I've just fitted new crank seals and piston rings. The bike was running before I worked on it, but it wasn't running that well (hence the decision to fit new seals and rings).
I have a spark (but I can't guarantee that it's sparking under compression). Fuel appears to be getting through. I even tried squirting some easy start into the air box to see if it was a carburation problem.
I've checked my seals again. No problem.
I'm wondering whether it's a CDI problem. Has anyone had experience of anything like this? It's driving me mad.
At least you're on the right site now for help man. Had you signed up a month ago i'm sure someone would have met up or just leant you one. Get into the community and reap the benefits mate. Hope you get this sorted and please update
At least you're on the right site now for help man. Had you signed up a month ago i'm sure someone would have met up or just leant you one. Get into the community and reap the benefits mate. Hope you get this sorted and please update
i was saying about the neutral light because on my bike it was the side stand switch -_- like selki said, go ask your local yammy dealer if theres a way of testing the cdi unit, or even ring them up.
The barrel is unscored but compression seems poor ( you can turn the flywheel round by hand). this was why i put new rings and crank seals in. but i am now going to have it rebored because compression is still poor. i bought a compression tester on ebay and i cant even get a reading! Either than means that the compression is truly appalling or the tool is a piece of crap!
The way you have described it, I think it is unlikely it is a CDI. You have a spark and the CDI probably wouldnt have been disturbed on an engine rebuild.
When I get a problematic engine, I always try a few drops of petrol down the plug hole. This is usually enough to fire it up, even if only for a few seconds. If that doesnt work theres a good chance it is an ignition problem and more likely to be something that hasnt gone back together right. Take off the flywheel and make sure the woodruff key hasnt sheared. If it has, lap the flywheel onto the crank and fit a new woodruff key. As a last resort try a new plug. If you still suspect the CDI, remove the suppressor cap and see if you can get the spark to jump across a gap of about 6mm onto the head or a convenient earth. If you can that should be good enough under compression.
Thanks for good advice. I checked the woodruff key. All OK. I've tried a new plug. But I'll try the HT lead spark trick to check on the power of the spark. Someone else has suggested stale petrol (sounds unlikely), so I will put fresh juice in the tank. I also wonder whether I should try warming the plug. Anyway, it's dead, dead, dead. Maybe it will stand a better chance of firing up when I've fitted the re-bored cylinder. The CDI still worries me a bit. I read somewhere that when they malfunction they do so progressively, so you see a spark but it's just in the wrong place. If none of the above stuff solves it, I guess I'll have to address the CDI so that I can rule it out. It's a hideous process of elimination and it's driving me madder by the day! I'll keep you posted.
Dont expect a wonderful reading off a compression tester. The corrected compression ratio is about 6.5:1 on the DT. The corrected ratio takes into account the fact that you dont get any compression until the exhaust port closes. TBH ours is pretty pants as well when you turn the flywheel by hand (and thats after a rebore!) so its not a good guide at all, but the thing goes ok. At 6.5:1 I guess the compression tester should be reading about 90 - 100 psi on a good day. Try the trick I mentioned in a previous post about putting oil down the plug hole after the first compression test and then re-test it. If the reading goes up by a fair margine that means the rings/bore seal is poor.
Thanks for the tips. Makes sense. I've already committed to a re-bore now (just ordered the o/s piston), so the bike should at least be good on the compression front now, which rules that out as a factor.
My friends DT went all messed up after a rebuild (sounds exactly like your problem), he had a spark, loads of compression, bike sounded pretty healthy, just wouldn't start. He tried bumping it over and over to no avail, dragging it with a car, no avail... then tought "fk it, ima try a new CDI" got one, and boom away she went. He took it to our "local bike mech" to see if he'd know why this happend and he said when he was putting oil in his bike, he's spilled some over the top of the CDI, and the mechanic came to the conclusion that: the oil had made a connection from the oil light plug to the CDI and had blow it up when he over revved/went over powerband on the bike... If you've got the DT with the CDI attached to the Oil Tank, perhaps you've done this mistake aswell?
