Keihin CV carbs

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.

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

All welded by oneself DAZZLER! Cheeky sod.

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

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!

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?

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.

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.

Thought you wanted flames coming out the pipes???

Get a few more flames with the FCR's.

fair comment