I’ve got a 300cc quad made by xtm but is the same as the Linhai/buyang quads. Wont fire, backfires through the carb and sometimes will spit a flame out exhaust, timings 100% right, has compression and a new carb, valves are in spec, has a clunk when start fluid is sprayed down the carb I suspect it’s the starter clutch which I have a new one coming. Also it won’t crank off the starter switch as the reverse light is on when in neutral, would anyone have any ideas? Die they have a neutral switch? The bike will turn over when power is put to starter. Any help would be appreciated thanks

 

Backfiring and spitting flames from exhaust are usually indicators of timing out. Have you checked that TDC by the piston is TDC by the flywheel mark? If it isn't, the ignition timing will be out and, if you have set the valve timing by the flywheel, they will now be out too. I don't know your model at all, but it will have a switch for neutral and one for reverse. Sometimes these are separate switches, sometimes a rotary switch is used. Starter clutches usually scream when giving trouble, you may get a clunk from them when you turn engine off if they are sticking a bit.

 

Yeah timing at the flywheel and tdc are correct, can a faulty cdi cause the same thing? And it has 2 sensors going into the cvt, one says up and other says down, there the only sensors I can find on it and no other types of neutral switch, and the starter clutch let go last night so now starter spins but doesn’t turn the engine over

 

If the CDI has sent the ignition timing out, or the trigger coil, it could be sparking at the wrong time. Never come across it, though. This, if over advanced, could wreck the starter clutch as it tries to knock the piston back down as the starter is trying to push the piston up. However the opposite can also occur, if the starter clutch slips and piston stops just before TDC, when most compression is against it, because engines fire just before TDC, you again get the piston trying to force the engine backwards. This I have had, if you remove the plug lead and the engine spins over easier on the starter, this indicates one of the two faults above. I have also had an idler gear bearing gone in the starter geartrain, giving the same effect. So check the position of the trigger coil and any idler gear bearings, when you are fitting the new starter clutch. Some CVT systems have the neutral/reverse switches in the control box under the forward reverse lever and many bikes have a wire from the neural switch to the CDI to give a better spark in neutral.

 

Yeah will do thanks, is there any giveaways as to which neutral switch set up id have? Is there a single wire going to the cdi for neutral? On the high-low selector there’s no wires going to it so can’t imagine being a switch in there.

 

Whether rotary or individual switches, the wires that go into the gearbox are individual and, on any I have seen, earth out each wire when the lever is in that position. However those that go to control levers may be microswitches and can work on the positive side of the battery. Again on any I have come across that have this set up, a wire goes from the neutral light circuit to the CDI, there is often a diode in that circuit too.

 

So I’ve replaced the starter clutch and think I’ve narrowed it down to faulty cdi, if I try to start it and spray fuel down it locks up but if I take spark away and spray fuel down it turns over with no issues, that to me seems like the cdi has sent ignition timing out, also it did fire for 2-3 seconds but then afterwards it went back to locking up when trying to crank it, I’ve only been able to have it fire twice in the time of trying so I think the cdi module is sending spark at random times

 

If there is an F mark on the flywheel, you could check ignition timing with a strobe. Do it with plug out so the engine doesn't lock. If there isn't an F mark, you may be able to check timing with a strobe and timing disc, but it is probably easier to fit a new CDI and see what happens, unless your CDI is an expensive one.

 

It only locks up when fuel is sprayed down it so can still crank It with the plug in, I had a new cdi in as the old one would only spark on the first 2 rotations but I think the new one might be sending spark at the wrong time, it was a cheap ali express one as it’s the only place I could get one but I have another one on its way and if that’s failed I’ll just make my own harness to work for another common one