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1991 zx11 help please

1K views 10 replies 4 participants last post by  spratt1973 
#1 ·
Hello all. I have a 91 zx11c with a muzzy race engine and a 4 into 1 header. just bought the bike recently and am having some low rpm misfire issues on #1 and #2 carbs. pulled all plugs 3 and 4 are perfect color. 1 and 2 are very carbon fouled. idles great mid range and high rpm are fine. sputters and hiccups around 1800 rpm or leaving a stop under power. pilot screws are 2.5 out on all carbs. float bowls are very clean and cant seem to find any obstructions. compression is good and even across the board. valves are within specs. i have no idea what size main jet has been installed. obviously #1 and #2 cylinders are running rich, but why? Coils are ruled out because they cross cylinders and 3 and 4 are perfect. do i need a hotter plug? is this a float height issue?
Why would only 2 cylinders on different coils run rich ?
thanks in advance.
 
#10 ·
Could be the o-rings that seal the float bowls to the main jet bodies. They tend to get hard and crack over time. Replace all 4. Cheap insurance. I doubt that the float height could change enough to foul two plugs. Check to see if those two fouling cylinders are on the same coil.
 
#11 · (Edited)
Thank you . As i stated above though #1 and #2 cylinders are fired by different coils, so I have ruled that out. From what i have been reading on the forums, I think the plugs are fouling at idle due to improper pilot jet setting. They should be no more than 1 3/4 out max and they were set at 2 1/2.

O.K. massive failure. Adjusted pilot jet per forum recommendations and tried starting engine. Ran horribly and was leaking gas from the idle adjustment line. So , I backed out pilots to original setting and tried again. It started and idled ok for about 30 seconds then died. Now it wont start at all. I am doing trial and error with the carb settings without the airbox attached for accessibility. The bike should run the same without the airbox hooked up because there is absolutely no way you could synchronize the carbs with the airbox on. So I am guessing I gas fouled the new plugs from the previous attempt of enriching instead of leaning the pilot jets? Does anyone have any suggestions on what i should try next, besides cleaning or replacing the new plugs and trying it again with the original pilot settings? I'm just about fed up with this bike. I had an '87 zxr750 Ninja that had twice as many miles on it as this zx11 and I literally tried to blow it up and it ran flawlessly until the day I sold it without any issues,ever.
 
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