Spitting out Spark Plugs?

[slawenm]

I have a friend who owns a Sym Jet 50cc 2 stroke scooter it was made in 2000 covered about 24k miles so its pretty old but still runs strong.

his engine is the Yamaha clone as told me by the mechanic who writen the thing off claiming it would never work again, because he was wrong about ever getting it working again I'm unsure if his labling of the engine may be right too, I cant find any markings on his CVT casing for the engine code too.

Hes very accident prone and has had a total of 6 so far each resulting in minor damage to him and his poor scooter

he had a bad one not so long ago and his insurance company made his scooter an economical write off, it was off the road for a few weeks and after him annoying me to use mine all the time I decided to carry all my tools to where the scooter is being stored and at least get the engine running.

so after tinkering replacing small things like Spark plug HT lead, New belt, a second hand but working carb his engine sparked to life but was running doggy, only started with lots of throttle applied and wouldnt idle, I sorted that out with some re-jetting and adjustments

anyway after all of that its running strong but keeps spitting out his damn spark plugs while he rides, I know little about 2 strokes but from the plugs hes been through recently they dont look to be too lean.

because his engine is running fine until the plugs are fired out of the casing I have no idea what could be wrong. the plugs are fired out with some force but they dont seem to strip the threads..... maybe working themself loose. he also randomly gets some popping from his T&T pipe if we've climbing some steep hills I know his pipe has a gasket leak where the chamber meets his muffler cause his exhaust cost him over £100 he wont let me fiddle with it to seal it again.

[jmkjr72]

sounds like the plug was cross threaded in or over torqued at some point

you have 2 options get a new head
or take the head off and get a helcoil kit and replace the threads in the head

[slawenm]

The brand new plugs hes always putting in thread in fine and are snug once tight they just fire out after some miles is put on them we check it every time he rides for tightness yet still it will randomly fire out sometimes, I'm not sure if his engine popping and the firing plugs is the same thing hes just told me it starts pops a few miles before a plug will shoot out.

And hes saying its not as fast as it used to be but I've done that by putting in lighter rollers cause hes too damn dangerous to ride fast,could the lighter rollers be making it run too high RPM and overloading the engine pressure and shooting out his plug?

[jmkjr72]

im still willing to bet there are only a couple of goot threads teh plug is catching on so it feels tight
but after it warms up out they go

poor threads in the head are the only thing that will blow the plugs out unless there not screwed in properly

[slawenm]

ahh okays thanks for the info I doubt we've going to replace his head the scooter is too damn old and beaten for brand new parts to be put on it. and even if the heads are cheap I dont know enough about two strokes to change the head on his engine

this is a picture of his scooter anybody have an idea what it may be a clone of

[jmkjr72]

its actauly realy simple to pull the head on a 2 stroke

pull the cooling shroud off and then take teh 4 nuts off that hold the head on and slide it off

get the helicoil (thread repair) redo the threads
put the head back on
torque the 4 nuts back down

it will take more time to take the body work off then to do the actaul job

[90GTVert]

I agree. I'd repair/replace the head. Like jmk said, it's really simple to do the head on these. No moving parts in there like the 4T.

[lshigham]

Feb 1, 2012 20:30:10 GMT -5 slawenm said:

And hes saying its not as fast as it used to be but I've done that by putting in lighter rollers cause hes too damn dangerous to ride fast,could the lighter rollers be making it run too high RPM and overloading the engine pressure and shooting out his plug?

Unlikely, but if you want to make him go slower stick some real heavy rollers in to keep the revs and power down. Another trick is to put a 4-5mm shim in the vari to keep it from closing properly so limits the gearing.

[stepthrutuner]

Ideas to try:

Replace compression washer on plug with star washer.
Wind some fine copper wire in the recesses of the spark plug threads.
Use Copper Coat metal gasket sealer on threads.
Mechanically restrain the hex drive surfaces on the plug's flanks from turning.

Cheerio laddie

[noodoggy]

Feb 1, 2012 20:19:48 GMT -5 jmkjr72 said:

sounds like the plug was cross threaded in or over torqued at some point

you have 2 options get a new head
or take the head off and get a helcoil kit and replace the threads in the head

Just helicoil. I just did that recently with my 50cc Venus, and it works fine. Got the right size at Napa auto parts. Works great now. Just gotta be real careful and straight. But it is easy. Search online for how to put a helicoil in. Runs about 40 - 50 bucks.

[stepthrutuner]

$40-$50? Lord, you could get an AM or used head for that.

[jmkjr72]

i think i paid 30 bucks for a kit that had the tap the install tool and enough coils to do 5 or 6 heads at autozone
then a 12 pack of more insterts is like 10 bucks

its good to get if you will do many but if you only have 1 try to find a shop that might loan you the tools

some parts stores have the taps and install tools on the loan a tool program if you buy the inserts from them

[vvtr]

tbh its probably a lot cheaper to just replace the cyl head.

[Fox]

The hardest part about changing the head is removing the body plastics to get to the head. After that it's 4 nuts and a gasket. You can try a little bit of High temp thread lock on the plug threads. That might work.