Banshee misfire on right cylinder

[adamson350r]

I have a banshee misfire on the right cylinder. I don't know if it is sucking air, but could stator install cause this to happen?

[adamson350r]

The yamaha dealership only charged eighty bucks, but they had the bike for two and a half weeks and couldn't find out what was causing the misfire.

[Muggzy]

Do you know what diagnostics they did? For $80 they better be able to tell you EXACTLY what they did at least and what the results were? I never heard of a factory dealer that can't find a problem.

First swap plug wires and see if the problem follows. This will eliminate or confirm electrical.
Can you tell us when this started? Did you do anything to the bike before this began? what were the results of the leak-down test that the shop should have done?

[adamson350r]

Before the motor started misfiring the stator went out. I called and had the yamaha shop replace it for my dad. The right piston burn down shortly thereafter. Bored, new pistons, and cool head domes fixed the initial damage.

Some more history is that it has a one into two carb system. One exhaust would seem to smoke more than the other. After the last fix it misfires through all rpm ranges. Cold smoke comes out of the exhaust without much gusto. Can last up to eight seconds then it will fire like a heart in afib.

I swapped spark plug wires, swapped ignition box with another banshee, swapped reed cages, checked compression.

Dave moore took out the crank and replaced the pieces that hold the crank and true and welded the crank.

Yamaha shop tested all the electrical and crank case pressure and more. I just can't remember everything they did.

[Muggzy]

When you bored the cylinders, did you re-jet to a higher size? I'm betting you're running way lean. They have more volume now and therefore sucking more air. You need to add more fuel.

Close your air screws equal amounts 1/4 - 1/2 turn at a time if they're not too low already. You can move your needle clips down a notch to test this too. If you're definitely too lean, put your needle clips back and go up a size in pilots and three in mains. Then do a jetting run and see what your plugs look like. Essentially, you need to re-jet.

[adamson350r]

We did mess with the jetting already but we can sure do it again.

I have one of the old domes from before the bore job and new pistons and domes, I might put the old dome in and see what happens.

[Muggzy]

Originally posted by adamson350r
We did mess with the jetting already but we can sure do it again.

I have one of the old domes from before the bore job and new pistons and domes, I might put the old dome in and see what happens.
Uhm, "mess with the jetting" and "one of the old domes"
As for changing ONE dome. Don't do it.

Now about your jetting, It's more than just "messing with the jetting" If you tell us what mods you're running and your altitude and temp, someone on here ought to be able to ballpark you. DO NOT RUN LEAN

You'll have to do a jetting run and a plug chop to read your plugs:
You'll need a long, straight place to ride and a set of brand new unused NGK B8ES plugs gapped to 0.022" (mine have never fouled) in your pocket...

1) Warm up the engine really well
2) Change out the existing plugs for the new ones
3) ride it from 1st - 6th gear at WIDE OPEN THROTTLE
4) When you hit 6th, pull the clutch, kill your engine and coast to a stop. Put the old plugs back in and ride back to your starting point.
5) cut the threads off at the base with a dremel or hack saw.

You're looking for a 2mm wide ring that is coffee brown at the base of the cone. white or grey, you're too lean. Go UP on your main jets.
If it's dark grey or oily looking, go down. from what you've said, you'll have to go up. Don't ride it this way or you'll be redoing your top-end.
Then adjust your needle clip position to get a smooth transition from half throttle to full. Then adjust the pilots so that you start and idle smoothly. Technically you can do jetting runs at mid and 1/4 throttle too but most just do it the way I've just described.

An alternative to the jetting run/plug chop is to put in larger and larger main jets until it starts to bog at full throttle under load and then drop back down a size. The rest is the same. Problem with this is you'll potentially need a big selection of main jets.

[adamson350r]

I figured it out. You are right, it was the carb. It wasn’t the main jetting. I have done enough plug chops since I started riding two strokes in 1992 to know it wasn’t the main jetting. I am just not familiar with the one into two system. The way I figured it out was turning the idle way up and noticed as I turned it up the misfire was going away. That’s when I started calling myself bad names.
When you twist the throttle or put on the gas it fires correctly, but when the throttle lets off and or held above idle, the left cylinder fires and it could take several seconds before the right cylinder kicks engages.
So when I noticed the idle being turned up was solving the problem it hit me I need to change the pilot jet and check the height of the needle. The rest is history. I am so happy it wasn’t anything major.
One thing that was really throwing me off was that when the choke was pulled it exacerbated the misfire. I would think to myself if this is an even pull system it shouldn’t make a difference. Well the port for the choke is on the left side and does feed the left cylinder more than the right.
Now that I have the problem fixed my wife wants the plastic changed and a thumb throttle put on it. Women can be picky.

[Muggzy]

Good Troubleshooting! Glad you got it worked out