150cc GY6 engine starter defeated by engine compression

[randscaping]

Hey all, this will be my first post in a scooter forum so I'm anxious to see how awesome the fellas on this site really are !

So I have one of the VIP scooters (TaoTao I think?) that I have been trying to get it running reliably since I took it off the hands of its previous owner who drove it daily. It is a 150cc GY6 engine

The problem I'm running into is, it won't smoothly crank. I presumed it was the starter, so I got a new one off my fave stock parts site, (vmcchineseparts.com, if anyone wonders) and it made zero difference. I get the best cranking attempt by the engine when bridging the posts on the starter solenoid. The engine does turn but only as far as compressing the fuel-air mix in the cylinder. Before this happened, the engine would get past this point but only to make an awful grinding noise from the area where the starter gear meets the "flywheel". When looking at the cooling fan while it was making this racket, it looked like the starter would turn the engine to a point (resistance from achieving compression) then "bouncing away" (rotating backwards with the starter still engaged) and being pushed right back to that point by the still engaged starter. (that's why I faulted the starter).

So it is perfectly logical to think, "well, common sense tells you that if it's doing that, you're not getting enough power from the battery!" However, this is occurring even when I have a fully charged battery on the scooter, AND hooked up to jumper cables to a running 1998 Dodge minivan.

What I recently did to this scooter besides replace starter:
-new keyed ignition cylinder
-new CDI box
-new NGK spark plug
-new ignition coil and lead wires
-new engine cutoff/ignition button/throttle assembly
-new 9Ah scooter battery
-new intake/exhaust manifold(studs broke off old exhaust port), Scooter has run and drove since this was done, so we know the timing, valves and intake seal are good.

-new carburetor w/auto-enricher.

All Parts Replaced are stock and rated for the 150CC gy6.

So, with that being said, maybe one of you awesome readers/responders knows that this was posted before and resolved already. If this is the case, I have no problem following a simple link to that thread, even if that is the only content of the reply.

Thanks in advance for everything guys, http://www.scootdawg.net/images/smilies/thx2.gif can't wait to get this thing on the road! http://www.scootdawg.net/images/smil..._scooter_2.gif

P.S. If it makes any difference, the last time the scooter was running and driving, it sputtered and stalled while I was riding downhill on it and it has not fired up since, even if only to die half a second later.

[Roscoe]

From what you described it sounds like the timing is advanced when starting. I'd try a different CDI box and make sure the flywheel is on the shaft in the proper position and adjust the valves. Does it kickstart OK ? I suppose what I'd do is take the spark plug out and see how it cranks without any compression, this would also should show a problem with the clutch and variator if there are any, check for spark, adjust the valves. There ought to be a way to check the ignition timing while cranking.. do you have a timing light?

[randscaping]

Thanks Roscoe!

I have no kickstart on this scooter and now I am wishing I do.
I have tried 3 different CDI boxes and it makes no difference because the starter doesn't even push the piston head far enough to reach the apex and so there's no opportunity for the spark to fire yet.

As far as how the engine behaves in the absence of compression I have done this test as follows:
-remove spark plug
-engage starter
-result: engine spins perfectly. To verify the problem I covered opening for spark plug with my finger with starter circuit still engaged, and engine stops turning over when compression is achieved(with my finger over the spark plug opening) I also turned the engine by turning the cooling fan past the point where it stops while having the starter engaged. The engine continues to turn but stops again the next time the compression is achieved.

no timing light.
as far as advanced timing, I beg to differ because I had it running and driving since I replaced the engine intake/exhaust manifold and re-set the timing.

[Roscoe]

Sounds like a starter problem now. Check the grounds and cable to the starter. If you have to, remove the starter and run it right off a good battery, it should have a decent kick when energizing. Good battery, good starter, good cables, good connections (including ground), good solenoid. It's got to crank. These little starters won't take a lot of abuse, go easy when cranking them. Mine was gummed up and oil soaked and a burned section on the armature. It would still get the old scooter started but it drained the battery pretty fast doing it. Be sure to check the valve clearance. Be sure to check the cable end terminals where they attach to the cables.

[randscaping]

Okay, I'll be trying some new things once old man winter is done with his current fit. I have a new battery and new starter on the scooter. Battery has even been hooked up to a running vehicle with jumper cables and that didn't make any difference. So I will post an update once I try the following:

-disconnect current positive wire that supplies voltage to the starter (removing positive wire spanning from starter solenoid to the starter).

-leave in place the ground wire spanning from the engine valve cover to the chassis since this does both provide negative for the engine(spark) and also a negative lead from the starter back to the battery.

-connect separate positive and negative wires to the battery and route this circuit directly to the starter, connecting the circuit with a momentary push-button switch

Hopefully this direct connection from the battery to the starter will pump enough cranking amps through to let me know I need to work on some wiring within the scooter itself, with focus on the engine ground.

[blueboy5000]

Sounds like a sticking starter clutch. It's common, and is an internal engine part.

[randscaping]

Thanks, Blueboy5000. I will definitely research this engine component further and see what I need to do to make it stop sticking.

So I finally wrapped up slapping some new parts on the scooter and tinkering around with things.

New since last post:
-new starter solenoid
-new positive and negative wires off battery
-
-new CDI(ended up sticking with old CDI)

Result: Still the same engine behavior when attempting to crank. So I started pulling apart some of the sheathing that keeps the wiring bundled neatly. I found where the ground wires from the various components merge to one wire and capped it so the copper wiring was not exposed. Also finally installed the wires that came with the ignition coil I had in. Ran that green side directly back to the negative battery terminal by itself. Still no spark when running starter and holding spark plug gap to engine casing. So I inspected the black-with-red wire from CDI to the hot side of the ignition coil and found no shorts. I replaced new CDI with the old one and it produced spark immediately upon retrying.

Successful ending:

Upon observing a dependable spark, I immediately reassembled the parts and compartments I had open and placed the CDI and starter solenoid back on their mounts. For good measure I added some ether to the intake and hit the starter button. It started making its usual racket and not smoothly turning but I let it try for about 7 seconds before BOOM!

The ether (starting fluid) had finally ignited. So I sprayed some more in through a straw via one of the vacuum ports on the intake and tried cranking again. This continued for about 2 minutes before I finally achieved a started, running scooter.

Summary: I feel the issue of failure to start/crank that I reported was a result of a lack of rich intake air and a fault in the wiring of the scooter. Whether it was the ground only or the hot side coming off the CDI box I can't really tell.

What happens next: I really don't like the racket it makes that sounds like grinding gears when the starter is attempting to turn the engine over. So I will be looking further into this sticking starter clutch that blueboy5000 spoke of. I'll be keeping an eye on the oil since it makes sense that a properly oiled engine will be easier to turn (over). I did get to ride it a little bit today before I let it stall seeing if it would idle. Trying to restart it independently (no jumper cables/battery booster) seems like a lost cause as the battery dies before I get it running. So if I stall at a light I'm effectively stuck there to push my ride to the curb and begin CPR, so to speak.

Sorry I wrote enough to be an autobiography here. However, I did intend to include as much detail(or storytelling, depending on how you look at it) to try to help a reader who might need it. Blueboy5000, would you mind elaborating a bit on how the sticking clutch would cause my reported problem?

[blueboy5000]

The starter clutch is an internal driven bendix-style gear/clutch. Kind of like a combination of a flywheel and a bicycle freewheel.

[randscaping]

So is that the mechanism that is above the rear axle on the left side in the long case that says "4 stroke"? (the belt inside this case spins it)

[Roscoe]

I'd try making sure the engine is topped off with motor oil but not overfull and run it through a few hot/cold cycles. It might get enough oil to get the little sprag rollers loosened up enough to work like it should. If the clutch starter is bad and has to be changed, watch a few youtubes on how to do it. It's not a hard job but it's one of those things you can learn a lot easier watching how others did it than learning the hard way, you'll know what tools you will need, and the nuts that are left hand thread.
Just type in starting clutch gy6 with youtube and you will see. Also sprag clutch just to see how they work, or are supposed to work.