Originally Posted by lstzephyr
Alright gents I need a couple extra opinions on my current situation. I can't get my bike to start again after it died the other day. It was running fine on a new engine rebuild until I turned into the bar and it sputtered and died. I figured it was low on fuel and didn't bother with it. When I went to leave I couldn't get it to start. It hasn't started since.
- New fuel
- new petcock
- new fuel line
- new spark plug
- new coil
- new wiring harness
- new stator
- new coil pickup
- new woodruff key on crankshaft
- Checked for spark(has spark on spark tester and when holding plug to head)
- Top end is fresh(new piston/rings/valves/seals/tensioner/cam chain etc less than 8 engine hours ago)
- Checked cam chain, cam timing, valve clearance(all in spec)
- Cleaned the carb thoroughly ( tore it down completely and had it dunked over the weekend by the local machine shop)
- Attempted bump starting (the bike only locks the back tire, I need a bigger hill)
- pulled cylinder off and checked valves/piston. Everything looks fine.
- Swapped cdi with ebay xr400 cdi that was stated as pulled from running bike
- I'm working in a 70 degree shop so temp is not an issue.
After the carb cleaning it would periodically fire 3-4 revolutions then die. Barely more than the spin of the kick. Starting fluid has no effect other than raising the amount of backfires.
I swapped on my recently rebuilt HS40 Carb (mikuni tm40) to see if it was still a plugged pilot circuit. No change except it will fire 3-4 revolutions every other kick now. I think that is because the accelerator pump allows me to toss fuel in. I didn't want to add another variable(new carb) but I wanted to rule out the stock carb as the issue.
So my thinking is that it could be one of a few things:
- Loss of compression(it is still more difficult to kick than before rebuilt so it appears to have compression)
- CDI(only failure symptoms I can find say that there is no spark with a dead cdi, I have spark so probably not cdi)
- Plugged pilot circuit in both carbs (I checked both thoroughly, especially the hs40)
- Misadjusted idle in both carbs (I have moved the idle screws around while trying to start it)
- automatic decompressor
I get a pretty impressive backfire every few kicks and it has spark when held to the head. It is getting fuel because of the backfires. About the only thing left is carb or cam.
Any other ideas?
Alright I'm bumping this back up with new components and even less of a guess. I've got an entire new electrical system because I thought it might have incorrect spark timing. I replaced the woodruff key thinking that might contribute to missed timing. No change.
Any help would be greatly appreciated!