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74 MT250 Elsinore problem


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on my Elsi that i have been restoring. I got her insured and registered yesterday. took her out then after 10 min of riding around, the engine started to rev out of control. The throttle or cables did not feel stuck or sticky. After i got it stopped, I restarted an figuered to let it run me back home. It would then bog out like i was in third gear. It idles fine but after it gets warm it starts to rev higher. Carb is rebuilt with a new screw set. I have not replaced the throttle cable because it feels ok but its got that weird split cable for the injector and carb. Any suggestions??? Keith 👍

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Did you splitt the case during he rebuild and replace the crank seals??? Any chance you have an air leak from the rubber intake boot?? Are you turning the bars when the throttle starts to race. Are you able to stick a mirror down the airbox intake to see if the slide is moving when turning the bars?? I ended up selling mine to a friend in Illinois, I miss it already.

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I did not split the case on this since it is a low milage machine with good compression. So all the crank seals are original. I will double check the intake boot. The handle bars were not turned at the time of engine race. Once I got back, restarted, then let it heat back up, then gradually it would start to race again. I was sitting on it with the bars straight letting it idle with some engine blips to keep it from loading

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It would then bog out like i was in third gear... Carb is rebuilt with a new screw set.

My guess is that something happened to the carb during rebuilding, which seems to be the rule rather than the exception. 👍 The bogging indicates a lean condition to me, most likely in the pilot circuit (the pilot jet and the replaced? screw). I assume you've adjusted the idle mixture screw already?

My friend's MT250 would idle fine too, but if I turned off the fuel petcock the bike would gradually race higher and higher; I believe I posted about it in another thread. The carb was running so rich that the idle speed screw had to be turned way in to get a decent idle speed, then as it ran out of gas the mixture turned correct and the rpm headed to the moon.

When the engine races, try adjusting the idle speed screw down for a normal idle speed; this should change your symptoms to "motor won't idle when cold", which I think may be easier to troubleshoot. I would carefully check the pilot jet and all associated passages, and you might want to try the old screw set if you still have them.

Ray

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Ray Rivers is on it. try running the air fuel screw in until it stops, back it out 1 1/2 turns and then adjust idle with the idle screw to around 1200 RPM. If adjusting acrb screw is ineffectual then the crank seal is leaking, most likely the left one, as it is not bathed in oil.

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