Popping under acceleration

[Keith S]

Hi everyone - I need some help troubleshooting an issue. Under moderate to hard acceleration, I get a loud popping sound from the front cylinder. I first thought it was exhaust coming out of the compression release, but they look normal. It just started and I have only ridden it about 4-5 miles since I noticed the issue. No exhaust residue at the exhaust port and I don't see any oil leaks / signs of a blown head gasket although these may have not had enough time to develop.

Background -

I went on a long ride and had an overcharging issue. Melted a fuse so the battery slowly went dead. When the overcharge happened, my tach stopped working. On the way home, I got stuck in traffic and the motor got pretty hot. Dumb decision on my part. I should have shut it down and had it towed home.

I replaced the fuse and checked the ground on the voltage regulator. I also installed a voltage monitor. I took it for a short ride and it was still overcharging, only this time, the fuse was stronger and did not blow. Under moderate to hard acceleration, I got a loud popping sound. Under normal power, no loud popping. At high RPM and no load, there is no popping. I brought it back home to find the bad ground.

I had the battery tested and sure enough it was bad. I also checked all of the other connections. I rode it tonight and I think I have the overcharging issue fixed with the new battery. It was at 12.89v at around 2000 rpms (guessing because tach still does not work). The loud popping still happens under moderate to hard acceleration. I only rode a couple of miles and came back home.

Any ideas are appreciated.

 

[woodbutcher]

don't know about the popping, but that voltage at the battery with the motor running should be reading between 13.5 and 14.0. 12.89 is a little low. that is what you should be reading with the motor not running.

 

[Keith S]

So I slept on this...starting to think it could be an exhaust gasket.

- Only happens under high compression
- sounds like exhaust from front of cylinder



Also - thanks for the input on the voltage. I thought it was low too. The battery is brand new and was not fully charged. I put it on a charger last night and will try again tonight and see if it reads normal.

 

[blacktopper]

So I slept on this...starting to think it could be an exhaust gasket.

- Only happens under high compression
- sounds like exhaust from front of cylinder



Also - thanks for the input on the voltage. I thought it was low too. The battery is brand new and was not fully charged. I put it on a charger last night and will try again tonight and see if it reads normal.

Sometimes a blown head gasket will "chirp" when you first start the engine

 

[Keith S]

That's just it...no chirping, no ticking. Engine runs great except under acceleration.

 

[Olde Man]

I don't know about an air cooled MC, but in a car popping at full throttle high rpm happens when you are lean. Usually right before the end of the quarter mile.

 

[Sven]

How old are the spark plugs?

 

[johnny2]

I had a popping at one time and kept on dumping more fuel to but it would never clear. This was after I had it in for some warranty work as it turned out the seal on the y pipe for the carb got sucked in, I replaced it and it was of course very rich after rejetting again it was good for a short time but then pulled in again. It is now held in with windshield sealant

 

[pauly]

It only takes a minute to check if there is an intake manifold leak.

Paul.

 

[1mndg]

Check to make sure all vacuum ports on intake are plugged or being used. Popping comes from an air leak somewhere. Intake or exhaust. I would bet intake. Make sure intake gaskets are good too.