Accelerator Pump??

Shields

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Jun 29, 2009
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This is my first post, but I love this site. I have used it quite a bit in the past. Thanks in advance for any replies.

I have a 1995 3.0L Volvo Penta. 2 bbl carb.

My problem is that my boat will not start after sitting for a day or so? It appears as though the accelerator pump on my carb does not seem to be working. I unhooked the throttle linkage and pumped the accelerator pump manually at the carb and no fuel is pumped. I can hear it pumping air, but not fuel. Obviously there is no fuel getting to the carb. I guess my question is this.....I don't understand where this fuel for the accelerator pump comes from? The carb is much higher than the tank and the fuel pump is only active when the engine is running. So, is the accelerator pump just using residual fuel from the bowl when you first start it? I assume it you pumped it enough without turning the engine over (to pump more fuel into the bowl) you would eventually empty the bowl?

Once I start the engine by priming it with some fuel down the ole carb, it seems to be good to go and will start with no issues from there on out.

Any help is greatly appreciated.
 

maxxman04

Petty Officer 1st Class
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Mar 30, 2009
Messages
352
Re: Accelerator Pump??

you are correct. acc. pumps draw gas out of the main bowl, which always has a certain amount of fuel in it, whether running or not. it should anyway. your issue could be in the carb itself, or could be something in the fuel delivery, i.e. fuel pump, fuel filter. check the simple first before tearing carb apart.
 

slydog75

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Jun 15, 2009
Messages
90
Re: Accelerator Pump??

I'm not familiar with the exact carb on your system, but in general your assumptions about accelerator pumps is correct. They rely on the fuel in the bowl. Once that empties then it won't squirt anymore. However, in many cases by that point the engine would likely be flooded. Oh, BTW, your fuel pump also kicks in as soon as you start cranking your engine, so it is active when starting as well.
 

Maclin

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May 27, 2007
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Re: Accelerator Pump??

If there is no fuel in the carb the accelerator pump will have nothing to squirt.

The accelerator pump is part of the carb and uses fuel from the fuel bowl. There are passages that lead into a chamber that can be compressed by a diaphragm or a plunger activated mechanically via linkages from the throttle lever. As the chamber is squeezed the fuel is forced thru other passages that lead to squirters at the top of the carb that aim into the throat. More fuel is drawn into the chamber when the plunger or diaphragm returns to the beginning of it's stroke (throttle moved back towards closed).

The accelerator pump squirts fuel into the throat of the carb anytime the throttle is opened, the engine needs the fuel right away to mix with the influx of air but the carb main metering cannot begin to flow that fast right away so the accelerator pump shot covers up this gap. The shot is only needed for a very short amount of time, and is controlled by the linkages to the plunger, the volume of the chamber and the size of the squirters.
 

Shields

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Re: Accelerator Pump??

Outstanding...you all are fast :)

Here is another symtpom I forgot to mention. My WOT wasn't near what it should have been either?

A little history. I bought the boat and it had a cracked block (The ubiquitous water jacket crack on the 3.0....unfortunately found out about it 5 days after sealing the deal :mad:). Anyway, I replaced the shortblock with new. The new block has the vortech highflow head on it. I was wondering if my low WOT issue was being cause dby my carb mixture being slightly off now due to this different head configuration? I hope not, because I don't want to have to rejet or do whatever this might require!
 

Maclin

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Re: Accelerator Pump??

That one took me a while to type in! and slydog's post was not there when I started, but all good stuff to know....;)
 

Bifflefan

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May 27, 2009
Messages
2,933
Re: Accelerator Pump??

If it sits for a couple days and there is no fuel in the pump or bowl, then it is leaking out somewhere. it can't (i stress that) go back to the tank. So you have a leaking gasket or a plug in the carb thats seeping. Really would help to know the manufacture of the carb tho.
If its a holly then you need a new bowl and metering plate gasket, and bowl seals.
If its a Rochester (or most any other type) then its most likely a plug. there are repair kits for this. but NOT recomended for a novice person.
Eather way its a good time to rebuild the carb or if your not to sure of your skills then have someone else do it.
I hope this helps.
 

Shields

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Jun 29, 2009
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Re: Accelerator Pump??

Carb is a Holley 2 barrel. I would assume you are right about the leaking...seems like you would have to be right. It has to go somewhere! I just can't remember seeing any fuel lying on the manifold.

Anyway, I ordered a carb rebuild kit this morning and will install and see what happens.

Thanks for the replies. Much appreciated.
 

maxxman04

Petty Officer 1st Class
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Mar 30, 2009
Messages
352
Re: Accelerator Pump??

holleys can leak internally, thus causing a "flooding" condition, too much gas.
 

bruceb58

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Mar 5, 2006
Messages
30,454
Re: Accelerator Pump??

You probably need to rebuild the carb but do this first:

1) Get the engine started by pouring a little bit of gas down the throat.
2) turn off engine and pump throttle while looking down carb throat to see if you are getting fuel squirts from the accel pump.

At least after this you can tell if the accel pump is all clogged up. This is more likley than the fuel bowl leaking in my opinion.
 

Shields

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Jun 29, 2009
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Re: Accelerator Pump??

Bruceb58....you are right on. I do start it by priming it with fuel down the throat. After that, it starts fine. Once the engine has run and the float is full, the accel. pump works. So, I guess it is ok.

I am going to rebuild the carb. Any ideas on why I am lacking power at WOT? Maybe the carb rebuild will solve it?

Thanks for all the replies.
 

Bifflefan

Commander
Joined
May 27, 2009
Messages
2,933
Re: Accelerator Pump??

As for WOT problem, you may find that when you rebuild the carb it goes away. You may have a partly pluged air bypass thats not letting it get all the fuel it needs. also could be a varnished up passage in the metering block. Anyway use a NEW, GOOD brand of carb cleaning dip and let it sit in there over night. That sounds like it will do the trick.

One more thing, dont loose the ckeck ball under the squirters.
Just thought id throw that in, just in case.

When you have it back together, 1.5 turns out from a light seated position is a good starting point for the idle screws.

Oh yea, one more thing. Use the BLUE gaskets on the float bowl and metering block. (red are ok too) These are the High Performance ones. They cost a little more but the dont stick like the brown ones. Makes things alot easier down the road.
 

Maclin

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May 27, 2007
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Re: Accelerator Pump??

Hey b-fan,

always good to meet another Biffle fan and Holley man...;)
 

Shields

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Jun 29, 2009
Messages
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Re: Accelerator Pump??

OK...just rebuilt the carb moments ago. It started and then died. The accelerator pump squirters (sorry don't know tech name!) were still dripping fuel out of them when I went back and looked in throat.

Bifflefan...you mentioned little ball that has to do with the squirters? Not sure what that is, but sounds like it might be a check valve arrangment. Unfortunately I don't remember any little silver balls, but there were some in my kit :eek:

Also, my manual only had the procedure for rebuidling a similar carb...not mine exactly. The one thing that worries me is the float. I didn't mess with it as the float specified in my manual was a side-hinged float. My float hinges from the back. I am wondering if the float isn't shutting the inlet valve needle?

Thanks guys. Appreciate all your help thus far. I am thinking about getting a row boat :(
 

fossill

Chief Petty Officer
Joined
Jun 20, 2009
Messages
427
Re: Accelerator Pump??

Carb jobs are best left to the pros. Even then, very few are good at it. Lots of trade secrets with various models. Not knocking your skill level, just my experience from working many years on cars. For the average joe, your always better off getting a rebuilt unit.
 
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