Hey everyone,

I just to delivery of a 1975 F350 with a 460 with an edelbrock 1406 carb and performer 460 manifold, and I've just started tinkering. I have an issue where, when accelerating from a stop (idle), it hitches and sputters until it picks up a little speed, and then it smoothes out. From what little I know about carburated engines, this would be the point where the idle system and primary system transition. Also, the two times I've driven it, I've gotten to a point where, after running for a while (to full temp) I come to a stop, it will idle rough and stall, and will not start until it cools. It seems to idle fine and run fine throttle part open at neighborhood and highway speeds. The truck was shipped to me in Miami, FL from Las Vegas NV. What I am thinking is that whomever put the Edelbrock on it calibrated for higher altitude (LV is about 2100 ft above sea) and therefore I'm running way too lean. Before I go changing jets and rods I wanted to get some opinions. Am I on the right track? Anyone with more experience with these trucks have someplace else I should start? The only thing I can come up with regarding the full temp stall is that I am running hot from being so lean and boiling off what little fuel I am getting. I don't know the truck enough to know if I am running hot (the temp gauge needle is steady on the first arch of the "m") but between the Miami heat and lean running, that seems to make sense.

Thanks for any tips in advance.

Jason

 

First thing to check when it stalls on you take the air cleaner lid off and make sure the choke is fully opening ..

One of the biggest reasons 460's from 73-87 generally run hot is retarded timing ..
1) determine year of the motor .. Internally balanced or externally balanced ?
2) Ask previous owner if the timing gear set was changed out for a pre-emissions straight up timing set ..
3) ask him if he did anything to recurve the distributor ?

Once you get an answer for those questions we can go from there ..

Take a picture of your motor with the air cleaner off .. Front shot and one from each side and post them here ..

 

I'll pull the pull the casting number on the block when I get home. Will that tell me the year? I have no reason to believe the engine is not original (although anything is possible). If it is a 1975, then it would be internally balanced, yes?

I don't have access to the previous owners beyond the last two. The one I bought it from just bought and sold it, and the owner before that did a tranny rebuild, but no engine mods. That owner goes back to 1995, but I don't know anything prior to that.

What is "hot" for this engine? At this point I only have the original "idiot" gauge on the dash, which is running with the needle in the first hump of the "m" in the TEMP across the range.

 

Correct ..
IMHO that would be on the high side while running it down the road at even 30mph .. The factory gauged are some what a guess at best ..

Try this clean the area at the base of the distributor and the block while the engine is cool with some brake clean so you can make a good mark with a sharpie on both the distributor and the block .. Next loosen the hold down on the distributor and rotate the distributor clockwise about 1/8" tighten the hold down and test drive .. Observe the temps and performance and report back ..

 

Thanks for the replies, RedRoad.

I'm going to look into the carb tuning before I get into the timing, but you did point me into a whole new direction of things to look at.

I appreciate it.

 

Just as a follow up to my previous post, I pulled the Edelbrock 1406 and checked the rods and jets, and sure enough it was calibrated 6% lean (#7 on the Edelbrock owners manual chart) which seems ridiculously lean for 2100ft above sea level. Based on Edelbrock's calculation, at that elevation, it should be no more than 3% lean at that elevation. I put the stock jets back in but left the narrower diameter rods, which actually pushes it up to 4% rich in cruise mode (#24 on the Edelbrock owners manual chart). I figured if that was too rich, I could replace the rods with the carb on the engine. It is running MUCH better and MUCH cooler now. I still have the stumble transitioning between idle and part-throttle, but I'm going to bump up the accelerator pump to high setting from the stock middle.

If that doesn't resolve the stumble, redroad, I am going to start looking into the timing. I am honestly oblivious to timing, so I am trying to read up as much as I can to prepare.

 

It sounds like your making progress .. Yes changing the timing on an emissions 460 motor will give you what your looking for ..

 

What do you mean by "emissions 460"?

 

In 1973 Ford was required to comply with emissions standards .. These standards were in part based on GVW rating of the vehicle .. For example an F150 had more emissions equipment then lets say an F350 .. A couple of notable changes to the 460 motor were cylinder head design and timing of the motor to comply with emissions standards .. A somewhat backwards approach but it is what they did non the less .. A more sensible approach would have been to have the motor burn more efficiently which was what they did later by introducing the fuel injected motors and bringing back the straight up timing set again ..

What many have done to the emissions 460 is to undo some these emissions changes by
a) Changing out the emissions timing set to a straight up timing set of the pre emissions 460 ..
b) recurving the distributor so the total timing ( initial + mechanical = total timing) for the 460 is in the 34*-38* total timing range for an average truck motor ..
This accomplishes a more efficient burn in the power band where the average truck needs to make it's power .. If you make these changes along with the further dialing in of your 1406 you and your 460 will be much happier ..

 

Got it. Carbs I know. Timing is totally new animal to me, but I'm always happy to learn new things.

 

You sound to be on the right path with carb changes. You may need to change some on the step up springs. Look into getting the strip kit for the 1406, if you haven't already. Also check to see what vacuum port your distributor is connected to . I'd doubt it's a locked out distributor unless it has a beefy cam. I've always adjusted these using a vacuum gauge after jet, rod,spring and accelerator pump changes with great success. Before you start changing too much just make sure to check base timing.

 

Ok, so I resolved the issue with the stumbling by enriching the carb and turning up the accelerator pump, however it's still not drivable as every time I drive it, once it reaches full operating temp and I come to a stop and idle, it runs rough for about 10 seconds and stalls. It will not restart until it cools. I can get it to fire one cylinder once when cranking it each time it does this, but it won't stay lit until it cools. Keep in mind, it also did this before I made any changes to the carb.

I know the Duraspark modules have a tendency to stop throwing spark once they get hot if they are on the verge of failure, but I have solid spark when this happens, so again, I am back to a fuel delivery issue. Could it be vapor lock? The only thing I can come up with is that it is boiling the fuel, but for the life of me, I can't figure out why or where.

Thoughts?

 

Subscribed to learn more about timing....and get help on my next project.

 

I don't have much to add regarding the timing, but I did find the source(s) of the stall issue at idle.

1. Fuel pump was going bad. Pressure cold was +-3psi, and 0psi when hot, so I replaced that. New pump is spot on 6psi all the time.
2. Timing was advanced to much (18°BTDC) so I scaled it down to 12°.
3. Idle mixture was too lean, so I enriched it and adjusted the idle speed accordingly.

 

Resurrecting an old thread because it absolutely solved my problem. Truck idles rough but only when when in gear and engine is up to temp. Also a little hesitation or stumble when accelerating from idle.

I did a full tune up and fluids when I recently bought the truck. I had already checked and resolved all vacuum leaks and cleaned up carb. I don’t feel like I throwing part at it because all needed to be done. Each made it run better but still has the stumble or rough idle but only when truck was warm and sitting in gear as a stop light.

This thread lead me to installing a fuel pressure gauge. Found fuel pressure was 3psi when cold and continued to drop to as little as 1psi when up to temp. New fuel pump is on its way.

1979 F-250 460 C6 2WD