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Help ! Cbr900rr 96 Not firing on number 3 cylinder

1K views 6 replies 3 participants last post by  tommoturbo 
#1 ·
Hi Guys sorry my first post is a cry for help i bought a 96 that in the last 18 years only covered 800 miles so i began to refresh the bike. new radiator, hoses, coolant housing, water pump seals and gaskets, sump gaskets, exhaust gaskets, Carb overhaul kit ,fuel petcock also flushed and cleaned the tank.
during this i damaged no2 carb body as the pilot jet was welded in situ as most of the others where but i got those out ok. so i bought another bank of carbs split them down and cleaned overhauled it and rebuilt my bank (all new jets ,seals, o rings etc). refitted the carbs and and erratic idling - more tweaking and now my no3 cylinder not firing. so done so far
Checked spark on all 4 cylinders - OK
Checked compression on all 4 - OK (all the same 170psi)
checked fuel bowls - all have fuel in them
squirted easy start in all 4 - only no3 dosn't respond to it
carefully covered all inlet trumpets and the sliders respond apart from no 3.

Split no3 carb used carb cleaner again on all holes, blown through with compressed air, checked diaphragm no splits rebuilt and re installed - same issue.

Vac tube on no 3 checked and is ok - no splits

so im at a loss, my next check is to see if the exhaust manifold is leaking massively on that cylinder, visually looks ok.

any help appreciated

regards Ian
 
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#2 ·
Hello Ian, have you checked the spark plug on cylinder 3 to see if its wet or dry? If you've checked for spark and it is present you will either be missing fuel or air to complete the mixture, if the spark plug is wet I would suspect you have too much fuel getting through (I had a similar issue approx. 2 years ago on my 95 blade after a carb overhaul as it had been parked for 10 years, I rebuilt the carbs but used pattern float valves -never again- which leaked like a sieve, replaced with genuine Honda ones and problem solved!), if plug is dry (maybe sooty?) then it could be not enough fuel getting through (float valves?) or too much air, check to see if the airbox is seated correctly over the carb mouths and that their are no splits/pin holes in the rubber boots between airbox and carb mouth as that will allow too much air through and weaken the mixture. spark plug colour will give you a good guide as to what is missing from your mixture and guide you in the right direction to hopefully resolve the issue. There are far more experienced guys on here but those are things I'd check to start with, hope it helps!

James
 
#3 ·
One of the key 4 items is not working. Spark, fuel, air, compression.

I would doubt and exhaust manifold issue would kill #3.
Swap the coils and see if #3 is still dead.

I had a similar problem with #4 on my old 99. It would run intermittently. Turns out I using an older dirty filter in line with my drop/remote tank and got more crap in passageways. I cleaned that one carb about 4 times before it finally cleared up.

my guess would be still not getting enough fuel for whatever reason into #3 if the spark is as good as you say it is.
 
#4 ·
Thanks chaps for the responses, when i pulled the plug it was slightly wet but i dont think too emuch, as i only ran it for 30-40 seconds on the choke and it wasnt firing. checked spark again and is good, im in the process of swapping coils then going to pull no3 apart again.
Airbox is off while im diagnosing and have a temporary tank connected. Im goint to crack on with the coil swap and see how that goes

thanks all
 
#7 ·
Right just an update I did more tests today it looks like I've two problems when I swapped coils over I only noticed no 3 cylinder was cold today I used small amounts of easy start on no 3 and it's firing but then no 4 is cold. 1 & 2 are scorching hot (lean) and 3 + 4 cool rich? so tweaked the pilots and bench synced them got it running much better i think its more a fuelling issue that was suggested earlier. just need to work out how to tweak it. thanks for your help guys
 
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