So I recently traded for a really clean 2003 Yamaha Banshee. Very clean and stock/unmolested, but also neglected.
I got it in trade for something that I feel was worth significantly less. Here's why:
It's got a serious misfire on the right cylinder. Fires when cold and the choke is on, then when the choke goes in, it stops firing on that side. PO said it ran good 2 years ago but has been sitting since.
In the interests of cleaning it up and getting more aquainted with the bike in general, I did a compression test. Both sides are low-ish, but not low enough to not fire. 115 psi on the dead side, 112 on the good side.
I did a crankcase pressure leakdown test. Passed with flying colors. Held 6 psi for 10 minutes with no leakage noted on the gauge.
I swapped plug wires left to right to see if the miss would follow the ignition. Nope, still missing on the right side. (note I have not changed plugs yet)
Carb on the dead side is dirty and has large amounts of schmoo/mung inside the cap and on the slide. I haven't taken the bowls apart yet.
Here's what I've narrowed down the possibilities to:
-spark plug
-reeds (maintenance part, will be replaced anyway)
-carb issues(most likely I think)
Anything else I should consider?
clogged pilot jet and or the passage inside the carb is most likely.
Clean out the carbs, make sure every air passage and jet is clear. You mentioned the reeds, definitely replace them before trying to run it again.
With compression that low you really need to pull off the jugs. Even if your carbs were right, it wouldn't run very good with that kind of compression readings. Hopefully the bores will be ok, and you can just hit the pistons and rings. The Banshee has electric power valves right? Make sure they are intact and working.
In reply to HappyAndy:
From my reading and talking to a few people with experience, those compression numbers aren't THAT low for a totally stock Banshee. But yes, I will do a top end anyway. Cheap and easy. No power valves on the Banshee at all. It's what gives them their famous "light switch" powerband. It also makes them very easy to service.
In reply to doc_speeder:
I never knew that. I always thought that the Banshee engine was identical to the RZ 350. 
yamaha
MegaDork
8/9/15 7:34 p.m.
In reply to HappyAndy:
I think those power valves are what give the RZ more oomph than the banshee.
Idk what was done to it, but we had an RZ up here throw down 71whp last week. 
Sounds like a carb issue, those run an enrichment circuit, not a real choke, which is likely feeding it fuel.
In reply to yamaha:
It's not very hard to build a Banshee to 75 whp. I think the power valves broaden the power band but I don't think they contribute much to peak power.
In reply to Kenny_McCormic:
Agreed. But now that I pulled the top end, one cylinder is pooched so that will get attention while the carbs are being rebuilt/cleaned.
