150GT Johnson won't start when hot

[z1968]

I'm new here and hoping to get some help.

I have a 1986 150GT Johnson. It starts up fine when cold, however after a good run at or near full speed (to full operating temp.) it won't start again. Battery is strong and it t turns over fine, however the starter bendix doesn't seem to stay up long enough to get the engine to start before it starts to bounce off the flywheel and then drop down. Having said that, I would expect it to start up instantly when the engine is hot, and the bendix does stay engaged for at least 2 or 3 seconds before it starts to drop which should be enough time, so I don't know if the starter is the issue, or something else.

I recently had the lower end rebuilt and it works well. the waterpump was inspected and is good (no broken fins), there is a solid water stream coming from engine, and the thermostat is working, so the engine is not overheating. I also just had the carbs rebuilt (it actually idles and cold starts much better than it used to). Compression is good (100 on four, 95 on two).

I haven't yet done a link & sync. I'm also not sure if the engine could simply be getting flooded when hot...

Any thoughts or advice would be a huge help!

Thanks in advance.

 

[Joe Reeves]

Re: 150GT Johnson won't start when hot

Normally a rather big difference in compression of say 15 or 20 psi will cause the starter bendix gear to pop out of the ring gear of the flywheel. However, if there is only a difference of 5 psi as you state, that normally does not affect the bendix gear. Check the top edge of the bendix teeth and the bottom edge of the flywheel ring gear teeth...... it's possible that the teeth have been beveled to a point whereas the bendix cannot stay engaged properly. I assume that you've doublechecked the compression readings.

Strange that the bendix will pop out only when the engine is hot.

If the engine should crank over via the electric starter properly without having the bendix gear pop out, cranking over quite a few revolutions without starting when warm/hot.... the stator (beginning of the charging & ignition system) under the flywheel may be failing. When the engine is shut down, all of the heat under the hood rises to the flywheel area... notice how hot the flywheel becomes. The stator has a series of coils lining the sides of the stator that pertain to charging and there are two larger black coils that provide AC voltage to the powerpack. In time, especially with the 20 ampere stators, the stator may overheat and the larger black coils which are at the rear portion of the stator will start to melt down, dripping a sticky looking substance upon the powerhead area. This results in a voltage drop that results in weak, erratic, and eventually no ignition.

A melt down of this nature may have the stator function properly when cold... but fail when hot (intermitent). This may have nothing to do with your problem but it's worth mentioning.

 

[z1968]

Re: 150GT Johnson won't start when hot

This is just the type of brainstorming ideas I'm looking for. I'll check this out tonight and report back - Thanks Joe!

In the meantime, if anyone else has thoughts or suggestions, please let me know..