Odd running 50 cc qmb139 engine By jbcoasty (Read 602 times)

[jbcoasty]

I have got a 2010 jonway 49cc qmb139 scooter with 16,500 miles on it never been laid down still is all orig. i have done all the steps cleaning and checking the carb, checking the valves and i am at .4mm intake and .3mm exhaust exclent spark (new upgraded coil) because the old cap cracked and kept falling off the plug. the only thing new is a replacement paper air filter like the original. now this thing wont start properly in the am It has allways been a cold blodded on the first start in the am. but after it does start and warms up for about 10 min it runs really good i have done the carb adjustments also. The only thing different is that i moved from Las Vegas to Tucson and the altitude is the same Any hints on somthing i have missed?

[cruiser]

Welcome to the forum.

If you did use the .4 mm and .3 mm gauges, then you are lucky to have your scoot running at all. .4 mm =.016 inches and .3 mm = .012 inches. The intake should set to .003 inches and the exhaust should be set to .004 inches.

[jbcoasty]

typed wrong spec it is inch not mm sorry

[alleyoop]

Good, so you set them to .003 inchs and .004 inchs.

Well with that many miles on it, check the COMPRESSION. If you don't have a compression gauge take the plug out and at least check with the finger trick.

Hold your finger in the hold nice and snug and hold the throttle wide open and crank it.
If if has decent compression it should blow your finger off the hole if you just feel some pressure then it is low on compression.
If low on compression, then pour a teaspoon of oil into the hole and do the finger compression again.
Let us know the results.
Alleyoop
Let us know what

[jbcoasty]

Thanks alleyoop will try tomorrow when the bike is cold for a better read on that

[alleyoop]

Yea don't won't to burn you finger on a hot motor .
Alleyoop

[jbcoasty]

alleyoop tried the good old finger on the plug hole some compress then did the oil test same feeling so went back to the valves ding dong me when i tightened the exhaust it was wayyy to tight so i did the readjust and that bugger lite up on the first crank drove around the block and it is wayyy better So moral of story is If in doubt double check everything out i learned that the hard way i guess

[alleyoop]

FANTASTIC!! Yes next time you adjust them before you put on the valve cover and button it up turn the motor over a couple of revolutions and RE-CHECK them.
Alleyoop