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Discussion Starter #1
OK, here is a tough one....

The rear cylinder has intermittent firing when at low RPMs. I can rev past it. I noticed this at St Anthony too so it is not related to the engine since this one is all new.

Things I checked.

I leaned out the idle, still did it, richened it, still did it.

Checked for spark. I took the spark cap off while the engine is running. You can see sparks jumping from the cap to the engine just like it should.

Just to be sure I swapped coils from rear to front. Same. Front runs super clean, rear barely fires at low RPM.

Re-set the valve clearance on rear jug. Same.

With the spark cap off the rear (only), the bike will start normally and run off the front cylinder alone.

With the cap off the front (only), Running only on the rear jug, I can get it to start if I try really hard and it will only run for a moment and die.
 

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Something very similar happened to me a while back, ended up being a bad cdi. Put back the stocker and it stopped. Just a thought if you haven't tried that yet.
 

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Discussion Starter #3
Crap forgot to add that to the list... I switched to the stock CDI same.. I might try the dyna too. That would be 3... :)
 

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Discussion Starter #4 (Edited)
tried the dyna, makes 3 CDIs.. same. Really doesn't want to fire on that rear jug until I rev well past stall of the comet black.... very weird.

I took the rubber jacket off the spark cap thingy... so it was just the wire and the cap that plugs into the sparkplug.

With both caps plugged in the bike will run off the front cylinder fine... but the rear is not firing. If I hold a screwdrive up to the naked cap, no rubber boot... I can see the spark jump from the naked cap, to the screwdriver, to the engine.

No better confirmation it is getting spark.. hell it was plugged into the spark plug while I did that.
 

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Have you changed the spark plug yet?
 

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Sounds like a plugged pilot jet. Not getting any fuel out of it at idle, but as soon as you begin to open the slide, it gets enough fuel from the main to let it run.....
 

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Discussion Starter #7
Sounds like a plugged pilot jet. Not getting any fuel out of it at idle, but as soon as you begin to open the slide, it gets enough fuel from the main to let it run.....

I checked and changed the pilot jets. I did it multiple times. I check the plug.. looks good as new just ugly from raw fuel. Cleaned and replaced.

It did this at St Anthony and it had different carbs....

Doesn't make sense. There is nothing in common bettween this motor and the one I had in St Anthony. If it was electrical why would it spark to the engine? Valve specs are perfect... frustrating..
 

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I know you said you checked the plug Erik but just try another one, in the many years of working on engines even something as simple a a brand new spark plug can be faulty, I'm not trying to undermine your intelligence but until you've elliminated everything you can't look elsewhere
 

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Discussion Starter #9 (Edited)
I could try but these are not the same plugs as St Anthony. Nothing is the same except the wire harness, not even the bottom end. I'll try tomorrow.

At St Anthony it did something else too... related maybe. The rear (I think) would just stop working all together.. but it would come back after I turned the engine off and on again...

Something isn't right.
 

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Discussion Starter #10
Another weird thing to add to the list...

If I start the bike using the rear cylinder ONLY... it will idle at about half throttle... any less it will die. If I give it full throttle it will VERY slowly increases RPMS but never really rev up... and it is puffing raw fuel up through the REAR air filter...

If I connect both plugs and just run the bike normal... it will NOT puff raw fuel through the rear air filter.. LOL No pressure coming out of it at all. It will only do that if I disconnect the front plug... ha ha. :lol:
 

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Discussion Starter #11
Alright I turned the carbs around backwards.. and the rear works! LOL...

Glenn is right sort of.. the idle jets are not clogged... it must be clogged higher up... like alky crap again... Probably what was happening at the races too.. ..

Amazing that it happened like this with different carbs and engine at St Anthony.
 

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Stay awa from gas that has alot of ethanol in it. Trust me. I'm rebuilding my wife's carb because someone left the fuel on. I could get fuel from carb but couldn't get fule from the carb to the cylinder.
 

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time to start purging right.... glad you got it sorted out.
 

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Usually when you have raw fuel coming back up or out the carb it is either valve timing or a burnt intake valve,from my experience anyways.
 
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