Power Valve Adjustment cause rich condition at idle???

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GrimReeper67

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Oct 25, 2012
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Cedar Rapids, IA
Just replaced my top end after finding #2 cylinder plating was flaking off and damaged piston. Had the cylinder replated and purchased new pistons. Have everything back together and followed manufacturer recommendation on pre-mixing fuel at 50:1. Now that everything is back together it has a hard time idling and will backfire every so often when idling. When it does this, the motor sounds like its running on 2 pistons.

I am assuming this is because of the extra oil, but wanted to see what you guy thought. Was also wondering if it could be due to the power valves not being adjusted after I had pulled them for cleaning...?
 

When you say backfiring, do you mean out the intake or exhaust. This seems like a timing, electrical issue to me. Nothing to do with the powervalves. I'm assuming you have fresh plugs in there, but did you ohm out the plug caps yet ? They do wear out and can cause some gremlins. That's where I'd start. Good luck and keep us posted.
 
ssrrxx said:
When you say backfiring, do you mean out the intake or exhaust. This seems like a timing, electrical issue to me. Nothing to do with the powervalves. I'm assuming you have fresh plugs in there, but did you ohm out the plug caps yet ? They do wear out and can cause some gremlins. That's where I'd start. Good luck and keep us posted.
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^^X2. Mine backfired and blew the donut gasket apart on the exhaust (it needed replaced anyway) when the plug caps were bad.
 
Just my opinion. But if oil pump is working no need to premix. You are running a hair lean now do to all the extra oil causing the backfire. The PV would have no effect the n this but as easy as it is I would adjust them.
 
Was cases split? Oil system opened up? If NO I see no reason to pre-mix as oil system should be 100% ready to go. Still single piped or tripled? Can you tell which cylinder isn't firing? Carbs clean?
 
GrimReeper67 said:
Just replaced my top end after finding #2 cylinder plating was flaking off and damaged piston. Had the cylinder replated and purchased new pistons. Have everything back together and followed manufacturer recommendation on pre-mixing fuel at 50:1. Now that everything is back together it has a hard time idling and will backfire every so often when idling. When it does this, the motor sounds like its running on 2 pistons.

I am assuming this is because of the extra oil, but wanted to see what you guy thought. Was also wondering if it could be due to the power valves not being adjusted after I had pulled them for cleaning...?
Click to expand...

Have you cleaned the carbs lately? The low speed jet is the one you want to look at, you need to run a wire through it to get the crud out. I use stripped stranded wire, place about three strands through the jet and twist the wire. Then you can run the jet up and down the wire.
 
A lot of people recommend running the first tank on a rebuilt or new motor with a little premix in addition to the oil injection. The dealer where I bought my Viper did this to my first tank, no issues in the way it ran. I have no idea if it's really required or not, but I do know that I didn't have an extreme lean condition causing it to run poorly.
I would also start with making sure the pilots are clean and the fuel screws are where they should be.
 
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