Odd misfire.

A while ago I started noticing a slight miss on the Left side of my 850. After playing around switching coils, plug wires etc I thought it was related to ignition. My coils tested ok but had been damaged by the wrong clamps at some point & my Boyer was so old it was literally falling apart. So in went a new duel output coil & Tri-Spark. Nice, clean & simple. All new wires too. Starts great, timed at 29' after verifying my timing marks with a degree wheel etc. Revs good but I still have a miss on the left. Running a single Mikuni, valves and cam chain adjusted. I'm going to do a compression check today so I will know more then but if it's not a spark or carb issue what would you think of next?? Plugs are new, gapped etc. could it be a sign of a worn cam, or valve issue?? After reading the recent thread on Champion plugs I think I will try a set just to see if it doesn't like the NGKs anymore... Thanks.

New plugs are about as simple a solution as you can try.

You say you switched wires but did you switch the NGK plugs side-to-side?

As everything shared up to the HT leads, this only leaves HT leads, plug boots and plugs as cause. Bad cam lobe does not missfire just gives popo power loss as rpms climb, UNLESS the worn lobe slack put a whip lash of chain delay in ign triggering but then would affect both sparks the same. Might look after dark. Its possible to have intermittent short that vibration cause in conductors that puts a make-break plug fire signal in on top the normal ones but again should affect both side the same but maybe for the ~15% weaker spark on the reversed polarity gap. If possible one side has a oil leak but would expect some smoke or smell. Maybe one the manifold inside bolts has backed out interupting flow at times and can catch it now before inhaled. Best wishes or may mean just not man mechanic enough to get a fully fettered Commando, ugh.

gtsun said:

A while ago I started noticing a slight miss on the Left side of my 850.

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Idle? light load? Heavy load? If at idle, definitely act on the following!

hobot said:

Maybe one the manifold inside bolts has backed out interupting flow at times and can catch it now before inhaled.

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Light misting from the tube of brake or electrical cleaner will help pin-point where it might be coming from, if a manifold leak is the culprit. Be sure to spritz a bit up ahead of the manifold where the two inner bolts protrude through.

Nathan

Well all good thoughts guys. HT leads are new Taylor's that came w/new coil from CNW, seriously doubt there is a problem with them. (Thanks Matt). As for the intake manifold bolts I was just in there and checked them so doubt they are loose. Going to do a compression check & re check valve adjustments tonight. And as for my "manhood" Hobot? No it's intack, my sanity however has always been in question but then I wouldn't have been playing with Nortons since my teens if it wasn't.. Thanks.

gtsun we seem to share similar self enactment hobby wisdom world views but just occurred to me there are also two unshared exhaust exits to seal and air leaks there known for miss fires so who knows hobot hammering the minions down cold first time every time might be in your future. Every get out on a limb to hand saw it and sag traps saw so ya ease to far side of cut to open the wedge but pure even torque load does not free it so must bounce shock the cut till cracks right open all the way down ...... two birds one stone.