Hi all,

Hope I'm posting in the right place. I am completely out of ideas on this one and would appreciate any input...

I have a (mostly) 1983 F-150 with the 300 inline 6. Somewhere along the way a previous owner welded up a custom intake manifold and bolted a 2 barrel Holley carburetor. It's ran great the 5 years I've owned it up until the following.

In the fall the truck stated stumbling and loosing power on acceleration. This got worse to the point it would completely die out and stall within a mile from the house. I parked it up for a while and am just getting back to it now. I rebuild the carb which helped and the trucks now idling great. Whenever I actually drive it though, it'll stumble when shifting and backfire. The new spark plugs quickly get extremely sutty throughout my attempts to fix this. Here is a list of all that I've done so far:

Double check the carb is reassembled correctly
Checked the accelerator pump is not torn and functioning correctly
New gaped spark plugs
New spark plug wires
New ignition coil
New distributor advanced by 12 degrees
New fuel filter

The float level is set correct as per the sight plug. The adjustment screws are backed out about 1 1/4 turns.

Anyone got any other ideas?

 

Have you ever changed the ignition module yet?

 

What model Holley v2 carb you running?
To me it sounds like a 2300 as it has a sight plug to check the float bowl level.
Next do you know if it is a 350 CFM or 500 CFM, 500 tend to be too large for a six.

As for running rich, when you rebuilt the carb did you replace the power valve (PV)?
What was the value I am guessing 6.5 as I think that is what comes in rebuild kits.
What dose your truck have for vacuum at idle? As a start for the PV it is half when the idle vacuum reading is.
Also if the motor backfired up thru the carb it most likely blew out the new PV as old Holley carbs did not have the anti-backfire check ***** in them.
Dave ----

 

If im not mistaken the 83 is the 1st year of the feedback carb/, TFI ignition system set up. The go between fully carborated and EFI. If it is, and any of its sensors have gone out then it will lock into the early version of “ limp home mode” and run rich. That would explain the stumbling and fouling. Does your distributor have vacuum advance or does it have an odd adapter with about 6-7 wires feeding into it?

 

Thing is someone installed a Holley v2 (2300?) carb so no longer has the feed back carb but you do bring up the TFI / distributor wonder if that has been swapped out?

But it was running good with this setup before and not running poorly & rich and why I pointed to the carb a blown PV will make it run rich as it leaks fuel.
Dave ----

 

Excellent point. Please post a picture of the carb, or the model number if you know it. Depending on the model, the power valve location was different.

For a quick test, engine at idle, try turning in the idle mixture screws all the way closed. The engine should starve for fuel and die. If the power valve is leaking, the engine will continue running. It may even idle a little more smoothly as you close off the normal supply of fuel, so the mixture is not so rich.

 

Great input. Definitely thinking you may be on to something with the power valve (event though I'm not overly familiar with what that is). The truck was running great with this carb before and I have previously rebuilt the carb using the same rebuild kit, so compatibility


wouldn't be an issue.

Karl made a real good point though. When I crank the mixture screws in it does seem to run even smoother. I'll attach some pictures of the ol' girl on her homemade throne as well as the model. It's a 0-4412S by the looks of it.

 

More details on the power valve for a 2300 series Holley:

https://www.holley.com/blog/post/how...xn4OEjeM6EfvwB

 

I did not check out Karl's link but that is a 2300 and without looking up the list number would not know if 350 or 500 CFM but if running before the CFM should not be a big deal other than 500 is a little to big for the 300 motor.

On a Holley the PV is a go between from idle to high-speed parts of the carb to help from running lean.
Also if holding steady throttle when driving and you feel "surging" the PV is just at the "tip in" point and opening & closing and you would need to go larger or smaller to stop that.
I have only had 1 carb, a 2300 also, that did that and think I went larger and it ran great after that.

Thing to know about the Holley 2300 it is half of their v4 carbs and get tuned the same way, just half of it.
BTW the Holley 2300 is a direct bolt on replacement for the Motorccraft 2100 / 2150 carbs used on the Ford & AMC v8's and you can use the factory air filter and no one will know you have a Holley on top of the manifold
Dave ----

 

Pulled the PV out today. Left it in the shop but I think it was stamped 4.5 Any good way of checking their functionality out of the vehicle? Seems to be in good shape.

 

Not that I know of or none that I know of ATT. I have just changed them with rebuilds and did not look back LOL

4.5 was that the one from the rebuild kit? All I have ever seen were 6.5 in kits.
Do you know what your vacuum reading is at idle in gear if auto?
As a starting point they say you want a power valve half of what idle vacuum is.
Most good motors have 18 HG or more at idle so half is 9 HG so dont know why they put 6.5 in the kits?
To use the 6.5 in the kits your vacuum would be 13 HG.
The 4.5 you would have 9 HG of vacuum I dont even know if the motor would run with that vacuum?
Dave ----

 

Threw the 4.5 PV back in, set the mixture screws to around 1 1/4 turns out. Had a tough time getting the truck to idle steady, I'm going to blame the extremely fouled spark plugs for that. At around 925 RPM I'm getting 19/20HG.

I've ordered a 8.5 PV (I know there's a 9.5 but 8.5 is the only one I can get cheap and quick in Canada). It'll be here Monday. What I can't understand is how the truck ran so well after the last rebuild when I used the same AED rebuild kit that came with the 4.5PV. Unless I forgot to swap out the PV that time? Unfortunately, I have lost track of the PV I took out of the carb this time.

I'll let ya's know how it goes.

 

Please see post #26 for details of how to test a power valve:

https://www.ford-trucks.com/forums/1...l#post21581960

As Dave mentioned, 4.5 is probably too low with a stock cam. That could be a factor if the mixture is too rich. Typically you'd want 8.5 or so. 4.5 is something you might see with a hot cam and resulting low manifold vacuum.

 

I see Karl beat me to the link of how he tested his PV and that was a first for me
Dave ----

 

UPDATE:

I think we got this situation sorted with that power valve. I put the new 8.5 in and headed to town and back (60mi). It backfired twice. I picked up new spark plugs, air filter, a can of Sea Foam and did an oil changed. I've put another 60mi on since with no backfires or stumbles at all.

Thank you Karl and Dave especially.