Missfiring cylinder, Is it my carbs??

Are you sure the spark plug wire to #4 is in good condition?

yea. i replaced them. they ohm out ok and i have switched #1 and #4 with no change in symptoms.

i feel that I have been quite thorough with all the obvious stuff. but maybe there is something that I have missed.

when it is at its worst I get popping out the pipes a little. not much maybe once every 15 seconds on average.
i have removed the air suction valve(or whatever that emissions stuff is called).

I'm thinking intake valve sticking open. Maybe I'm daft, but wouldn't that give you the exact set of symptoms? good spark, running for a little while when the cylinder is dry and new plug is in, wetness on plug after. It seems that if the valve was not closing completely then it would slowly flood that cylinder right? If you get a few minutes out of it after replacing the plug, I'm wondering if it's the fact that the cylinder got time to air out. Could you try pulling the plug, cleaning the plug or torching it clean and then waiting 10 minutes for the cylinder to dry and then trying it again?

Also have you tried draining the carb bowl manually, cutting the gas off and then starting it right after you cut the gas back on, so the bowl doesn't have time to overflow? I think you'll find that the carb isn't the problem because you have already swapped all the parts out and cleaned it 14 times. Unless you forgot a seal or are putting it back together incorrectly. That's what I'd do, slap it back together wrong and blame the bike instead of myself. But that's just me.

But really, trust someone with more experience than me.

88alltrac wrote:

...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 feel that I have been quite thorough with all the obvious stuff. but maybe there is something that I have missed.

.

I suspect the bike's battery of reportedly unknown condition is failing to hold charge, and has not been load tested (which test it may likely fail).

Mis-fire being specific to a particular cylinder is not particularly significant or dispositive to the issue of battery failing to hold a charge. This means a real charge -- not simply measuring 12 volts across the terminals which even a bad battery may muster.

but maybe there is something that I have missed -- one thing missed is failing to report results of running off the car battery, or even if this test has yet been performed. If not yet done, remember when doing so to install a brand new spark plug in the suspect cylinder.

Good Luck!

i have not yet done the battery test. due to some odd circumstances it has been hard for me to get ahold of a good charged car battery.
i will listen to your reprimand :blush: . no more complaining about it on here until I finish this test.
i guess that the battery thing just didnt make sense to me at first. i thought that it being on just 1 cylinder disproved this. maybe #4 has just a little bit of a disadvantage to start with so it is the first one to not fire?

well i will try to borrow my fiances car tonight and test this bugger.

88alltrac wrote:

...the battery thing just didnt make sense to me at first. i thought that it being on just 1 cylinder disproved this. maybe #4 has just a little bit of a disadvantage to start with so it is the first one to not fire?....

Yes. Like the weakest link in a chain.

Having more than once personally experienced a single misfiring cylinder due to failing battery, am thinking such may be the culprit in this case.

But if not, it will at least be ruled out so we may look to other areas.

Good Luck!

hear ya loud and clear.
this battery could be 10 years old, who knows.
i get stuck thinking it turns over strong and has never died so it must be good. i know this isnt always the case though.

I have been watching this thread since the beginning and keeping my mouth shut because Patton really knows what he's talking about but something caught my attention a few posts back

Quote
when it is at its worst I get popping out the pipes a little. not much maybe once every 15 seconds on average.
i have removed the air suction valve(or whatever that emissions stuff is called).
End Quiote

I dont have experience with this emmissions stuff but am wondering what did you do when you removed this stuff ? Did you use block off plates or did you connect one side of the valve cover to the other and were there hoses going in or out of the carbs which need to be capped ? Could ther be something overlooked here ?
Just a thought

I connected a hose from one side of the valve cover to the other and all the ports on the carbs are plugged and the hole in the airbox is plugged. I have checked all over for vacuum leaks.

I did the car battery test with a new plug. Cylinder #4 still didnt fire. Pulled the plug after trying the car battery and the spark plug still looked brand new. Not wet, no color. nothing!

i pulled the boot between the carb and airbox off just a little bit and it didnt really feel like there was much if any vacuum there. This would explain the clean spark plug but is it possible to have good compression and have the cylinder not bringing in any air.

i guess it cant be the vacuum thing. when i synced the carbs that would have shown up.

88alltrac wrote:

...did the car battery test with a new plug. Cylinder #4 still didnt fire. Pulled the plug after trying the car battery and the spark plug still looked brand new. Not wet, no color. nothing!....

Thanks for the progress report. So turning attention back to carbs. Probably already noted, but are pods or original airbox fitted?

On the premise that engine will crank up and run for a short time hitting on all 4 cylinders, until #4 begins misfiring, at which time plug is dry and looking brand new, and there's a visibility good spark quality when tested outside the cylinder.

Is #4 mis-fire symptom the same regardless of whether bike is being ridden or on centerstand with engine running? (Preferably using a foor fan for cooling while testing). Symptom may be worse while riding due to increased fuel requirement.

Given these conditions, misfire might be resulting from fuel starvation in #4 carb. Dry plug is evidence.

With bike on centerstand and engine running while hitting on cylinders #1/2/3 and misfiring on #4, could spray some starting fluid into #4 carb intake (okay to remove pod if so equipped) or remove standard air filter (if airbox being used) and spray into air intake. To determine whether #4 cylinder momentarilty begins combusting with aid of starting fluid.

Above test will help determine whether fuel starvation is the issue in #4.

One possible cause underlying fuel starvation in a single carb is an obstructed vent to the floatbowl. Would assure the #4 carb floatbowl is properly vented. One test could be (shoot me now :lol: ) to temporarily loosen the floatbowl screws enough to allow outside air to enter the float bowl through the gasket area (which assures venting) while test running engine with bike on centerstand. If decide to do a short road test with loosened floatbowl screws, there'll likely be some fuel leakage, so be mindful of it and keep the roadtest as short as possible, just to determine whether #4 cylinder begins misfiring.

If fuel starvation is confirmed, and it's not due to improper floatbowl venting, another cause could be obstructed passage in the pilot circuit (that all the lemon juice, carb soaks, air pressure, and prior cleaning efforts have failed to resolve).

Some of the pilot circuit passages require more than blasting with carb spray to adequately clear them. Sometimes a small guitar string (e string), wire fish leader, or other physical assistance is needed to knock out the crust. WEAR EYE PROTECTION while blasting passages with carb spray.

If #4 cylinder isn't getting fuel, but runs okay when getting fuel, it indicates a carb problem, most likely in the pilot circuit or insufficient floatbowl venting, or possibly clogged orifice in floatneedle seat.

Let us know about the test results with starting fluid and assurance of floatbowl venting.

And just for good measure, try a test run with the fuel tank cap left ajar (not snapped down) just to assure necessary fuel tank venting.

If not already done, with engine not running, also disconnect fuel line from petcock and look for ample continuous flow of fuel from petcock. And assure inline fuel filter is clean. All to assure ample fuel supply is reaching the carb fuel inlet.

Good Luck!