GY6 150 1P57QMJ No start pops though exhaust kicks back By bigkahuna427 (Read 6,112 times)

[bigkahuna427]

I have this scooter given to me that doesn't start after it sat for a while. An early discovery was the starter clutch slipping and not engaging. I can get it to engage sometimes. Here are the symptoms and what has been done to troubleshoot:

Does not start, kicks back and will pop out through exhaust. This seems like preignition.

The ignition system works and has spark

Tried a new module and coil

Checked cam/crank timing

Checked to ensure the piston was indeed at TDC when at TDC (T) mark on the flywheel

Checked stator and trigger using ohm meter

With meter in AC mode and with engine cranking (when I can get starter clutch to not slip) I have .5V at pickup and 70V at power supply from stator (that 70V seemed high)

With the spark plug out engine kicks fine. With spark plug in engine kicks fine. With plug in and spark plug wire connected engine kicks back.

With plug out I checked ignition timing with a light and it is pretty advanced. There is a T mark and F mark and two marks up from that. The ignition is firing at around those two higher marks. I might have suspected a sheared key but I checked that by ensuring the piston was at top and TDC lined up on the flywheel.

I did disconnect an aftermarket looking alarm system that I thought might have some odd effect on the ignition system.

I do have a starter clutch coming but I know it is not going to fix the no start.

Anyone have any thoughts on this? I am kind of scratching my head at this point.

[seanstr]

Dec 12, 2016 13:43:22 GMT -6 bigkahuna427 said:

I have this scooter given to me that doesn't start after it sat for a while. An early discovery was the starter clutch slipping and not engaging. I can get it to engage sometimes. Here are the symptoms and what has been done to troubleshoot:

Does not start, kicks back and will pop out through exhaust. This seems like preignition.

The ignition system works and has spark

Tried a new module and coil

Checked cam/crank timing

Checked to ensure the piston was indeed at TDC when at TDC (T) mark on the flywheel

Checked stator and trigger using ohm meter

With meter in AC mode and with engine cranking (when I can get starter clutch to not slip) I have .5V at pickup and 70V at power supply from stator (that 70V seemed high)

With the spark plug out engine kicks fine. With spark plug in engine kicks fine. With plug in and spark plug wire connected engine kicks back.

With plug out I checked ignition timing with a light and it is pretty advanced. There is a T mark and F mark and two marks up from that. The ignition is firing at around those two higher marks. I might have suspected a sheared key but I checked that by ensuring the piston was at top and TDC lined up on the flywheel.

I did disconnect an aftermarket looking alarm system that I thought might have some odd effect on the ignition system.

I do have a starter clutch coming but I know it is not going to fix the no start.

Anyone have any thoughts on this? I am kind of scratching my head at this point.

The CDI is it standard or is it performance. I heard that some of them can cause timing advances iterate your timing is off.

[bigkahuna427]

Yes it is the performance module. I did switch back and forth between the old and new module with the same symptoms. Sleeping on this it's not rocket science. I guess I have to thoroughly go back over everything I have done. I must have missed something.

[jct842]

pull the rocker cover and go thru the timing check on valves. then set the valve clearance. There are youtubes around on proceedure as well as instructions in our library. richs scooter manual gets into it also (scooterdoc manual)

and get any old gas out of there.

Even though you have checked timing it has to be off for it to be kicking back. see that the timing chain is tight and the tensioner is working.

one other thought...could some one else installed a big bore kit and end up with too high a compression?

[cyborg]

I think it being a used scooter someone messed with it and either the cam chain was installed one tooth off ,,and I would also recheck the flywheel key,,,that's where my investigation would start

[jct842]

One check is to put a straw into spark plug hole and turn engine over by hand slow and find top dead center...then see if the flywheel marks line up as they should.

[bigkahuna427]

HI Guys,

So here is my update. Basically this thing is up and running. I certainly have found plenty of things that would make this engine run lousy but the kick back on start eludes me at this point.

Here is what has been done so far:

Should be noted this scooter is a 2006 Lifan although the title says 2008. It was elderly owned, garage kept with 680 miles on it, has not been started for two years and free to me. It was taken to a "master scooter tech" who told them he had cleaned the carb, flushed the tank and that once running had an engine noise like a bad connecting rod 45 days ago.

I put this scooter right up on a bench which made it so much easier to work on.

Went back over cam timing, location of timing marks relative to piston TDC which were ok and and checked valve adjustment.

Checked again ohm meter and voltage readings on exciter coil and pick up coil.

Cleaned gummed up carb, plugged jets, stuck slide.

Flushed tank which had water in it.

Replaced fuel lines, filter and vacuum petcock which was leaking.

Replaced slipping starter clutch. The old one the allen headed crews were loose and had damaged threads.

Flushed out crankcase.

Replaced gear oil.

Inspect drive belt variator etc.

Repair ignition switch which had fallen apart.

So It now starts and runs pretty decent. Remaning items:

Variator is pretty smooth but tuned to get up into a higher "gear" to soon for me. My 125 Yamaha Vino is much quicker off the start.

Engine surges a bit at steady throttle cruising speeds. I suspect the carb is still lean but have not looked at the plug. Carbs are so cheap I may just buy a new one.

Still is the kick back on start issue. The kick back can really be felt when kicking and using electric start. On electric start it will lock the motor briefly. Does have a new battery. I have looked at the timing with both modules I have. The aluminum finned "racing module" and the original black module both are advanced when checked with a timing light. The timing does not change at all from idle to higher RPMs. When looking at the timing with a timing light the timing is between the 3rd and fourth mark on the flywheel and in the same location with either module. The lick back seems to be the same with either module. Most engines I have seen the timing is lower at idle and start then advances with RPM. My back ground is automotive so I am not sure what I should be seeing with this engine. Can anyone offer any suggestions here?

[tvnacman]

your pulse coil is triggered by the raised magnet on the flywheel (very basic). I have seen on the kymco's in relation to the keyway the trigger magnet is in a different spot (knocking off crank position) pull the cover and the fan and snap a shot of the position of the keyway and pulse magnet.

I had a guy call me looking for a flywheel for a two stroke. His center hub broke when they welded it back on it was out of position and it would not run. The flywheels I have are for 4 stroke GY6 50 and 150cc. I did not have the parts he was looking for but did help him figure out why he was destroying stators and had a no start.

You might try to beef up the wires to the starter, engine, solenoid, grounds and battery.

John

[bigkahuna427]

That makes some sense and something I had not thought of yet. Should I assume at this point the ignition timing has no advance curve or does not change from idle to high speed?

[tvnacman]

It depends on the cdi you have.

John

[bigkahuna427]

I have a couple of pics of the fly wheel position and at first it looks like the key and and raised section on the flywheel are 90 degrees apart. I pulled the flywheel traced it out and located the key. So, with the diagram you can see that the key is greater than 90 degrees. I can leave this apart over night and do anything you think I need to figure out the keyway position.

Well haven't figured out the pics and my photobucket account won't let me upload. So to describe what I am seeing raised portion of flywheel at 12 o'clock keyway at 3:30.

[bigkahuna427]

These images were rotated counter clockwise 90 degrees sorry..

[tvnacman]

That looks like the stock flywheels. I would do as JCT said line it up TDC make sure the cam and crank marks line up together.

I post a magneto pic later.

John

[tvnacman]

[bigkahuna427]

I have been over the cam crank timing twice. Runs too good for that to be a problem. Has anyone put a timing light on one of these engines? Where are the marks supposed to be?