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Discussion Starter #1
Got an '81 sr250 that was found in the trash. Sweet little bike. 65 mpg in the city. Been running fine since I fixed it up, but now it will be running fine and then all of a sudden it will act like id's not getting gas. If I let it set for a while it will be fine for awhile and then boom it happens again. I think maybe it has something that clogs the jet and if I let it set it will unclog. Am I right? I'm going to have to fix it on the side of the road so I want to have a good idea of what I need to do.
 

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Sounds like trash somewhere in the fuel system. Look for a filter but if that's not there you are probably looking at tearing into the carbs. Doesn't take much to plug those little holes. The other possible is vaccum lock. Next time it does it open the fuel cap and see if it runs okay or will start immediately.
 

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Discussion Starter #3
Got an '81 sr250 that was found in the trash. Sweet little bike. 65 mpg in the city. Been running fine since I fixed it up, but now it will be running fine and then all of a sudden it will act like id's not getting gas. If I let it set for a while it will be fine for awhile and then boom it happens again. I think maybe it has something that clogs the jet and if I let it set it will unclog. Am I right? I'm going to have to fix it on the side of the road so I want to have a good idea of what I need to do.
Ok, I have a new filter that clear so I can see it's getting gas. But I just put the filter in so there may have been crud in it already.
 

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Yeah, three major possibilities. Crud in the carb, crud in the tank, or vent line to the tank blocked so air can't flow in to replace the fuel flowing out and it vacuum locks.

Hog's already suggested opening the filler cap when it stalls; that will diagnose #3.

Carry a can of starter fluid with you and next time it stalls, see if you can get it to restart and run by spritzing starter fluid. If it does, then you've confirmed a fuel starvationproblem.

At that point I'd remove and rinse out the tank, and if crud doesn't come out, plan on pulling the carbs off and paying a professional motorcycle mechanic to rebuild them for you. You can go ahead and order the kit(s) from BikeBandit.com or whereever.
 

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Another possibility is the valves are too tight and when they get hot they stop operating properly. Either don't open or won't close. On a bike found in a dumpster it's worth checking/adjusting them.

Pull the plug quickly and check compression within 20 seconds of it shutting down on you. Just put your thumb over the hole and see if it blows it off/sucks it in. Might be a little hot....
 

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Check the connection between the carb and the cylinder head. I don't know exactly how that connection works but my '82 Suzuki has a rubber intake boot and an O-ring seal. If either of those two components is bad, you get 'unmetered' air into the engine. If the rubber is just starting to crack you would get intermittent spurts of running lean. I just learned this as I found my newly acquired bike has bad O-rings and has been running incredibly lean.
 

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I had a similar problem with my Yamaha xs750 for a little while. I was so confused because it would start up and work for awhile but then eventually bog down and die.. I cleaned the carbs and it still did it.

Turns out, the guy who owned it before me had waaaaaaay too many things affecting the fuel line.... He had the two petcock lines merge to one line with a T-hose fitting, then they went to a "fuel safety shutoff valve" that I believe shuts off fuel if the bike is on fire or something, then it went to two separate in-line fuel filters, and then split into two with another T-host fitting, and then FINALLY to the carbs.... Because of all those things, there were some kinks in the hose, and basically it was starving the engine of fuel... Hence why it will run for a little while but eventually stop.

After I redid the fuel lines it fixed the problem.
 
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