50cc not starting By myhotdelta88 (Read 681 times)

[myhotdelta88]

I am working on a Q139 50cc Chinese scooter. I have spark, fuel, 120 on the compression and exhaust is clear. She still won't star. New intake installed after the fuel suction pin broke off. Tried all the tricks, carb cleaner into the spark plug, into the intake directly, NOTHING.

ANY ideas?

[Alleyoop]

Well first off 120PSI is on the very low end for a motor to run. Also Carb Cleaner is not very good to get a fire going with in a motor. Squirt a little bit of gas down the Vacuum hose connected to the Intake Manifold directly down the intake and put the hose back on. If it has SPARK and enough compression it will FIRE at least once.

The only other thing is the timing might be off.
Alleyoop

[myhotdelta88]

So here is what I got as to how it stopped running. My friend was riding along and it sputtered to a stop. He looked inside and saw that the fuel suction hose had broken off. He put the copper tube back into the hole and reattached the hose. It did the same thing. He then parked it for a month or so. I replaced the intake with another one and the carb. I tried putting fuel directly down the hose and that did not work. When the battery is recharged I will try the timing and see if that is off. Will also look at the valves and see if they are out of Adj. Thanks for the quick response and if you have any other ideas. Two strokes are easier I think??!!

[Alleyoop]

Oh Sorry I thought it was a 2 banger. Since its a 4 stroke, yes by all means the low compression can be caused by the EXHAUST valve not sealing so set them both to .003 inchs that will make a big difference and should bring your compression up.
Alleyoop

[myhotdelta88]

Put the fuel down the suction line into the intake and she did almost start. She seemed to speed up like she was going to start and then just wouldn't turn over. I am going with adjusting the valves next. Had to stop and take a break. Thanks again.

[tvnacman]

it needs a little more gas in the vac line then you put in . put an ounce of fuel in a shot glass let the vac line suck it in . Do your valve adjustment . If you put a spoon full of oil in the spark plug hole , put the plug back in crank the oil through , it will bring the compression up a few pounds . Maybe enough to get her to start .

John

[myhotdelta88]

Timing is TDC and valves are adjusted. When I put the fuel down the line as suggested, she wants to start, but once the fuel runs out she doesn't. She almost wants to turn over but just doesn't get to that point. Any other suggestions?

[tvnacman]

MORE GAS !!!!!!!!!!!!

John

[myhotdelta88]

The more gas worked. It is running. Now for the new problem.......

Now that she is running better, I have found that she still has trouble starting, but not as bad. When I first took her apart, I didn't open the air box, I just took it off. After some time and realizing I missed checking to see if the filter was clogged, I opened the air box and oil poured out of it. Now that the box was off I noticed smoke coming from the carb, but a very slight smoke from the exhaust. I was thinking the smoke was from old bad gas. With the compression at 120 and the oil in the carb and air box, I am thinking the rings are going or have gone bad. This would be the reason for the hard starts. When she is running she runs fine but has a bad idle, so I am thinking the more she runs, the more oil I believe gets into the carb and compression chamber. Thus making it harder to start. Just confirming before tearing the engine down and replacing the piston, rings and cylinder?

[Alleyoop]

Verify that it is blowing oil past the rings, Take the spark plug out and see if is wet from oil.

Also make sure the VALVE COVER VENT hose is not kinked or plugged up it has to vent otherwise IT WILL squirt oil out and fill your AIR FILTER. Also make sure the filter is clean and not full of oil the VALVE COVER VENT HOSE has to vent and if not it will create to much crankcase pressure.
Alleyoop

[myhotdelta88]

Thanks, will check that out. I still think two stroke is easier........

[myhotdelta88]

Smoke and oil coming out of the valve cover relief line going to the air box. Thus oil is getting into the carb, which is very oily on the intake side. I pulled the line off at the cover while running and my finger got covered in oil and the engine compartment filled with smoke. Going for a top end rebuild now. Can I be wrong on that?

[tvnacman]

white smoke ?
I'm happy you put more gas in it and got something to happen .
I have top end rebuild kits .

John