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1973 65 HP 1st real trouble

J

jim18611865

Regular Contributor
I have had this boat out 10 times now (7 last summer, 3 this year) with this engine. Refurbed but not re-built. All new fuel components. Carbs re-done with factory kits, coils new, and plugs new. New water pump kit and lower fluid changed. (All done approx. 5/2009)
Engine is pushing a 17' 1968' Starcraft Tri-hull weighing 1200+ lbs.

Today it started to bog down, and up, and down at full throttle. We had been going full throttle for the longest we ever have. About 15-20 minutes. 2 laps around the lake.
I also had put a new prop on but it ran fine for the first 20 minutes. (A little slower, and lower RPMs than the other prop)
I do not have a tach.

It started about 2 minutes after switching over to my last tank of winterized gas. I throttled down suspecting that is what it was, and swapped back to the other tank of fresh gas. It didn't seem to get better after a minute, so I shut it down and we swam for 20 minutes.
I checked the head and exhaust jacket with my hand. Both very cool. Like cool tap water/lake water.

It started right back up, and we drove it for another 10-15 minutes without it bogging down.

1 Where should I start, if anywhere?
2 I have a themostat on hand, should I replace?
3 Troubleshooting on the water does not appeal to me.

Thank you all, for all you have done in the past.
 
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When this surging takes place, is it a somewhat slow smooth up and down surge (fuel problem)?

Does the fuel primer bulb look like it has a tendency to be drawn flat? If so, that is indicates a fuel restriction problem.
 
I did have my son pump the bulb while under way and the problem was happening, but it was already firm and it did not help.

It did seem like that, because on our maiden voyage last year it did it more severly, but we had a pinched fuel line. (We couldn't get to WOT for more than 3 seconds.) Unpinching it solved it immediately.

I will be changing back to the old prop, replacing the t-stat, and retesting with more of the new fuel.

Is it a problem (damaging) to run a prop that likely puts the WOT at around 4000RPMs?
Is the cool head an indication of a t-stat stuck open?

Thanks again.
 
You: Is it a problem (damaging) to run a prop that likely puts the WOT at around 4000RPMs?

Me: That sets up a condition we refer to as "lugging". The throttle butterflies are wide open BUT the rpms are restricted by the propeller pitch. This causes a rapid build up of a waxy like substance within the combustance chambers..... a huge amount of waxy substance!

You: Is the cool head an indication of a t-stat stuck open?

Me: Yes it is. Either that or a non existent thermostat.
 
Interesting info. I had never heard of "lugging" before.
Maybe it is time to install a tach as well.

Thanks Joe for all you do. That engine would have been parts if it wasn't for you and a couple of others on this board. Take a break once in a while unless they start sending you paychecks.
 
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