OMC 4.3 1989 v6 will not start when hot

[beanhauler]

Here is a particularly irritating problem.
Leave boat for one week.
Put the boat in the water stone cold and turn the key ...fires up almost immediately...in the time it takes the pump to prime the carb.
Tear up and down for a bit skiing/ringo's stop the boat ten minutes and fires up again no problem.Do not need to give it any throttle.Ticks over at 800rpm and does not miss abeat..perfect.Stop the boat and start again immediately fires up no problem.
No give it a long run 1 hour say 3500 rpm constant.Temp shows mid range risers are warm but not too hot.Stop the boat and start it immediately no problem.
Stop for 30 minutes to one hour and it will not start.
Half throttle full throttle/hand over carb/choke flap closed just point blank refuses.Check spark at coil ...nice and red leaps a mile.
Loads of petrol in carb from pump jet on carb.
It does not even try...not even a cough.
Leave some time and then open throttle completely wide.It will then fire up after some coughs and then not miss abeat all the way back.
Now I did not take the plugs out to see what they were up to but i have a theory that maybe when the risers are red hot ...or maybe one...then a crack is letting in water while its in the water and causing the bad starting.
If when i get it running I steam all the way back for an hour and take it out of the water on the trailer...put a muffler on it and start it its on the key first try.
Has anyone else experienced this kind of a problem caused by duff risers?
I have replaced the plug leads/points/condensor but not the plugs so far but looking at the above why does it start if its not in the water?
Is this pretty conclusive?
As i say it does not miss abeat when its running again and ticks over at a smooth 800 rpm.
Think i'd better drop the risers off for a look methinks.
Anyone got any other ideas?
Thanks in advance.
I will update this post when i'm a little wiser.

 

[rs2k]

Re: OMC 4.3 1989 v6 will not start when hot

I would recommend looking at the spark plugs first. They could be fouled. I had trouble starting my engine when warm. It turned out to be fouled plugs.

 

[danond]

Re: OMC 4.3 1989 v6 will not start when hot

If it was letting in water, it wouldn't turn over at all. Water won't compress.

Try a new coil. Some get crappy when they get hot. It's a cheap test.

 

[beanhauler]

Re: OMC 4.3 1989 v6 will not start when hot

I'll whip the plugs out and change them for the sheer hell of it.
Then i will try another coil.I did change it last year [brand new]after i had some starting problems so will grab another from the scrappy to prove if its duff.
Ive noticed some rusty water round the new coil top but have ignored it as its virtually brand new.
I'm beginning to wonder if the coil should be mounted upside down to try and keep any water off of it but worried in case the oil leaves the copper wire
uncovered.In any event the coil puts out a fat spark when you open the points.

Thanks for all your input so far...food for thought.

 

[beanhauler]

Re: OMC 4.3 1989 v6 will not start when hot

If it was letting in water, it wouldn't turn over at all. Water won't compress.

Try a new coil. Some get crappy when they get hot. It's a cheap test.

Thanks Dan

I just wondered if it was a little water and not too much ...like a dribble which found its way into the exhaust ports on one bank.I'm not suggesting that the complete cylinder was full of the stuff.
If you give it a wide throttle it clears eventually which got me thinking.
However once it runs it really does not miss a beat and ticks over fine so i can not believe it is a water leak as i think it would show itself in other ways.
I'm hoping for the plugs and the coil to see what happens.


Love the pictures on the boat repair.
Must have taken a while to do.You have the same lump as me 4.3l with the original risers by the look of it
Great info on the repair of the ram units...another job to do during the lay up this year.

 

[danond]

Re: OMC 4.3 1989 v6 will not start when hot

Thanks. Took me 4 months. Lots of evenings, weekends and in-between head scratching.

Good luck.