1 cylinder cold, what to check?

[grabberblue]

My number 3 cylinder is not firing, exhaust tube is cold. I checked spark and there is one but looks kind of weak in my opinion. All other tubes get hot, although # 1 is not as hot as #2 and #4. Compression checks out OK with #3 the highest. What might be the culprit? It is getting gas, is this possibly the coil wire problem inside the advance unit?
Thanks, any feedback is welcome.

[garyrc]

try to cut back about 1/4 inch off your plug wire. reset the boot. also pull the drain plug from #3 carb drain fluid and set your tank to prime. let alittle fluid run out for two resons. 1 to flush out any dirt and to make sure your are getting gas. if this does not work try replacing the plug in #3.. one other thought is that if the carb is flooding this would cause a dead #3.

[grabberblue]

Thanks Gary,
Yes I did cut back the lead wire and reinstall cap, I also checked drain for gas. I also replaced the plug with one known good. Same results.

[garyrc]

check to make sure that you are not flooding the carb on #3 i am not an expert but i would think if it was electrical it would be on at least to cylindes. sounds like a possible carb problem

[garyrc]

The only reason i keep stressing the carb issue is that my number one was not firing spent about a week very mad because i could not find the problem turns out i had a float sticking causing drowning. also if this is the case make sure fuel has not gone into the oil. the best way to check that i have found is the old stick test.

[grabberblue]

Yes I have been fighting carb issues. I have another carb I can put on to seeif this helps. Carb is not flooding I have checked that, might be too lean as Pod filter might have hole?
Thanks,
John

[TopCatGr58]

Hey GrabberBlue,

Simply swap #3 and #2 wires/plug caps with the other cylinder, and if the #3 cylinder then gets hot, and #2 doesn't, then you know it's in the COIL, wire, plug cap! IF #3 stays cold, then you know it's the carb.

With a weak spark, and high compression, it may not be strong enough to fire under pressure!? Keep at it!
T.C.

[skids]

Like TC sez, Caps do go bad and they are cheap to replace!

Originally posted by TopCatGr58
Hey GrabberBlue,

Simply swap #3 and #2 wires/plug caps with the other cylinder, and if the #3 cylinder then gets hot, and #2 doesn't, then you know it's in the COIL, wire, plug cap! IF #3 stays cold, then you know it's the carb.


T.C.

[thumperjsa]

Are you positive you are getting gas to it?

I had one cylinder not getting hot, sprayed some wd40 on the intake and found out why. If you have a vacuum leak at the intake manifold, you won't get fuel in the cylinder to fire.

[tab1324]

the dreaded choke hole

I'm willing to bet it's the choke hole in the float bowl on the suspect carb that's the problem. Is it getting hot after the bike is warmed up and run for a while or is it just at start-up and takes longer to heat up? If this is the case, try cleaning the choke hole.

There's a very tiny hole where the choke tube gets it's fuel from located in the float bowl flange. There's a photo somewhere in a thread that shows it very clearly. I had this exact problem - wasn't the coil, wires, caps - it was the choke holes.

What ever you do, don't drill them out with a drill. Clean them with a very small stiff wire like a bristle on a wire brush.

Let us know if this is it. That's what my money is on.

Tom B.

[tazcu]

i have a cold pipe on number 3 also...running like crap when i first start the bike...pipe gets hot after awhile...back fires alittle 2...lightly pops while i'm driving it...will do a couple of checks on it this weekend...rebuilding a 4x4 so i have been busy on it...did anyone find the pic of the hole for the choke...not to sure where it is located...should be sycrinized but i have to get ahold of someone to send me a sycrinizing tool so i can do it...i don't have one myself...

[grabberblue]

After all the great replys I went to work on it this weekend.

I had already checked the little jets in the float bowl a couple of weeks ago after reading a post on them.

First I wanted to tripple check to see if there was gas, swap wires, and check vaccum leak, as prescribed in other posts.

The first thing i see is that the chrome cap from the POD on #3 is missing. This must have happened sometime during my last ride as it was on there when I put the carbs back on. I guess that explains why it was running better at the start of the ride vs the end.

I went to the bike shop and peplaced the POD, started up the bike and noticed that #3 is now firing!! Great news except now #4 is cold!! WTF?

So now anyone got any other ideas? I would greatly apprecdiate them.... TIA
John

[Mullineaux]

I know this is an old thread but because google indexes this site well and helps me fix stuff I thought I'd post my fix. I just had this same problem on cylinder #2. Couldn't find any leaks so I checked the resistor in my plug wire. It tested fine but then I noticed the spring that goes in there was all corroded. Sprayed it with contact cleaner and wiped with a rag a few times and poof! #2 is back in business.

[MPittma100]

Wtf

Another fuel related problem is that a float can stick in the closed (up) position and cut fuel supply to that cylinder. It can get stuck on the bowl gasket. So you may get fuel initially to that cylinder until the float closes (the needle) for the first time and then it sticks and will no longer fuel the cylinder. This will (can) happen when carbs are installed after a cleaning/repair.

MP