Missfiring cylinder, Is it my carbs??

I hate to see a man suffer !!


1. Cylinder good.

2. You have Good Spark.

3. Carb,s are clean.


??
Pilot circut ?
Did you check to make sure that you replaced the "O" ring and washer behind the pilot screw ?
The "O" ring and washer are only as big as this ( O )
Take a look at this, might help ?
www.thegsresources.com/files/GS%20Carb%20Cleaning%20Series.pdf

Alright I will try to address everything.
First, original airbox with new clean filter.
Flow out of petcock is good.
Fuel filter is new.
Have tried running it with the gas cap open.
I have sprayed starting fluid into the intake of #4 carb before and then it does fire for a short burst.
So it must be something in my carbs then.
I just got 4 new float valves in the mail that i will put in but i am not sure that is any of the problem anymore.

As a side note I did a compression test with the engine cold and it was 140. then i did one hot and with the engine running and it was only 80 psi. is this normal for it to drop when it is running instead of just cranking with the plugs out?

oh and i am not sure where or what my carb vents are. i will try loosening the float bowl. i probably wont get to all of this till sunday or monday but i will report back.

The float bowl vents are the little brass tubes between 1nd2-3and4 carbs if these are plugged it wont run right they need to be vented.i ran the lines from mine down between the pod filters and just let them hang.assuming it misses at idle try turning the mixture screw on #4 carb all the way in then back it out and see if the cylinder picks up for a few seconds if it does you have a fuel problem.possibly a partially plugged low speed circuit.

88, Red Flag. repeat comp. check..140 psi cold 80 hot. many guages are unable to cope w/ running engine. if #'s agree w/ Kicking/cranking dead-eng.hot, 2 possibilities come to mind. 1st, valve clearance going away hot, 2nd valve/s sticking when up to temp. rule of thumb, compression needs to be @ 90 psi to support life.hope this helps, G

compression is only at 80 when the engine is running. if it is just cranking hot with the plugs out it is close to the 140 psi mark.

76 LTD wrote:

The float bowl vents are the little brass tubes between 1nd2-3and4 carbs if these are plugged it wont run right they need to be vented.i ran the lines from mine down between the pod filters and just let them hang.assuming it misses at idle try turning the mixture screw on #4 carb all the way in then back it out and see if the cylinder picks up for a few seconds if it does you have a fuel problem.possibly a partially plugged low speed circuit.

dont have these tubes. i have a set of bs34's. original to this bike.
i am not really sure where they vent too but i have no brass tubes on the outside of the carbs.

ok here is an update. i ran a guitar string into all the little holes i could find. it didnt go through any of them because of the bends they all take but i stuck it in as far as it would go. i also replaced the float valves and seats. now it runs way better. i just replaced all the plugs but the old ones where a nice tan color. all 4 of them. #4 pipe gets hot.
one little problem still. it pops a little out of the pipes. i am not quite sure what is causing this. my carbs might need synching which i will do again soon. there is still a little hint of a vibration higher up in the rpm range but much better than it was before.
so i got it running much better but it isnt quite perfect yet.
and i didnt try loosening the float bowl on #4 and running it like that.

ok so i took the bike on a quick 150 mile ride today and it performed beautifully. it ran great.
topped off the gas when i got back and parked it. came back 4 hours later and there is a puddle of gas that has dripped out of my airbox. start it up runs like crap. obviously fuel fouled spark plugs. now i know my petcock isnt working but shouldnt the float valves hold it. they are brand new.

88alltrac wrote:

ok so i took the bike on a quick 150 mile ride today and it performed beautifully. it ran great.
topped off the gas when i got back and parked it. came back 4 hours later and there is a puddle of gas that has dripped out of my airbox. start it up runs like crap. obviously fuel fouled spark plugs. now i know my petcock isnt working but shouldnt the float valves hold it. they are brand new.

At least one float valve is leaking for whatever reason. Could be grit or crud. Maybe a float issue.

Would hasten to assure that fuel has not invaded the crankcase and contaminated the oil. Sniff-test and physical examination of oil condition.

As this problem may also occur while riding, a properly functioning petcock is not the ultimate solution.

Good Luck!

every time it does this i check the oil and it never seems to make it that far. i guess it runs into the airbox but not down the crankcase breather.
the float valves and seats are brand new and i have a fuel filter on it.

perhaps the floats are binding up somehow.

maybe they get stuck either open or closed on #4 and that would explain switching intermittently between either a horribly fouled plug or one that looks brand new