Bike still running lean after jet changes

My '81 kz750 ltd four (apparently bored out to 810cc) is still running lean over 4 thousand rpms. Im using stock keihin carbs from an '82 kz 750 four but ive raised the main jet to 138 and raised the needle about as far as it can go.

Should i go bigger with the main jet (id be up to a 140-145 size) or is there anything else i should be tweaking. i havnt messed with the pilot jets at all and the float height and fuel bowl level is the same as it was when i had the carbs on my other engine. The jet setting on the other motor was 125...i feel like im going way higher in the jets than i should have to be even with the extra cc's in the new motor

Thanks alot,
B

Brady Jenn wrote: My '81 kz750 ltd four (apparently bored out to 810cc) is still running lean over 4 thousand rpms. Im using stock keihin carbs from an '82 kz 750 four but ive raised the main jet to 138 and raised the needle about as far as it can go.

Should i go bigger with the main jet (id be up to a 140-145 size) or is there anything else i should be tweaking. i havnt messed with the pilot jets at all and the float height and fuel bowl level is the same as it was when i had the carbs on my other engine. The jet setting on the other motor was 125...i feel like im going way higher in the jets than i should have to be even with the extra cc's in the new motor

Thanks alot,
B

turn the air screws in,

hi there, before attempting to do any jetting mods ensure that you have good fuel flow to the carbs.remove the fuel tap & clean the in tank filter.then remove the bowl filter in the tap & ensure that its clean.re-assemble the tap to the tank fill with fuel, place the tank on a bench & check how much fuel can flow out of the tap with a small piece of fuel hose on it.measure it over ten seconds in to a measureing jug.write down the results. then add a inline filter to the fuel hose (if you use one) & repeat the test.when i did this test on my 900 fuel flow was reduced by 30% when using an in line filter.so this is when you must ask your self is the jet too small,or is the engine using fuel faster than it can flow into the bowls?i think that if you intend to use a inline filter the other filters in the tap should be removed.Also accurate jetting is impossible with out the use of a wide band oxygen sensor & meter.then accuracy is garranteed.good luck wayno

Wayno has a very good point.
I'll add that if you start going up that far in main Jets, you may very well need a larger dia float valve.