35 HP 1970s Chrysler Low Spark Lower Plug

[pearlking]

S/N on motor is 356HK. With top plug wire on and bottom plug wire off it runs the same as with both plug wires on. When only bottom plug wire is on it won't run. Bottom plug spark looks intermittant and weak. Changed the plugs, swapped the plug coils, swapped the points & condensers (this motor has an alternator type ignition system). The alternator looks good, no burned areas). I have not ohmed out the wires to the ignition coils. I'll do that next (probably should have done that first). Can you think of any other reason why I have a weak/intermitant spark on the lower plug?<br />Thanks for any insights.<br />-Pearl King

 

[jim dozier]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

While its clear from your description that you have lost a cylinder have you confirmed that there is no spark there? When you swapped electrical parts did the bad cylinder swap also?

 

[pearlking]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

The bad spark did not move when I swapped components, it always remains on the lower cylinder. This seems to validate that it is not the ignition coil or the points or condenser.<br />-Pearlking

 

[jim dozier]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

Have you switched or replaced the spark plugs themselves. Its either another unchecked ignition part (not a lot of experience here) or maybe spark isn't your problem. Did you say the spark was visibly weaker on the lower cylinder? Did you try jumping a spark without the plug? Perhaps if you have adequate spark the problem is fuel or compression. Have you done a compression check? Try squirting some pre-mix in the offending cylinder and see if it picks up.

 

[pearlking]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

I replaced the plugs and even swapped them and the plug wire. The problem stays with the lower cylinder. The spark is very weak and intermittant.<br />Is it possible that there is a kill circuit in the ingnition switch that is shorting out?<br />-Pearlking

 

[jim dozier]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

That would affect both cylinders not just one.

 

[steelespike]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

It is a battery type ignition, if you were very careful to follow the point adj. procedure in the manual then I think with all the tests you have done the voltage to that coil is comprimised in some way.Measure the voltage at the battery<br />should be around 14 volts when running at charging speed.Be sure the ground side of all components is sound from the battery to the<br /> ignition plate.

 

[norman158]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

replace the wire leading from the points to the coil. sounds like it has a break in it inside the insulation.

 

[scotiany]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

This question may be off but, have you checked the puddle valves to make sure they're not clogged up. It's usually the lower cylinder that's affected by it.

 

[skeets]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

Blocking Dioade??

 

[pearlking]

Re: 35 HP 1970s Chrysler Low Spark Lower Plug

Problem solved! Thanks to everyone for the input. I went back through the basics and found it was a bad spark plug! Plugs were brand new last year and I must have confused them in the very first test I did. Oh well, I sure learned a lot about this old outboard! One last note. The woodruff key for the flywheel is not standard. I broke this somehow removing the flywheel and wnet to the hardware store to get another only to find they were all much deeper than the one I broke. Ended up grinding one of the deeper ones to fit.