w4jeh
New Member
Posts: 11
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Post by w4jeh on Feb 11, 2007 16:07:12 GMT -5
Hi, Folks, I'm new to the forum and glad to be here! I have a dilemma that I hope some of you can help me with... I bought a 1978 SR500E with 8500 miles on it from a friend of mine who used to race on the AHRMA circuit. He bought the bike new, and wound up taking the engine out of it to build up as the engine for his (now mine) race bike. So, the bike now has a 4R8 engine, which I understand is newer. I can roll start the bike and get it running, but it just won't run below 3500 RPM! I've tried just about everything I can think of - I've had at least three carburetors on it (Mikuni VM36s and 38s), as well as at least three sets of alternator stator/flywheel assemblies. I checked the low speed impulse coils on the alternators, and found one that had a wire shorted to the stator plate and fixed it, but other than that, all the alternators check out okay. I also tried two different CDIs, but i'm still getting the same result. My next step is to pull the alternator off the racer, but I was hoping I wouldn't have to do that....! I've been through all the wiring, and everything seems to be fine - anyone have any ideas? I'm betting I'm overlooking something really obvious.... Jim
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Post by G Man on Feb 11, 2007 19:09:21 GMT -5
Hi Jim. Always hard to diagnose from a distance. It sounds like you have covered a lot of the bases concerning the carbs and stators. Any engine internal issues? Check the valve adjustment? If the intake is too tight, you may experience some issues like this. Other than that, continue to check all specs and go through the process of elimination. Good luck!!!!!!!
G Man
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Post by wotavidone on Feb 11, 2007 23:06:29 GMT -5
I had a car with this problem.
Turned out the inlet manifold had a leak and was sucking air. At about three grand she kicked in and ran properly. According to my mechanic mate this was about where the leaking in air was insignificant to the overall fuel/air ratio and the mixture became actually rich enough to burn.
How might this relate to your bike? 1) Maybe your carb has a blocked idle circuit - unlikely because you have tried 3 different carbs, or 2) Maybe you have a bad leak in you rubber carb holder.
Mick
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Post by Retread on Feb 21, 2007 21:27:24 GMT -5
perform a compression check - maybe a bent valve.
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Post by colinjay on Feb 21, 2007 22:33:08 GMT -5
Jim,
I had a similar problem many years ago with one of my SR's, in 1992 I think?
The problem ended up being a faulty low-speed coil in the alternator/ingnition pickup. I had the coil rewound by a company here in Aust that used to specialise in motorcycle electrical repair.
CJ
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