Misfirin- bad gas?

[Perry]

I have a 2004 Chopper with about 25000 miles on it. Accidentally put regular gas in it and drove it about 30 miles to get a new tire. Started misfiring on the back cylinder. Changed plugs and filled it with premium 90. Didn't solve it. Took it to a repair shop and asked them to clean up the carb and fuel system.

They didn't do that, but performed a leak test. Reported rear cylinder was very lightly scarred and ring was looking compression. They hadn't addressed fuel system. Feel like they're wanting to make work.

Haven't had any trouble with it, and it isn't smoking, so I'm questioning. I once dealt with somebody pouring a coke in my tank and bike behaved similar to the misfire I'm having now...only worse. Any advice?

 

[Perry]

Typo..."loosing" compression

 

[john sachs]

Typo..."loosing" compression

What was the leak down percentage? What area was the cylinder or head leaking from ? Exhaust, Intake, Rings, or Head Gasket. They should be able to tell you. How much air pressure did they use for the leak down test. Was the engine smoking from the rear pipe? Any oil on the spark plug? Regular gas won't hurt your engine for 30 miles, or even several hundred miles unless your timing, or compression ratio is in the ozone.
John

 

[Perry]

I just topped it off with premium thinking it would improve. The bike would start up and run ok for about a mile or two before it'd start misfiring. I just decided to put it on a u haul trailer and take it to get it flushed out.

 

[Perry]

What was the leak down percentage? What area was the cylinder or head leaking from ? Exhaust, Intake, Rings, or Head Gasket. They should be able to tell you. How much air pressure did they use for the leak down test. Was the engine smoking from the rear pipe? Any oil on the spark plug? Regular gas won't hurt your engine for 30 miles, or even several hundred miles unless your timing, or compression ratio is in the ozone.
John

What was the leak down percentage? What area was the cylinder or head leaking from ? Exhaust, Intake, Rings, or Head Gasket. They should be able to tell you. How much air pressure did they use for the leak down test. Was the engine smoking from the rear pipe? Any oil on the spark plug? Regular gas won't hurt your engine for 30 miles, or even several hundred miles unless your timing, or compression ratio is in the ozone.
John

Thanks for the response. Compression on front was 187 and rear 190. Leak down Tested at 100psi. Leak down for front was 40% and rear 50%. Said the rear ring had some micro cracks.

On borescope he notes cylinder walls have scoring.

 

[Perry]

... I don't believe there is any visible smoke from exhaust. He did say the rear plug had a little oil on it.

 

[john sachs]

Thanks for the response. Compression on front was 187 and rear 190. Leak down Tested at 100psi. Leak down for front was 40% and rear 50%. Said the rear ring had some micro cracks.

On borescope he notes cylinder walls have scoring.

With the leak down percentage he gave you, something does NOT sound right with the test. With 40% and 50% leakage, it's a wonder the engine even runs. It certainly doesn't coincide with the compression test PSI. You shouldn't be more than 10% cylinder leakage. You may want to have someone else check it.
John

 

[Mikeinjersey]

I have a 2004 Chopper with about 25000 miles on it. Accidentally put regular gas in it and drove it about 30 miles to get a new tire. Started misfiring on the back cylinder. Changed plugs and filled it with premium 90. Didn't solve it. Took it to a repair shop and asked them to clean up the carb and fuel system.

They didn't do that, but performed a leak test. Reported rear cylinder was very lightly scarred and ring was looking compression. They hadn't addressed fuel system. Feel like they're wanting to make work.

Haven't had any trouble with it, and it isn't smoking, so I'm questioning. I once dealt with somebody pouring a coke in my tank and bike behaved similar to the misfire I'm having now...only worse. Any advice?

I wouldn't get too far into the weeds yet. Do some basic troubleshooting first. If your certain it's your rear cylinder try swapping your plug wires and see if the problem moves. This troubleshooting guide may help.

 

[knothead]

With the leak down percentage he gave you, something does NOT sound right with the test. With 40% and 50% leakage, it's a wonder the engine even runs. It certainly doesn't coincide with the compression test PSI. You shouldn't be more than 10% cylinder leakage. You may want to have someone else check it.
John

I agree with John totally....odd you got 190 but 50% leak down and the other with 187 with 40%....doesnt sound right at all to me....and you compression is that low considering the miles on it....just doesn't add up ....i would take it somewhere else like John said

 

[HMAN]

Just for shits n giggles, check and/or replace the rubber caps on top of your carb. Should be two of em....aint got nothin to do with your leak down test but may explain the sudden poor running issue?

 

[Sven]

Grooves in the cylinder are normal... few meaning. Tick [when piston changes direction] is loose piston skirts and it would snowball and lock up by now.

187 and 190 is runnable without induced misfiring. So the narrow down is either fuel or spark.

Leakdown #'s go something like this as per high performance or standard teardown time v. leak loss.

100% leak is hole in piston or bend valve.
10% leak is normal production bike teardown.
8% leak is high performance teardown.
1-2% is production/race ready.

A night test with a spray pump bottle filled with water is to let the bike idle., spray the plug leads. You see a spark jump... there is your misfire.

 

[Jersey Big Mike]

And just in the weird possibilities, does it misfire across the full rpm range.
I had a bad coil a while back that misfired my rear cylinder under about 3000rpm, then it would fire enough at least that the bike ran ok. No visible cracks, but new coil fixed it. (I never get normal problems!)

 

[Perry]

Guys, I really appreciate all the information. The bike was running as strong as ever until it started misfiring that evening. It was missing across the whole range, but I was trying not to push it too hard. Just tried to keep it running to get me my last mile home. Ended up shutting her down and went and got new plugs. Those got me home but still sputtered at higher range. I didn't expect the leak test, and the numbers meant little to nothing to me. When I test rode it Tuesday morning, it ran about a mile pretty much normal, then started sputtering pretty bad, so trailered it over there.

Thanks!

 

[Perry]

With the leak down percentage he gave you, something does NOT sound right with the test. With 40% and 50% leakage, it's a wonder the engine even runs. It certainly doesn't coincide with the compression test PSI. You shouldn't be more than 10% cylinder leakage. You may want to have someone else check it.
John

And just in the weird possibilities, does it misfire across the full rpm range.
I had a bad coil a while back that misfired my rear cylinder under about 3000rpm, then it would fire enough at least that the bike ran ok. No visible cracks, but new coil fixed it. (I never get normal problems!)

Thanks! I'll check it out.

 

[Mickmorris]

Guys, I really appreciate all the information. The bike was running as strong as ever until it started misfiring that evening. It was missing across the whole range, but I was trying not to push it too hard. Just tried to keep it running to get me my last mile home. Ended up shutting her down and went and got new plugs. Those got me home but still sputtered at higher range. I didn't expect the leak test, and the numbers meant little to nothing to me. When I test rode it Tuesday morning, it ran about a mile pretty much normal, then started sputtering pretty bad, so trailered it over there.

Thanks!

How did you make out with this problem? Did you find out the cause?

 

[Rottweiler]

Sounds like that shop wants to make some more money. I would start with easy cheap stuff first. Drain all gas and replace with good fuel. Buy new plugs and wires. If still missing trouble shooting ignition system. Coil / pick up wiring ext.

 

[Mikeinjersey]

I totally agree with Rottweiler. Your quote" it ran about a mile pretty much normal, then started sputtering pretty bad" is way more indicative of an ignition system problem rather than a compression failure.

 

[Jersey Big Mike]

The other stupid test if it's ignition based is to start the bike and while sitting wait for it to misfire and then use some ICE over the cam cover where the ignition module is and see if when it cools a little bit if the misfire stops.

 

[Mickmorris]

I totally agree with Rottweiler. Your quote" it ran about a mile pretty much normal, then started sputtering pretty bad" is way more indicative of an ignition system problem rather than a compression failure.

Totally thinking that too.

 

[Perry]

How did you make out with this problem? Did you find out the cause?

I intend to review it with the owner of the shop tomorrow. I haven't worked with them before, but hope we can regroup and trouble shoot fuel and ignition, and figure out whether there is anything to these leak test results they came up with.

Sven mentioned the scoring, and associated with the possibility of loose piston skirts that could cause some serious trouble. Brought to mind ticking noise I noticed after I backed it off the trailer and started it up. I don't know...my original diagnosis of bad gas, progressing to a bad leak test...now I'm paranoid!

If I had my bike, I'd go have a drink!