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1986 260hp 350 problem!!!

M

maa37maa

New member
Ok where to start... The boat idles and revs up fine under no load. But when trying to plane out the boat misses... I have changed plugs, plug wires, coil, dist cap, fuel water seperator, and rebuilt carb... Carb was clean when taken apart to rebuild no ethanol build up. Ive done a compression test and cylinders were all low... No smoke no burning oil or anything to make me think rings... Now i have had 4 different plugs what looks like to me has burnt... On the porcelain about 1/8th" under the tip is burnt off... I have had one plug blow completely out of the socket. The socket was still screwed into the block and the porcelain blew out ... I had never seen that before. I think i have added everything i know of... Please help thanks!!!!!!!
 
what were the numbers ? Yea i have seen porcelain burnt cracked all kinds of stuff .

They the right plugs to begin with ?

Heres how to read the plugs.

Spark Plugs

Get back to us with the numbers.
 
Oh yea and has lost power! Well i only checked a few cylinders b4 i got ill and quit messing with it forthe day lol i checked 1-0lbs, 2-70lbs, 4-15lbs, and 6-0lbs... Ill recheck all of them tomorrow...
 
NO! You need a marine engine. You need to see if you have a one piece rear main seal. Do your valve covers have center bolts or perimeter bolts. DO NOT PUT IN A NON-MARINE ENGINE!!!!!!
 
Listen post the numbers all of them 0 compression means the valves are fugazied. Or the head gasket went.

DO NOT BUY ANYTHING YET !

DO NOT BUY ANYTHING YET !

DO NOT BUY ANYTHING YET !

Jeeez

Your gonna have to pull the heads wait till you do.
 
chiefalen said:
Listen post the numbers all of them 0 compression means the valves are fugazied. Or the head gasket went.

DO NOT BUY ANYTHING YET !

DO NOT BUY ANYTHING YET !

DO NOT BUY ANYTHING YET !

Jeeez

Your gonna have to pull the heads wait till you do.
Click to expand...

Cheifalen,

The Engine is an 1986. You can put heads on it, But Why? The engine block is beyond it's service life in salt water. Nothing good ever comes from doing this kind of repair on an old engine, unless it is FWC and has 500 hours or less on it.

Just my business sense talking. Cheaper in the long run to replace the long block. Easier too.
 
Ok so i pulled valve covers today and all valves seemed to be lifting as they should... Could it be a fuel problem or possibly a dist problem?
 
Ok i ran it today it planed out decently but not like it should after i ran it a lil while let it warm up then it got to where it barely would plane out...
 
1 what plugs are you running
2 compression numbers for all cylinders with the carb wide open, anything less than 120-130 is a very tired engine.
 
Dude your motor has had it. Just went thru the same thing with a 1987 model. Ended up having bad bearings, scarred crank, cracked heads, and three burnt valves. Just finished building a vortec engine for it with a mild cam and it gained 13 mph over old engine. If you want the recipe for a bad a$$ small block shoot me a message
 
If i was goin to rebuild it do i have to get marine specific parts such as internal or can i get automotive? Im wanting to hype it up :)
 
I used the block and vortec heads from a 1997 model truck. Had the crank balanced, block decked, used 10:1 compression pistons, lt4 hot cam kit available thru gm performance parts, edelbrock performer rpm intake manifold, 650 demon marine carb. All of the other parts such as starter alternator exhaust etc etc I used from the original engine, took my boat from 52 mph to right at 65 mph. I'm guessing it somewhere between 375-400 hp
 
87concord said:
I used the block and vortec heads from a 1997 model truck. Had the crank balanced, block decked, used 10:1 compression pistons, lt4 hot cam kit available thru gm performance parts, edelbrock performer rpm intake manifold, 650 demon marine carb. All of the other parts such as starter alternator exhaust etc etc I used from the original engine, took my boat from 52 mph to right at 65 mph. I'm guessing it somewhere between 375-400 hp
Click to expand...
Assuming he has the original drive in his boat. A first generation Alpha 1 drive will not stay in service very long if he puts that kind of power through it.
 
Mine has a gen 1 alpha as well, the fact that they are only rated for 300 hp is true. I am very easy on mine coming on plane and if I get any air I back off the throttle before re entry. Not saying it's not going to blow up tomorrow but so far it has held up well.
 
Ether way the heads got to come off.

You could get a good running used marine complete motor for around 1000 bucks. Ideal fresh water.
 
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