Loss of power unresponsive throttle

[Nickgb55]

I have a 1985 Supra sunsport with. 3.5l Ford Windsor.

My current issue is that the boat will not get to above 3k RPMs and has a top end speed of about 20 mph with no one on board. With these low RPMs, the secondaries in the Holly carb are not opening. The engine idles fine but under load opening the throttle it backfires and you can hear the engine start to miss. After that point these is no more power to be had.

Here is what I have completed so far;
Plugs/wires (old plugs where badly carbon fouled)
New coil
Checked timing
Gapped points
New ignition coil
Carb was put in new last year from previous owner (he was having the same issue with low top end power)
Checked throttle cable/linkage at carb assembly

Have been all over the forums, keep thinking I got the problem kicked but still no improvement.

What y'all think?

 

[Scott Danforth]

its never the coil

start with the following:

do a compression test, do you have 140-150 psi in all 8 cylinders
check fuel pressure at the carb, do you have between 3-7 psi
check the contents of your fuel/water filter to make sure you have only clean fuel
check your anti-siphon valve
go thru the carb, your either running lean or your dwell/timing is off
put a dwell meter on your coil, measure your dwell, are you within spec (~ 37 degrees)

 

[Bondo]

The engine idles fine but under load opening the throttle it backfires and you can hear the engine start to miss.

Ayuh,..... Welcome Aboard,...... It's goin' Lean,.... Not enough gas,.......

Check the Contents of the fuel filter for anything but clean fresh gasoline,......

 

[Nickgb55]

Next time I'm at the dock I will look into it. My worry is the distributor is bad and the total timing advance is off.

I checked base timing and the distributor does advance and retard as it should during idle but my worry is that that it is not allowing it to fully advance in to the higher RPMs.

I hope it is just a fuel problem..that is a cheaper fix for sure.

Thanks y'all.