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simon20.69

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Nov 13, 2009
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31807
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1980 Carver Mariner - 350 Cursaders (Chevy)

Recently went on a long trip and had issue with the boat back firing at high RPMs in the middle of the trip - ran great up till that point. Changed ingnition while traveling (wires, rotar, condenser, coil, plugs, D cap, points)and had no luck.

Once I noticed problem kept the boat at low RPMs 1500 - 2000 and it ran well. Did not idle well though.

Got back home and did compression test. Two cylinders failed 55 - 0. Figure it's a head gasket - having head gasket replaced - best case.

Guesses on who thinks the block got knotched between the cylinders.... or on other potential issues. I'll report back on who gets it right.

Engine was just completely rebuilt 3 years ago.

Making the best out of a bad situation.

No bets, just bragging rights. I'll answer any questions you have. Engine will be opened up sometime in the next week.

Have fun all you motor heads!
 
Sounds like valves to me, either stuck or mushroomed. May need to rebuild or replace heads.
 
Sounds like an interesting thread to watch. Which two cylinders have low compression? Need a little more info before.
 
Being that it is two cylinders and if both are on the same side I see why you are thinking head gasket. Any unusual noise???
 
Timing was checked.... was good - right at 10.

Cylinders are side by side.

No unusual noises, actually sounds great at mid RPMS and runs quite well when engine is cool.

Temp got hot for a bit during trip - nothing over 200. Added more coolant and temp went back to normal - 160/170.
 
I think the answer will be obvious when you pull the heads. Whether it's just a gadget or a valve job. On my last boat I went through three head jobs the good news is the boat run great when completed.
 
Install new fuel filters. That cures everything. This is totally untrue, but it's the best that I've got.
 
Well the final verdict is in....

Head gasket between cylinders was blown.

One of the valves was elongated and got stuck up in the head. Mechanic removed the valve and took it to a machine shop to be rebuilt.

Cost unknown at this point.
 
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