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Fail to start after 2 days

L

LLucky

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"1992 Mercruiser 350 Mag.
Run

"1992 Mercruiser 350 Mag.
Runs great starts great, unless you let it set for more that 48 hours.No fuel in accelerator pump.
Replaced fuel pump and anti-sihpon valve,same results.
Hooked up pressure/vacuum guage to INLET side of fuel pump and it shows 1.5 lbs pressure when you crank start it.
The only way it will start is if you put 2 or 3 ozs. of gas directly down the carb throat.
2 bad fuel pumps in a row??
Runs fine after you prime it..
The tank vent is clear,
the fuel line is not leaking, Holds 5 lbs of air pressure for 15 minutes.
No fuel line restrictions.
Any other ideas before I return the fuel pump?? The original had the same symptoms.
Thanks for the help...."
 
"Ayuh,...

Is that a Merc./

"Ayuh,...

Is that a Merc./ Weber 4bbl. sitting atop that 350 Mag,..??

The bowls leak into the intake over time....

There was probably Nothing wrong with the Old fuelpump,..??..."
 
"Yep. Weber. I understand that

"Yep. Weber. I understand that it might leak from the bowl. But why won't the fuel pump fill it back up? You can crank the battery dead, and it will not pump any fuel out of the pump."
 
"Ayuh,...

Or if you've

"Ayuh,...

Or if you've got the electric fuelpump,...
The starter should be feeding power to the fuelpump, while cranking,+ the Igntion takes over after start up....

Check to see if it's powering up when it should..."
 
"I dont belive they used elect

"I dont belive they used electric fuel pumps in '92 on carbed v8's.

With the engine running and your fuel pressure gauge connected in line between the fuel pump and the carb you should see 6-8 psi at 2000- 2500 rpms.

If you do not, than you have a fuel pump problem or like what was said your pump rod is bad ot the cam lobe that drives the rod it round and not egg shaped anymore.

Even with all that said there should be enough fuel in the carb to start the motor.

What I would suggest is to get the motor started and run it for a short while till warm.
Shut it down and let it sit for day or two. disconnect the throttle cable at the carb and activate the throttle and look to see if you are getting a accelerator pump sqirt.
If you are not then,
Pull the top of the carb OFF and see if there is any fuel in it. If there is no fuel in the carb let us know."
 
"Mechanical pump, No fuel in c

"Mechanical pump, No fuel in carbuetor. Weber modified Carter AFB on a liscensing agreement if I remember right..40 year old design... good job Mercruiser...No fuel output at cranking RPM..

Does anybody know what the fuel pump rod movement should be if I hook a dial indicator up to it??

Probably a bad cam...I'll let you know after the holiday weekend, when I solve it....Thanks for the input."
 
I would switch over to an elec

I would switch over to an electric pump before I would fool around changing worn cams or whatever. Simple to wire up to an existing engine.

Rod
 
As far as what the pump rod mo

As far as what the pump rod movement should be I can not answer that but if you crank the engine over and put a 3/8 exstention against the rod (with the pump removed) crank the engine over (with coil wire REMOVED!!) you should be able to get a rough estimate of the travel then compare to the travel needed to move the pump lever by hand.
 
"Wait a minute,

You said yo

"Wait a minute,

You said you hooked up a gauge to the INLET side of the fuel pump...........Correct?

That is the vacuum side there should not be any pressure!!

Please clarify.........."
 
Yes. Hooked up the guage to th

Yes. Hooked up the guage to the INLET side. 1.5 lbs pressure at cranking speed. 1 inch of Vacuum at running speed....My guess is bad check valve/seat on both original and replacement pumps.
I will forward more info after I solve the mystery...
 
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