston goes down it sucks air through the intake valves. Total air volume allowed through is determined by both the degree to which the valves open (lift) and duration of time that they stay open.

Relative “sudden-ness” of valve opening and closing plays a role as well, all of which above factors are determined primarily by the camshaft (and secondarily by valve lash.)

Intake vacuum pulse is mathematically calculable and thus 100% predictable insofar as frequency, amplitude, and duration. The designers used this to balance flow through the entire system, from airbox to exhaust tip. Let's not forget that Honda had the EPA breathing down their necks at every turn and were forced to make changes that didn't necessarily translate to better performance OR fuel economy. (Okay so that's a little understatement. LOL)

Airflow through the venturi is by no means steady like a flowing stream of water, but rather is very jagged.

Air is “stretchable,” which is to say that airbox resistance increases the duration of the vacuum pulse and smooths out the jaggedness.

When we take away airbox resistance, vacuum pulse duration is shortened. The result is that the jets have less time to do their jobs, hence less fuel comes through them.

So we jet up.

As for dynojet, I stay out of that discussion. There are instances where it's a viable solution and others where it makes things worse.

For one thing, if you install a DJ kit when compression isn't perfect you're in for a world of hurt, and you may come away believing that DJ is fundamentally bad science. Nothing could be further from the truth but the predicate conditions must be met before you can have an objective take on it.

The same holds true for any mod to succeed. Compression is king. Let me repeat for those who are hard of hearing: COMPRESSION IS KING.

In the case of pods it's equally vital that the accelerator pump circuit be in perfect working order AND that valve lash is on the money.

OP clearly has this worked out, which is a testimonial to his skills as an engine/carb builder.

Beyond that it can come down to factors as seemingly obscure as fuel quality and elevation above sea level.

With the number of variables in play it can indeed seem like a crap shoot and like I said there are times when mods/DJ are just not going to work.

This is why I ALWAYS advocate for stock setups, while being open to those times where I'm satisfied that everything is in order to safely make the mod.

History bears this out, which is all that matters.

OSC
 
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r3d1100f
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Joined: Sep 02, 2013
Posts: 114
Location: North Carolina

PostPosted: Wed Dec 04, 2013 7:25 pm Reply with quote Back to top

I would like to chime in with a question and some comments.

Does the air box or the pods change the amount of air needed (not delivered) for the proper F/A mixture to be burned in the cylinder?
I think no.

I believe that if you run the air box it is only gonna let "X" amount of air into the carb where the jets will mix it with "X" amount of fuel.

I believe that if you run pods, they are only gonna let "X" amount of air into the carbs where the jets will mix it with "X" amount of fuel.

Our goal is to find the "X" amount of fuel delivered by the jets in order to get the proper F/A mixture for whatever set up you are running be it pods or air box.

We can do this by changing the size of the jets to create a F/A mixture that burns well in the cylinder.The jets are being the changeable variable in this equation as the air being delivered is set at whatever is being run, pods or air box.

Alternatively we can also do this by limiting the amount of air being delivered to the carb. The air being delivered is now the variable as the jets are gonna deliver a set amount of fuel to the cylinder.

Both can be adjusted obviously, the amount of fuel and the amount of air. Its your choice where to make the adjustments.

The key is the fuel air mixture, how you obtain it is the question.

So we chase the dragon and follow the wisdom of those that have practical experience.

Volumetric efficiency is the true king.( the volume of the cylinder to the volume of the F/A mixture we have in the cylinder on the intake phase through the compression phase) That's why adding boost from turbo's and superchargers make so much power. They increase volumetric efficiency over 100%. However naturally aspirated engines are no where near volumetric efficiency of 100% and that's due to atmospheric pressure and other variables beyond our control. Having a sniffer allows us to tune off of the exhaust gases and therefore gets us a more accurate viable F/A mixture but most of us tune by the seat of the pants.

Stoichiometric F/A mixture is ideal yet unobtainable and the closer we get to it the hotter the engine runs. Not so good for the internals especially on oil splash/air cooled motors.


The real bazillion dollar question is how to make the efficiency of the internal combustion engine better than 25 to 30%. A majority of the power our engines make is wasted as exhaust gas..... so sad.

Just my thought outloud. Its been a long time since i have been to school for this stuff.
 
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cliffiec
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Joined: Mar 02, 2006
Posts: 5282
Location: Central Maine

PostPosted: Wed Dec 04, 2013 8:01 pm Reply with quote Back to top

r3d1100f wrote:
I would like to chime in with a question and some comments.

Does the air box or the pods change the amount of air needed (not delivered) for the proper F/A mixture to be burned in the cylinder?
I think no.

I believe that if you run the air box it is only gonna let "X" amount of air into the carb where the jets will mix it with "X" amount of fuel.

I believe that if you run pods, they are only gonna let "X" amount of air into the carbs where the jets will mix it with "X" amount of fuel.

Our goal is to find the "X" amount of fuel delivered by the jets in order to get the proper F/A mixture for whatever set up you are running be it pods or air box.

We can do this by changing the size of the jets to create a F/A mixture that burns well in the cylinder.The jets are being the changeable variable in this equation as the air being delivered is set at whatever is being run, pods or air box.

Alternatively we can also do this by limiting the amount of air being delivered to the carb. The air being delivered is now the variable as the jets are gonna deliver a set amount of fuel to the cylinder.

Both can be adjusted obviously, the amount of fuel and the amount of air. Its your choice where to make the adjustments.

The key is the fuel air mixture, how you obtain it is the question.

So we chase the dragon and follow the wisdom of those that have practical experience.

Volumetric efficiency is the true king.( the volume of the cylinder to the volume of the F/A mixture we have in the cylinder on the intake phase through the compression phase) That's why adding boost from turbo's and superchargers make so much power. They increase volumetric efficiency over 100%. However naturally aspirated engines are no where near volumetric efficiency of 100% and that's due to atmospheric pressure and other variables beyond our control. Having a sniffer allows us to tune off of the exhaust gases and therefore gets us a more accurate viable F/A mixture but most of us tune by the seat of the pants.

Stoichiometric F/A mixture is ideal yet unobtainable and the closer we get to it the hotter the engine runs. Not so good for the internals especially on oil splash/air cooled motors.


The real bazillion dollar question is how to make the efficiency of the internal combustion engine better than 25 to 30%. A majority of the power our engines make is wasted as exhaust gas..... so sad.

Just my thought outloud. Its been a long time since i have been to school for this stuff.


The "wisdom" is that because the bikes came with "CV" carburetors ("CV" stands for "constant vacuum"), that the airbox provides the vacuum used to lift the slides, since they are not "direct lift" carbs. So we're searching not just for the correct FA mix, but the correct lift of the slides, as well. I'm just starting to get my feet wet in this, I'm sure that someone with much more experience than I will help out...

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1982 CB 900F (the Animal)
1982 CB 900F (the beast)

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AGDT
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Joined: Sep 25, 2013
Posts: 62
Location: Tasmania

PostPosted: Wed Dec 04, 2013 8:17 pm Reply with quote Back to top

CV stands for (constant velocity). These type carburetors are normally used on motorcycles. A CV carburetor (Constant Velocity) incorporates a vacuum operated slide that varies the venturi size within the carburetor, thus maintaining a constant velocity. The slide also holds a needle that when lifted by the opening slide varies the amount of atomized fuel delivered.

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