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Loss of power after prolonged period of WOT... and backfire?
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Author:  captkevin [ Mon Jul 15, 2019 7:15 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
To me it sounds more like a fuel pump issue then carb.
Author:  cdig [ Mon Jul 15, 2019 8:33 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
babbot1 wrote:
Sounds like you are getting close. If you didn't see water or crud in the filter and all the screens are clear then seems like a delivery issue.
I had a similar issue but different engines. It was the booster fuel pump. It was getting enough to run the engines from the main pump but not enough for full throttle. The inline fuel flow gauge should help determine that issue.


Yeah there's only a few things left to replace! Sad part is, I may only get one or two more days on the water to test it this summer... Hopefully I can get it figured out this year and have a 'no tools at the lake' summer next year 8) That would be bliss.
Author:  captkevin [ Mon Jul 15, 2019 8:38 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
I thought only the fuel pumps on the fuel injected engines were pricey. Did you shop the price on fuel pumps for the carb motor?
Author:  cdig [ Mon Jul 15, 2019 8:41 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
captkevin wrote:
To me it sounds more like a fuel pump issue then carb.


I agree... it may very well be. I'm going with a 'process of elimination and what's cheapest to try first' methodology... and carb kits are cheaper than fuel pumps :mrgreen:

My thoughts with the carb rebuild are that it's possible this carb was setup with the float being set to low... so if I'm going through more fuel than the float bowl can store, or maybe the jets are clogged and not letting enough fuel into the bowl... then that's why it's starving for fuel?

It's either that or the pump, and the carb is likely due for a tear down anyway... so I'll go the cheap route before trying a pump.
Author:  cdig [ Mon Jul 15, 2019 8:44 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
captkevin wrote:
I thought only the fuel pumps on the fuel injected engines were pricey. Did you shop the price on fuel pumps for the carb motor?


I'm just going by what the guy at the marine shop said when I was picking up the anti-siphon valve this weekend. It's an electric fuel pump that supplies the carb, so it likely could be that expensive. I didn't ask him to look it up and price it out, but he was the owner of the shop so I took his word for it. It may be worth a second look, If it's $50, that's easier than a carb rebuild.
Author:  LouC [ Mon Jul 15, 2019 10:42 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
The electric pumps for the carbed engines are not as expensive as the ones for the EFI engines because they are low pressure pumps, like 5-7 psi max is what they should put out. I'd probably do a pressure and volume test before tearing into the carb. The mechanical pumps like the one I have on my old Pre-Vortec 4.3 are pretty cheap, like $100 or so, takes about an hr. to change, but you have to fiddle with that pain in the neck pushrod that is run off the camshaft. The plus side is that mechanical pumps, last a very long time...in fact I just replaced the original one on my boat last summer. With electric pumps the issues you can have sometimes are bad wiring connections that don't put full voltage to the pump and relays that can fail intermittently. Myself I prefer the simple mechanical pump but the newer engines have no provision for them...

http://www.volvopentastore.com/Fuel-Pum ... _id.776028

not sure if this is the right model # for yours but you can see why I prefer mechanical pumps! If it turns out to be the pump you might be able to find a less expensive aftermarket pump, it is probably made by Carter, if you can find out the actual Carter part # you might be able to get it a lot cheaper than what Volvo charges for the same thing...

https://www.michiganmotorz.com/volvo-pe ... 9_292.html

these are probably aftermarket, you can see the price difference, you first have to find out how to check the pump and then go from there.
Author:  cdig [ Mon Jul 15, 2019 11:19 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
LouC wrote:
The electric pumps for the carbed engines are not as expensive as the ones for the EFI engines because they are low pressure pumps, like 5-7 psi max is what they should put out. I'd probably do a pressure and volume test before tearing into the carb. The mechanical pumps like the one I have on my old Pre-Vortec 4.3 are pretty cheap, like $100 or so, takes about an hr. to change, but you have to fiddle with that pain in the neck pushrod that is run off the camshaft. The plus side is that mechanical pumps, last a very long time...in fact I just replaced the original one on my boat last summer. With electric pumps the issues you can have sometimes are bad wiring connections that don't put full voltage to the pump and relays that can fail intermittently. Myself I prefer the simple mechanical pump but the newer engines have no provision for them...

http://www.volvopentastore.com/Fuel-Pum ... _id.776028

not sure if this is the right model # for yours but you can see why I prefer mechanical pumps! If it turns out to be the pump you might be able to find a less expensive aftermarket pump, it is probably made by Carter, if you can find out the actual Carter part # you might be able to get it a lot cheaper than what Volvo charges for the same thing...

https://www.michiganmotorz.com/volvo-pe ... 9_292.html

these are probably aftermarket, you can see the price difference, you first have to find out how to check the pump and then go from there.


So... Question: is it possible that the electric fuel pump for a 2BBL setup would be different than that of a 4BBL setup? It just dawned on me that the original motor in this boat was a 2BBL. when I replaced the engine awhile back, the new one came with everything, fuel pump, wiring harness, etc... Hence why I have a spare fuel pump kicking around.. somewhere. Awhile back I had swapped out the pumps thinking it might be the cause of one of my past issues. I can't remember if I ever put the original pump back on... So I could potentially be running a 2BBL pump on my now 4 BBL engine.

Could this be why it would be starving for fuel? Or would the flow rates be the same for all electric pumps for a 4.3L?
Author:  captkevin [ Mon Jul 15, 2019 11:26 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
If you can find it I'd probably switch it out & see. Price is right.
Author:  LouC [ Mon Jul 15, 2019 11:34 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
Plug your model number into Volvo Penta's on line catalog and see if they differentiate for the 2bb or 4 bbl. I doubt it seeing as how carb engines will have the same mechanical pump no matter which carb it has. So you may get lucky there if that turns out to be the issue. Michigan Motors also has an aftermarket electric fuel pump set up for carbed engines that they sell on their partial engine packages (for example if you're replacing a Pre-Vortec engine that came with a mechanical pump with a newer Vortec that can only use the electric pump) that might also be a less expensive option to the Volvo Penta OE pump.
Author:  babbot1 [ Mon Jul 15, 2019 11:51 am ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
I agree, I doubt the 4bbl will demand that much more fuel that a 2bbl. Try it out. Those pumps usual pump way more than is required from the carb, well when they are working properly anyways.
edit: keep in mind the pump on your shelf could also be bad. A gauge is really the only way to know if the swap doesn't work. Or a new pump obviously.
Author:  captkevin [ Mon Jul 15, 2019 12:49 pm ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
Was just rereading thread from beginning and one thing that jumped out is you state you are only getting 4000 rpm at full throttle? 4.3 should be somewhere betweed 4500 - 4800 rpm wot.
If you are really only getting 4000 rpm's there is another issue that can be contributing.
Author:  cdig [ Mon Jul 15, 2019 1:05 pm ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
captkevin wrote:
Was just rereading thread from beginning and one thing that jumped out is you state you are only getting 4000 rpm at full throttle? 4.3 should be somewhere betweed 4500 - 4800 rpm wot.
If you are really only getting 4000 rpm's there is another issue that can be contributing.


Good catch - my tach has a redline at 5000 rpm, so I haven't actually pushed it to the far end of the throttle in fear of hitting that line... it will go more, but I stop at 4000-4200 as the increase in speed is negligible for the few extra rpm I might be able to squeeze out of it before redlining. Sorry for the mis-information!

Thanks for taking the time to re-read. I sincerely appreciate the effort to diagnose this bug.
Author:  cdig [ Mon Jul 15, 2019 1:10 pm ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
LouC wrote:
Plug your model number into Volvo Penta's on line catalog and see if they differentiate for the 2bb or 4 bbl. I doubt it seeing as how carb engines will have the same mechanical pump no matter which carb it has. So you may get lucky there if that turns out to be the issue. Michigan Motors also has an aftermarket electric fuel pump set up for carbed engines that they sell on their partial engine packages (for example if you're replacing a Pre-Vortec engine that came with a mechanical pump with a newer Vortec that can only use the electric pump) that might also be a less expensive option to the Volvo Penta OE pump.


I noticed ROP has electric fuel pumps for ~$34-$47 USD on ebay... has anyone used this off-brand and had good results? For that kind of money it's almost worth it just to eliminate the possible problem.. as long as the quality is there.
Author:  cdig [ Tue Jul 16, 2019 10:49 pm ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
Well I managed to find my spare fuel pump. Installed it tonight and ran it on muffs to make sure it still works... boat ran nicely for 30 seconds and then would stall... had to keep pumping the throttle to get it to stay running... so it's NFG. I did confirm however that it's the same pump as the one I originally had installed. Different part numbers, but as I understand it they both change up to the same pump.

I'm thinking for the price I may as well pickup a new one, probably the same price as a fuel pressure gauge and the necessary fittings. 10 minutes to change it out vs. a couple evenings to pull apart the carb and rebuild.

THAT HAS TO BE IT, RIGHT?! Yeah, that's what I figured too. :lol:
Author:  captkevin [ Tue Jul 16, 2019 11:04 pm ]
Post subject:  Re: Loss of power after prolonged period of WOT... and backf
Sounds like you could be on the right path
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