Help with carburation

nana800 · Post by **nana800** » Sun Nov 09, 2003 9:21 pm

Can anyone help ? I bought a 750 genesis and it runs poorly above tickover, If i crack open the throttle it does not respond very quickly(sounds like its choking itself or gettin too much air) same without air box. Had the bowls off and i think this was the 1st stripdown so should be standard. mileage 37k non std exhaust but apparently always did this before new exhaust fitted. Any pointers lads as Im stuck and I want to sort it meselfand learn in the process. Cheers Gray<img src=http://www.ezboard.com/images/emoticons/mad.gif ALT=">:">

flyingcircus68 · Post by **flyingcircus68** » Tue Nov 11, 2003 11:19 am

look for carb modifications to your slides first such as lighter springs or drilled out signal holes in the bottom of the slides. If that's not it we could dig a little deeper.

fzrnut · Post by **fzrnut** » Wed Nov 12, 2003 12:46 am

Can you give me more info?Does it come right above 3000rpm or is it the same,what about up to 7000rpm,or what about top end ie 7000 - 11000rpm.What i'm trying to do is isolate what part of the system is at fault, pilot needle or main jet.Let me know thanks fzrnut<img src=http://www.ezboard.com/images/emoticons/pimp.gif ALT=":hat">

flyingcircus68 · Post by **flyingcircus68** » Fri Nov 14, 2003 11:30 am

Before you start playing with the jets, check the float levels and make sure that the vent tubes are not plugged. Are your main jets stock? It could be a too large main jet. A way to narrow the list of possible suspects is to do a roll on test. Try second gear, slowly bring the RPM up in gear to 5000 rpm and then nail it. Try the same technique at 7k, 8k, 9k. See if it stumbles when you nail it. Test all these rpm again, but this time bring it up slowly to the target RPM, then quickly let off to idle and nail it. If your bike does not stumble with test 1, but does with test 2 then you have an rich pilot circuit condition. If it stumbles with both tests, at any of the rpms listed, You have a rich main jet. If it stumbles in the mid rpm, and not at the higher rpm for test1, then the needle jet is rich. Try that out and see how it reacts.

nana800 · Post by **nana800** » Thu Nov 27, 2003 1:03 am

thanks for tips i will look at the ideas given (when time) and give more feedback.will have to reassemble first as stripped brakes, forks etc valves not checked yet and haynes manual confusing which model (2mg013345) Do valves(shims)wear tighter and keep valves open and what effect would it have ? also any settings would be helpful I am just fiddling with this bike as not touched my bikes since the rd400 & 400/4 days so am rusty, but willing to learn (currently running vfr800) Keep it on the black stuff Gray

scoexup · Post by **scoexup** » Sun Nov 30, 2003 4:56 am

Check valve clearances first,Yamaha recommend doing them at 28000.They get tighter with age.Are you in the uk?

nana800 · Post by **nana800** » Tue Dec 02, 2003 1:08 am

yes scoexup i am in uk, york to be exact, where are you hanging and what you riding. please excuse the slow replies as lots on and little time spare. I got a haynes manual but engine frame nos dont tally with manual so dont know what settings, inlet/ exhaust ta for fork help yes only comp setting so done 39mm with light oil for road use. gray Edited by: <A HREF=http://pub28.ezboard.com/bexupbrotherho ... nana800</A> at: 12/1/03 11:13 pm

scoexup · Post by **scoexup** » Sun Dec 14, 2003 10:11 am

I am in the midlands,now riding a 89 EXUP or anything can get my hands on.Valve clearences are Inlet 0.11 - 0.20mm Exhaust 0.21 - 0.30 run them on top limit they do perform better,then move onto your carbs.I have some shims and could probably get hold of more if you need them.

nana800 · Post by **nana800** » Wed Mar 10, 2004 12:33 am

Hi all finally got some work done on the FZ (notfzr),put it all back together so now can give more info started ok tickover ok, when warm if i open choke a little it stops riding to test rollon-it seems to stutter or misfire from 4k to 10k then possibly clears, also when i slow down i get small backfire. I have been assured by previous owner (mate) that all is standard except exhaust,problem gradually got worse not related to exhaust. cant test if better warm or cold coz runnin really crap and also no tax and test etc so keepin noise to a minimum Can anyone give proper float height when running as my manual for FZR gives uk600= 3.8 to 4.8 FZR 1000= 10.5to 11.6 & 1987/88 model =7.3 to 9.3 FZR750 7.8 to 8.8 but dont know if this is static or running using tubes Also when bike warms up it gets misfire due to arcing under tank, what is best way to replace leads as they look like part of coil or can i get covers to inulate ? forks are really nice with new oil VERY GRATEFUL OF ANY HELP Gray Edited by: <A HREF=http://pub28.ezboard.com/bexupbrotherho ... nana800</A> at: 3/10/04 9:09 am

flyingcircus68 · Post by **flyingcircus68** » Mon Mar 22, 2004 11:41 am

If your getting arcing on the high tension wires, I wouldn't bother playing with the carbs until the ignition is in top shape. Check your plug caps resistance and coil resistance against the manual. If that all jives, check your pick up coil resistance. I had a bad pick up coil wich caused misfire at revs above 4 - 6k, regardless of throttle position. If the problem did get worse over time and the jetting seemed fine at one point, it would either be a dirty fuel system, or the iginition system. read my posting on this problem for details. good luck

nana800 · Post by **nana800** » Wed Mar 24, 2004 12:33 am

flyin circus cheers for help,carbs ok and all check out now gonna eliminate ignition, time permitting as usual ! Iwilltry and find your thread Gray

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