MOPED ARMY

OEM Gurtne 12mm.

You may have soft seized it. No replacement carb comes jetted specifically for your bike. On a two stroke, the oil for lubrication is carried with the fuel, and metered by the jet. Too small jet=too little lube=kaboom

What carb did you buy? A dellorto Sha 15/15 with a 1mm shim is the recommended replacement if you don't replace with a bigger intake manifold, and runs around a 70 jet. The stock gurtners are notoriously unreliable and the clone replacements come jetted wayyyy to lean.

I'm not trying to be mean, just letting you know that unlike a four stroke, no carb you can buy will work plug and play.

Can't really trust the compression as the rings haven't gotten hot for years, but is is a good idea to check

You can check the cylinder visually by unbolting the cylinder head and looking into the bore. If the sides are smooth and without scoring or smearing your probably fine. But with a bike that old, you may be looking at a tear down to replace the bottom end seals

It's important that you say what carb you installed and what jet is in it....that way we can tell you what jet to run, you want to handle that first so you don't seize it when it does run.

The best option would be to clean the original carb and reinstall it. Or if you did buy a factory replacement style gurtner, put in the jet from the original carb.

These are single jet carbs. (edited)

Sorry, missed that it's an OEM gurtner. Try cleaning the original carbs jet and putting that in. At least then you'll know it's not gonna seize when it does run, as it's the same carb.

The gurtners can be very finicky. If you hadn't just bought an OEM one is advise you to get a dellorto...but I digress, at least get an in line fuel filter from an auto parts store. They hate any particulates.

You could have fouled the plug too, when it ran. Was it idling? Or with throttle?

Basically none. There are no valves, cams pushrods or anything in the head. Four bolts and it will slide off, it's just a chunk of metal with fins... then you can look. And hopefully just put it back on. Use some kind of penetrating lube, even wd40 so you don't strip the bolts, go gently. But otherwise not a big deal.

There may be a decomp valve, which could be causing a problem as well. But it'll just be connected to the head with a cable. Don't need to remove the cable it'll stay attached just fine.

If your cylinder looks good, but you have low compression. The decomp valve can be at fault. But really don't worry about that now. I'm more concerned about the cylinder bore.

I'm here all the time by the way and although I'm no genius I'll do my best to help. (edited)

Do you mean you replaced the whole throttle assembly? Removing just the grip shouldn't affect the decomp cable at all.

You can remove the the head without taking off the cable.

Do your controls look like this? If so, once the cables are removed and the control housing is off the bar, the lever should just sort of slip out. There may be a screw-in retaining pin that goes in behind the front of the brake lever and into the bar itself to keep the control from rotating.

I took the cylinder head off, the bore looks fine. And the piston moves freely when I turn the fly wheel. I am getting spark, fuel into the carburetor and air. Still won't start. The spark plug is dry. Fuel isn't getting to it. Any thoughts? Suggestions?

Have you examined your reeds yet? Will the bike reliably run by spraying some starter fluid in the spark plug hole?

Other than that, perhaps broken piston rings.

Thank you Pat Splat, Joey P, Jai Dot, Aaron Blair,

Thank you for your comments and suggestions.

So last night I pulled the new carburetor off and replaced it with the old one after disassembling it and giving it a deep cleaning (less the air filter). Spaying starting fluid directly into the carburetor and into the cylinder via spark plug opening. It ran for 10 seconds (the time it took to burn the starting fluid). I repeated process but only got choking and coughing, but not starting. It was getting really close to starting, but not. Pretty much the same results not using starting fluid just applying the choke and peddling like heck. But the fact that it did start for a short time can I assume that wiring and grounding is good.

Almost like my timing got off center?? But I don't see how that could be because it ran somewhat okay just the other day. Maybe something with in the ignition? Compression? How can I trouble shoot compression / ignitions issues? Better question is should I trouble shoot those areas? Once again I feel obligated to mention am a novice at this and my comments and questions may not be on target.

All comments are useful, because I don't know what I don't know.

Thank you to Moped Army folks and everyone have a productive day.

Earl

Yeah, based on your issues, I completely agree. At some point, fuel isn't getting into the cylinder. You said that fuel comes out when you pull out the main jet. Let the carb drain completely dry, put the main jet in, attach the fuel line / turn on the fuel, and then remove the main jet. You should have fuel flow out of there fairly quickly.

If not, one of your passages is still clogged.

If the bike has done some caughing or poping when trying to start yes it could be that the flywheel timing has slipped. Maybe the PO had the flywheel off and it was not cranked down tight enough.

You can check a rough estimate of the timing by just removing the spark plug and then use a small screwdriver to feel for the top of the piston. When the piston is at the very top of the stroke then glance at the rubber grommet that holds the spark plug cable and you will see the arrow line will be about 3/4 if an inch to the right of the center of the rubber grommet.

If its like roughly in that area give or take a 1/4" it will start. If it's 2-3" on either side your timing has slipped

(edited)