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Mercruiser engine power loss

P

pmr

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I own a 1987 Sea Ray 28'-0

I own a 1987 Sea Ray 28'-0" Sundancer with twin small block Mercruiser V-8 gasoline engines. The starboard engine will run perfectly anywhere between 3000 to 3500 rpm for 15 to 60 minutes and then will start to drop power. If I let it continue with out pulling the throttle back it will die. If I reduce the throttle back to 2000 or lower and let it run for a few minutes and then advance the throttle it will run prefectly and then repeat the same problem. If I shut the engine down and let it sit for 10 to 15 minutes I can run at 3500 for 10 to 15 minites and then the problem will repeat itself. If I take the engine out of gear and let the engine run at 2500 to 3000 rpm it does not lose power. I have recently changed the fuel filter and had a tune up but this has not corrected the problem. Any ideas this is driving me crazy? I have had it looked at by several mechanics but it won't repeat the problem in the shop. Help!!!!!
 
Patrick
A shot in the dark he

Patrick
A shot in the dark here. It is possible that ice is forming in the venturi.???
Bert
 
"Bert,

Thanks for your resp

"Bert,

Thanks for your response. What would cause this and what is the fix. In airplanes this is called carb icing . Is this the same thing?

Thanks,

Patrick Ratigan"
 
"Did you change the fuel filte

"Did you change the fuel filter in the pump and the carburetor screen?

Look at your fuel vent lines for low spots that could trap fuel and check the outside vent screen for a spider nest. When this problem begins, check the vent line and the short rubber fuel line to the pump for a section that is collapsed."
 
"Guy,

I did the pump filter

"Guy,

I did the pump filter but not the carb screen. I'll also chek out your other suggestions. Thanks for your help!

Patrick Ratigan"
 
Patrick:

Do you have good a

Patrick:

Do you have good access to your fuel tank(s)? Your siphon line in the tank may be picking up debris from the tank. Is it aluminum or PVC?
 
"Guy,

The tank is Aluminum.

"Guy,

The tank is Aluminum. Is it posible that only one siphon line would be picking up debris?

Patrick Ratigan"
 
"Patrick
Basically the same t

"Patrick
Basically the same thing. I don't know your weather where ever you are. I had a car do this to me several years ago on high humidity cool days. It was the Thermactor valve not mixing warm air into the carb. Drove me nuts for a few months until my mechanic had a brain surge.
It was the classic run for 15 min's slow down and stall, sit for 5 min's (engine heat melted the ice) start and run again.
Bert"
 
Patrick...
If people are shoo

Patrick...
If people are shooting in the dark...
Any chance something is loose in the exhaust system and somehow restricting exhaust flow? The same thing happens to cars in the winter when mufflers freeze or baffles come loose inside mufflers and block the outlet. Maybe something is in there that shouldn't be.
Wrench
 
Patrick:

The one siphon tub

Patrick:

The one siphon tube could have crud in it. Wrench has hit a good point. Check the exhaust shutters at the top of the "Y" pipe. They may have rusted and/or broke on the shaft or are sticking. That would cause back pressure which drops the RPMs.
 
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