clone running rough , backfiring at startup

[turn-n-burn]

Hello quick question. Doing a lifan 420 conversion for a friend of mine. Got it all running perfectly and when wiring the ignition switch he shorted out the kill wire to the coil and the coil blew up. Replaced the coil and set the air gap and now it backfires through the carb when you choke it to start it. And at idle it seems like it runs rough. Seems off time. Any ideas?

[turn-n-burn]

I looked for a good amount of time for a replacement coil from lifan but could not find one. The new one I noticed had a thinner stack of metal wafers where it mounts to the block but it is running true down the center of the magnet. Any way this could cause the problems?

[turn-n-burn]

Swapped out the coil stands to the new coil it did not help. Still back firing out the carb on ignition and surging at idle and constant throttle... Bent timing key?

[Streetbu]

That would be my first guess...Partially sheared key.

[sho305]

Check the flywheel first, some times it helps to lap the taper in then install it. I did mine when I put the advance key in. The gokart guys do that and run them with no key so they can set the timing where they want. Just put some valve grind compound on and spin it on there for a few, clean it all off, and put back together with key. I'd highly doubt the coil is doing it but you never know. Also look at the pushrods and rockers for proper movement while you turn it by hand.

Maybe you will find something there before you buy anything.

[turn-n-burn]

Timing key appears to be fine. This is really strange to me as this is a brand new engine with 20 hours on it. Took the coil off my vc 440. Same result. I wonder if this int a special coil I fried. It is off the lifan with the 18 amp charge coil and looks different than tge replacement

[slonomo]

Did you check the valve lash? If it's backfiring through the carb maybe the intake valve is sticking or lash is off.

Also, how are you supplying fuel? The clones need to have the vacuum for the fuel pump run off the intake spacer, not the valve cover. If you are on the valve cover you will get inconsistent fuel pressure. You also need to run a "t" fitting from the fuel line to run extra fuel back to the tank. The stock carbs don't like a lot of pressure, they are designed for gravity, not pressure.

So if you are not getting enough fuel it will run lean and backfire/puff through the carb. Check fuel pressure and check float level. Are you running a filter?

[turn-n-burn]

Fuel flow is good. Have a filter and a t fitting to tank as recommended. I got to looking at the coil that blew and it has skme type of circuit board inside of it. I'm thinking this has some sort or retard, advance feature. Or possibly sonething to do witg the 18 amp charge coil. I'll be calling lifan in the morning.

[sho305]

Some new engines have a retard in them, I'd be surprised to see it on a clone yet but it is possible. Its solid state in the coil, honda and B&S are all using them. They don't change the timing that far but enough to cause issues. You would need to run the old flywheel I bet, easier is to make a bracket so you can move the coil and just time it if using a different coil.

[turn-n-burn]

I spoke with a tech guy at lifan. He says they do have variable timing of some sort inside the coil and tgat the only way to disable it would be to run a different flywheel, thus eliminating the use of the 18 amp charge system. He was nice enough of a guy to send me a replacement free of charge! Lucked out there...
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