Missfiring cylinder, Is it my carbs??

there is some evidence of combustion. it does fire once in a while. but it isnt wet or sooty really.

i have dipped the carbs. sprayed carb cleaner through them and blew them out with compressed air.
i dont know how to get them any cleaner.
i may have to just try to get them professionally cleaned.

i dont think it can be a clogged jet because when i switched them to a different carb the problem didnt follow.

Concentrating for a moment on ignition, if not aleady done, would assure battery terminal connections are clean and tight, and also the attachment of negative cable to engine.

Install another brand new sparkplug in #4, or swap known good plug from another cylinder. Important to remember a brand new NGK plug may quickly fuel foul beyond recovery while still appearing absolutely beautiful and pristine, and even while having noticable spark when viewed outside the cylinder. Don't know why NGK's act like this, but they do.

Would jump bike battery from known good car battery (car engine not running) and test run bike engine to see whether assured bike battery voltage makes any difference in combustion, especially #4.

This is to rule out possible issue regarding condition of bike battery. Bike charging circuit is not critical at this juncture.

Good Luck!

all battery connections are clean and tight and ground is good.
when i swap the plug to a different cylinder it fires fine in that cylinder so it cant be too bad.
i have charged the battery on a charger and i am pretty sure it is good but i will try running it off my optima yellow top and see if that makes a difference.
ill go get some more new spark plugs and see if that makes a difference.

i tore down the carbs again and this time boiled them in lemon juice.
i also fully charged the battery and put in a fresh new spark plug.
it ran pretty good (not perfect) for about 2-3 minutes then started misfiring again.
when i pulled the spark plug it looks very clean though. almost brand new with maybe a slight hint of tan. not wet at all.
when i first fired it up #4 was getting warm but by the time i got back from riding #4 was cool enough that i could almost grab it.

i will drive it more today and check the plug again but it does not appear to be fouling.
it feels like the carb is only giving gas at certain times but that doesn't make much sense either.

88alltrac wrote:

...also fully charged the battery and put in a fresh new spark plug.
it ran pretty good (not perfect) for about 2-3 minutes then started misfiring again.
when i pulled the spark plug it looks very clean though. almost brand new with maybe a slight hint of tan. not wet at all.
when i first fired it up #4 was getting warm but by the time i got back from riding #4 was cool enough that i could almost grab it.

While the problem may indeed be a carb issue, "fully charged" battery might be failing to hold a charge, or charging system is failing to keep it charged, or for whatever reason the "fully charged" battery might be shortly thereafter losing it's charge and thereby failing to furnish sufficient voltage to the ignition system.

When this happens, it sometimes runs okay a little longer with the headlight turned off to allocate most battery power toward the ignition.

Many a "fully charged" battery fails to hold its charge. If not already done, would also assure proper fluid levels in battery.

Good Luck!

i will run it off a car battery tonight to see. but wouldnt that make other plugs not fire as well. the battery is of unknown age so it could be bad. but this problem is very specific to this cylinder.

i drove the bike today quite a bit and when i was done i pulled the plug. it is kinda a brown color and it is kinda oily almost. not like drenched in oil but just a light coat. would gas cause it to become oily or do i have a small amount of oil leaking past valve seals or oil ring maybe. i never have seen it smoke but maybe it is just so slight i dont see it or something.

thoughts?

i have a haunting feeling it is the valve stem seal on the intake side. maybe it just smokes so slightly that i dont notice it.
is it possible to see the intake valve at all from the spark plug hole. i am going to try it. is there any other way to find out if your valve seals are leaking.

if the valve seals are leaking it will smoke pretty noticeable on start up also you will smell oil.

i was just thinking since #4 probably doesnt have oil sitting at the top of the valves when the bike is on its kick stand it maybe only leaked when i was driving or on the center stand.

Am doubtful about #4 mis-fire being attributable to leaky valve stem seal(s).

anyone have any more ideas. If i pull the exhaust off can I get a pretty good look at the inside of the cylinder and the valves? I have time and tools i just really dont know what to do anymore.