Clinician
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Post by ndog1 on Nov 4, 2012 17:28:39 GMT -6
Found the problem, the o-ring was shot on the fuel screw...had to fish hook the old one out. Went ahead and got the whole rebuild kit and an 80 main.
Idle circuit is great now, returned clip to middle and but in many of the components including 80 main jet. Was very surprised that it was cutting out above mid throttle.
Being a 4 stroke and having tried 85 and 80 now....started to get really frustrated. I pulled the carb back off and looked around at the new rebuild components.....very inconsistent. put back most of the old stuff.
Im thinking the problem is the float height....the new float needle and float were much higher meaning less gas.
What exactly is the float height for the stock carbs? Around 16mm??
The rebuild kit was like 18+.
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Post by ndog1 on Oct 25, 2012 18:40:06 GMT -6
Just to clarify....I have been building race scooters for a long time...just never 4 stroke chinese.
I am aware that the internet has many names for the mixture screw the acts with the pilot circuit. So fuel screw then. (But the air from the venturi drives it LOL)
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Clinician
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Post by ndog1 on Oct 25, 2012 18:14:01 GMT -6
INTAKE MANIFOLD vacuum nipple connected to the FUEL TANK PETCOCK VACUUM. Apologies should have added petcock. The vent hose is fine.
As I said, it is a QMB139 50cc 4 stroke engine and the screw to the left on the manifold side is via the manufacturer the "Air Idle Adjustment Screw"
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Post by ndog1 on Oct 25, 2012 14:16:36 GMT -6
I got rid of the whole mess of emissions plumbing on a Jonway GY6 with the QMB139 carb. Im running directly from gas tank to carb, manifold vacuum to tank vacuum, check valve gone, plugged all the holes with nipples on the airbox and soforth and am running the crankcase vent upward with a little filter catcher on it. Fuel tank vent is fine.
Seems like the jetting has been affected more than anticipated. 1. There are no fumes from all the sources coming in just pure air. 2. There might have been an increase in vacuum with simpler direct routing, causing the carb to suck more thru its jetting and circuits.
I am in South Florida which is obviously warm, humid and at sea level. What mainjet and pilot jet do you guys recommend for this climate? The stock was a 34 pilot and 74 main with the clip in the center.
It totally cut out anything over mid throttle so I got a hold of an 85 main and put a 35 keihn pilot and it runs good but seems rich up top. I have dropped the needle to the second leanest position and it helped but I am going to have to hunt down another mainjet. One other strange thing is that it will not idle with any pilot (even the stock) unless the air idle screw is turned all the way in clockwise.
Half the diagrams show a rubber washer, half dont....my only other guess is that it is missing (this is a friends scooter)
Thank you all
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