To recap from another thread, bike had been sitting 2yrs. and would not draw fuel. I took the carb off; needle valve was clogged. I cleaned everything I could, except the passageway of the air/fuel mixture screw. The head is buggered, and it will not turn more than 2 turns out, so I left it there for the moment....Put back together, and bike ran GREAT ! Apparently a little rich though, since it would start without the choke. Cruised along at 65 with no problem, and lost no speed going up hills. So before I put the plastics back on, I told Mr. redninja to ride it, since it is his bike. He said it was "surging" at high speed. Since he is notoriously poor at describing things, and prone to exaggeration, I took it for a ride. It was AWFUL ! At full throttle, speed uphill dropped down to 40-45. And the "surging", I would describe it more like an invisible had puts on the brake, the releases it, all in a nanosecond, causing the bike to jerk, repeatedly. This happens only at higher speeds. And, it would not get up over 55.

So here is the mystery....why did it run so well the first time, then not ? The only thing that was different between the 2 rides, was I had put some Seafoam in the gas. So, I empied the tank, and put pure gas in. No help. I'm thinking maybe the Seafoam might have loosened a speck of gunk, and that might be clogging something ?.....Will remove carb again and re-clean, and try to get the mixture screw out. Anything else I can do ??

This is the first time I have ever fooled with a carb, and all I know is what I've been reading here, so I'm not real accomplished in this area, to say the least.

It sounds like it's starving for fuel and since it was ok the first run, maybe the gas cap is not venting. Check that and also the fuel flow out of the petcock. Catch it in a bottle and let it run a while to make sure it doesn't slow down.

Ok, thanks skypupbob. I know the fuel is running fine, since I drained a couple of gallons out of the tank to replace the gas with the Seafoam in it. How do I check the gas cap venting ?

Vacuum leak?

Ooooh, I hope not, since I know LESS THAN ZERO about that.

Surging is usually caused by a lean condition, which means too much air. The fact that ran fine one day and not the next tells me something came loose. Another symptom of a vaccum leak is what's called a hanging idle, it that the idle runs high. That can be intermittent.

The usual suspect for vacuum leaks is the intake boot between the carb and the cylinder. Other sources are the 2 plastic covers on either side of the carb (choke and coasting enrichment).

Thanks, peejman for info.....AHA...the vacuum leak part I have covered.....already replaced the intake boot, and the covers you mentioned have been inspected and appear good.....After this weekend (Oktoberfest music business), I'll get back to it. I'm still thinking of removing the carb to re-check the cleanliness, and try to remove the stuck fuel/air mixture screw.

It certainly could be something plugging up one of the jets. Also look at the plug on the intake vacuum port. Mine failed recently and the change was dramatic.


http://www.xt225.com/forums/ubbthreads.php?ubb=showflat&Number=144820#Post144820

Jackpot ! Well, maybe. Thanks for that info, peejman. The plug was there, but has a large crack in it. For all the money I paid for the new boot, I don't know why a new plug wasn't included. I had to use the old one, and didn't think to inspect it before putting it on. So I will get a new one, and keep my fingers crossed........

Well, I finally got around to testing 2 more things on the bike.And the results are............confusing. I replaced the intake vacuum port plug; it had an all-the-way through crack on its side. Went out riding.The bike still "surged", but not nearly as much as before. And, I was able to get it up to 65, and it didn't lose much power going up the same hills as before; I was able to go up at 55 or so instead of the 40-45 the previous time. So, its better than it was, but not perfect. Next thing I did was loosen the gas cap, but that did not make any difference. ........Any more ideas before I remove the carb again ? I think I'll ride it a few more times to see if it magically continues to improve.