Motoplat ignition advance

New to me 1988 (apparently) 250 XC. I say apparently because, while the frame and engine numbers point to 1987, I understand that most 1988’s appear as ‘87 builds. And mine is an XC with Motoplat ignition, which indicates a late ‘98 build (maybe). Maybe because a prior owner may have swapped from SEM to Motoplat some time.

Just got the bike running and experienced several strong kick-backs. Checked the mechanical ignition timing and it appears to be set at 2mm before TDC. The technical reference sheet for 1988 with Motoplat says timing should be 9.5 degrees or 0.61 mm BTDC, which would certainly explain the kickbacks.

Any thoughts? TIA.

Yes .61mm sounds correct. 2mm would be for 400/430
Kick back will brake the engine cases!! Ask me how know??

Thanks Jim. I’ll dial back the advance and see how it goes.

Well, I can’t reduce the advance enough on the stator plate to reach the 0.6mm BTDC spec. The screws bottom out in the slots of the stator at about 1.2 mm BTDC. Started an ran it at that and it still gives some kick back when warmed up.

This is a Motoplat Mini-6 external rotor on a 250 XC. I ordered a flywheel puller so I can see if the flywheel has rotated on the crankshaft. I assume the flywheel is keyed, right? Or is it possible to mount the flywheel wrong on the crank?

If it’s not one of those two things I don’t see how it’s possible to reach 0.61mm BTDC advance.

Yes keyed flywheel. Someone has been in there before and mounted the motoplat to the backing plate in the wrong position. You will need to pull the flywheel off and rotate Just the backing plate until it lines up right. Only three different positions. Been there before!!

FYI Left handed threads on the fly wheel nut.

Have you downloaded and read the Owners manual and Service manual?

Thanks, yes I have owners manual, engine manual and parts manual. Is there another service manual?

I’m starting to think that I may have an ‘87 or early ‘88 XC that was upgraded from SEM to Motoplat by someone. It also has a Acerbis headlight mounted on it, which the XC didn’t cone with, so maybe that was the incentive?

I’ll see what I can find when I get the flywheel pulled off of it. I did not realize that there was a second “backing plate” that the stator screws to. I thought it just bolted up to the engine case like other bikes. I guess the backing plate is an adapter to allow mounting of various ignition systems to the standard case holes. Makes sense.

Whoever set up my bike previously did not dig deeply enough to realize that the various ignition systems require varying advances, and had it set for a hair over 2mm BTDC. I’m confident that I’ll find that interface plate is jacked up.

I really appreciate your help.

Got my flywheel puller today. Worked great. When I got inside the ignition I found that the backing plate was mounted in the correct (lass advanced) screws, but the three screws holding the stator itself to the interface plate are through slotted holes, so I was able to loosen them, rotate the stator full CW and achieve the lower .6mm BTDC advance.

Did give it a start after and it seems easier. Thanks for your help.