Why is my engine back lashing?

[Dmonies]

Can somebody help me figure out why my motor keeps on back lashing after firing a couple times. Is my Timing wrong?

[Stig / Major Tom]

Can somebody help me figure out why my motor keeps on back lashing after firing a couple times. Is my Timing wrong?

Need more information.
What scooter?

Stig

[eamartin]

I'm not sure sure what "back lashing" is.  As Stig said, we need more information.  What scooter is this, have you had it for a while, was it performing correctly previously, have you done any maintenance, repairs or modifications recently?

[souzamoto]

You likely mean that while turning the motor over with the electric starter, it's slows and the starter kicks out. Yes?
Is the battery fully charged? Sometimes a low battery will cause this.
CJS

[scooterfan]

I think you are probably referring to what's more commonly known as "engine backfire" - where the fuel ignites with a load bang inside the exhaust or intake (outside the combustion chamber).

If so, there could be several reasons - i.e. incorrect valve clearances (exhaust valve open when the spark plug is sparking / burnt exhaust valve / inlet valve open when the spark plug is sparking).

Is the scooter an EFI or carburetor model ?

[CROSSBOLT]

Please describe carefully what you do, what it does and what it sounds like. Take and post a video with sound.

[stuo]

Back firing can be caused by improper timing, intermittent spark, burned exhaust valve, tight valve lash, lean mixture.

[Dmonies]

Im not to sure what model of scooter my engine was originally on. The head jugg and the block are all stamped LEA3. where most is horizontal engines serial mumber is located my engine doesn't have one all it says is KYMCO LEA3. I do know it was originally EFI but I don't have the whole scooter all have is engine and efi intake. iv got a normal 50cc scooter carb in the efi intake. but Iv got it sealed up good I do believe

[eamartin]

So you don't have a Kymco scooter.  You have a kymco motor.  And the motor did not come with its' EFI.  So you installed some small carburetor on it and now it won't run right.  Is that correct?

[Dmonies]

I have 2 200 kymco likes. and a 150 movie as well as the 50cc kymcopmotor. I really have questions about all of these. but for now the 50cc motor. iv made my own wiring harness for the 50cc kymco motor. it fires and it did run once upon a time. for about an hr. I don't have the whole efi system so stuck a 50cc carb on it and made it work. well I didn't fool with the engine for a week or so and when I came bak to it it wouldn't start at all. Had good spark and everything just not starting so I messed with carb for a while. still wouldn't start. I just recently got it to act like it wants to run again but while im cranking it over it makes a god awful noise(like it is coming from starter maybe) and it jolts the engine forward and keeps trying to crank. Iv noticed one thing strange about this motor. Its that it has 2 small intake valves on the same rocker arm and only 1 exhaust valve.

[scooterfan]

Im not to sure what model of scooter my engine was originally on. The head jugg and the block are all stamped LEA3. where most is horizontal engines serial mumber is located my engine doesn't have one all it says is KYMCO LEA3. I do know it was originally EFI but I don't have the whole scooter all have is engine and efi intake. iv got a normal 50cc scooter carb in the efi intake. but Iv got it sealed up good I do believe

Modifications like this can easily cause a lot of headaches. Not knowing the mileage cocered by the engine might be a problem as well. If possible, I would at least try to do a compression test on the engine to see if i’ts worth spending time on getting the engine going properly.

My 2cents, good luck.

[Dmonies]

Modifications like this can easily cause a lot of headaches. Not knowing the mileage cocered by the engine might be a problem as well. If possible, I would at least try to do a compression test on the engine to see if i’ts worth spending time on getting the engine going properly.

My 2cents, good luck.

it has excellent compression and id say only test miles were the only thing ever put on the motor. when I bought the motor I was told it was suppose to be destroyed(Im assuming that being it doesn't have any kind of serial number on it) but a friend of mine who works at a salvage yard brought it to me because he knows I like small motors etc. it was brand new still tho I don't think it had even had oil put in it yet. the rings are excellent and all. but here is something else strange I thought. the motor has probably 25 pickup contact things on the flywheel instead of only 1 like most, and the flywheel reads LEA1 while the motor reads LEA3

[CROSSBOLT]

Just to let us know what the facts are, please describe how you know the compression is good. That means some pressure reading on a gage or a compression tester. It sounds like you have been running the starter a LOT trying to get it to fire: that may be the awful noise you hear. '24 contact things where there is normally one' could be coils of the alternator. Have you interchanged 'coils' with 'contact?' Just now a thought: are you working through a translator?

[scooterfan]

it has excellent compression and id say only test miles were the only thing ever put on the motor. when I bought the motor I was told it was suppose to be destroyed.....................................it was brand new still tho I don't think it had even had oil put in it yet. the rings are excellent and all. but here is something else strange I thought. the motor has probably 25 pickup contact things on the flywheel instead of only 1 like most, and the flywheel reads LEA1 while the motor reads LEA3

To be honest, a couple of things you mentioned about this engine sounds a bit strange. It almost looks like this engine is far from original - which will make it very difficult to get it going properly:
1.  The motor has 25 pickup contact things instead of one.
2.  Flywheel reads LEA1 while the motor reads LEA3.
3.  Engine was brand new and you don't think it ever had oil put in it yet. (??)
4.  Original EFI system has been thrown out, and a carb has been installed. (Carb jets might be incorrect ?)
4. The motor was suppose to be destroyed. (For what reason, if it was still "perfect" ?)

This makes me think there is a possibility that you will find it quite difficult to get this engine going properly. It sounds like you at least  need professional advice to get this engine going.
This engine has probably been stripped for parts previously, and has been re-assembled by using bits and pieces from other engines. This scenario would make it very difficult  for even the best of qualified Kymco mechanics to give proper advice.

Again - good luck !

[stuo]

If it's back firing through the carburetor you probably have timing too retarded or mixture too lean.