I purchased a 1983 F250 a short time ago. After I got it running I realized that the distributor makes it about a 1975 motor that has been rebuilt or a later rebuilt that has a points system installed on it. So I consider it a 1975 when tuning/parts, etc. It is a 351W and seems to be in pretty good shape. I have been on the forum before and found out a lot of the information and it has been a big help.

My problem now is that after a complete tune up including new ignition wires, cap, rotor, etc. I still have a random miss at idle. Of course the miss could continue into higher rpm's but I cannot tell. The overall power is very good but mileage seems to come up short. I have also installed a manual choke and a new accelerator pump. The carburetor seems to be in pretty good shape, sure it was replaced probably with the rebuilt motor.

Does anyone have any ideas to try and find the source of the random miss without paying to put it on a computer?

 

Move sparkplug wire #5 and #6 as far apart as possible and see if that makes a difference. They are physically close to each other on the engine, and they are side by side in the firing order also.

Also, I am assuming your carb mixture is adjustable(adjustment screws uncovered) and you have tried tweaking them?

 

I have a wire loom to try with the plug wires and I have tweaked the carb. Thanks, I will let you know how it turns out.

 

I did move the wires and it did make a bit of a difference. I am going to pick up some more looms and put all the wires in place. Being an Auto Zone set the wires are a bit long but I think I can make it work. I am also going to completely redo the carb adjustment and see if that helps also.

I have thought about replacing the idle adjustment screws and seats, do you think that might help?

 

you probably dont want to hear this,but chuck the point type distributor for the duraspark 3 dist.anytime you look at your engine numbers remember if it starts with c=1960 d=1970 e=1980,etc.the first number after the letter is a part from that yr,ie; e5 is 1985

 

That's a good point I missed. Have you set the dwell on the points? That's all part of the old points systems. If you do not want to mess with that and don't want to swap out the dist, you could plop a pertronix unit in this distributor. It will give you a hotter spark and more consistent dwell. But before you do that, grab the rotor button(after you take the cap off of course) and pull it back and forth and see how much play is in the distributor shaft. If it flops around some, that will mess with the dwell and could cause a miss also.

On your mixture adjustments; You can pull them completely out(it may be easier to take the carb off first) and if they are not grooved, bent, or have any deep scratches, they should be ok.

 

I don't think he wants a "duraspark 3" as the DS-III is computer-controlled. I think you meant DS-II, which is an electronic replacement for the points.

Edit: I forgot to say that an occasional miss at idle in my experience has been due to carburetion, not ignition. I'm not at all saying it isn't your plug wires as Dave suggested, but that if you still have an occasional miss after that it may be due to an improper air/fuel mix. I'd go there next, using a vacuum gauge to set the mix, meaning to max out the vacuum.

 

Thanks for the info. I have set the dwell but I am now betting that it is the carb and I will work on that sometime this week. I changed out the fuel filter when I was trying to get it running but I think I will change it again because it had been sitting quite a while. I have found a rebuilt carb for a decent price @ Gauranteedcarburetors.com. Has anyone had any experience with these low cost rebuilds?

The distributor is in very good condition, no slop. I am trying to keep my cost down on parts so I am going to forgo the electronics for now, maybe later. If I spend too much on this project Momma is gonna slap me silly. I also have all the necessary tools for this type of system.

The truck is in very good condition and starts at just a tap of the starter. The manual choke is the best thing I have done to it. All the emission stuff has been removed or was never there on this 1975 style motor. I have found many vacuum leaks that have all been fixed. When working on the carb I will pull out my old vacuum pump/gauge again and see if I have found them all. I also have the vacuum reserve can on the right wheel well, since all the emission stuff is gone do I really need this reserve?

18ntpianist22, you mentioned an engine number, where should it be? I have looked it over and have not found any such ID. Being a rebuild, all the original mfg tags are no longer on it.

 

Well, it is the carbureter. I have tuned out most of the random miss but it is obvious that I will be ordering a rebuilt unit and installing it just as soon as possible.

 

You need the can on the pass side fender. It's beyond a check valve in the line that goes to the HVAC system(that line enters the firewall over near the pass side hood hinge). When you pull a long hill, you lose all the vacuum to the system, and your HVAC system would switch to defrost if you didn't have the storage container and the check valve to keep it going till you stop pulling the hill.

 

How did you figure that out w/o pictures or symptoms? The Great Carnac? What did I miss?

 

I disconnected the can and that cured all the vacuum problems so I must have a leak there or it was the check valve. I do not have a HVAC system. The heater hoses are there but no A/C and I do not have a blower motor working. In this part of the country there is rarely enough moisture to condense so a defroster is not needed. I have lived here for many years and have never used a defroster.

Do I still need the reserve knowing this?