1997 Volvo 4.3 GL PLKD rough running/carb questions.

[Davidscott]

I've got a 1997 Regal Destiny 2100 CC deck/fishing boat with a Volvo 4.3 GL PLKD engine with about 700 hours on it. Last couple of trips I've noticed that the engine when idling has gotten kind of rough and the idle which normally is pretty solid at 1000 RPM's is surging...bouncing from 800-1200 RPM's. Also started smelling gas. Thought it might be bad fuel since I had been running 93 octane and switched to non-ethanol 89 when the gas station started carrying it and the problem was noticed at about the same time. Added a can seafoam to get rid of any water and it made no difference. Then checked plugs which looked good. Volvo plug wires are only a year old and I assume still good. Checked to make sure firing/plug order was correct...it is. Removed idle adjustment screws and found both had a small deposits of some type on the ends...which I removed and then replaced the screws...no difference. Replaced the cap and rotor because they had some wear and what appeared to be oxidation/corrosion on the contacts. Replaced fuel filter. Took her out on another trip with more non-ethanol 89 octane and same rough running/surging...although it did seem to lessen after running for awhile at mid-throttle. Anyway now I'm thinking carburetor. The carb is a Holley 2300 # 80312-1 which I believe is 350 CFM. I was able to find rebuilt carbs for around $250 not including core or shipping and so I thought I'd look at new. Apparently Holley doesn't make this exact model anymore. They have a 2300 with 300 CFM and a 2300 with 500 CFM both are about $430. Would either of these work even though the CFM is different? There's a seller on Ebay that has Holley 2300 500 CFM new carbs/old stock for $239...thoughts? ​http://www.ebay.com/itm/282025131842...witem=&vxp=mtr

 

[Jim Lucier]

I am having similar issues with a 5.0L and Holley carb, mainly rough idle. Corresponded with a Holley tech just last week as to which Holley replacement carburetor to buy (they couldn't make an exact match to the numbers on my carb). By their calculation, the 5.0L theoretically requires a 340CFM carburetor. Admittedly this is a "conservative" calculation. I am leaning to the 500CFM as a good replacement for a 5.0L engine. I would expect the 4.3L engine would be a perfect candidate for the 300CFM carburetor. You may want to contact Holley and confirm your application.

 

[jerryjerry05]

Do a compression/ spark test.
​Start it and remove 1 plug wire at a time.
Any water in the filter when you replaced it?

 

[Jim Lucier]

This is the equation that Holley uses per Josh Johnson.
Your symptoms are indicative of a fuel issue.
And yes it is easy to over carb an engine!

Jim.
We use a conservative and more complicated equation to figure optimal CFM size but it figures in RPM and volumetric efficiency/engine modifications:
CID X Max RPM=(x) X divided by a constant of 3456=Y Y Multiplied by volumetric efficiency in % , 80% stock 85% mild 95% heavily modified and 100% for full on race. Comes out to roughly 340cfm for your rig.
Josh

 

[Baylinerchuck]

Not sure why you would buy a carb. Have you taken yours off and cleaned it? I personally wouldn't buy a carb unless it was a last resort. In my experience a thorough cleaning with a rebuild kit fixes most issues. Besides your carb is already tuned to your engine.....theoretically speaking.

 

[QBhoy]

Hi
Have you tried disconnecting the automatic choke ?

 

[Davidscott]

Do a compression/ spark test.
​Start it and remove 1 plug wire at a time.
Any water in the filter when you replaced it?

I did check for spark using the method you described and have spark at all 6 cylinders. It does sometimes sound like a miss which led me at first to think it's an electrical problem. Probably a stupid question but how do you check for water in the fuel filter?

 

[Davidscott]

Hi
Have you tried disconnecting the automatic choke ?

Have not tried that yet.

 

[Davidscott]

Not sure why you would buy a carb. Have you taken yours off and cleaned it? I personally wouldn't buy a carb unless it was a last resort. In my experience a thorough cleaning with a rebuild kit fixes most issues. Besides your carb is already tuned to your engine.....theoretically speaking.

Just because I'm a bit worried about my ability to rebuild a carb and not screw it up! But maybe I should give it a shot since I can't seem to source a new exact match.

 

[Davidscott]

This is the equation that Holley uses per Josh Johnson.
Your symptoms are indicative of a fuel issue.
And yes it is easy to over carb an engine!

Jim.
We use a conservative and more complicated equation to figure optimal CFM size but it figures in RPM and volumetric efficiency/engine modifications:
CID X Max RPM=(x) X divided by a constant of 3456=Y Y Multiplied by volumetric efficiency in % , 80% stock 85% mild 95% heavily modified and 100% for full on race. Comes out to roughly 340cfm for your rig.
Josh

Thanks for that. On the Holley website there are two 2300's available...one is listed as a 300 CFM yet on the specs tab it says it's 350 CFM...I think I'll give them a call or send an email and verifiy the numbers. https://www.holley.com/products/fue...arburetors/marine_carburetors/parts/0-80320-1

 

[Jim Lucier]

I have rebuilt several carburetors over the years. At some point you have to upgrade to a new unit.
You can't fix lose throttle plates or warped air horn surfaces.
The Holley web site prices are very reasonable considering what you are getting.

 

[rkilpa]

Not sure why you would buy a carb. Have you taken yours off and cleaned it? I personally wouldn't buy a carb unless it was a last resort. In my experience a thorough cleaning with a rebuild kit fixes most issues. Besides your carb is already tuned to your engine.....theoretically speaking.

Is it even necessary to remove the carb to clean it? Couldn't you just spray some carb cleaner through it while it's running to see if that helps?

My 4.3GL PLKD has just started to give me concerns at idle speed after running great for 19 years. It purrs at speed, but it wants to stall sometimes when I bring it back to idle after a long run. I need to put it into neutral and raise the RPM's so it doesn't quit. Not convenient when it's time to trailer it.

I am going to look at it this weekend when I do the end of season services. I already purchased the new plugs, cap and rotor because it's been 7 years since they've been replaced. I've never needed to make adjustments to the carburetor before, so I'm wondering it carburetor cleaner is all I need to get things right, or if I need to reset the idle adjustment screw to increase the idle speed.

Any opinions about spraycan carburetor cleaners?

 

[Baylinerchuck]

Is it even necessary to remove the carb to clean it? Couldn't you just spray some carb cleaner through it while it's running to see if that helps?

I only use spray can carb cleaners to remove varnish and gum during a rebuild. Simply spraying them in the air horn won't clean any of the small passages in the idle circuit, primary or secondary jets. You would be better off adding sea foam to the fuel stream.....

 

[jerryjerry05]

Too test for water.
​Remove the filter and dump it in a pan or glass jar.

To clean the carbs little holes and orifices.
At any auto parts store.
​Its by Chevron a black or grey bottle.
The label says
chevron with Techron.

​I mix it 1 can to 1/2-1 gal fuel.
Then run it through the fuel system.
Not in the tank but just through the carb and fuel pump.

​Bought a Ford Ranger with a v-6.
Ran kinda rough.
I ran it till it was almost out of fuel.
​Then added a big bottle of the techron.
You could feel the difference as I drove it down the street.
​It cleaned the inside of the throttle body and ended up with smoother running and more power.