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 Need to pump throttle even when warm
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Author Previous Topic: Engine compatibility Topic Next Topic: 460 ford timing  

headnsouth

RO# 25768

Posted - Feb 07 2019 :  16:24:37  Show Profile  Reply with Quote
98 Mercruiser 5.7 with carburetor.
After sitting for a weekend I expect to have to pump the throttle to get fuel to the carburetor.
But after it's all warmed up I still have to pump the throttle to get it to start.
Is the fuel draining back that quickly?
Why is it doing this? BTW it's always done this. Choke has been adjusted.

No performance issues besides this.
Would an inline check valve help?
Fuel pump is original.

Homeport: Georgia

Cam

RO# 1558



Posted - Feb 07 2019 :  16:36:55  Show Profile  Reply with Quote
Sounds like the carburetor float is not working. Might be time for a rebuild kit.

" If you think nobody cares, try missing a few payments " (author unknown)

Homeport: Bentley Yacht Club- Staten Island, NY Go to Top of Page

headnsouth

RO# 25768

Posted - Feb 07 2019 :  16:50:56  Show Profile  Reply with Quote
Carburetor was rebuilt a few years back but I'll check into it.
Thx



Homeport: Georgia Go to Top of Page

DeeVee

RO# 645

Posted - Feb 07 2019 :  17:55:40  Show Profile  Reply with Quote
I though that is how Carb works, when cold, pump the gas pedal to do two things, set the choke and give the intake manifold some gas to distributes to cylinders, when warmed, pumping gas pedal(not as much as when it's cold but stills needs) to give some gas to the manifold/cylinders. Just like fuel injected engine(no choke but IAC instead of), instead of pumping gas pedal when cold/warm, the injectors would spray some fuel to the manifold when the key is turns to on. I may way off base here since the last time I play with Carb was back in the early or mid '80.


Homeport: PA Go to Top of Page

headnsouth

RO# 25768

Posted - Feb 07 2019 :  18:10:19  Show Profile  Reply with Quote
quote:
Originally posted by DeeVee

I though that is how Carb works, when cold, pump the gas pedal to do two things, set the choke and give the intake manifold some gas to distributes to cylinders, when warmed, pumping gas pedal(not as much as when it's cold but stills needs) to give some gas to the manifold/cylinders. Just like fuel injected engine(no choke but IAC instead of), instead of pumping gas pedal when cold/warm, the injectors would spray some fuel to the manifold when the key is turns to on. I may way off base here since the last time I play with Carb was back in the early or mid '80.


I never had to pump the pedal on my vehicle's unless there was an issue.



Homeport: Georgia Go to Top of Page

Sandy

RO# 1159

Posted - Feb 07 2019 :  18:16:24  Show Profile  Reply with Quote
When fully warmed and you are about to try to restart, 1st take off the flame arrestor, hold the choke and throttle plates open and pump the carb throttle once.
Can you see a strong spurt of gas down the throat from the accelerator pump?

If so, you have sufficient gas sitting in the bowl. If not, perhaps you have classic Quadrajet leak down in which case the cylinders may actually already be flooded . If you suspect the latter, without pumping at all try moving the control throttle lever to say 3/4 or more throttle position and see if it starts faster ( being ready to reduce to idle position immediately.)

If you don't see the squirt of gas, your 1998 likely has an electric fuel pump so instead of pumping try cycling the ignition key from OFF to ON/RUN several times without trying to actually start.
That should cycle the pump and hopefully ensure fuel pressure is sufficient to the carb.

Then move the control lever all the way forward and back & try starting with no or maybe one pump .


Are plugs and dist. cap and rotor in very good condition and timing to spec. to optimize chance of initial ignition? And fuel is fresh, not degraded?

Your boat's fuel supply system likely already has a "check-valve" ( besides the carb float valve) in an anti-siphon valve (ASV) at the top of the tank where the distribution line attaches. It is required any time the fuel supply line dips below the level of the top of the tank at all on its way to the engine's fuel pump. FWIW- A little debris in the float valve & ASV could allow drainback.


Sandy

Homeport: The Vineyard Go to Top of Page

headnsouth

RO# 25768

Posted - Feb 08 2019 :  06:21:30  Show Profile  Reply with Quote
Thanks for the information. It's starting to warm up here in Georgia so as soon as temps allows I'll check all of the above.
Pretty sure I have a mechanical fuel pump.



Homeport: Georgia Go to Top of Page

pdecat

RO# 842



Posted - Feb 08 2019 :  09:11:12  Show Profile  Reply with Quote
What Sandy said.

Bruce



Homeport: Gulf Coast FL Go to Top of Page

easttnboater

RO# 23415

Posted - Feb 08 2019 :  09:55:41  Show Profile  Reply with Quote
Which carb do you have? 2bbl, 4bbl? Mercarb or Rochester?


Homeport: Johnson City, TN Go to Top of Page

JVM225

RO# 28365

Posted - Feb 08 2019 :  10:05:47  Show Profile  Reply with Quote
Try just pushing the throttle all the way forward just once and then return it to a position just off idle before starting.
Repeatedly pumping shouldn’t be necessary and results in flooding causing the cold engine to run rough or stall.


2002 Sea Ray 410 Sundancer
95 Eastern 22'
05 Maxum 18' Bowrider
C6 Corvette Convertible
68 GTO


Homeport: Farmingdale NY Go to Top of Page

headnsouth

RO# 25768

Posted - Feb 10 2019 :  19:36:45  Show Profile  Reply with Quote
I'm hoping for the weather to warm up here soon so I can get on this project. Thanks to all that have put in their suggestions. I'll check it out as soon as I can. And I'll report back.



Homeport: Georgia Go to Top of Page

jtybt15

RO# 3300



Posted - Feb 11 2019 :  20:38:09  Show Profile  Reply with Quote
A slight chance the choke is adjusted too tight. When warmed up, check that the choke plate is fully open.

Another thing to check, air leak in intake side of fuel delivery between carb and filter..check clamps. Won't get to the anti siphon valve yet...starting with difficulty of access.





Charlie

There is much to be said, in a world like ours, for taking the world as you find it and fishing with a worm.-Bliss Perry, 1904



Homeport: Ca Go to Top of Page
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