I just recently did alot of upgrades to the 410 in my 76 F250 including intake, carb, and headers.

After setting everything up i have a stumble or hesitation when i first press the gas or put it into gear. Truck has been parked in my yard for a while but it drove fine when i parked it. I put a brand new Holley 4160 600cfm aluminum carb on it. I got it off craigslist from someone who bought it but opted for an edelbrock on his chevy.

My first thought was maybe the jets were too small. Checked the old carb and they were 66's so i asked the guy i bought it from what it had he said 65's. I dont know much about jetting or anything but i do know i opened the flow in the motor alot with the upgrades i made.

Would one jet size make that much of a difference? Or does it need to be bigger than 66's? My next thought was accelerator pump maybe being too small or maybe need to retime it. Im positive i put the distributor back in correctly but ive never done timing.

Its a 410FE from a mercury full size. Pretty sure its stock internals and cam or maybe a very mild one. It now has an Edelbrock Permormer intake and Sanderson headers. Any help is appreciated.

 

Forgot to mention i had to put a 1" spacer to clear the manifold with the throttle linkage. I think thats a big part of it just wondering what i should do now.

Thanks

 

I think it might require a different accelerator pump cam to address the bog/stumble. Jet changes.. maybe.

Here's a thread from Holley's blog on pump cams: How To Cure Carburetor Stumble - Blogs - Holley Performance Products Forums


The spacer is fine... it'll add plenum volume and is worth some low end TQ with a dual plane manifold.

 

Good info HIO.
I just went thru the same thing on my boys truck. The power valve was our headache. I'm not real computer savy, so someone else may have some technical info on that.

 

I had an issue with my 390 it might not be the pump cam it could be a vacuum leak

 

i had that carb you have before on a stock 390 and my father in-law has one as well on his. Both seemed to like #70 jets here where we live about 600ft above sea level I believe it is. Also both had stick power valves in them which I believe is 6.5. When it came down to it the stumble was cured by lengthening the accel pump adjustment till it went away. Both also used stock 30cc pump I guess it was. I know it wasn't the other one which is 50cc I think.
I'm pretty sure if you were to check it off the idle circuit say cruise at 2k rpm shut it off the plugs will be white. When I had 66's in they were white as could be.

 

The carburetor I eventually put in that 76 had two 50cc pumps in it and it would blow a little black smoke when you hit the gas if you're into that sort of thing (I grew out of it when I got the the gas station)

 

Yikes blowing smoke lol....too much fuel. When your your getting close on your setup you should be able to even see it at the tail pipes. If they are getting a tan/black look your doing it right. Sooty black it's not right.

 

You're just jealous

 

Lol no my Quick Fuel 780 on my 445 is blowing smoke too..I'm good. This one I think is going to take a little more experimenting to figure it out.

 

Still havent gotten the truck on the road just because ive been so busy with work recently. I am getting antsy now and want to get it driving.

Im pretty sure the majority of my problem is the timing. Right now its just got open headers so i think that is a big part of it and also the 1in spacer. I got some pretty nice newer 2.5in exhaust off of another highboy in my area. That was nice because the local shop wanted alot to bend new pipes. Im going to weld that up and then try to mess with the timing once it has the back pressure it will have on the road instead of doing it twice.

I have never done timing before but i would like to learn. The truck has a 410 FE. Does anybody have some timing guidelines for me?

Thanks for the replies

 

I am set at 14 initial 38 total . Set the gap on the accelerator pump helped with hesitation . I called Holley tech about jet size .