77 F350 460 C6 4x2 Holley 4160 family 80452, 4 barrel, vacuum secondaries, electric choke

Last week, the accelerator pump diaphragm started leaking. The truck starts quickly when cold, but has been hard to warm start, needing lots of cranking time. So I decided to rebuild the carburetor.

I bought the $100 "Trick Kit" from Summit, several cans of spray cleaner and a galllon of Berryman dip. Took the carb all apart, and threw all the small parts in the dip tray. Larger parts went into a bucket.

Several hours in the dip, then cleaned everything up with a toothbrush and spray cleaner. Put it all back together and installed the carb on the truck. Put rags under the barb to catch any spills and activated the fuel pump to fill the bowls. In just moments, I had two fountains of fuel from the vents.

Shut down the pump, and adjusted the fuel level way down. A couple cranks later, the truck was running. Opened up the sight plugs and adjusted the fuel level, front and rear.

Then I adjusted the choke.

I had read that, for the 4160 family, start the idle mixture screws 1-1/2 turns out. Then I read that the 80452 richens when you turn the screws in. So I adjusted for best vacuum-about three turns out. The gauge reads about 17, but it does read 44 (metric)

I set the idle speed to about 700 and took it for a drive. Ran much better than before, and hot-started better, too. The emission sticker says 650, but that seems kinda unstable

However...the idle speed varies, but not consistently. Every so often (like every minute or two), the idle speed will drop, like 100 rpm, then go back up. Not sure what is causing that.

Also, when stopped at a stop sign, when you let off the brake and get on the gas, it will bog or hesitate for a moment, then pick right up. I think it also does this at cruise speed-if I'm coasting, then get on the gas, there seems to be a hesitation.

The timing is set to 12 btdc, the vacuum advance is disconnected and all extra vacuum sources are capped

I'm open to suggestions! Thanks in advance for your help

 

I've never liked Holley's. I guess its just from my personal experience. My 460 has a 750 Edlebrock sitting on a Edlebrock intake. Instant starts hot or cold and no hesitation. I have found that the metering block on some older holley carbs will shift just enough to cause issues. If the bowl screws are over tightened or not tightened in a sequence evenly, the problem is that the gasket will squeeze enough to partially close off ports.

 

Don't know much about Holley but with hesitation like that maybe accelerator pump?

 

I'll take a look at that tomorrow. Should be easy enough to check-just look for two big squirts of gas!

When I was reassembling the carb, the accelerator pump seemed to be working-as far as I could tell when it was dry. By the time i had it running, it was dark

 

I had similar problems after my old Holley was rebuilt. I ended up buying a new carb from Holley. It was a direct swap and they only thing that might have to be adjusted are idle settings. I left mine as-is, and its running fine.

 

Papa,
there is more to tuning a pump shot than just "it squirting fuel"

I would make certain that the second the throttle is touched there is fuel. Also make sure that the accelerator pump isn't bottoming out at WOT, should be a lil more play (.030)

Also, if you removed the accelerator pump cam when you did the rebuild, make sure you used the right hole for the screw with the pump cam (there are two).

Fluctuating idle points to the idle mixture screws. Make sure you do all those adjustments while the engine is hot. Doing them cold will not yield good "at temp" performance. After you get the highest vacuum, richen them up 1/8 to a 1/4 turn.

Also make sure the transition slot is set correctly on the primaries. I set idle speed with the secondaries. Failing to have enough of the transition slot exposed can cause a small bog as you are experiencing, having too much can cause a run on/dieseling condition. The transitions need to activate in a way as the throttle is opened. By having a small amount (.020) exposed under the throttle blades it can stay near active as it is seeing real vacuum prior to opening the throttle.

For future reference, I just set the floats parallel with the bowl roof, this works 99% of the time.

Another note, I've built probably 40-50 carburetors in the last few years, and for a 4160, I feel this is the best kit available at 1/4 of the price of a Holley trick kit.
https://www.summitracing.com/parts/qft-3-2002qft

Also of note, hot restart issues are mostly due to the bowls boiling the fuel out of the boosters or out of the accelerator pump.
A carb spacer typically handles this issue, luckily on our trucks you can use from a 1/4inch to a 2inch spacer with little hood clearance. If the problem persists, open the throttle half way while cranking and the engine should fire right up (it's flooded due to the fuel that leaked into the intake and needs more air)

Drew

 

Good info there, DeepRoots. I just got ahold of a Holley 4160 model# 80457-1 that needs a few parts and a rebuild. It's missing needles/seats and the plastic floats appear to be non-adjustable...am I misreading that?

Sorry for the hijack, PapaBearYuma...just displaying my ignorance from behind the shield of internet anonymity.

 

Emmisson style Holleys do get richer in idle as you turn the screws in. Varing idle speed might be a small vacuum leak but having you idle screws out so far seems to indicate a rich condition. Maybe too high bowl level. Look down the carb at idle speed. You should not see any fuel from the boosters etc.

Emmission style carbs are hard to tune.

 

So rebuild it. Most kits come with the parts you need (not the floats tho)
All floats are adjustable perse.... some are not externally adjustable. You'd have to take the bowls off to adjust them.

 

Broke out the vacuum gauge to adjust the mixture screws. About 1-3/4 turns out produces the best results. Seems to have taken care of the idle speed issue.

The bog seems better, but still there.

 

And the vacuum advance is disconnected ?

 

Thanks for all the info, especially on the accelerator pump and transition slot. I'd read here previously about the transition slot, but couldn't identify it when reassembling the carb. I'll check it out again this weekend.

As I mentioned in another post, a swapped-in the 4160 from the yellow truck. Adjusted the idle speed and it runs like a champ! So it's not a timing issue or other significant problem in the engine.

Maybe that was obvious to everybody else, but I needed the confirmation for myself

 

Thanks for all the info, especially on the accelerator pump and transition slot. I'd read here previously about the transition slot, but couldn't identify it when reassembling the carb. I'll check it out again this weekend.

As I mentioned in another post, a swapped-in the 4160 from the yellow truck. Adjusted the idle speed and it runs like a champ! So it's not a timing issue or other significant problem in the engine.

Maybe that was obvious to everybody else, but I needed the confirmation for myself

 

One of these days I'll do a post with 100 pictures, showing how to get an initial setup with a Holley carb.
It's easy, but if you don't know the basics, you can spend a huge amount of time chasing your tail, trying to figure out the little things.

 

Just wondering why the vacume advance is disconnected?