Volvo Penta 4.3GL-C bogs and surges when hot

[tctdc]

2007 4 Winns with Volvo Penta 4.3gl-c. It had been unused for two years. I added fresh gas. New fuel filter. It ran well for the last 4-6 weeks till just recently. After 15-20 minutes of smooth running at 3000 rpm the engine will surge and bog. Usually 200 RPM up and down sometimes more. Going to idle then back to plane corrects it for about 3-4 minutes than it returns. Changed the anti siphon valve. No change. Suggestions?
Seems to be going through a lot of gas, but this is my first v6...

 

[Scott Danforth]

did you drain the tank, or just add good gas on top of bad?

check fuel pressure
check vent line
check contents of fuel filter.

 

[tctdc]

did you drain the tank, or just add good gas on top of bad?
tank had less that a 1/4 of gas in it. I filled tank and added 2 bottles of Heat. That was in June. It ran fine till about two weeks ago

check fuel pressure
Did that today - constant 5 (about) psi to 2000rpm

check vent line
Its there. Runs between tank and fill port. Not sure how it verts past the cap. Looks like factory.

check contents of fuel filter. Clean gas - no water

 

[Lou C]

If it sat for a couple years it may be time to go through the carb; might need a cleaning and re-assembly with new gaskets. The problem is that evaporated fuel leaves behind deposits that clog jets and passages. Same thing with small engines. The more you use them the better they run.

 

[Scott Danforth]

did you drain the tank, or just add good gas on top of bad?
tank had less that a 1/4 of gas in it. I filled tank and added 2 bottles of Heat. That was in June. It ran fine till about two weeks ago

well, the crud that was in your tank is now in your anti siphon, fuel pump and carb.

that 1/4 tank of varnish sludge got broken up into floating bits of crud by you adding isopropyl alcohol. then you added good fuel to that to have a tank full of floating crud fuel.

check the strainer in the fuel pickup tube, clean the carb, change the fuel filter

 

[tctdc]

If it sat for a couple years it may be time to go through the carb; might need a cleaning and re-assembly with new gaskets. The problem is that evaporated fuel leaves behind deposits that clog jets and passages. Same thing with small engines. The more you use them the better they run.

I appreciate the reply. It ran great for 2 months, went through a full tank of gas. Runs fine for 10 to fifteen minutes (till its hot) then it bogs and surges. Tested the fuel pressure today 5PSI from idle to 2000rpm. Wouldn't a carb problem be constant and not only when its hot? Again , Thanks.

 

[alldodge]

Dump the contents of the fuel filter into a clear container. If there is anything other then clean gas. Most likely filter will have some crud in it. Might even be clogging up

 

[tctdc]

well, the crud that was in your tank is now in your anti siphon, fuel pump and carb.

that 1/4 tank of varnish sludge got broken up into floating bits of crud by you adding isopropyl alcohol. then you added good fuel to that to have a tank full of floating crud fuel.

check the strainer in the fuel pickup tube, clean the carb, change the fuel filter

Thanks for the reply, Changed out the anti siphon, screen on the end of the tank tube was fine, used carb cleaner, new fuel filter. Second tank of gas.
Why does it happen after 10-15 minutes? Seems like it only happens when it is hot. Thanks again...

 

[tctdc]

Dump the contents of the fuel filter into a clear container. If there is anything other then clean gas. Most likely filter will have some crud in it. Might even be clogging up

Thanks for responding. Did that. Nice clean gas, no crud or water. New filter.

 

[alldodge]

Something is missing
If pressure is constant and carb is clean and working then it should run. One last thing that might cause the issue is if your carb is a Holley then the power valve might be damaged or sticking

 

[Scott Danforth]

I would pull the carb and spend the $40 on new gaskets and go thru the carb

 

[tctdc]

Thanks all for your help. Can anyone get me a part number for the correct carb. I prefer fresh rather than trusting my rebuild skills (Did that a few times with a stock car - years ago)

 

[Scott Danforth]

you realize a new carb is about $600 where a rebuild kit and supplies are less than $50 and they are a very simple thing to rebuild (my buddys 7 year old has been rebuilding them for 2 years)

 

[alldodge]

(my buddys 7 year old has been rebuilding them for 2 years)

 

[Lou C]

Is this a 2bbl or a 4bbl?
https://www.holley.com/products/fuel_systems/carburetors/marine_carburetors/parts/0-80402-1 2 bbl $642

https://www.holley.com/products/fuel_systems/carburetors/marine_carburetors/parts/0-80492 4bbl $689

These carbs are not hard to rebuild, the main thing is the cleaning, there are many vids that show how to do it. you are basically taking it apart, cleaning every passage and port, replacing the needle valves so they seal, the power valve, and re-assemble with new gaskets. I did my Quadrajet it is a bit more complex than the Holley but once you've done it once, easy. Back in the old days we were told that these carbs were too complex for beginners (I'm old enough that the contemporary cars we drove came with them as new vehicles). Well I found out that's not true at all. Not rocket science. If you're going to own a boat with a carb engine, its a very good thing to know how to do, just like all the other relatively simple maintenance jobs (tune up, oil change, pulling the drive each season, etc).

 

[tctdc]

Ahhh, found a broken terminal on the Choke actuator(?) Ground wire was good, Power wire terminal was corroded and disconnected.

 

[Lou C]

Lucky simple solution, those chokes need a constant supply 12V to stay open. So your engine was running way to rich.

 

[tctdc]

No need to reply, I just wish to summarize for the next boater in this situation:
Problem: Boat was surging and bogging at plane - when hot and running for 15-20 minutes. Going through LOTS of gas. Cold and warming up ran fine.
Suggestions and actions:
Replace anti siphon valve. No Help
Test fuel pressure (borrowed a test kit from O'Reilly's) tested consistent 5 PSI. No Help
Cleaned spark arrester and PVC valves. No Help
While doing so noticed a wire loose from the Choke Thermostat housing. The terminal had corroded off. This controls the choke by way of an internal bimetal spring which heats up when the engine runs opening the choke slowly. Its failure was keeping the choke closed. (normally opens when warmed up) Hence the running fine when cool and even a bit warm, but bogging and surging and the large amount of gas burned when hot.
This is a Holly carb and I got the replacement from O'Reilly, watched two youtube videos and life is good.
Feel free to improve on this.....