Is this a carb, timing, or other problem? 3.0L Penta

[Glastron175]

Engine info: 3.0GS MEFS, 3869051, SN 4012036649
The problem is that it runs fine at any speed, but anytime I mash the throttle, it stalls and even dies unless I quickly back off the throttle. I can accelerate slowly with no problems. I suspected the accelerator pump and put in a new Holley kit (it is a 2 barrel Holley carb) and did not solve anything. I disconnected the throttle link so that I could manually advance the throttle and when I do it squirts two streams of gas as it should.
Could the problem be timing, or advance timing not working properly? I don't have an inductive pickup on my timing light so haven't been able to check it yet. Also, could the power valve be the wrong size. My vacuum measures 15 inches at idle, and I have a 3.5 power valve. Any ideas or comments appreciated.

 

[Don S]

Re: Is this a carb, timing, or other problem? 3.0L Penta

It could be the timing.
You should also have a 2.5 power valve, not a 3.5
Here is from the manual.

 

[Glastron175]

Re: Is this a carb, timing, or other problem? 3.0L Penta

Thanks for the reply Don. It could be a 2.5 rather than 3.5. It was kind of hard to read the stamping on the valve. On the timing, since it runs great at either low speed or high speed, I assumed the timing was ok. It only hesitates when punched (from any speed, including idle). It also does in on muffs as well as in the lake under load. The reason I questioned the power valve is that the Holley website has an article for cars that says the power valve should be 1/2 the value of the vacuum at idle. Since I have a 15 inch vacuum, that would mean a 7.5 power valve. Are marine engines that much different from car engines?