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Post by Moat on Sept 13, 2014 15:43:22 GMT -5
hmmm...here's what I just did....I pulled the check valve out of the compression tester and applied 30 psi to the engine at TDC and it would not hold any air. It just came out the carb along with fuel. So I'm gonna go ahead and pull the head and check the intake valve. It can't hurt at this point just to check it out. Even if I did this "leak down" test wrong...I'll let you guys know. Thanks Whoa, there! No need to pull the head off yet - like alley said, your compression is fine. You were likely on TDC of the exhaust stroke during this 30 psi test - not the compression stroke (although there's the remote possibility a valve was sticking open). Bob |
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Post by tvnacman on Sept 13, 2014 17:15:23 GMT -5
have you done any jetting in the carb ? If not pull the carb drip some fuel into the cylinder while cranking , see if it fires . no air filter on the carb could be creating too lean to fire .
John
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Post by onceler on Sept 13, 2014 20:16:21 GMT -5
Sorry, the heads already off. I did the pressure test with the timing mark lined up at 3 different consecutive rotations of the crank. Each time air blew out of the carb along with fuel. I have both valves out and I re-lapped them. Tomorrow I'll stick them back in and re-install the head and go from there with further diagnostic/trials...could still be a fuel issue but I just had to pull the valves to put my mind at ease.
I'll let you all know tomorrow???
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Post by tvnacman on Sept 13, 2014 20:50:28 GMT -5
double check the mechanical timing , if you get the same thing dump some fuel bypassing the carb or cover the air intake with your hand restrict the air a lot going into the carb when trying to start the engine .
John
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Post by onceler on Sept 14, 2014 13:26:14 GMT -5
Ok I re-assembled the head and installed it. Same issues as before, no start. I re-did my 30 psi test and found out that the pressure was pushing the piston down and opening the intake valve causing the air to flow out of the carb along with fuel. So alleyoop is right I do not have a compression problem. Here's my carb settings atm: 40 pilot jet  ,  , or  Main jet. (I got them all mixed up and can't tell the difference) air/fuel screw out 2.5 turns When I crack the throttle while cranking it almost stops cranking until I release the throttle and it will start cranking normal again. When I spray starting fluid in the vacuum line it will fire a fuel times, but i've never been able to get it to run without the starter turning. |
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Post by alleyoop on Sept 14, 2014 15:00:03 GMT -5
WOW!! a 40 pilot jet dang man your flooding the poor thing, that is why it is locking up sometimes. The stock carb on those 139s come with a 29 to 32 pilot jet.
NO MORE than a #35 if you have the stock pilot try that one.
Alleyoop
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Post by millsc on Sept 14, 2014 15:28:27 GMT -5
40 is too big on the pilot some of my modded 50s I had to jump them off a non running car to get that first start. Let it run 15 minutes before taking off.
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Post by onceler on Sept 14, 2014 19:41:49 GMT -5
ok I'll put the stock pilot back in and give it another try this week. Thanks for all the help. I'll keep you all updated.
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Post by onceler on Sept 15, 2014 16:54:10 GMT -5
I just installed the pilot jet that came with the carb. It sounds like it fires but just not enough to keep running on it's own. When I pull the spark plug it is black. FYI I have the stock air box and muffler on it.
This thing is getting on my last nerve. I've never had this much trouble starting an engine (I've never really messed with a scooter engine, though)
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Post by alleyoop on Sept 15, 2014 16:57:44 GMT -5
Turn the fuel ratio screw clockwise until it stops do not force it just until it stops then turn it out 2 turns counter clockwise.
It is to rich.
Alleyoop
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Post by onceler on Sept 15, 2014 18:24:13 GMT -5
ok...I turned like you said, alleyoop. It still wouldn't start, so I kept turning it in in 1/2 turn increments and trying to start it each time. It finally bottomed out and still wouldn't start.
I'm thinking about putting the smallest jet (original jet) in and give it another try tomorrow.
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Post by alleyoop on Sept 15, 2014 19:22:38 GMT -5
Did you try counter clockwise opening it more than 2 turns? Also does your carb have an ENRICHER?
If it just turns over without firing, Stop and take the spark plug out and see if it is WET or DRY, that will tell a lot.
IF DRY then no gas is being sucked in if WET then the plug is not firing. IF IT FIRES and the plug is still WET then to much fuel.
Alleyoop
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Post by millsc on Sept 16, 2014 14:13:11 GMT -5
Take off the airbox and try it
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Post by onceler on Sept 17, 2014 18:38:12 GMT -5
It sounds to me like it fires on each compression stroke, but it doesn't have enough power or something is holding the piston back cause it won't stay firing without the starter turning it over...not sure if that makes sense to you guys but that's what it seems to be doing no matter what I do to the carb. Today I put in the original 75 main jet and and cranked and cranked while turning the mixture screw and working the throttle....but wouldn't run. The plug got black but wasn't wet.
I did notice something right when I was cleaning up for dinner...the oil is overfilled. I drained some of it off but it was coming out of the dipstick hole. If this is the root cause (too much oil) I think I will cry. I'll let you guys know tomorrow hopefully after I can dump it to the right level.
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Post by onceler on Sept 20, 2014 13:52:02 GMT -5
Ok, I drained the excess oil, but of course it still won't start. I have the stock pilot jet, 75 main jet, and the air/fuel mixture screw all the way clockwise until it stops, with the throttle plate closed my spark plug is wet after a few seconds of cranking... Any thoughts on why?
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,
, or 
Main jet. (I got them all mixed up and can't tell the difference)
..BAD TO THE BONE..
