Help CDI intermittant spark

[opsled]

The stock 540 secondary is not an overdrive clutch either so it won't be the "cure all" if this is your trouble. Check here - http://www.vintagevmax.com/vvforum/viewtopic.php?t=23 for my thoughts on the issue.

I'm not sure if there is an overdrive secondary that will fit a stock 78 jackshaft. There are aftermarket shafts (1"keyed) that will but I wouldn't spend the money for one until you get all your other problems ironed out.

If your engine was siezed it may be in the gearcase due to a leaky water pump and until you know what you have your just guessing. You gotta check all these things out to narrow down the problems before you can fix anything. Assesment takes time but it's not wasted, it's nessessary.

As for timing lights, I never use them on these animals. I dial indicate and go from there. Stock settings should be good for a stock engine. If it's had the ports raised you may need to advance some but there isn't much else that can be done. Nothing is adjustable except initial setting unless you change the CDI so it doesn't do much good and if your spark has been erratic I don't think you could trust a timing light anyhow.

opsled

[Bob Vehring]

Listen to what Phil said, as always, its very good advise. Several things could be your problem, you have to systematically eliminate things one at a time to get to the bottom of this.. Many things could limit your top end.
The link he provides on clutching is very helpful, it helped me sort mine out without having to go through all the testing myself. This is a fantastic forum, the answers are probably already on here, but you still have to do all the sorting to get to the issue.
Remember, the harder a problem is to solve, the better you feel when you get it fixed,
(well ok, I know that doesn't make you feel any better right now)

[agfirecat]

do you have a set of 540 pipes if so id give them a shot even though they might not fit in that chassis very well. if u could get them hooked up and run it then you could rule out the pipes . the 440 pipes are considerably smaller.and may be giving you problems. even with out the muffler u could still wind it up on the stand

[opsled]

do you have a set of 540 pipes if so id give them a shot even though they might not fit in that chassis very well. if u could get them hooked up and run it then you could rule out the pipes . the 440 pipes are considerably smaller.and may be giving you problems. even with out the muffler u could still wind it up on the stand

Another issue I overlooked. Good job on pointing it out.

opsled

[TommyMoEmDown]

Thanks for all the good info
I replaced the CDI box, It started like a yamaha. I pulled the rope and fired right up first pull.
I know alot of guys say CDI are good or bad, but my CDI was screwed up.

I checked my stator coils with a lab scope, with the box unplugged , spark plugs out, keeping the motor spinning with the rope, I got clean patterns on brown-red whtie/red- red and white/green - black. I put the plugs back in and cdi connected, fired up and ran then hic-kupped then continued running, I caught the action on the scope and it lost the charging coil pattern for an instant. I believe the CDI has an internal intermittant short and draws too much current.

[Vmax540]

Tommy, this is interesting.... good troubleshooting skills ! It is just way less likely that a CDI is intermitten instead of completely failing.

[tyler440]

hmmm yes i am definitly making note of this (intermitten cdi)! so when you put the orignial cdi back on it runs like crap again?

[TommyMoEmDown]

Ok now that I had reliable spark, starts great, runs good, I decided to go back to the timing light.
I hooked up the light and still got bad readings. nearly 55 deg timing.
I'm using a snap-on MT241-a Timing & ignition Advance Light. Now how does the timing light calculate what 1 degree is? The only input is the inductive trigger from the spark plug wire. I thought I'd try another light, so I went looking in an old Bear Engine Anylizer cabinet. I pulled out something interseting. It was a Snap-on MT255 Distributorless Ignition Adapter. We use to use this to correct the RPM when cars started using D.I.S. Without it, the rpm would read double do to the waste spark. On a four stroke with DIS the waste spark occurs near TDC. But on a 2 stroke twin, the waste spark occurs at BDC, when the piston is at the bottom. So that means 2 sparks per revolution on a 2 stroke, vs 1 spark per rev on a 4 stroke. The timing light does not recognize this, it thinks the engine is going twice as fast and calulates degrees as 360 degrees between spark.

Confused yet? I hooked up the DIS Adapter to the sled, & the timing light to the adapter. Shazam, the timing marks showed up. Ok now bring up the RPM to 3500 and the timing advances. See the Chart.
That's it for now. I don't know if it's correct yet, but now I,m in the ball park. Next I will check that the marks are correct by finding True Top Dead Center an a degree wheel. More later. Now it's time to leave South East PA and head to Upstate Brantinham New York I should get there around 3AM. Maybe still snow there!!!

[Vmax540]

"South East PA" Heck, Tyler and I are from N.W. Pa. near Clarion off of I-80 Exit 60 !

[TommyMoEmDown]

It's depressing, all the snow hast gone away