Last summer my niece bogged down (2 people on, uphill in 5th gear) my brother's Moto4 and since then it can't be started by towing it anymore. We had a hard time getting to to start on the pull cord so we tried to tow start it and that's the first time it didn't work so I assume that's when the problem started. We eventually got it going and it drove normally (shifted fine and no clutch slippage) but the motor doesn't turn over when you push or tow it in any gear. We had tow started it many times before that. I've tried adjusting the clutch but it didn't help.
It has been sitting for a while and I'd like to get it going again and it would be nice to be able to tow it to get it going instead of wearing out our arms (and the recoil) on the pull cord.
Any ideas?

 

Pull the spark plug and see if the engine can turn over when you pull it.If not, could be the engine or tranny may have locked up ?

 

It turns over on the pull start, it just doesn't turn over when I tow it in gear. It acts like it's in neutral when it's towed, no matter which gear it's in but it shifts and drives normally otherwise.

 

Classic example of why you shouldn't tow start Quads. You will have wrecked the one way clutch behind the centrifugal clutch.

 

I wish I had known the damage tow starting could cause. . We've done it for years with no issues but we may have just been lucky.
If the one way clutch was bad, would you still have engine braking (gearing down to slow down)? My nephew has the bike now and has been driving it for the past couple weeks and it still slows down when gearing down like it used to.

 

Easy test, go down a steep hill, fairly fast, with no throttle, if the centrifugal drive disconnects, the one way clutch is bad.

 

Whatever was going on, it "fixed" itself this weekend. My nephew broke down with it and I had to tow him home. We were going about 40 km/h and all of a sudden the rear wheels locked up. I don't know what gear it was in but he upshifted a few times and it fired up. It's nice to have the engine slow you down on the hills again.
Another question. What would cause it to run really hot and act like it's running out of gas? It seemed ok at slower speeds but it would act like it was running out of gas if he went any distance at higher speeds. If we pulled over and waited for a few minutes it would start up again and would be fine as long as we drove slowly. We thought it might have a fire problem at first so I pulled the spark plug but it was dry so I tried pouring a bit of gas down the plug hole to prime it but it was so hot, the gas would evaporate instantly. I discovered that the foam part of the air filter was completely gone so I thought it might be running too lean like my Bayou did when I first bought it because the previous owner had modified the airbox but he replaced the filter yesterday and it's still doing the same thing. I suggested cleaning the tank and the fuel shut-off in case it's plugged and starving it for gas but they haven't got back to me to let me know if it helped.
Does anyone else have any ideas?

 

Dirt or water in the carb or the vent in the filler cap blocked.

 

I never even thought to check the filler cap. I had the same problem with my Bayou when I bought it and that was the problem. Thanks.

 

Ok. Within the last 3 days I have put an air filter in, cleaned the carburetor, fuel shut-off and tank, tried a different carburetor, and tried adjusting the pilot screw everywhere from 1/2 to 2-1/2 turns out and it still runs about the same. The only difference is that it's backfiring now, which it started doing about 4 days ago, before I did the things I mentioned above. He said sometimes if he hits a bump it will work great for a minute or so and then start's bogging and backfiring again. I thought it might be dirt in the fuel system getting knocked loose and then plugging something again but the fuel system is spotless now so I doubt that's the problem. It's getting hot really quickly too (which could be caused by it running lean) so I checked the intake boot for leaks/ cracks but I didn't see anything.
I'm leaning towards a wire shorting out somewhere but I can't see anything, even though that wouldn't explain why it's getting so hot so quickly. Anyone have any other ideas?