G1 good fire and compression won't run

[cinejeff]

I'm working on a friends G1 that came to me non running, no spark. Stator ohmed out around 340, no pulsar coil so I traced the problem back to a disconnected wire w/g to trigger. Ohmed trigger at about 14.7 ohms. Connected and cleaned up all ignitor wires and voila nice strong blue spark!!!
Checked compression to be 120psi, brilliant!!! Turns over great, forward and reverse. Added some premix gas to the cylinder. Turned it over, nothing. Tried in reverse, same thing. Pulled off exhaust thinking maybe it was plugged, no difference. Tried it a couple dozen times, swapping / drying plugs with torch nothing. Got it to run for about two seconds once, then never again... ?? Thoughts, bad seals?? But compression is good. Timing?? Swapped the trigger wires in case I they were messed no help. Any suggestions??? Can a bad seal cause this problem?? I would expect that with gas put directly in cylinder with 120 compression and good fire i would expect it would fire momentarily every time.

[Spicyunicorn]

No with fuel in cylinder bad seals won't come into play it should at least fire if you have spark compression and fuel it almost hast to be timing pull the fly wheel off and make sure the timing plate isn't out of wack

[icyveins]

make sure the wiring coming from the stator going to the cart harness are plugged onto the correct colors. I made that mistake once and I was getting fire but it was not on the compression stroke

[Lochlin]

I once worked on a Columbia for a camp neighbor that had a similar issue. He told me he recently did the seals yet the cart wouldn't run. Like you did, I checked everything and there was just no logic to the cart not running, even with adding some gas directly into the cylinder. I finally checked the seals and found that the flywheel side one had popped off. Here, when he tapped the seal in he wasn't careful enough and warped the seal a bit. It popped off when the engine pressure hit it. In that case, the missing seal was enough to prevent the engine from running. That's a really extreme case, though. I am not sure if the same thing would apply to a Yamaha but I suppose it can't hurt to check the seals if all else fails.

[cinejeff]

I double checked and the wires coming out of the stator are matched up and confirmed them with a meter. I even tried swapping the pickup wires in case they were the issue cause it to fire out of time. I did notice something added under some silicone just before the bullet connector on the white/green pickup wire on the engine. Anyone else have this, looks like maybe some diodes under there?? It struck me as odd and not factory.

I'll pop off the flywheel side tonight as I don't have a puller yet for this engine and I report back. Getting new plugs tonight as well. It did fire once so I'm not sure if the timing is the issue but I'll have a look at the timing plate, maybe it was put on wrong. I noticed from picts here on the forum that there appears to be a witness notch on the engine and plate. The plastic cover side bolts were loose, so who knows who messed with it before me. Not fond of basket cases with electrical issues!!!

[Lochlin]

Timing via electronic systems is pretty stable. Even if the timing was way off you'd probably still get the motor running, just not as well as the cart being timed right. Heck, even with the older points systems the engine would still run when the timing was off. Granted, they would run like poo but still get you something. That you are getting nothing at all leads me to believe it's not timing but that's just one guy's opinion.

[blizzrd]

Take the carb off and give it a good cleaning.

[cinejeff]

Changed nothing and it fired right up today. Runs like a top. I must have flooded it badly I guess. I cleaned the carb and new plugs this weekend. Starter belt frayed and got caught up in the clutch and stalled the engine. Thought I blew it for a second but it turns ok by hand. Anyone know what size the starter belt on the g1 is???

[cinejeff]

Starter belt is A32.5 / 4L345. 1/2" x 34.5"


Sent from my iPhone using Tapatalk

[Lochlin]

If you take that belt to an auto parts store they'll be able to match you up one.