my 900f on the dyno!

Posted: Fri Sep 28, 2007 4:51 pm

had some spare time at the shop here this am so i decided to do some tuning with the new set up.

vhr chrome megaphone system
kn pods
124 dynojet main jets
82 primary main jets

5500 ft.SAE corrected runs.

im pretty happy with the way it runs. carburates perfectly.no flat spots.

this is cramming the throttle wide open at 2,000 rpm in 4th gear.

Posted: Fri Sep 28, 2007 7:01 pm

Nice gig you have going there, burned.
Spare time spent playing on a dyno? Outstanding!
Close to 80 hp, is impressive.

Posted: Fri Sep 28, 2007 7:07 pm

Lose the shitty pods and put the air box back on and gain about 8 HP to put it where it was before you broke it with the jet kit & pods.

Posted: Fri Sep 28, 2007 7:31 pm

no jet kit.stock needles.never had the air box.

please point me to the proof that the stock air box makes 8hp more.

this isnt my first day.

so if i did have air box and installed it that would put this bike into the basket case i put it together from? Rolling Eyes

Posted: Fri Sep 28, 2007 7:41 pm

smurdoch wrote:

Nice gig you have going there, burned.
Spare time spent playing on a dyno? Outstanding!
Close to 80 hp, is impressive.

yah,its good gig.

ive been running a dynojet dyno for 17 years.

i build high end supermoto race motors for a living.

i generally be found at thumpertalk.com

i have my own jetting forum and im the senior member there.40,000 posts.

Posted: Fri Sep 28, 2007 9:49 pm

Congratulations you are getting slightly more HP than a 750F. Wink

Where did the other 10hp go??? I am not being negative or putting you down, just curiously intersted in this subject.

From this Forum's Home Page:

In 1979 Honda introduced a new type of motorcycle to the world, the CB750F SuperSport. This bike came with an impressive 748cc 4 cylinder engine , dual overhead cams with bucket and shims instead of rocker arms and four valves per cylinder making 72hp. This bike raised the bar with its superior engine performance and handling, making it stand above the rest in its class.

Available to the rest of the world sooner, the CB900F SuperSport was introduced to North America in 1981. The 900F had a slightly shorter wheelbase than the 750F, weighed 22.5 lbs more, but boasted a 902cc motor with 84hp instead. The 900F also came with a larger diameter fork, adjustable dampening shocks, stiffer frame, as well as larger valves and carburetors. The CB900F also served as the basis for Honda's Superbike racing efforts in the capable hands of Freddie Spencer and Mike Baldwin, lending further eyeball appeal and prestige. And perhaps best of all, the suggested retail price of the 900F made it an irresistible bargain.

Now I don't know really what a 900F that is 26 years old should produce as I am sure it would have some degradation from being new but I have heard that it is tough to determine the effect of the pods versus the stock airbox. Maybe what you are seeing is due to the pods or maybe just due to age or even the 84hp claimed being wrong? What are your thoughts?

Dave

Posted: Fri Sep 28, 2007 10:00 pm

that is claimed at the crankshaft.

where is the dyno graph from a stock cb750 making 72hp?

had your bike on a dyno?

Posted: Fri Sep 28, 2007 10:12 pm

How much does a dyno run cost? It'd be cool to see what my 900F puts down, I've just always imagined that sort of thing is expensive.

Posted: Fri Sep 28, 2007 10:16 pm

burned wrote:

that is claimed at the crankshaft.

where is the dyno graph from a stock cb750 making 72hp?

had your bike on a dyno?

I do not know and that is why I am interested and asking. I have a 900F and it is pretty much stock except for the Cobra Pipe but it has never been on a dyno and I am not sure there is even one in Alaska for bikes.

If those figures I reported were from the crankshaft, I would guess that there would be quite a bit less hp at the rear wheel so the numbers you are showing for your 900F could be what should be expected.

Dave

Posted: Fri Sep 28, 2007 10:22 pm

no worries,i was just wondering if you had for comparison sakes.

there is a pretty good loss thru the drivetrain..

manufactures all make claims at the crankshaft.

Posted: Fri Sep 28, 2007 10:25 pm

CoolCat wrote:

How much does a dyno run cost? It'd be cool to see what my 900F puts down, I've just always imagined that sort of thing is expensive.

depends on the shop.typically $50-100 for baselines.

for members of various boards im on i do them for free.

if your thru denver,look me up.

Posted: Fri Sep 28, 2007 10:29 pm

My parents live in Fort Collins, so if I'm ever out west with my ride perhaps I can get the 750F(non-stock) dyno'd and my dad can get one of his Guzzis done, that would be doubleplusgood.

Posted: Fri Sep 28, 2007 10:42 pm

motomoon wrote:

My parents live in Fort Collins, so if I'm ever out west with my ride perhaps I can get the 750F(non-stock) dyno'd and my dad can get one of his Guzzis done, that would be doubleplusgood.

not a problem.

i would be handy to have a data base of different F's on my dyno.i can post them easily.

as i remember (its been many years and dyno computer crash ago) my 1980 cb750f made 62ish hp.stock air box with a kerker pipe.

Posted: Sat Sep 29, 2007 3:41 am

As you go up in altitude the jetting should be leaner. 124 on a 900? I used 130 in an 1123cc version using 900 carbs that had the pod filters. It also had the dynojet needle and was rich using 74 in the primary main.

I truly believe it is not just "airflow" but the resonances in the airbox and only "A" to "B" comparison shows how bad the bikes run with the pod deal. No matter what you call it you cannot see if the slides have fully lifted or stay lifted,and a big piece of metal definetly restricts airflow. If you are real rich on the main jet the slides will stop at the 3/4 lift point because the vacuum drops due to the rich mixture.

Every body knows how to jet direct lift carbs. Vacuum carbs are different. At full throttle after a decent run slightly close the throttle,bike slows down a little,go back full throttle,bike speeds up,jetting is close. If after a certain amount of throttle twist the bike goes no faster the throttle seemingly having no effect,it is lean. Too lean or too rich and the slide is not at full lift.

Posted: Sat Sep 29, 2007 5:48 am

fasterspider wrote:

Lose the shitty pods and put the air box back on and gain about 8 HP to put it where it was before you broke it with the jet kit & pods.

Posted: Sat Sep 29, 2007 11:27 am

sonicrete wrote:

As you go up in altitude the jetting should be leaner. 124 on a 900? I used 130 in an 1123cc version using 900 carbs that had the pod filters. It also had the dynojet needle and was rich using 74 in the primary main.

I truly believe it is not just "airflow" but the resonances in the airbox and only "A" to "B" comparison shows how bad the bikes run with the pod deal. No matter what you call it you cannot see if the slides have fully lifted or stay lifted,and a big piece of metal definetly restricts airflow. If you are real rich on the main jet the slides will stop at the 3/4 lift point because the vacuum drops due to the rich mixture.

Every body knows how to jet direct lift carbs. Vacuum carbs are different. At full throttle after a decent run slightly close the throttle,bike slows down a little,go back full throttle,bike speeds up,jetting is close. If after a certain amount of throttle twist the bike goes no faster the throttle seemingly having no effect,it is lean. Too lean or too rich and the slide is not at full lift.

you can see exactly what my a/f ratio is doing by the a/f sample on the graph.i left i slightly rich as i go down in elevation more than i go up.

120's would be perefect.

the dynojet needles have way more taper and a smaller end demension.the basically block the needle jet less and use smaller main jets.

you most definately can see if the slide are fully open on the dyno.just take the air filter off and look.

the only way the slides would drop back to 3/4 open is if the motor will not go full rpm.if the motor is all full rpm the slide are fully open.period.

you will have to alter the main jet so that the motor will go full rpm with the filters off.

there is no vacuum once the throttle is open on any motor.

its velocity that raises the slides not vacuum.

i think you guys are basing all this pods vs air box deal on a by product of 20 year dynojet needles.

they were less than stellar back then.

im not saying the pods are better .its quite possible the motor makes a little less power.i dont know for sure since i dont have a stock air box.

but this bike certianly does not have any bad traits becuase of them.

where are the flat spots?

i still havent seen one bit of actual data to support any of the claims of seen here.

every one that claims to have had issue getting the bike dialed was using a dynojet kit..........

Posted: Sat Sep 29, 2007 4:24 pm

Hmmmm... I though vacuum raises the vacuum slides...

no vacuum at WOT? OH NOES!!! I better hook up the hoover to my brake booster if I drag race my car today Shocked

Posted: Sat Sep 29, 2007 4:39 pm

My bike had a flat spot between 4000-5000 with the Pods. I didn't have the knowledge or experience and skills to try various configurations but I do know for a fact that putting the stock airbox back on cured the issue. I did not do anything else except change the main jet back from 120 to 105 and stick the airbox back on. The plugs were showing super rich and now they are showing lean but it runs perfectly. I decided that I'd not mess around with the CV's and get better carbs to maximize my value for the dollar/time. The PO took his Mikuni Smoothbores off the bike but left the Pods and it never ran right again for him and thus he let it sit for 12 years. Due to this being the first thing I learned and making this change my bike was resurrected very easily.

Matt at PSB used to say most everyone will come to this conclusion somewhere along the way. Performance for the dollar tells me not to waste my time with the CV's as there are other issues with the CV carbs as well. From what I gather the single best performance upgrade reported on these engines is to put on smoothbores (round or flat). Why would I mess around with the CV's if I can get such a dramatic increase in performance with better carbs?

Again, I am trying to get a thorough perspective as I am currently saving my pennies to buy some CR-S carbs this winter.

All of this dialog is highly valuable to me. Should I really just move on to CR-S (so far it is yes) or try to fiddle and configure these CV's (I am not convinced that that is in my best interests at this point in time to keep the CV's).

I also certainly respect the opinion of someone like Matt who in essence was trying to save folks money and aggravation by recommending the replacement of the CV carbs to folks like me who don't have the knowledge and would possibly learn the hardway (read that wasted $$$$$ and time) otherwise.

Does adding Pods and spending time and money with the CV's really make much sense or just spending the money to get superior performance make better sense in the long run? Is there any performance gain at all (conclusive) in adding Pods to the CV's and dialing them in? The long run answer is what I am most interested in right now.

Here is an article on a Project 900F that was working with Jet Kits but is it worth the trouble of messing withthe CV's???

900F Performance Article - 6 Megs
Dave

Posted: Sat Sep 29, 2007 4:40 pm

F-n Double post grrrrr

Dave

Posted: Sat Sep 29, 2007 4:42 pm

I have witnessed plenty of stock carbs with pods running well and their owners plenty happy with their bikes.

Now we have someone with a dyno and a bike, and he seems to know how to tune it. Before we go trashing the mans work why doesnt someone send him an airbox and let the proof be in the pudding once and for all. It even looks like this bike put out if not the same but more power than a certain 1132cc FCRed modded bike with all the bells and whistles. Thats right, the cams were off a bit. Razz

I'd love to see the bashers send this guy some stock filters already. I'd love to see more power made so I can keep my stock airbox, until then I dont want to see the word "pod" typed like its some kind of king and queen seat on an F. Anybody live nearby? This is actual data we're looking for. Data to help our bikes. I've bought two bikes with pods and no stock airboxes. I'd feel better knowing they could stay that way.

Posted: Sat Sep 29, 2007 5:02 pm

AlaskaGriz wrote:

All of this dialog is highly valuable to me. Should I really just move on to CR-S (so far it is yes) or try to fiddle and configure these CV's (I am not convinced that that is in my best interests at this point in time to keep the CV's).

I'm going to buck convention here as I've just been through a series of rapid swaps from CV's to CR's to CV's then finally back to CR's;

Jetting problems on my CR's led me to reach a frustration point whereby I swapped my original CV's and airbox back on to the bike. Sure CR's offer an increase in performance, are simpler to work with and have an added benefit in eliminating the stock airbox (and of course, there's always the 'bling' factor) but...... there's nothing wrong with a set of CV's that are working well - in fact, I would go so far as to say that the bike was nicer to ride with the stock CV's (so shoot me).

Prior to fitting CR's I had read much on the subject of 'rolling' on the throttle. My impression was that a heavy hand would bog the bike and a whole new way of riding needed to be learnt. This is far from the case - you do need to roll on a little, but there is little chance of overwhelming the engine unless you are determined to do so - in all, the CR's are easy to adapt to and don't require a huge adjustment in riding style or throttle use.

The CR's pull much stronger through the rev range and it feels like the bike makes more power lower in the revs compared to the CV's. While you certainly gain more power, you loose the 'wow' factor that the stock CV's provide when the tach hits 7 or 8K. The CV's make smooth progressive power of a different nature than the CR's - this is going to sound odd, but I feel I could ride more smoothly with the CV's on a set of twisties than I can with the CR's. The CV's are also quieter and while we all hate the stock airbox, it does a great job of keeping the filter clean and out of the line of moisture and the elements.

If CR31's weren't becoming so difficult to find, I would have likely sold them shortly after refitting the CV's. I only refitted them because I found a jetting problem I had missed earlier, and I didn't want them to 'beat' me. I am glad they are back on the bike, but the stock CV's on a good running bike are fine as well. Where CR's begin to make real sense is when the stock CV's begin to develop problems beyond a simple dismantling and clean - these carbs are 25+ years old and when the slides start to wear or any other major deterioration begins, CR's are probably a more economic solution - they are a 'new' carb after all.

Posted: Sat Sep 29, 2007 5:15 pm

PTG~

Very good and unbiased feedback. Much appreciated. Still going to save me pennies and maybe I will keep my CV's instead of selling them off. Dunno right now.

Did you see the posts I made on the remanufacture services for the CV's. Maybe that is an option to explore if the carbs are getting long in the tooth but the cost is still about $400. When does it make sense to make the change to the CR-s?

I would love to see the conclusive evidence of the CV's making more power without the airbox and what the configuration setup was. I have a spare airbox on the shelf that I will gladly donate and pay the shipping to send to Burned for testing purposes.

Dave

Posted: Sat Sep 29, 2007 5:25 pm

AlaskaGriz wrote:

Did you see the posts I made on the remanufacture services for the CV's. Maybe that is an option to explore if the carbs are getting long in the tooth but the cost is still about $400.

I saw the rebuilt carbs and in all honesty, I think they're a rip-off. $400 will get you into a reasonable used set of CR's, VM's, TMR's, RS's and unless those rebuilt carbs include new slides etc., they are simply a rebuilt 25+ year old carb with all that that implies.

AlaskaGriz wrote:

When does it make sense to make the change to the CR-s?

Yesterday - if you're talking about a 900F, finding a set of CR31's is getting more difficult with each passing day. I picked up both my sets from Yahoo Japan, but I've not seen any used sets there or on eBay for some time. FCR's may be a better option in terms of availablity (but not price).

Posted: Sat Sep 29, 2007 5:32 pm

While I can't really give conclusive evidence with Dyno numbers and data, I can say I went from a very clean set of stock CVs with airbox to Mikuni VM29s with velocity stacks way back in about 1987 on my 900. Those carbs tuned up easily, just a few jet changes, and made dramatically more power, evidenced by the fact that I could then almost keep up with my buddy on his V65 Magna.

As for pods on the CVs, I've got nothing. The word was back then was it's not worth the headache, just like now. I knew guys that swear it was possible, but it was a lengthy process, because it's so much trial and error. Dynos weren't so plentiful back then either.

Posted: Sat Sep 29, 2007 6:03 pm

i plan to go to FCR's once i gather the rest of my motor build parts.

FCR's are the way to go,but thats me being partially biased as i have spent the last 10 years tuning the FCR on 4 stroke singles (mx'ers,offroad,supermoto).

the needle codes are easy to understand and the tuning parts plentiful.

ive tuned numerous F's with the pods.never a complaint.i DO NOT use dynojet kits in the F carbs.

i believe in dynojet kits and have been closely involved with them over the years.i worked at one of the very first dynojet centers.

however there are several kits they make that needle just flat has to much taper.the F kits are one of them.

overall at the current moment i happy with the stock carbs.it runs perfect.

the number one issue i see with the stock carb when the bike come in is the accelerator pump not working.

regardless,im not doubting that people had poorly running bikes with pods.its the jetting not the pods.

the easiest solution for most would be just to reinstall the stock stuff.im good with that.

i spent a total of 45 minutes tuning my F.

i think a wideband a/f meter would open alot minds around here.

Posted: Sat Sep 29, 2007 6:20 pm

PTG~

Really the reason I haven' t bought them yet is just due to the riding season up here being so short and the amount of time I have on my hands in the winter to make these upgrades. I'll have something this winter for sure.

I called SUDCO last month and they told me they had 31mm CR-s in stock but even if not, I think I'll be able to round something up although I might ask (read that plead) for some help on any Non-US purchases.

I'm still trying to learn before I make a purchase but I was under the impression that FCR's were not available in the correct size for the 900's. I could get the money in a second if the right deal came along. In th e past I thought I'd have been buying FCR's until I was given the impression that there isn't a correct size for my bike in the FCR models.

Now I am really confused............. help someone. CR-S or FCR for a basically stock 900F (it won't stay that way forever though). Right now, all I have are a Cobra Pipe and a Dyna 2000 for performance stuff? Carbs are going to be next and I have about 9 months to get it done.

Dave

Posted: Sat Sep 29, 2007 6:28 pm

AlaskaGriz wrote:

I'm still trying to learn before I make a purchase but I was under the impression that FCR's were not available in the correct size for the 900's.

FCR's are available in a dizzying array of sizes. They are most definitely available in a bolt-on configuration for all of the F's (750/900/1100). Here's just one 750/900F example:

http://page4.auctions.yahoo.co.jp/jp/auction/d78678421

FCR's are a better carb than CR's, but they're not 'period' correct if that's a look you're going for.

Posted: Sat Sep 29, 2007 6:37 pm

exactly,the FCR is superior carb but not period correct.

every circuit of the fcr is 100% tuneable.

Posted: Sat Sep 29, 2007 6:39 pm

razor02097 wrote:

Hmmmm... I though vacuum raises the vacuum slides...

no vacuum at WOT? OH NOES!!! I better hook up the hoover to my brake booster if I drag race my car today Shocked

just hook up a vacuum gauge and watch it.

you have a funny way of drag racing,wot and on the brakes.

Posted: Sat Sep 29, 2007 8:46 pm

Alrighty then. FCR's is my goal. Period correct is not my first requirement.

Thank you for the helpful feedback.

Dave