Panhead misfire : V-Twin Forum: Harley Davidson Forums

yamabob · 02-09-2009, 11:24 PM

I am working on a 61 panhead. The problem is it misfires on the rear cylinder. It had the original linkert carb on it until recently and it missed then but on the front cylinder. I replaced the coil and it seemed to remedy the situation. Now I have put a 38mm mikuni vm on it and it misfires out of the rear cylinder. I have tried different jets and it doesn't help. The coil is good. The rear cylinder will only fire every 2-3 seconds at idle and doesn't get much better when revved up. Front cylinder runs great. I have been playing with this thing for a couple of days trying to get it right but I need some help.

springer- · 02-10-2009, 05:00 AM

Have you checked/changed plug & wires?

Is it a distributer? How are the points and condenser? Is it timed properly?

Does it have a fuel filter on it? Is it clean? Does it touch the heads or cylinders in any way?

Have you checked for good fuel flow to the carb?

Other potential issues would be valve to seat seal, lifters, pushrod adjustment (if it applies).

Start with the simple stuff first.

route66paul · 02-10-2009, 11:39 AM

check the bushing on the distributer. If it is too loose, you set it for one and the other fires wrong.

yamabob · 02-10-2009, 01:06 PM

The plug wires are brand new and when switched on the coil makes no difference. The plugs need to be changed but I switched the plugs front to back and it made no difference.

The points and condensor are new. The timing is questionable, might play with it.

The fuel filter is clean and good flow to the carb.

The pushrods seem to be adjusted right and we did a compression test not long ago and both cylinders were the same and ok.

The thing that gets me is that it switched. The misfire used to be on the front cylinder and I replaced the coil, wires, and plugs. It ran good for a while and now it misses on the rear cylinder.

springer- · 02-10-2009, 02:07 PM

Have you checked for any intake leaks? Get new plugs to continue troubleshooting.

yamabob · 02-10-2009, 03:57 PM

I did check for intake leaks. I think it is a carb issue. I was playing with the floats and now the rear cylinder runs better but the front is lean. Actually they are both lean but the front is missing now and shooting flames out of the exhaust.

What I need to know now is what is the float arm height for this carb? It is a 38mm mikuni vm roundslide with independent floats.

I'm also going to reseal the intake and put plugs in it. I'm sure its something little and stupid that I'm overlooking.

atrick · 02-10-2009, 06:27 PM

Had same problem with 78 glide and it ended up being intake leak on rear cyl. One of the o rings was cracked and it would come and go with engine tempurature change. When i would play with carb I guesss I moved it just enough that it would go away then show up latter a couple days latter. Finally got tired of playing with it so I pulled the intake and there it was.

yamabob · 02-13-2009, 02:33 PM

Ok so I resealed the intake, reset the float and put new plugs in it. It is still missing on the rear cylinder. I'm now thinking that it may be a timing issue. It only misses bad below 1/2 throttle. Above half I really can't hear it but it feels better. I will check the plugs later and let you know.

baggersport · 02-13-2009, 02:51 PM

Have you checked the gap on the contacts to be equal on both sides of the lobe in the distributer (front and rear)? Wiggle the shaft as paul mentioned. If the bushing is good and you have different measurements.....tap the mounting bolt for the cam lobe in the direction needed to get even measurements (to spec.) on both openings.

.

nmaineron · 02-13-2009, 06:49 PM

Are you trying to do this with the bike on the side stand?Reason is that if you have a heavy rake or extension that puts the bike high in the front and low on the left side you could be flooding your rear cylinder and fouling the plug.

yamabob · 02-13-2009, 10:04 PM

The distrubutor shaft has no play to it and the points are the same for both cylinders.

It doesn't matter weather it is on the kickstand or going down the road it still misses.

Tonight I pulled the plugs. The front is rich but dry and sutty. The rear is covered in unburnt fuel. I also played with the timing and niether advancing or retarding the ignition helps. Tormorrow I will play with the floats again with fresh plugs now.

Hillside · 02-14-2009, 07:39 AM

Take a look at the pushrod adj, and/or the lifter wheels, while your checking.

rbabos · 02-14-2009, 10:15 AM

deleted
Ron

rbabos · 02-14-2009, 10:23 AM

Quote:

Originally Posted by yamabob

The distrubutor shaft has no play to it and the points are the same for both cylinders.

It doesn't matter weather it is on the kickstand or going down the road it still misses.

Tonight I pulled the plugs. The front is rich but dry and sutty. The rear is covered in unburnt fuel. I also played with the timing and niether advancing or retarding the ignition helps. Tormorrow I will play with the floats again with fresh plugs now.

Same points, but how's the gap for each cyl? It uses a different part of the cam lobe for front and rear.
Ron
Ron

yamabob · 02-14-2009, 11:01 AM

Thats what I meant, same gap on the front and rear lobes.

I already checked pushrod adjustment, they are okay.