Left miss fire but great spark!

[CaseySmithersxs]

As the title says. Me left cyl is giving kind of a blump blump blump...blump blump...blump... If that makes any sence. Haha im also getting an excellent blue spark, brand new plugs, but the bar on top of the plug is sort of sticky, not black or covered in oil, just a very light film. I looked through the forum and didnt find what I was looking for. Soooo anyone?

 

[xjwmx]

Assuming it used to run okay, a sticky float valve can do that. A weak coil can cause the plugs to foul and start to cut out; one side acts up before they both do... You can turn off the petcock and run the gas out of the bowl to try to unstick the needle temporarily.

 

[CaseySmithersxs]

Hmm interesting, those parts are cheap so thats no biggie. But what would explain the sticky plugs?

 

[xjwmx]

The coil theory might explain the plug best. The weak spark doesn't produce the kind of combustion that will clean the plug. And the deposit on the plug doesn't help the firing either, so it soon crashes and won't fire at all.

 

[CaseySmithersxs]

But sticky with oil?

 

[xjwmx]

^Sticky with all kinds of nasty partially burned hydrocarbns. Basically tar. If it's motor oil then do a compression test to look for bad rings.

So time to get on it and get 'er done. Have you tried anybodys suggestions yet?

 

[CaseySmithersxs]

Okay, where can I get one of those gauges? Never seen one before or know what it looks like lol. And how would float not being set make it miss fire?

 

[xjwmx]

Compression gauge can probably be borrowed from parts store. Look around here for how to do a compression test.

Leaking float valve will make the mixture too rich for the cylinder to fire right. The higher the fuel in the bowl is the richer, and the lower it is the leaner.

 

[CaseySmithersxs]

Im 99% positive my floats are set to 24mm each. Could just the float valve be the culprit?

 

[5twins]

If your floats are set to 24mm then technically, you're off a little bit. The spec for the '76-'77 carb set is 25mm ± 1mm. At 24mm, you're at the rich limit of the spec so a little leakage from your float needle and seat may be making things too rich. Many times, a slight leak is compensated for by the spec range and/or you can burn the excess fuel before it causes a problem. You don't have that leeway with your 25mm setting.

 

[CaseySmithersxs]

Oh okay, so maybe if I lean out both of my floats to 25mm, it could make the missfire stop? The coil is firing in every stroke, or so it seems. But when I put my hand over the exhaust I can feel the misfire.

 

[weekendrider]

Compression gauge can probably be borrowed from parts store.

If you use a borrowed gauge set up, be a little leery of the readings.
I recently used one. Numerous and repeated tests would only show 60 lbs.
Since the bike starts, runs and rides I think the gauge is questionable.
Could be my technique though.

 

[CaseySmithersxs]

so maybe if I lean out both of my floats to 25mm, it could make the missfire stop? The coil is firing in every stroke, or so it seems. But when I put my hand over the exhaust I can feel the misfire.

 

[5twins]

It's worth a try. It would be a free fix if it works. If it makes things better but doesn't totally fix it, that would point you towards excess fuel in the bowl as the cause and maybe a float needle and seat that's leaking bad enough to need replacing.

Does that left carb start leaking gas if you leave the petcock on after shutting the motor down, say like within an hour or so? That would be another sign of a bad float needle and seat. With a slow leak, it wouldn't immediately start puking gas. It would take some time for the bowl to slowly overfill and start leaking.

 

[CaseySmithersxs]

10-4 thanks buddy, what would explain the sticky residue on the plug? I know the norm is rings leaking, but I'm hoping it could be something more simple. Lol

 

[5twins]

It could be the excess fuel mixing with the oil coating inside the cylinders. Maybe it will go away if you fix the carb. If not then a compression check would be a good idea. One of the reasons running too rich is no good is because it can wash that oil coating out of your cylinders and cause excessive, premature wear. If you've been running the bike for a long time and many miles with that rich 24mm float setting, maybe this has happened.

 

[CaseySmithersxs]

Alrighty. Can I do a compression test without elect start?

 

[xjwmx]

Numerous and repeated tests would only show 60 lbs.

Sound convincing and they will break a new loaner out of stock.

 

[xjwmx]

Alrighty. Can I do a compression test without elect start?

Yep, read on here. Keep kickin until the needle stops going higher. Be sure to have the key off and the throttle floored.

 

[TwoManyXS1Bs]

...what would explain the sticky residue on the plug? ...

Leaky intake valve seal can do that. With the carb off, flashlight up into the intake port. If backside of valve appears shiny/oily/slimy or worse (layer of built-up coke, looks like coffee grounds), then that guide seal may be bad. It would allow oil mist to collect on plug...