Ignition coil

[sezian]

Just got my bike MOT'd and on the way home (flat out down the duel carriageway) she feels like she’s about to seize, so quickly in with the clutch and coast to a stop !!!

No ignition lights? Checked the main fuse and that’s blown, put the spare in, I now have ignition lights back, but when trying to kick the bike over there’s very little compression !!!

Wait for the nice RAC man who has a quick look, we remove the spark plug and kick it over, he say’s there’s a spark but a week one. Eventually I get loaded on a trailer with the bike and get home after a couple of hours sitting by the side of the road.

So off with the head and barrel, the rings have welded themselves in the groves and the piston has some lovely scars, the barrel looks marked although according to my local engineering shop it only needs honing out, but he does say something has obviously caused the problem ???

So what was the cause? The engineering chap said a week spark could cause it? Is there a way to test the ignition coil? Having looked on the web (wemoto.com) my coil looks different from the replacement part, in fact it looks more like an early version DT coil ???

I’m now pretty confused, is there anyone who can possibly shed some light on why the bike seized and what the difference is with these ignition coils.

Many thanks.

[Airhead]

Just got my bike MOT'd and on the way home (flat out down the duel carriageway) she feels like she’s about to seize, so quickly in with the clutch and coast to a stop !!!

No ignition lights? Checked the main fuse and that’s blown, put the spare in, I now have ignition lights back, but when trying to kick the bike over there’s very little compression !!!

Wait for the nice RAC man who has a quick look, we remove the spark plug and kick it over, he say’s there’s a spark but a week one. Eventually I get loaded on a trailer with the bike and get home after a couple of hours sitting by the side of the road.

So off with the head and barrel, the rings have welded themselves in the groves and the piston has some lovely scars, the barrel looks marked although according to my local engineering shop it only needs honing out, but he does say something has obviously caused the problem ???

So what was the cause? The engineering chap said a week spark could cause it? Is there a way to test the ignition coil? Having looked on the web (wemoto.com) my coil looks different from the replacement part, in fact it looks more like an early version DT coil ???

I’m now pretty confused, is there anyone who can possibly shed some light on why the bike seized and what the difference is with these ignition coils.

Many thanks.

Oh thats a real bummer mate

But how come you were "(flat out down the duel carriageway)" you have just done a rebuild and didnt you put new rings in or have I got that wrong?

Have you ever checked your oil pump and after the re build did you bleed it and force it to full stroke to expel any air in the system?

I have never heard of the weak spark theory you mention, so cant really comment right or wrong!

As for checking the coil, use an ohm meter, the primary winding is checked from the small wire to the metal mounting of the coil, result should be 1.0 ohm +- 15%, the secondary winding is measured from HT lead (without cap) to the metal mounting and result should be 5.9 ohm +-20%

...Paul

[sezian]

Hi Paul, thanks for the reply.

I had just completed the rebuild although I used the old piston and rings, maybe this was a mistake? I did also manage to remove the oil bleed screw on the pump and get shot of any air, the oil pump was fully bled and had full 2 stroke oil right through the tube as you had previously advised.

I'm not sure what caused the bike to seize, perhaps it was to much full throttle for an extended period, although I did think these bike were fairly indestructible ???

I only mention the weak spark theory as it was mentioned to me as a possible cause, although the engineering shop did say after I picked up the barrel that he thought it was probably a fuelling fault ?

I did have the mixture screw on the carb turned out 1 and 3/4 turns from fully in. Having gone through the manual I now read the screw should only be turned out 1 and 1/4 turns, was this a possible cause ???

Any thoughts, suggestions, what should I check before re-buid ???

Thanks.

[Cynic]

Hi Paul, thanks for the reply.

I had just completed the rebuild although I used the old piston and rings, maybe this was a mistake? I did also manage to remove the oil bleed screw on the pump and get shot of any air, the oil pump was fully bled and had full 2 stroke oil right through the tube as you had previously advised.

I'm not sure what caused the bike to seize, perhaps it was to much full throttle for an extended period, although I did think these bike were fairly indestructible ???

I only mention the weak spark theory as it was mentioned to me as a possible cause, although the engineering shop did say after I picked up the barrel that he thought it was probably a fuelling fault ?

I did have the mixture screw on the carb turned out 1 and 3/4 turns from fully in. Having gone through the manual I now read the screw should only be turned out 1 and 1/4 turns, was this a possible cause ???

Any thoughts, suggestions, what should I check before re-buid ???

Thanks.

Unlucky, although considering how far out the fueling was on mine b4 i took it down i don't think a couple of turns on the mixture screw did it, i managed to do what you did about 15 years ago and that was down to the fact that the engine don't take any notice of the red line on the taco, she would hapily run to 9500 even 10000rpm and i did EXACTLY what you did. Smeared the rings down the piston and heat siezed her. On a dual carriageway the other side of Milton Keynes. Its to do with the engine not being able to get rid of the heat fast enough at higher rpm and the ally piston swells more than the steel sleeve in the barrel and nips.

You can either ride the torque and plod or have a race bike but not in between, for dual carriageway flat out stuff at high rpm set the mixture (needle height main jet) so you get a nice rich colour on the plug at full chat. The extra fuel keeps the combustion temp down and therefore the engine stays cooler.

The only prob then is the bike will be unresponsive at lower rpm because she will be massively rich ( bit like a 350 ypvs with the servo stuck wide open) at lower revs. Or keep the revs lower i kept to about 8500 on longer runs. Or avoid the DC and use the country roads and thrash away.......

[Airhead]

I agree at this stage it might be an idea to buy a main jet one size up from the one you have at the moment, are you on 130? Also what about the barrel fins...hope they arent powder coated I believe this can cause heat retention problems and so should be avoided.