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Post by davids on Aug 6, 2016 21:34:09 GMT -5
Roketa 139qmb 50cc, 4,400 miles....
Previous owner stripped the spark plug threads.... I had bought a new ebay carb and head to get this scoot running, and it ran great for a few hundred miles until all of a sudden I got intermittent power surges that mimicked a clogged carb. I had been running the scoot without an air filter so I assumed some debris clogged the carb. But after cleaning the carb didn't work, I bought a brand new Kleihn carb, petcock, iridium plug, coil wire, battery and I still can't get the darn thing to fire up.
I pulled the plub and can see that I have spark. When I pulled the hose, I have fuel (both the ebay and Kleihn carbs). If I spray the carb with starter fluid it will turn a few times and then sputter out.
Any suggestions? At this point am willing to just pay to have it fixed if anyone is near St. Augustine, FL. Ugh....frustrated....
-David
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Post by niz76 on Aug 6, 2016 22:27:32 GMT -5
Well, gotta have the trifecta to run- spark, fuel, and compression (all assuming the timing is correct). If you've got fuel and spark the next thing to check is compression. (Did you upjet the carb for no filter? Lean conditions may have wreaked havoc on your rings and/or cylinder). Anything over 100 psi and it should start and run...
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Post by badpumpkin on Aug 6, 2016 22:33:11 GMT -5
With an unrestricted air flow in you will need a big main jet,my keihin with 85 jet and free flow intake ran for a day, also. Put an intake on that is relative to the exhaust system. You can only flow a certain amount of air/fuel through a 18/19mm hole. Watch the ytube faq on carb tuning on the left of this screen and it will set you on a sound course.
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Post by davids on Aug 6, 2016 23:14:55 GMT -5
Well, gotta have the trifecta to run- spark, fuel, and compression (all assuming the timing is correct). If you've got fuel and spark the next thing to check is compression. (Did you upjet the carb for no filter? Lean conditions may have wreaked havoc on your rings and/or cylinder). Anything over 100 psi and it should start and run... Thanks for the reply. I have a compression gauge but not small enough to check the scoot. I'll have to look into an adaptor or another gauge. What PSI is normal for a 50cc 139qmb?
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Post by niz76 on Aug 6, 2016 23:27:43 GMT -5
Somewhere around 120 to 160 or so...
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Post by gsx600racer on Aug 7, 2016 1:57:59 GMT -5
The only thing that has caught my eye is that you ran it without the air filter.
The air filter/air box puts a small amount of restriction to the air flow thru the carb. Your carb was jetted for this restriction. Now that you ran it without this restriction there is a good chance your scooter ran lean. Lean is bad. The carb needed to be up-jetted(larger) to compensate for the removed air filter. Your engines compression will tell you if lean condition took place with low compression numbers. Plus without a air filter you could of sucked up something small that might of scored the piston of cylinder too.
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Post by davids on Aug 8, 2016 12:00:01 GMT -5
The only thing that has caught my eye is that you ran it without the air filter. The air filter/air box puts a small amount of restriction to the air flow thru the carb. Your carb was jetted for this restriction. Now that you ran it without this restriction there is a good chance your scooter ran lean. Lean is bad. The carb needed to be up-jetted(larger) to compensate for the removed air filter. Your engines compression will tell you if lean condition took place with low compression numbers. Plus without a air filter you could of sucked up something small that might of scored the piston of cylinder too. Question: For the 1st ebay-style replacement carb, even at full throttle the scoot would die if I connected the air filter. Makes me wonder if it was too lean for the filter and just right without it?
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Deleted
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Post by Deleted on Aug 8, 2016 15:00:35 GMT -5
I would check for a vacuum leak, especially around the intake/carb. interface. A seemingly small cut in that rubber, or a bad fit will cause a very, very lean condition and can make it not fire up. I would do this after a good compression check as was stated earlier.
Bill
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