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 Keihin CV carbs

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Mig

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Join date : 2011-07-11
Age : 46
Location : Shevington

PostSubject: Keihin CV carbs   Thu Aug 25, 2011 2:05 pm

I have been doing some research into running pod filters on my CB750, which has stock Keihin CV carbs.
The consensus is that if you run pod/remote filters you are likely to cause problems with fuel metering, problems include poor performance, loss of fuel economy and jetting issues.

I have joined the CB750 DOHC forum in the states and they say that to get the best from your CV carbs its best to run the stock airbox. This poses a problem for me as the airbox is the ugliest bit of the bike.

So i have started to fabricate a new airbox, thats a lot smaller and looks more in keeping with the cafe racer style, i have no idea if it's going to work until i have the bike on the dyno to do some comparison runs.

The air box is important to balance the air flow coming in, instead of 4 seperate filters.

Anyway heres a picture (not finished yet) and i will keep you informed of the results.

Need to make and fit the filter element over the rear of the airbox.

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Dazzler

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PostSubject: Re: Keihin CV carbs   Fri Aug 26, 2011 8:37 am

Hope it works for ya pal. Are you going to TIG weld the ally as a sealed unit? I'll let you know if I come across a decent welder Very Happy
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Mig

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PostSubject: Re: Keihin CV carbs   Fri Aug 26, 2011 10:36 am

All welded by oneself DAZZLER! Cheeky sod.
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Dazzler

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PostSubject: Re: Keihin CV carbs   Fri Aug 26, 2011 1:09 pm

Fully weld it and I'll get it dressed at work for ya.
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pauliexjr

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PostSubject: Re: Keihin CV carbs   Sun Aug 28, 2011 3:00 am

Nice job Mig, think that will look very smart and neat when it's in place.

I'm going down this route with mine



I know the carbs will need rejetting and balancing, but I've got to agree, the airbox on the CB750 is the fugliest thing about the whole damn bike!
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gray



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PostSubject: Carbs   Fri Sep 09, 2011 11:09 am

Hiall, Mig That engine is a real beauty...well done, i am currently starting a project cb750 and cb900 engine, but have the same dilemma about the pod carbs, what sort of Jets sizes will i need for the mains, also how did you get such a great finish on the engine?
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Mig

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PostSubject: Re: Keihin CV carbs   Fri Sep 09, 2011 11:44 am

Gray, i completely stripped the engine down and whilst waiting for new shells, chains, tensioners etc i had the case's ,head and cyclinder block aqua blasted at FJ Motorcyles.
Produce a great finish. Painting can cause overheating problems, and the bike will be kept clean and oiled to maintain the finish.

As for the carbs, i have since fitted ramair filters as i think they look better, but time on the dyno will tell if i can dial out lean spots with jetting and needle positioning.
I know the needles are fixed, but by placing small washers under the needle should help to get the correct metering.

I will keep all informed as and when on the jetting issue's.

BTW if i win the lottery i will fit some Keihin FCR's. Laughing
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Mig

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PostSubject: Re: Keihin CV carbs   Mon Oct 24, 2011 10:49 am

Well i can confirm that running CV carbs through pod filters DOES NOT WORK, the engine would not run properly (FLAT AND BACK FIRED).
So i put the aluminium filter box on, and ran sweet as. Its all to do with the vacuum pressure to operate the throttle slides.

I will know keep my eye out for a set of 35mm Keihin carbs, more BHP and a lot more reliable. Only thing is that at £800 (new) there not cheap.
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Dazzler

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PostSubject: Re: Keihin CV carbs   Mon Oct 24, 2011 11:42 am

Thought you wanted flames coming out the pipes??? Very Happy
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Mig

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PostSubject: Re: Keihin CV carbs   Mon Oct 24, 2011 12:27 pm

Get a few more flames with the FCR's.
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Dazzler

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PostSubject: Re: Keihin CV carbs   Mon Oct 24, 2011 12:52 pm

fair comment
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