I don't think it's overloading, Pulled a 24 ft boat that weighed much more than the trailer, never did this. The only thing I did not do is replace the spark plug wires. Only about 10,000 miles on them . I will try that first though as they have been on quite a few years. I will go from there... Thank you all, and I will let you all know .... fish...

 

Hook up a vacuum gauge and watch it when you're pulling. You'll know when your bogging out and when to downshift. A tachometer is very useful too.

I'm sitting on the same side as Orich. Doesn't sound to me like there's anything really wrong except maybe tuning.

 

Things to do before you buy new wires.
Orich

 

It seems a vacuum gauge would come in as a handy tool for your situation.
My .02 , I think its timing, points and condenser...

 

Ok Guys, went ahead changed spark plug wires, new vacuum advance, rechecked timing, 9 degress BTC,pts .17 thous. vacuum is almost 18 tuning carb, will not pull trailer for about a month. I will let you all know what happens. Thank you all again!!! Frank... (fish)...

 

You might check the harmonic balancer for slippage. The rubber sometimes separates from the metal and the timing will be off.

 

Thought of that too, but 18" vacuum is pretty decent. Hm...

 

Beings you said " ( It is since I put the new carb on it though.) "......2X mountain dewd on the carb tuning. I think you need to install a power valve that comes in quicker. And if it's a vacuum secondary Holley put a secondary diaphragm spring in it one step stronger.
What is the "list" number stamped in to the front of the carb's airhorn? Did YOU buy it new or off somebody else that might have went in the carb and changed things? Was it a 2V carbed 390 just before you installed the Holley? I.E. was this Holley it's 1st 4V? If so, what else did you change? Headers, gears, duals, cam,etc.

 

I just found out in the other thread, it's a 4bbl. Double pumper or vac secondary? What is the list# on the choke horn?
Have you tried swapping on a known good carb?
4-speed with 4.10 should pull stumps out of the ground. My 71 F250 390, 4-speed would drag my dad's 20+ ft motorhome all over the place.

Crap Jeffafa I just saw your post

 

The carb is a 4160 series #80453 , the only number on the diaphragm is 953. I have the old carb here, Can I switch diaphragms without probs? Seems the secondary kicks in a little late in 4th gear. How do I tell spring loads for the diaphragm. ? thanks again guy for all you feedback .. fish...

 

Holly carbs can be a real pain in the azz if you get it out of whack with a pump cam linkage, this works your pump shot timing, If to slow then it will fall on it's nose by bogging down or popping back through the carb.

These carbs are like a watch with date mo. & day display. it all has to be in sink to work right.

There is tuning kits and a carb really needs to be tuned to your engine.
Main jetting, pump shot size, pump cam timing, power valve vac. opening, Some D pumpers have 4 corners air/fuel jets that has to be adjusted correctly an with one of these out of whack your going to have a problem.
So be careful what you do if you don't know what does what with these carbs.

Orich

 

Secondaries kicking in late? Well that solves one question I had. I was thinking maybe one of the tuning problems was the secondaries coming in too soon under load and the engine was bogging. For the secondaries I suggest getting a Holley part number 20-59 quick change cover kit and spring kit 20-13. 80453s (600 CFM)come with the strongest black colored spring. Stronger the spring is the later the secondaries start to open. Depending on altitude, engine condition and compression,etc I'm thinkin' the plain colored spring would be best for your rig. Purple would be better if it doesn't create bog. The springs go :
black.....strongest.
brown
plain
purple
yellow
short yellow
white................lightest.


My Holley chart does not tell me which main jets it's got. They are listed as N/A.
It's got a #39 secondary metering plate in it. This is equal to #69 jets. (.073 hole) This may be a bit fat for your rig. You'd have to read your plugs and see if it's running rich under the problem load.
It's got a two stage power valve in it. 1st stage opens at 10.5" and the 2nd at 5.5". These are great for fuel economy but I'm not a fan of them for towing. HERE LIES YOUR PROBLEM IMHO. I suggest you put in a 8.5" single stage power valve Holley part number 125-85.
It's got .031 accelerator pump nozzles. I'd leave these alone.

 

Thanks Jeff! I will give it a try . i'll keep you posted , as it might take me a bit to get the kit(s)... fish...