Volvo 4.3 Backfire During Acceleration- Need Help

[TexasTom1]

I have a 2001 Four Winns Horizon 180 with a 4.3GL-PEFS (serial number 4012036774). The motor fires right up and idles well, however the idle jumps around within a range of about 20-50 rpm. I have ran 15-20 tanks of fuel through the boat over the past few months. The issue is when I go from idling to a hard acceleration the engine backfires and it sounds like it's backfiring through the carb. (only under load) If I accelerate very slow it won't backfire, also if I do a couple quick pumps of the throttle and then accelerate hard it won't backfire.

Things I have done in the past week:
-rebuild carb with Holley marine kit
-new cap, rotor, plugs, wires, ignition coil and ignition module
-reset timing (the timing does advance)
-new fuel filter
-new fuel line

My thought is that I need to adjust the accelerator pump so that is squirting fuel earlier, not sure if this could cause my issues? Anything else I should try?

Thank you! I am running out of ideas

 

[alldodge]

The issue is when I go from idling to a hard acceleration the engine backfires and it sounds like it's backfiring through the carb. (only under load) If I accelerate very slow it won't backfire, also if I do a couple quick pumps of the throttle and then accelerate hard it won't backfire.

Need to get back into the carb and check adjustments like float setting, accelerator pump, main jet circuits.
Also with a Holley it may have a stuck power valve, or if it was replaced then could be the wrong one was installed

Its backfiring because of a lean condition. Was the timing set according to the service manual?

 

[Scott Danforth]

pull the primary bowl and metering plate...... clean out every passage and chase it with a fine wire or monofilament line

then install new gaskets, new power valve and new accelerator pump and check valve. then adjust your AFR

your running lean on your accelerator circuit, and most likely on the idle circuit as well.

 

[Lou C]

Believe it or not the Holley 4160 for the OMC/Volvo V6 does not have a power valve....I have one sitting in my garage....

https://www.holley.com/products/fuel_systems/carburetors/marine_carburetors/parts/0-80492

 

[Scott Danforth]

the GL should have the 2300 2-barrel.

 

[TexasTom1]

Need to get back into the carb and check adjustments like float setting, accelerator pump, main jet circuits.
Also with a Holley it may have a stuck power valve, or if it was replaced then could be the wrong one was installed

Its backfiring because of a lean condition. Was the timing set according to the service manual?

I have the service manual and followed the timing procedure using the timing shunt and timing light. Also verified the timing is advancing. The float setting was within spec, the kit came with 2 power valves, one was a 4.5 and the other was a 2.5, the one that was in the carb originally was the 2.5 so I put that one in.

I spoke with holley and they agreed it was running lean on the accelerator circuit and that I should verify that setting. If that doesn't work, I will try cleaning it out again.


Its the 2300 2-barrel

 

[97larson]

I have a 97 4.3gl PLKD with basically the same set up. The rebuild kit came with the 2.5 and 4.5 power valve. I ended up going with the 4.5 and had no problems with the carb once I figured out what the real problem was. I ended up finding a bad lanyard switch that was the real culprit, but that’s a whole other story in its own.