Vintage Dirt Bike Q & A

I'm currently working on a 74 MR50. I got the bike running and it runs fine under no load. Whenever I adjust the air screw minimally the bike dies. I recently got a throttle cable to work and was riding around the yard and it wanted to die if I went over 1/4 throttle and when I shifted into 2nd and 3rd gear. It sounds like it's running out of gas.

Has anyone had these same issues? Can someone provide me with the carburetor specs (jetting, float bowl gap, etc). Any help would be greatly appreciated.

Thanks for reading.

Paul

try the easy things first I had similar problem the vent hose for the gas tank was plugged also check the petcock screen or filter if you have one installed did you just get this bike? if the bike ran good before then it is not the jetting although the carb and jets might be dirty, are you running fresh gas? the air screw should be 1 1/2 - 2 turns out from lightly seated

Like craig said the jets may be dirty. Its very common for the tank to have a bit of rust in it and it will clog the jets. I always use a fuel filter and every time I dont I get crud in my jets sooner or later. That being said I am unsure if the mr50 has a steel tank or an alluminum one.

I'm running a test tank that I use for all bikes that I'm building. It's a 1/2 gallon plastic tank. I was using it on another bike that I'm putting together the same day so I don't think it's the tank unless the little motor is not creating enough vacuum. I always run 91 octane minimum.

The bike was not running when I got it. I put a different piston and ring in it and just got it running over the weekend.

I will tear apart the carb again and make sure the jets and ports are clean. Thanks for the air screw adjustment spec.

I will message back with my result.

Thanks for the responses.

Paul

look at the manual for carb-adjustment.
http://honda-elsinore.com/manuals/MR5074/OwnersManual74mr50.pdf
airfilter and exhaust are free?
ignition timing and contact breaker ok?
when engine is running and you see a spark at the contact breaker your condenser is not ok.

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