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Snowman56

RL250 carb adjustment

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Hi, I recently bought a 1975 Suzuki RL250.  It ran but not well.  I found that the main jet was plugged.  After carefully cleaning it out and blowing it dry with compressed air, I reassembled the carb, gassed it up and it started easily.  It runs for a while but looses power in a couple minutes and then stalls.  it will not restart until it cools down.  Any suggestions as to how to adjust the carb?  It has a 130 main jet.   I'm running modern synthetic oil at 40:1.    

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1 hour ago, Snowman56 said:

Hi, I recently bought a 1975 Suzuki RL250.  It ran but not well.  I found that the main jet was plugged.  After carefully cleaning it out and blowing it dry with compressed air, I reassembled the carb, gassed it up and it started easily.  It runs for a while but looses power in a couple minutes and then stalls.  it will not restart until it cools down.  Any suggestions as to how to adjust the carb?  It has a 130 main jet.   I'm running modern synthetic oil at 40:1.    

Original “Exactas” had the CCI lubrication system which delivered oil.  Beamish converted this to a premix system. For a modern synthetic - 50/1 is reportedly ok. Mineral would be 32/1.   This is from the mikuni 28mm Beamish black engine workshop manual.  Might not help you with your bike , since the later Beamish had a reduced choke-size (25mm)  - but this sort of specific info is out there on the web somewhere.  Note the use of a cooler plug.  Before you break-down that carb - the symptoms you describe could well be a spark-plug with cracked insulation , not always visible to the naked eye. Worth trying another plug.

BEWMall.pdf

 

Edited by Nebulous

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Thanks, I'll check those out.  I understand that a 140 main jet was std and I have a 130.  But like I said in the original post, the bike runs worse now than before when the main jet was plugged with debris.

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2 minutes ago, Snowman56 said:

Thanks, I'll check those out.  I understand that a 140 main jet was std and I have a 130.  But like I said in the original post, the bike runs worse now than before when the main jet was plugged with debris.

Worth looking into the history of the RL250. From ‘74 and including the ‘75 it had lower (sluggish) output than the later Beamish. By ‘77 he adopted the Keihin PWK28 carb with the heavy flywheel for the S model.  Somewhere in the middle is that Mikuni 28mm with the reduced choke-size. So a few variants to ponder.   40/1 way too much for a modern synthetic.

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Okay n thanks.  I see your a Montesa rider.   Nice Bike.  I sold my 99 Cota 315R and decided to ride vintage....  

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if it dies out after a couple min run time then insure proper fuel flow from tank and that it is vented properly.. there is a screen in the fuel petcock as well you know.

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This kind of problem can be due as already said a blocked tank breather or something in the ignition breaking down under heat, what sort of spark do you have immediately after the breakdown?

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still have spark when it stalls.  The air screw seems to have little effect on the engine.  When I bought the bike, the gearcase was full with oil, but after only a little running the gear case oil was way low.  I'm running 50:1 syn oil now but it is still smoking.  No visible leaks for crankcase oil.  Could the crankcase oil be causing the smoke and carb issues?  Thanks

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To burn that much oil you could send smoke signals to Alaska ! Gear / engine oil smells completely different from 2 stroke when burning, generally this will not stop the engine running, and if it did you wouldn't be able to restart without a new plug.

I'd go with suggestions above, either poor fuel flow, or electrics breaking down with heat.

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Okay, now my RL250 is running fine for a few minutes then it stalls or only barely idles even with a full throttle, and choking has no effect.  At this time I notice the breather tube from the rear right hand side (clutch side) has spewing out crankcase oil.  The airscrew has little to no effect when the happens.   Does this mean the crankcase seal is leaking?  thanks

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