Got a puzzle that I need help with.

[bugnut]

Here is the low down. Was out on the sand having a good old time. Riding from one to the other and taking it easy the engine all of a sudden lost power and was backfiring out the exhaust then quit. Installed new plugs and nothing. When I kick the engine over it will just pop and sometimes it will idle but it takes a lot of throttle to get it to idle. So I checked the carbs and found nothing wrong there. They were just installed for this ride. They only have a hour on them. Both the idle and mains were clean. After that I tried to start it again and while I was kicking it pop and snorted and then got very hard to kick after that. I pulled both plugs and still hard to crank. Took the pipes and carbs off with the reeds and found when the left piston at tdc and left at bdc is when the crank turns hard. Pistons still look brand new. Still have only an hour on them too. So I have two questions. Did the cdi go out and put my timing way to far advanced and tried to fire it moved the crank out of phase or bent a rod. Next question is why did it die in the first place. I am leaning towards the cdi is messed up. I checked the reeds and they are still good. No broken edges or anything. I haven't checked the stator yet or the pickup coil. This is on my 421 cub with 39 pwks jetting was 172 main 50 idle.

[locogato11283]

if its hard to kick over, you need to pull the cylinders off. sounds like something isnt right internally. i wouldnt try to start and run it anymore. you will just make it worse. pull the cylinders and see what the problem is.

[blowit]

I agree with above. A CDI will not fail like you are describing (boost timing). You may want to check to make sure your flywheel did not frag. Whatever it is, it is internal in the engine. Bearing failed, piston tried to seize, etc. Pull it down and start there.

 

 

 

B

[bugnut]

Right after it got hard to kick is when I stoped. I know something inside is messed up but what would cause it to happen when I was cranking and then it popped out the exhaust then it was hard. The pistons have a lot of oil on them so I don't think it is there. I will take the jug off tonight and see how it turns. The one thing I can think of to make it get that advanced timing is the flywheel turned on the crank but with the key in there it shouldn't. I have looked at the flywheel and it looks great. Need to hook up my degree wheel and check the crank and flywheel timing.

[locogato11283]

youre wasting your time with the degree wheel. it just sounds like something came loose inside and the timing would have nothing to do with it. pull the cylinders and you will find your problem.

[blowit]

Yep, you need to tear down and find your issue. Simply remove the flywheel and inspect the key to verify timing. Popping in the exhaust can be caused by many things so find out why it is hard to kick and you will likely find all your issues there.

 

 

 

B

[bugnut]

Got some good news. I found that I have a new two piece flywheel. That is what was causing the timing issue and the cranking hard. Once I put the flywheel back to where is was before it broke the engine turns over nice now. Thanks guys for your help. Now the only thing I need are some new reeds and a flywheel. Along with the stator and pickup coil. Then back to the drags.

Edited November 18, 2009 by bugnut

[blowit]

Got some good news. I found that I have a new two piece flywheel. That is what was causing the timing issue and the cranking hard. Once I put the flywheel back to where is was before it broke the engine turns over nice now. Thanks guys for your help. Now the only thing I need are some new reeds and a flywheel. Along with the stator and pickup coil. Then back to the drags.

 

 

 

What do I win??

 

 

Glad it was nothing serious.

 

 

B

[bugnut]

yeah, after I read what you said about the flywheel I took a closer look and sure enough. I also looked at the pickup coil and the outer case was broken. Looks like the flywheel was moving around a bit. I almost started to take the cylinder off, glad I didn't

[blowit]

yeah, after I read what you said about the flywheel I took a closer look and sure enough. I also looked at the pickup coil and the outer case was broken. Looks like the flywheel was moving around a bit. I almost started to take the cylinder off, glad I didn't

 

 

You need to take a close look at your crank. I would highly recommend testing runout in the bike with an indicator. If that sucker is wobbling, it will cause a huge imbalance of the flywheel and cause this. Sure good to know why that flywheel failed.

 

 

B