View Full Version : Calculating and adjusting ignition timing on a 2 stroke

Billy Golightly
11-05-2005, 10:16 PM
A little back ground on the problem, I was gonna go to the drag races last month with my 500R and after wrenching on it a couple days before I took it for a ride down the drive way, and on my way back up the thing died on me cold. Got it back to the shop and no fire. I tested the coil, stator, cdi pickup coil. Everything was within spec. The service manual gives no provisions to check the CDI box itself. I've spoke with gasmask from the forum here in the past and he mentioned he used a CR250 cdi/flywheel ignition on his 500 with good results. I tried sniping a complete CR250 ignition setup on ebay but didn't get it. So I bought Brandon's ignition he had forsale.

I've got fire now. With the CR250 flywheel, stator, cdi pickup, and CDI box. I've tried both my original CR500 ignition coil and the CR250 one he sent with the other parts. Both seem to work fine but the CR500 one I'd like to use so I dont have to try and figure out a place to put the other one. My problem now is that even though I'm getting great spark its not wanting to crank and run. We've pulled it all around out here and it just wont do it. It pops, 1-2 times when you first get the engine turning but after that it just turns over and wont do anything. So...back to the shop I went.

Pulled the flywheel and stator back off again. After comparing the 250 and 500 stator plates I noticed that the 250 stator plate has the timing alignment mark in a different place then the 500 did. So I scribed a new mark on the 250 stator plate in a similar posistion to the 500 one. I then had to longate the mounting holes to allow it to rotate far enough where the 2 marks would line up. I was pretty confident after that it would run, but it didn't. My next thought was perhaps the sensor on the flywheel and the posistioning for the crankshaft keyway were in 2 different places but they are only of a 1/16th or so. Not much at all.

So, here I am. Trying to get this thing timed right for it to run. I've tried using a screwdriver in the spark plug hole at TDC and seeing how close the flywheel sensor was to the cdi pickup. Its not acurate enough to tell much though...Tried using a dial indicator but I dont have anyway to hold it accuretly....I really really really really want to get this thing running before thursday so that I can get it going and take it down to the Florida ride down here but if I can't get it to run theres no sense in it.

11-05-2005, 11:31 PM
hmmmm, 500's are such bastards.....if you have spark it should run. bottom line, unless the timing is WAY far off...if its off by like 10 degrees it will still run, just really crappy, or you will put a hole in your piston. it doesnt make sense that it wont start. did you snap a reed petal off and its spitting all the intake back out before it closes the intake port? thats all i can think of maybe a extremely bbadly blown head gasket is putting alot of antifreeze in the combustion chamber? idk, my best guesses...

Billy Golightly
11-05-2005, 11:40 PM
It has had a leaking head gasket but I dont think it would be that bad. I already got the seat and tank off of it again today so maybe I'll pull the head and have a look see...could try pulling the reeds out and checking them too.

11-06-2005, 03:36 PM
man billy i hope that ignition works out.i'm glad your are geting spark now,what was wrong?is the spark hot enough that the massive compression of the 500 is not blowing it out?could be that the igniton is just not hot enough.if it fires a couple times then quits,a bad reed could be causing it.once the fuel/air build up and try to fire they are pushed back past the bad reed,or it's too much compression to ignite the weak spark.i dunno,hope you get it.

Billy Golightly
11-06-2005, 04:48 PM
I longated the holes in the stator plate some more this afternoon, and also ran a master ground wire from a headbolt on the engine directly to the frame. My dad said that when he use to work on dumptrucks sometimes the frame to engine ground would be disconected and cause problems. It seems to be sparking now, and consistently. Its just not cranking up. When we pull it around, the first time that the engine starts turning it pops and I can see some smoke come out of the exhaust. After that the engine just keeps turning over and never even pops or farts again. I also pulled the carb and intake and checked the reeds, that was all good. Ran a blow gun down in the crankcase to make sure it hadn't flooded itself out with fuel or anything, nothing came out. I dunno, I can't figure it out :(

11-06-2005, 05:04 PM
I dont know if this is the same senerio but when we ran our one atv low on oil it would spark real nice but wouldn't start. When you put more oil in it would start right up. Just an idea.

Jason Hall
11-06-2005, 05:19 PM
Man billy you got a good one goin on there. You need to pull the head, & set up a degree wheel on the flywheel. First with the stock flywheel on. Zero the degree wheel when the piston is at top dead center, then rotate the engine untill the f mark comes up. Then mark that spot on the degree wheel, also marking the piston position. Then do the same with the 250 flywheel & see if they are at the same place. If the port timings are way off from one engine to the other, it will never start. You can usually get a degree wheel at your local speed shop. I have one you can use but, I'm to damn far away. :w00t:

Billy Golightly
11-06-2005, 06:28 PM
Hey Jason,

Would a automotive style degree wheel work? That might be something I could conjure up from this shitty little town I live in :lol:

So after I get the degree wheel zero'd in on TDC, I rotate the engine till the F mark on ? What part comes up, the flywheel? I dont think it has an F mark on it. Haha man I've never had to do this before, does the degree wheel come with instruction? :D

Jason Hall
11-06-2005, 07:04 PM
An automotive style degree wheel will work, but you will have to figure out a way to mount it. If there is no f mark, then use the exhaust port, or the pulser as a marker. when the piston just starts to uncover the exhaust port, or the pulser is lined up mark the degree wheel. You are just trying to see if the pulser (magnetic pickup) is going to fire the coil when the piston is in the same spot in the cylinder. You can make a hillbilly degree wheel with a plastic coffie can lid, (it's 360deg) a full circle. All you have to do is make a pointer out of a coat hanger & line it up to a 0 mark on the can lid, when the piston is at T.D.C., then mark the can lid when the pulser is lined up, do it with the origional flywheel & the 250 flywheel. Then compare the 2 marks with the piston position. Just make sure the degree wheel stays still when turning the engine over.

Billy Golightly
11-06-2005, 09:42 PM
Hmmm, OK. This sounds the same thing like with what I did before with the screwdriver, except I didn't look at the posistioning of the piston and the ports then. I'll mess around on it some more I guess.

04-17-2017, 01:56 PM
I've got an 86 CR250R that has the same symptoms. Do you remember what you did to fix it?