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 Need to pump throttle even when warm
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Author Previous Topic: Use sealant on mainifold/elbow gasket? Topic Next Topic: Volvo Penta GXI-C idle quality  

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

headnsouth

RO# 25768

Posted - Jun 27 2019 :  14:45:53  Show Profile  Reply with Quote
Cold start this morning in the driveway after going out yesterday. Pull the flame arrestor off pumped the gas and plenty of gas squirted into the carb. :) Mid 80's temps and no choke movement. Choke has voltage going to it. Adjusted the choke and freed it up a bit. Not much restriction on movement but I figured less is better. Won't have time this weekend to give it a test drive but I'll report back with my findings.

Thanks for of the help.



Homeport: Georgia Go to Top of Page

LouC

RO# 10314

Posted - Jun 28 2019 :  09:41:43  Show Profile  Reply with Quote
If its a '98 then it should be a Mercarb/Weber carb. Try just pulling out the shift handle to disengage the shift system and putting the throttle forward about 1/4 or so. It should start then. Every carbed car I ever had was like that (always opened the throttle a bit to start hot) and so is my OMC (4bbl Q-Jet). Not pump just set it at 1/4-1/3rd throttle open.

1988 Four Winns 200 Horizon 4.3 OMC Cobra
1998 Jeep Grand Cherokee 4.0 Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi Quadradrive II

Homeport: Long Island NY Go to Top of Page

Stephen

RO# 14

Posted - Jun 28 2019 :  18:16:44  Show Profile  Reply with Quote
It may also be a two barrel carburetor, he never answered that question. I have a 98 MerCruiser and mine is a two barrel. I have found the carburetor to be very reliable.


Homeport: Matts Landing, NJ Go to Top of Page

JVM225

RO# 28365

Posted - Jun 28 2019 :  18:24:39  Show Profile  Reply with Quote
Is it an electric or mechanical choke?

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 - Jun 29 2019 :  09:29:25  Show Profile  Reply with Quote
2 barrel
Electric



Homeport: Georgia Go to Top of Page

JVM225

RO# 28365

Posted - Jun 29 2019 :  12:13:31  Show Profile  Reply with Quote
You already confirmed that your electric choke is getting power?
If you are starting the cold engine properly (throttle forward all the way just once then pulled back to just above idle before turning key) it should start.
You mentioned that it’s also giving you a problem starting when warm.
You shouldn’t have to pump it when it’s warm. Just advance the throttle a bit to start a warm engine.
You’ve already verified that you are getting a spray of fuel when you pump.
Continually pumping will only flood it and make starting even harder,
Might be time for a rebuild again.


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


Edited by - JVM225 on Jun 29 2019 12:15:08

Homeport: Farmingdale NY Go to Top of Page

Stephen

RO# 14

Posted - Jun 29 2019 :  14:54:55  Show Profile  Reply with Quote
If you have not changed your water/fuel filter recently, change it. If you have never changed the internal carb filter, change it. You must get the right one and don't just remove it. You might find it at West Marine or Pep Boys. Clean all of the linkage with carb cleaner and spray some on the butterflies as the engine is running at about 1000 RPM so it does not stall. I had some water in my fuel once and it ran crappy but after I got through the crappy fuel, the carburetor has been flawless without any rebuild. Remove the flame arrester and spray carb cleaner in it from the inside of the fins out. Shut it off and then come back the next day when it is cold. Remove the flame arrester and carefully open the choke butterfly so you can see down the carb. Do not turn on the ignition so the fuel pump does not operate. Push the throttle and the fuel pump should squirt gas in the carb. If there is no squirt of fuel then you might need a rebuild.


Homeport: Matts Landing, NJ Go to Top of Page
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