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Post by eman on Oct 12, 2018 13:23:10 GMT -5
A little backround. 2008 Jonway 50cc gator scooter. I bought it very used. It ran pretty good when I got it just needed a lot of bolts tightened and plastic repaired. I use it at the race track in the pits, doesn't get used on the road. A few years ago it acted up and I went through it and ended up repacing the ign module,coil and wire and installed a new carb. Old carb was a CVK and I bought a Chinese Keihin with a plastic top. Over the years it's run great. This spring I did my maintenance, basic oil change, spark plug, valve adjustment and such and it was running better than ever. About a week ago I was at a large track and riding it a lot. It was doing great and idling fine and suddenly while idling it shut off like you turned the key. It wouldn't start back so I parked it and let it cool. It started but wouldn't idle and would only stay running at partial throttle. When I got it home I swapped the ign module and it would run but I had to turn the idle speed screw uite a bit to keep it running. I pulled the carb, disassembled it and found nothing wrong. Ck'd valves and they are fine. Installed new plug and even a new coil and wire just because I had it. It will run but while idling it will be fine and then slowly start surging. The longer it runs the higher and lower the surge until it stalls. I have moved the mixture adjustment screw in very small increments and it seems to level out and then it will start the surge again.
My opinion is it's in the carb fuel system. I did change the fuel filter in the spring and changed it again just because I had one. Fuel flow is good, float level was fine. Compression was 125 at about 5 revolutions with the electric starter and went to 150 if I cranked it longer.
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Post by w650 on Oct 12, 2018 15:31:37 GMT -5
Look for cracks in the intake manifold and maybe a faulty vacuum line. When it starts spray around the carb and manifold with WD-40. If it changes sound or suddenly takes throttle you found the problem.
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Post by tortoise on Oct 12, 2018 16:31:34 GMT -5
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Post by eman on Oct 12, 2018 20:04:05 GMT -5
Look for cracks in the intake manifold and maybe a faulty vacuum line. When it starts spray around the carb and manifold with WD-40. If it changes sound or suddenly takes throttle you found the problem. Should have added I pulled the manifold and installed a new spacer as I suspected it leaking. Sorry I left that out. |
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Post by eman on Oct 14, 2018 12:05:16 GMT -5
I took the scooter with me to the track this Sat. It ran all day and is fine as far as poer goes. It still begins to surge up and down if you leave it sit idling. It also will idle very high at times and then settle down. A little hard starting and you have to tist the throttle. I feel it's in the fuel system more than ign. I'm going to ck again for any leaks at the manifold and spacer and go from there.
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Post by hillbillybob on Oct 14, 2018 19:01:32 GMT -5
If I was sure there is no vacuum leaking, I'd be all over the carburetor.
Sounds to me like...Dirty/partially plugged jets, or a malfunctioning auto enricher. Do you use gas containing ethanol? Ever run some kind of fuel treatment to keep the carb and upper cylinder components clean?
Or, if you don't have time to fiddle around...you can get a new carb for $20 or so. No reason to go name brand...the Chinese copies are just fine.
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Post by eman on Oct 15, 2018 21:40:21 GMT -5
I'm all in on carb, first I'm going to ck for vacum leaks I've had the carb apart and din't see anything but I might just buy another carb and try it.
Any recommendations on carbs?
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Post by hillbillybob on Oct 16, 2018 7:58:28 GMT -5
No recommendations, but I wouldn't over spend on one. The oem carbs start at $18 on Amazon. My Jonway's original carb, has spent 6 winters in hibernation, and covered more than 15,000 miles, without a problem.....( save the auto enricher, I replaced it a few years ago). I am fussy about what I put in my fuel tank, and I do add a few tenths of an ounce of fuel treatment ($0.05 worth), to each fill-up. Does any of that make a difference? Maybe....Maybe not.
Just don't get sucked into a $50 carburetor.
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Post by floridagull on Oct 16, 2018 11:08:26 GMT -5
Check out Parts for Scooters - good people!
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Post by eman on Nov 2, 2018 17:44:37 GMT -5
OK $18 carb later and I'm no further ahead!
Let's talk ignition timing. How do you check and set ignition timing on these scooters?
With the new carb I have the idle speed adjustment screw with the spring compressed to keep it running, not good. On my previous carb when it went to junk I had to screw the idle adjustment down to keep it running.
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Post by chewbaca on Nov 2, 2018 23:17:38 GMT -5
you don't set the time on a gy6
its factory set by the fly wheel key way
only maybe half a degree of play between the pickup and the mag tab
almost impossible to mess up
if you want to change the timing get an after market cdi
or shave the key
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Post by eman on Nov 5, 2018 9:20:09 GMT -5
So the timing is non adjustable? I don't want to change it, just thought it might have changed on it's own causing my problem. I rode it around all weekend. Performance is good, just won't idle and I've got the idle screw as far down as it will go. If I stop it will idle real low and eventually stall. It starts tight back and starts good and runs good. I changed the CDI when it first happened, I'm going to put the old one on and see what happens.
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Post by chewbaca on Nov 5, 2018 11:57:01 GMT -5
it sounds like you have low compression
most likely it is a damaged exhaust valve. A scored cylinder or chipped intake are also possible
a new head is about 34 to 45 $ on eBay or Amazon
however if you do a real valve job with new valve guides, seals, titanium retainers and grind new valve faces. You can gain about 1000 more RPM before valve float for about the same money but it's more work.
grinding your rocker arms smooth and optimizing the shape is good for another 1000 RPM but its even more work and you can ruin the arms temper if you're too aggressive
every gram of weight removed from the valve train makes every other gram removed more effective
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Post by eman on Mar 2, 2019 20:14:24 GMT -5
Sorry for the long delay in following up. Scooter got put away for winter and I didn't get back to it until today. I'd gone through and checked everything between the valves, compression, vacum leaks and I've swapped carburetors back and forth. Adjusting the idle mixture would make no difference. I could start it and ride it and when I would stop and let it idle it was fine for a monute or so and then slowly start surging until it died. It would start back with no problem. The only thing that gave me a clue was on restart at times I would have to open the throttle a little before it would start. I removed the vacum hose from the fuel petcock at the tank and plugged it and the scooter idled much higher. I set the idle down and it runs and idles perfectly. When I removed the vacum hose I did notice it appeared damp inside the hose. Evidently the diaphragm is slightly porous and it's leaking just enough fuel into the vacum hose to make it surge and stall. I've ordered a new fuel petcock and I'll post the final results when I get it installed.
Thanks for everyone that gave suggestions.
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Post by eman on Mar 6, 2019 22:12:40 GMT -5
Petcock is installed and the scooter is back to normal.
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