'98 600 sx twin misfire on MAG side question

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biglsells

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Grand Rapids, MI
OK, after 2nd rebuild, this time complete, went to take the sled for some snowy grass runs before the season really starts here. Ran great first 4 or 5 passes then mag side started mis firing. Limped to garage and the engine was running fine on pto side and firing every 2 - 3 seconds on mag side. Piston wash looked fine on pto side, just black on mag side. I had cleaned the carbs last season and never got a chance to use the sled since then but I took them off and cleaned them again last night just to make sure, have not had a chance to pop them back on and see what happens. Does this sound like a carb issue or could it be a coil?

-thanks-
 
Both plugs fire at the same time.

Flip the wires from one cylinder to the other. If the problem follows the wire to the PTO side it is a coil, wire, plug or boot issue. If it stays on the mag side you have another prloblem that isn't electrical.

opsled
 
Just as a backup I have another coil on the way but started wondering... There is 1 coil with two wires coming from it, if one cylinder was not firing but the other one was running fine, wouldn't that eliminate the problem from being the one coil I see? Or in the one round housing are there actually two separate coils? Just curious. Will test out soon and fill you in.
 
One coil fires both plugs at the same time, one is at TDC when the other is a "waste" spark that fires during the exhaust cycle at BDC.

Do a quick compression test, as well. Especially if you ran it for those few passes with old stale gas that was left in the tank...
 
Well I put the cleaned carbs on this afternoon, got it running and as it idled the right side was going in and out again, swapped the wires, pto side went in and out so I know the coil is bad. Yanked the coil from my 95 vmax which fit just fine, started fine and was able to give it some revs on the stand, little brake to simulate load and after about 20 seconds it started bogging reaaalllly bad, back firing non stop, bad enough it would back fire the exhaust off the manifold, what would be the cause of this? I could keep starting it but it would just back fire badly. I cleaned that carb top to bottom. Followed the guide in the tech section, the only changes I made to the carbs are - flex'd the floats to be parallel when bowl is full and one thing I never checked before but set that external screw on the bottom side of the carb (fuel mixture screw?) to 1.5 turns out per specs. It would hardly run. Ideas?
 
OK, since the one plug always stayed firing then highly likely it was the plug cap on that lead that had the issues and not the coil itself, but like you said they are one unit so have to replace the coil anyhow...
Electrical gremlins can be misleading as a fuel problem, so forget screwing around with the carbs for now.
Bypass the kill switches, I had an intermittent handle bar one on my 96 that caused a similar symptom.
Also check that the flywheel didn't come loose and sheer the key / rotate out of time. Had that happen once too.
 
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I'll try bypassing the tors next as well as the kill switch and see if that makes any difference. I took the plug cap off and trimmed the wire back and screwed it back on to see if that could be the problem, thats when the backfiring and bogging started.
 
UPDATE - Got the replacement coil pack installed, tried starting it, bam, blows exhaust off, tried again, same thing. Disabled TORS, same thing, new plugs, same thing. I was def by this time. Hoping it was not a timing issue with a sheared key I started thinking about my carbs as the backfiring started post clean. When I cleaned them I followed the guide that said to bend the tabs on the floats so that when bowl is full they are parallel with the flat surface of the carburetor. Bent them back, put it back together and it runs like a champ. What did I do wrong? I'm guessing I misread something in the guide. Regardless, back to running great, just need snow.
 
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