1997 banshee..
I thought originally I had fouled a plug. New plugs and it still sputters on the top end. I then thought I had dirty carbs. I cleaned them both several times, completely tearing them down. Still sputters. The gas is fresh.

It idles and starts fine and both cylinders fire. It revs up ok till it starts to get on the pipe. It slowly gets on the pipe then zings to the redline on only one cylinder. It still hauls butt but I can tell something isn't right and can hear only the one cylinder firing. There is good compression at the kickstarter.

I pulled the head just now. It looks new with no carbon buildup on the domes. The cylinders look almost new with the crosshatch from the factory hone still showing. There is a small amount of wear on the cylinder walls but no scoring and the ports all look good. The tops of the pistons have a little carbon buildup.

The TORS has been removed long ago.

The main jets are 270's with toomey T5 pipes and a completely stock air box with uni filter.

This thing runs great with the airbox lid removed, no sputtering and pulls hard.

It has ran great as is since I bought it new in 97. All of a sudden, it started to sputter on the top end so I assumed it had a plug problem. A buddy tells me it is too rich and that is when we pulled the air box lid and it screamed. There should be a reason though why it used to run fine and now it doesn't.

Any ideas? I am baffled.

Have you recently clean the air filter? Maybe you got too much oil on it? Also, since the tors are removed, check to make sure the carbs are lifting at the same time. maybe they are not equal and one is all the way open at the power band and the other not. New throttle cable? Adjustments a little off?

Curious though once the lid is rmoved it runs fine. Has anything happened to the snorkel or inlet to restrict air?

Are you running an inline fuel filter? Maybe thats messed, or there was a clog in your fuel delivery then it was passed?

Sorry thats all I got.

LAte

Your still messing around with that yamadog when you have a cr500af in your garage?
I sold mine last season and have yet to have any regrets.
I second the idea about the airfilter. Sometimes if I have too much oil on it the bike will run like its on choke...It will rev really fast at just a lite touch of throttle.

Is there still exaust coming out of both pipes after its warmed up?
It could also be electrical maybe. See if that one "dead" cylinder has spark for sure.

I've changed out the filter twice. It was doing it with a dirty filter. I put a clean oiled filter in and it still cut out. I then put a dry foam filter in, no oil. It still cut out.

I will check to see if both slides pull equally. That had been running around in the back of my mind. I had never done a carb sync though so I wanted to check out what I could first. Original throttle cable.

The snorkle is long gone and I checked to see if a rag had been left in the air box or a wasp had made a mud nest in there. No such luck.

No fuel filter. Fuel flows fom both inlet lines as it should. A blockage couldn't have passed as it runs oddly once the airbox lid is back on anyway.


Both pipes smoke on startup and when idling warm. Only when I rev the bike out does it not fire, warmed up or cold. I thought it might be electrical but was told that if one cylinder was firing, the electrical system was good as the cylinders share the same coil. As soon as the throttle is closed, both cylinders fire again. I'm gonna have to check the slides. That sounds like the most likely course of action at the moment.

I'm trying to sell the bike but don't wanna pawn off something with problems unless I know what it is and can explain to the prospective buyers. Once I find out what it is, I'll fix it.

A lot of times the spark plug cap where it screws into the primary wire gets corroded. When that happens, the resistence goes sky-high and tends to misfire at higher RPM's

What about reeds?

The sparkplug cap is something to look at also.

Cousin Itt, I'll check out the reads when I check out the slides. The thing has such low hours on it though that I doubt the reeds are suspect.

Thanks for the good ideas everyone. I knew there were some things that I had missed. The bike is at my parents house so it will be several days before I get back to it.

Do you have access to another ign module (blk/box) ?? Swap it out, to see if that may be your prob.

I had some similar sounding problems, swapped the box with another 'shee I had. The problem was the box, like new again. A 2 sec fix, to a problem that had me scratchin my head for a good day.

I wouldn't think it would be the reeds. When it's WOT, they're mostly open anyhow. You need to verify that there is good fuel flow to the weak side. One of my YSR's I fought a while with that.... Make sure to check below the needle/seat because trash tends to build up under there and limitthe fuel flow. Verify also the float level too....

Sunshine

I will give you 1k for it today.........

Frank, I went to a salvage yard and told em Esco sent me and he offered me 1.5K. Sorry brother, you have been outbid. Besides, this one doesn't flip over when doing donuts.

Touche moofer, hope you get it fixed so you can sell it..

I even rolled my new quad already (not doing donuts though) hahaha

Still got the boat anchor hmmmm.

Sounds like your CDI is going out, but then again it might be a fuel starvation problem like you floats are sticking and can't replenish the fuel fast enough to keep the higher RPM's.

Just my guess...

Since it's only running on one cylinder, I now know what it's like to ride a 250R. Kinda underpowered if you ask me though it would still look good sitting on the trailer.

I have ruled out the needle valves or floats sticking because it would take awhile for the mains to suck enough fuel out of the floatbowl to cause the misfire. The cutting out is instantanious when I open the throttle.

Well if your going to keep it on the trailer you better get a nice paint job on it so it at least looks good.
By the way it's river season and if you go to hot boats.com I'm sure someone there is looking for a good anchor...

Did you ck your main jet to see if there is anything logged in it. All it takes is a grain of sand...

That was my second guess after the fouled plug. The carbs were spotless.

Check the screw in the plug caps yet? You can screw an eraser(on the end of a #2 pencil) on and off the screw to polish it.

I haven't got up there yet sunshine. I need to clean up the head and upper cylinder and replace the head gasket before it will run again anyway. Great idea about the eraser.

I don't know if you found your problem yet but you should check the stators spec on the ignition coil side. A friends Banshee had the same problem and the resistance was only out a small amount. After trying my spare stator his problem went away.

Thanks SD Duner.... The problem turned out to be resistance in the spark plug wire caps, either the side that screws into the plug wire or the side that clips onto the plug itself. I cleaned em up and the bike runs great now.