TOPIC:

I'm havining a problem with one cylinder. The bike has been sitting for months so I Thought I'd put in new plugs and oil. Of course a new battery was also needed. She fired right up but I could feel that it was weak on one cylinder. I pulled out the plugs one by one and found one that is pitch black. I checked the old plugs as I took them out and they all looked normal. they probably didn't really need replacing but it sounded like fun. The new plugs are all sparking fine. Is this a sign of a stuck choke on that carb. If so any suggestions on how to fix it. thanks. SSalyer

a stuck float maybe but i doubt a stuck choke

Please put your bike year/model in your signature by editing your profile. Also your location would allow local members to provide help.

You didn't mention which plug is fouling. I would FIRST eliminate electrical issues before attempting to fix the problem by getting into the carburetors. The 1&4 and 2&3 coils are paired and those cylinders fire together. If the #1 cylinder is fouling, switch the 1 and 4 plug wires and see if the problem MOVES to the #4 cylinder. If it DOES move, the problem is electrical and if it stays on the #1 carb, then the problem is carb related. I know you mentioned you thought spark was good across the board but this is just standard troubleshooting technique.

If your bike is one with an accelerator pump on #2 carb (second from the left), it's possible that a diaphragm has ruptured and fuel can be drawn in behind the the slide.

- Nate >>

George, Thanks for the tip. It's firing properly

Nate, It is the second cylinder from the left. Any suggestions on further diagnosis
Scott

If it's a vacuum-type petcock (it'll have ON, PRI, and RES, with no OFF setting), be sure you're not getting fuel in the vacuum line. If the petcock diaphragm has a hole in it, and the vacuum line runs to that carb (running to #2 seems to be common), then fuel in the vacuum line will cause this behavior.

If it's not petcock issues, check your adjustment screws. If there are adjustment screws on top, your carbs have air screws. Screw it in until it seats LIGHTLY, then back it out 1 7/8 turns to start.

If there are adjustment screws on the bottom, they're fuel screws. Turn it in until it seats LIGHTLY, then back it out 1 1/8 turns.

These are starting numbers, and will get you in the neighborhood of where you want to be. Consult a factory manual or possibly the sticker under your seat for your specific bike to be sure.

ssalyer wrote:

George, Thanks for the tip. It's firing properly

Nate, It is the second cylinder from the left. Any suggestions on further diagnosis
Scott

take the #2 plug and put it on #1, see if the problem moves. NGK plugs are tempermental, if you drop them even an inch they may not work.
I banged my brains last year back and forth (right after installing new plugs).

they will fire outside the head, but not while screwed in.

Thanks, Chet. I forgot all about the vacuum petcock, even though I have a bike with one.

- Nate >>