Help me diagnose my motorcycle problem. (fairly lengthy explanation follows)
Soon after posting this question
, I ended up with a 1982 Yamaha XV750 Virago. It had only 5200 miles on it and was impressively clean for a 25 year old bike, so I bit the bullet and got it. One problem the previous owner told me about was the choke -- the bike needed the choke to be on all the time or else it stalls. He told me that it didn't really bother him and he just lived with it. Since it was my first bike, I really wanted it to be perfect, so following the advice of a coworker, I added some Sea Foam
to the tank (around 1-2 fluid ounces). The theory was that there was some kind of clog somewhere in the fuel line and this would clean it out. That's when the real problems started.
The day after adding Sea Foam, the bike would not even start any more. The engine would turn over but it wouldn't stay running more than about 5 seconds. The spark plugs were badly fouled (carbon). I replaced those and it ran again, for about 5 miles, then it stranded me. Same problem - it would crank but not stay running. I duck-walked it to a nearby parking lot and it sat there for a week until I towed it to a cycle shop.
The shop rebuilt the carburetors and replaced the rubber intake manifold boots which were badly dried out, worn, and brittle. I got it back Saturday morning and it was running beautifully.
I put about 30 miles or so on it. Toward the end of those miles, it was starting to backfire (? not sure if I'm using the term correctly - basically it was making occasional "pop" sounds). Soon after that I started heading home. It was getting less and less responsive to throttle. And then finally, in the middle of an intersection, it just died and would not start again. So I walked it to a nearby gas station, got a ride home, and came back and cleaned the spark plugs as best I could with a toothbrush, rag, and WD-40. After some struggling, it started up again, and I nervously rode it home.
This has been a nerve wracking and frustrating experience so far. At least I'd like to make a learning experience out of it. What the hell is going on with this bike?
I am of course going to follow up with the shop when they open tomorrow. But I'm looking for the metafilter second opinion.