1968 5 HP Johnson trouble starting when warm

[vzapp]

My 1968 5 HP Johnson is somewhat easy to start when cold, 7-8 pulls usually does it. When the engine is warm it's a real bear to start. In fact I usually wait for it to cool off then give it a try. Carb has been disassembled, thoroughly cleaned and rebuilt. New plugs points and condensers.
Additional questions that may or may not be germain to this situation are:
1) Is it possible for the timing to be off and cause this problem?
2) Could tweaking the point gap be an issue?
3) Could the gap between the flywheel and the magneto affect this situation?
Any additional information is much appreciated.
Thanks,
vzapp

 

[raczekp1]

Re: 1968 5 HP Johnson trouble starting when warm

starting problen when warm is caused by week condensers and week coils. i bet coils its time to get new one

 

[Chinewalker]

Re: 1968 5 HP Johnson trouble starting when warm

Part of the issue could be related to the fact that it takes you 7-8 pulls to start it cold. Should be no more than three pulls MAX.

Clean points, properly gapped at .020".
What are your compression readings?
Coil heals flush with the machined edge of the mag plate, just below the coils.

 

[vzapp]

Re: 1968 5 HP Johnson trouble starting when warm

Thanks for the replies. Now for some follow up

1) How does one test for weak coils?
2) Have no idea what the compression is. I had to replace blown head gasket and "machined" the head with 400 grit wet-or-dry on top of my table saw.
3) Coil heads flush with the machined edge.... I'll need some more info to understand what that means.
Thanks, vzapp

 

[Chinewalker]

Re: 1968 5 HP Johnson trouble starting when warm

1 - Typically, if the coils are not cracked, they're likely good. I can count the number of coils that checked bad but looked good on two fingers.
2 - Might be time to borrow a compression gauge and get a baseline reading. If numbers are off, then everything else you're trying to do will be wasted time.
3 - The heels of the coils are the outer edges of the laminates. They need to be flush with the machined rim of the mag plate, directly under the coils. Too far out and they'll hit the flywheel. Too far in and they'll produce weak spark.

 

[nwcove]

Re: 1968 5 HP Johnson trouble starting when warm

http://forums.iboats.com/engine-fre...-change-coils-set-points-old-omcs-294072.html

 

[vzapp]

Re: 1968 5 HP Johnson trouble starting when warm

Thanks to all for the added information.

 

[vzapp]

Re: 1968 5 HP Johnson trouble starting when warm

Might be on to something with my latest effort spurred-on by ya'lls information. When trying to figure out how to hold a compression gauge in place while pulling the start cord I came upon the idea of chucking-up a socket to my cordless drill to spin the engine. So, before launching an all-out search for the compression gauge I last used 10 or more years ago I decided to give the idea a trial run and at the last minute realized that this is a perfect way to check for spark. Guess what... no spark on the top cylinder. I swapped plugs to see if possibly it was a bad plug and had the same results.

Now what? Without swapping around the various ignition parts how do I determine if it's a coil, a plug wire or a condenser? I've checked gap and condition of the points. The plug wire to the offending cylinder has a small swollen spot in it. This swollen spot coincides with the point where it touches part of the engine when at WOT. Maybe go out after dark and spin the engine again and look for arching there? Keep the ideas and information coming...I might just get this old gal in to reliable shape yet.

Update. Snipped off a half inch of the sparkplug wire at the coil and still no spark. Swapped condensers and still no spark. Did a compression check and have about 60 on one cylinder and 65 on another. Engine was cold. In the morning I'm headed to a nearby excellent old-school boat boneyard that'll check the coil for me.

 

[nwcove]

Re: 1968 5 HP Johnson trouble starting when warm

How to test a coil in an antique outboard engine - YouTube