twin- one side rich, one side lean...help!

[Treebender]

I have been trying to understand why my 77 Panther 5000 engine has one cylinder much richer than the opposite side for a couple years and need some help from a 2-stroke genious. The rich side is the clutch PTO, and the fan side is way lean. Engine is single carbed Mikuni.

Here is what I've done so far..

Compression 120psi each side.

Swapped cylinders and swapped pistons from side to side, rebuilt lower crankcase twice with new seals each time, and added a new after market CDI. Ignition coil is also new. Upper end gasket kit replaced each time of rebuild.

Could the crankshaft be out of phase, or would there be something in the ignition that would allow greater spark at 180-degrees vs 360-deg? What else could make the engine so much leaner on one side vs the other?

PS: I hope this is the correct spot to put this thread.

 

[Treebender]

Over the weekend, I checked the phase angle of the sled by just measuring bdc and tdc, and the phase angle is good. I also took all shrouds off and sprayed carb cleaner around the engine for vacuum leaks...no leaks. I also tried a different fuel pump as I thought a diaphram might be bad, but no luck.

Is there a way that an engine can fire stronger at 180deg vs 360deg? I know that at every 180deg an engine fires. Could this yet be electrical related?

 

[mrnice]

I am not an expert, so please take this advise with a grain of salt. If you have 2 carbs make sure they are sync'd. It does make a difference and it is easy to do.

 

[Arctic Thunder]

Total shot in the dark here.

single carb so you can't stager your jetting.

How about your reeds?

Also how much difference are you seeing in temps. 30 deg or 200 deg.

30-50 is probably normal. 200 isn't.

Might want to check crank seals.

Thunder

 

[sled_guy]

It's completely normal for one cylinder to run hotter (lean) than the other. Heck, on triples they often all 3 are different. There are many things that can figure in... like cooling, air flow to the intakes, air flow through the hood compartment and then internal engine things like fuel pump pulse location, fuel pump strength, charge mixing in the bottom end and on and on.

You mention that the side that has the fan on it is the leaner one... I'm betting that is the reason right there. That cylinder gets cooled a bit more than the other side which changes it's efficiency.

With a sled with multiple carbs, it's just a matter of jetting up 1 size or so to compensate. With a cylinder carbed, twin... not possible. But they must be pretty close or you would have melted one down by now.

sled_guy

 

[NapaMatt]

It's completely normal for one cylinder to run hotter (lean) than the other. Heck, on triples they often all 3 are different. There are many things that can figure in... like cooling, air flow to the intakes, air flow through the hood compartment and then internal engine things like fuel pump pulse location, fuel pump strength, charge mixing in the bottom end and on and on.

You mention that the side that has the fan on it is the leaner one... I'm betting that is the reason right there. That cylinder gets cooled a bit more than the other side which changes it's efficiency.

With a sled with multiple carbs, it's just a matter of jetting up 1 size or so to compensate. With a cylinder carbed, twin... not possible. But they must be pretty close or you would have melted one down by now.

sled_guy

IN Bold..

SLed-guy took the words right out of my mouth!

Yes, temps effects jetting.. HUGE.. PERIOD!

Just need a weekend with snow.. Should have it Dialed!!
Hit the nail on this one!!

 

[Summit8]

I've been fighting this problem on an 02 Summit 800 for 3 years now, Mag side burned down numerous times, gave up on the 840 top end and went back to stock HO cyls. w/ stock head ( had RKT 14:7-1 which worked very good) and temps looked good if not a little lean on last ride of the year.
This season, EGT temps were off, cleaned carbs, no diff., last ride temps started to run together about 1050-1150 but was running 330's on mag and 310 on pto. The carbs had been rebuilt by Xtreme Perf. out of CO. and vented to the airbox w/ Jack Harris powerJets for compensation. Have adj. needles shimmed, plugs look good on color, just runs rich on bottom end. BJ installed new crank and trued when 840 kit was installed so crank has been gone through, what else could it be??
Intake boots have cracks on top but have beeb sealed w/ SealAll and no differance in EGT,have sprayed starting fluid around intakes and no differance, could be Mag seal or worn carb slides???
Any feed back would be appreciated. Gonna have a bunch of grat ZX chassis parts f/s soon.:face-icon-small-win