Evinrude powerhead gasket, and loss of power

[johnnybigrigger]

I bought an 84, 185hp Evinrude for my bassboat (18' Hydrasport). The motor came from a friend of mine as he purchased a new 150hp Johnson for his boat (18' Cajun) this spring. Our boats are the same size and close in weight, so I bought his 21p sst prop at the same time. When I took it out last week for the first time the engine only turned 4,800rpms, and reached 48mph. On his boat the rpms were around 5,800, and the speed was near 60mph. So, I rebuilt the carbs, and tried it out again. The performance result was the same, but I noticed a new problem. <br /><br />A cascade of water pouring from the lower cowling near the steering arm at WOT. I pulled the hood, and could not find any water inside the engine area. The water was coming out from an area that I could not see. I stopped by a local repair shop, and the fellow said the base gasket was leaking.<br /><br />When I ask if that would cause the loss of power, he said that was the problem. He went on the say that OMC had an updated gasket to prevent furture blowouts. Has anyone else heard of this causing a powerloss at WOT? I have owned several OMC outboards, but all were V4's. I never had a high rpm problem that was not cured by a carb rebuild.

 

[OBJ]

Re: Evinrude powerhead gasket, and loss of power

Evining John....<br /><br />First addressing the boats, all boat hulls are not the same. What worked for your friends boat and motor does not mean that it will work for you. A difference of a couple hundred pounds, chine placement all have effects on over all top end. A 21 pitch prop may not be the prop for your particular rig. Engine set up is also another factor. How high is it on the transom? <br /><br />Losing rpms is not always a carb problem. Timing, spark quality, general condition of the engine, all play a part in how the engine runs at WOT. Start with basics. Give the engine a good going over. Compression check, decarb, new plugs, the works. Don't forget to check fuel lines and fuel pump for general condition. If any fuel lines are stiff and have lost their flex, replace them. Check the engine recirc system hoses and fittings for leaks. Make sure the fittings are open. I do not think the water leak is the total problem but should be addressed. The gasket is easy to replace but requires that he power head be pulled. Hoped we have helped.

 

[clanton]

Re: Evinrude powerhead gasket, and loss of power

Look at the base gasket on the rear of the engine, if it is leaking exhaust gas, this gas will fill the engine cowling with exhaust fumes. The engine needs clean air not exhaust fumes. If the engine is 1976 or later 150 CID with flat exhaust cover, gasket pn is 333658. The engine with bubble exhaust and fig 8 seal will use pn 323214.

 

[johnnybigrigger]

Re: Evinrude powerhead gasket, and loss of power

Thanks for the replies. I did not notice any exhaust smoke under the hood. I am going to change the base gasket this evening due to the water leak, so I wont be able to check that out. On the prop issue, I am going to take my 19p alum prop I used on my old 115 Evinrude, and try it out tomorrow at the lake. My compression readings are all between 110-118psi, but I have not decarbed the engine. I read some postings on that subject, but to be honest...I am worried the cleaning liquid would damage the bearings. Any input on that would be appreciated. I do have an OMC service manual for the engine, but it is vauge on the function of the base gasket. I have a GM service dept background, and 2 cycle engines are a bit of a black-art science to me. Thanks again for the replies...I will let you know how the lake trip turned out!

 

[johnnybigrigger]

Re: Evinrude powerhead gasket, and loss of power

a follow up...The OMC powerhead replacement gasket also leaked water and exhaust the first time I ran it a WOT. I pulled the powerhead, and took the leaking gasket back to the local dealer. I told him the mating surfaces were clean and true, and he insisted the housing was warped. I left and called a fellow I met at a local car show that helps a guy with his racing outboard.<br /><br />He ask if I was using the updated gasket? The new style was thicker he said, and had a metal core like a head gasket. Armed with this knowledge I went back to the dealer.<br /><br />He called his aftermarket marine parts supplier, and what do you know.... there is an updated gasket. It is 3-4 times the thickness of a OEM. They developed it for racing applications. I will be putting the powerhead back on tomorrow, and will post the lake run results.