CB900F preparation for Production Racing

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Here's the first part of the story;

https://youtu.be/dTCefFm0Biw

Lots more to come.

Posted: Sat Nov 25, 2017 12:33 am

Show us more

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

https://www.youtube.com/playlist?list=PLJx6UQas4jz_EICbPNjJHSS79yjzm_ok6

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Here's the link to the video clips of the rebuild.

https://www.youtube.com/playlist?list=PLJx6UQas4jz_EICbPNjJHSS79yjzm_ok6

Carbs almost done !

G

CB1100F Joined: Jun 18, 2006 Posts: 2511 Location: UK

ItalianFan wrote:

Here's the link to the video clips of the rebuild.

https://www.youtube.com/playlist?list=PLJx6UQas4jz_EICbPNjJHSS79yjzm_ok6

Carbs almost done !

G

Hi

Nice to see you preparing a bike for production racing in the UK next year, you will have to post the calendar of race events when you have it

Just watched you valve clearance video and would like to make a suggestion

As you found negative clearance on one you checked and set to 004'' i would suggest you try and increase to .006'' as this may close up again as carbon builds up on the valve when running tight then when the proper clearance is restored it will tend to hammer the carbon of and close the clearance

Alough the Honda manual does state the clearance to be 0.002 - 0.005'' over the years members here have found its best to run at a mininum of 0.005'' and even 006''-0.008'' especially on a race engine

Keith

Posted: Mon Dec 04, 2017 3:35 pm

krgood0 wrote:

ItalianFan wrote:

Here's the link to the video clips of the rebuild.

https://www.youtube.com/playlist?list=PLJx6UQas4jz_EICbPNjJHSS79yjzm_ok6

Carbs almost done !

G

Hi

Nice to see you preparing a bike for production racing in the UK next year, you will have to post the calendar of race events when you have it

Just watched you valve clearance video and would like to make a suggestion

As you found negative clearance on one you checked and set to 004'' i would suggest you try and increase to .006'' as this may close up again as carbon builds up on the valve when running tight then when the proper clearance is restored it will tend to hammer the carbon of and close the clearance

Alough the Honda manual does state the clearance to be 0.002 - 0.005'' over the years members here have found its best to run at a mininum of 0.005'' and even 006''-0.008'' especially on a race engine

Keith

Well stated, Keith, and a big +1!

Rick

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Hi Keith,

Thanks for the guidance - always professional advice from you.

You are 100% correct that a zero valve clearance doesn't mean that a -5 on the shim size will get you back to proper running.

What I did earlier was to check the compression on each cylinder before messing with the bike and they were all 160psi+. Armed with that information I knew that there wasn't much passing the valves and so I could assume the "negative clearance" was minimal. I should have stated that in the video, but was just trying to show how to remove and replace shims.

Your comment about carbon build up is totally valid and what I'll show later is that I'll run the engine a bit (to set up the carbs) and let it get up to temperature and cool back down twice, and will then recheck the valve clearances. I'm sure there will be "bedding in" and that a few minor adjustments will be required.

And I will also make sure I have a bigger range of shims so I can get exactly the clearances I'm looking for !!

Cheers

G

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Here's a link to the video of the carb rebuild;

https://youtu.be/qmFHa6JC_GU

I'd stripped and ultrasonically cleaned each and every component and then rebuilt the carb with a new kit. Let's hope it works with the new needle profile.

CB1100F Joined: Jun 18, 2006 Posts: 2511 Location: UK

Wemoto are doing many of the Shim sizes very cheaply at the moment..£2.56 each..worth stocking up at that price

http://www.wemoto.com/bikes/honda/cb_900_f2c_sc09/82/picture/valve_shim_2.60_mm/

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Thanks Keith, definitely worth stocking up on shims at that price.

On with the rebuild. Here's the video of the loose carbs being assembled into a bank ;

https://youtu.be/MgryOhGOsl4

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Here's the video of the carbs being synchronised on the bench (or on the dining room table!)

https://youtu.be/GFEmm1jSFUc

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Here's the bench check of the carb float height :

https://youtu.be/b9c0K0f0jvM

And the rotor rebuild ;

https://youtu.be/CwswWr1_od8

More to come this week!

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Here we are just before Christmas :

https://youtu.be/ISRTg9Hrd8g

Still lots to do !!

Happy New Year to you all.

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

The next instalment

https://youtu.be/HNiB22AnqEk

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Here's her being started for the first time since having the carbs rebuilt.

https://youtu.be/-2ces1pMrN0

Running a bit fast (carbs aren't balanced and pilot screws well out) but at least it runs. Off to the dyno man to tweak her.

A few more details here : https://youtu.be/0KhYMeR7gJo

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Well it's been a while since I posted on here but we've had a bit of an up and down couple of years. We finished 4th in the British Historic Racing club "pre-1986 Japanese Air cooled class" in 2019 despite being hopelessly under powered (84 HP compared to the 120+ of the GS Suzukis). We had new shocks (YTT) and a higher ride height due to continual grounding of the belly pan, but everything else is still bog standard.

2020 was a wash out but I did manage a track day at Mallory park in September but I got punted off at the super fast Gerrards corner and it wrecked the bike, but luckily I was unscathed.

https://youtu.be/EO6ZDawL33g

We got her back together for early 2021 and had a couple of parades with the CRMC at Darley Moor and she was flying, albeit a bit loose.

https://youtu.be/UB5gogcfF0o
https://youtu.be/wb-5sawVcGI

I then entered the first race of the BHR season at Darley Moor, and it was cold and wet. Whilst overtaking a back marker in race 2 I went in too hard into the only left hander on the circuit and found myself on the deck - rookie error, but we got the bike rebuilt for race 4 on the Sunday but I had no confidence in the tyres and drove round like Mary Poppins.

We then went to the BHR meeting at Pembrey in Wales last weekend and despite the thunderstorms forecast, it was glorious and we had three good races before the carbs started pouring petrol out of the overflows. The over 50s race was the most fun and here is the link.

https://youtu.be/Z64RUgJaPgA

Only one more race for the 900 this year, and then the job over winter is to get more HP for the 2022 season.

Posted: Fri Jul 30, 2021 1:18 am

The track in the last clip looks like it would be fun to race on.
Wide, lots of run-off.
Well done getting the F out there, Gareth.

MB-5 Joined: Jul 03, 2017 Posts: 14 Location: UK

Here's a slow lap of Donington Park on my 1981 CB900F

https://youtu.be/SrF4VS-vJiI

The instructor who followed me said we are grounding out the exhaust collector, the silencer and the belly pan. Need to hang off the bike more and get more power from somewhere !

Posted: Thu Sep 02, 2021 7:15 pm

Hi Gareth
You may need some rear shock mounts, some 40 mm higher than stock, with no mods or welding needed