1982 erude 35 hp spark issues?

[schwar74]

I've been tinkering with this motor for the past couple of weeks and can't get it running right.

Tonight I checked the compression with a rented compression tester, and got 70 psi on both cylinders after warming it up. The way the male end fit into the plug opening and where the "bolt" head of the tester was in the recess it was hard get a wrench on it to snug it down completely. And it was a brass fitting with no o-ring. Wondering if the compression is low due to the tester not being quite tight in the opening. It didn't leak down quickly after testing though. Everything I've read on here says that a compression of 70 should be ok for it to run, and that equal compression is more important than the number, but I know it should ideally be closer to 90+.

I also checked the spark. Its very weak on both cylinders, with the top one barely sparking across a 1/4" gap and the bottom one sparking over ~1/2 inch, but again not a very bright, hot spark (like I've seen in videos of spark testing). The spark also seemed to be intermittent on the top cylinder.

The motor is tough to start, it seems like its trying to fire, but takes a while before it takes off. Then it kinda sputters for a short moment and takes off. It'll only run with the throttle in the start position. I had it running like this for several minutes. If I back it off to slow to idle, it dies. I've also put the motor in gear and throttled it up a little, no where near wide open. It'll speed up, but the second I back off the throttle it dies. Then its tough getting it started again.

I started the motor and pulled the plug wires. The motor died immediately after pulling each plug wire. Should it run on one cylinder only?

Do these symptoms sound consistent with a weak spark? Or should I be worried about the low compression?

If it is a weak spark, is there a common culprit for that? I looked at the cdi guide, but it doesn't have a trouble shooting guide for a weak spark only no spark.

Wondering about taking it in to a shop to have the electrical issue checked out, but don't wanna waste my time/money if its a compression issue.

Thanks for your help.

Scott

 

[jasper60103]

Re: 1982 erude 35 hp spark issues?

Regarding the compression tester. The end that you screw in the spark plug hole should have an o-ring (like in pic below). You shouldn't need to use an adapter. Good luck.

 

[Bosunsmate]

Re: 1982 erude 35 hp spark issues?

Since its intermittent spark- check your stators and your powerpack and coils, Buying a $10 digitalmeter and making a dva is cheaper than the first hour at a shop. They normally run, just, on one cylinder.
Or you can just get a new powerpack since its intermittant on one cylinder and weak on both. The powerpack would be the most likely common factor for that in my opinion as the stator and trigger work for both cylinders. However you could try testing the stators resistance without building a dva too but they are pretty solid. Also try checking the stator/trigger wires to ground to check theres not a short in the wires, they often crack where they bend going under the flywheel so short out a lot there
Also clean the ground wire connection to the exhaust cover plate off the powerpack. If its not needed a spare powerpack is handy to have onboard too.

A failing powerpack on these cause all those myriad of running problems you mentioned. They do go ok on lower compression