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Mercruiser 470 Hot Vapor Lock

R

r2d2

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"Engine runs well hot or cold

"Engine runs well hot or cold as long as I don't run at low speed for a while when hot(low wake) or shut down for a while and then restart. Under these conditions, comes out fine, but then hesitates and usually stalls like multiple "vapor" gaps in fuel supply. Once "vapor" gaps pass through, runs fine. This may take one or two restarts."
 
"Robert:

I'm going to g

"Robert:

I'm going to guess the engine is in a dog house w/a 3" air hose in/out. Do you run the blower a few minutes before starting and while underway?

The next time you are out and stop awhile, before you start the engine, open the dog house and feel the side of the carb and the fuel line from the pump to the carb. Are they very warm? both are absorbing engine heat.

A carb base/manifold spacer or thicker gasket will insulate it from absorbing engine heat. Is the engine temp. correct? Check it w/a laser thermal temp. gun. Check different areas of the engine and exhaust for high temps. Exhaust manifold and elbow could need cleaning to remove rust/scale buildup.

Check the air inlet for a closed off inlet w/o a hose. If there is one not used, open it up and connect a hose to it and direct it to the side of the carb where the fuel line connects. Check the air outlet for the same; open it up."
 
"Guy:

Thanks for the quick

"Guy:

Thanks for the quick response. I wanted to do some checking before responding. Answers to your questions:

-Yes, it is a dog house w/ 3" air hose in/out. There is a blank on the "in" side, but no blanks on "out" side. I intend to add an extra "in" hose as you suggested.

-Yes, I always run blower before starting and when running. I shut off blower when engine is stopped (parked for swimming, etc.).

-Carb to manifold gasket is less than 1/8" thick. Do they make a thicker one, or do you just need to get material and cut out to match current pattern?

-Engine runs at about 130-140 when warm and gets to about 150 pulling tubes, etc. Impeller is new.

-Checked carb and line temp. Generally they are relatively cool when checked just after running. They are definitely hot when parked for 1/2 hour with dog house closed.

Again, thanks for your help.

Bob"
 
Robert:

I changed my exhaus

Robert:

I changed my exhaust duct plate and motor to a 4" for my 4.3L. Are there circular air inlets on the front of the dog house? You can add them for a ram air effect while underway.

The carb gasket for my Mercarb is much thicker than 1/8". Don't know the part number. Need to go back to the dealer I got it from and get another so all can know the part number. Some fellas have successfully fabricated carb spacers. Some of the speed shops sell spacers.

Your engine temp. seems a little low. Shouldn't it be running around 160 deg. F. I know that may amplify the heat problem. You can insulate the fuel line; The cab would be a lot harder.
 
"I have a '78 GlasPly 17 w

"I have a '78 GlasPly 17 with the 470. I'm running the Ignitor and the matching Flamethrower coil. It has a new Baldwin water separating filter in the line. The fuel pump is brand new off the shelf. The plug wires are new, 8mm. The Impeller in the drive is new. The circ pump for the FWC is good. Its running the original 3" exchanger. Tank has been replaced, fuel is fresh. Elbow is clean and flowing fine. Thermostat is new. Today, out on Puget Sound I ran for an hour planing at 2900 rpm. Temp is steady at around 150-160. When slowed down to a little above idle, the engine stumbled and quit. It was an SOB to get started again. This happened several times over the last two days. All i can deduce now is some kind of percolation in the carburetor. I've wound the mixture needles in and out and still, it will sometimes fire, then quit when shifting into gear. I do run the blower continuously. Guessing I've gotta find the thick gasket you guys are speaking of. Also, I've been told to run the 92 octane gas in this engine. Ideas??"
 
"Guy,

I cannot find a part

"Guy,

I cannot find a part number / supplier for a 1/4" thick gasket for intake to carb. Do you have a part number / supplier??"
 
The gasket is more closer to 3

The gasket is more closer to 3/16" or maybe 5/32". I got it from a local Merc. dealer. I questioned if it was the correct gasket for a 1987 Mercab 2 BBL since it was thick and was told yes; it will allow better atomization. He was right.

Go to a major autoparts store (NAPA) and tell them what you want. Take the carb w/you. I have made many gaskets from a stock gasket sheet. If they don't have a gasket then ask for the thickest gasket sheet material they have. Take the old gasket and use it as a template to make one and cut it to fit.
 
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