rough idle

[darken7]

Gentlemen,
After a prolonged absence, I again return for advice from the FORD guys. I previously had trouble with an autolite carb, I have finally fixed that with the addition of a holley 2bbl on the FE. Now I have a new problem. The truck runs great when it is warming up, but when the truck is warm it starts to run like crap. it sounds like it is missing and I am stumped at the moment. If there is any other info I can add to help, please let me know. Is it possible that a spark plug is messing up when it gets hot. Maybe crossfiring? What are the symptoms of crossfiring? Any help is appreciated. Thank You

Darken 7

[convincor]

still running points? file them, re-gap.

[FORDification]

Cross-firing would occur whether the engine was hot or cold. Cross-firing is caused by certain plug wires touching each other on adjacent cylinders in the firing order, and which will foul those plugs. Cross-firing results from the magnetic field produced when an electrical current passes through a spark plug wire, causing two cylinders to fire at the same time. If cross-firing is allowed to occur, one cylinder has the spark plug firing ADVANCED 90° from the proper time. With that amount of ignition advance, it is only a matter of time until a component will fail. This is a known problem, and many service bulletins from all car manufacturers have been issued regarding this problem on various engines, depending on the firing order. Here are the Ford engines mentioned that have been identified as being susceptible to this condition:

Ford Engines (221-302, 332-348, 370-460) - 1-5-4-2-6-3-7-8
Ford Engines (302 HO, 351-C, 351-W) - 1-3-7-2-6-5-4-8

Try adding some additional plug wire separators and routing them through the separators as in the graphic below, which I just scanned from a Ford Training manual.



However, as I mentioned, I kinda doubt this is your problem. A failing ignition coil will sometime exhibit the symptoms you're describing.

[darken7]

Replaced points, condenser, & coil. Now it is running worse. I had to leave in my dad's garage. Gap is set to 0.021, i have two different chilton's telling me .021 and one telling me .017. I am at a loss, wife wants me to sell the truck, and I had one hell of a day in the garage. PLEASE HELP.

Darken7

[FreakysFords]

I'd start with pulling the plugs, laying each one in a row to represent the cylinder it came from. Then read the plugs and see what's going on in the combustion chambers. This will give you a good point to diag from.

Also, I need to re-read your post, but have you checked the fuel system? Filters and pump all the way to carb inlet.

[pasty63]

..... I am at a loss, wife wants me to sell the truck, and I had one hell of a day in the garage. PLEASE HELP.

Darken7

When it comes to old trucks, wives can be like children. Pre-occupy them with something they enjoy before you spend a day working on the truck. It'll be OK.

The problem feels more carb oriented to me than ignition. Since you messed with the points you'll need to set the timing again - which may be why it's worse than when you started. Reset the timing and warm the truck up - make sure the choke is working properly. Next, look for a vacuum leak.

It's never a good idea to change everything all at once when you're trying to find out what's wrong. It's as true for bumps as it is for anything else. Heck - it may even fix the problem, but you won't know why. Change only one variable at a time and then move to the next. It's a related system of problems rather than just a single issue.

You can't sell the truck until it's fixed anyway - that would be immoral. So tell wifey to go play and you'll wrestle this beast to the floor.

[darken7]

Well here goes,
After another day in the garage, and my truck is still sick. I thought I might take a step back and explain everything that has led up to this problem. The problem began with a weird, frustrating fuel problem with my carburetor. The initial carburetor was an Autolite 2bbl, and was having problems when it got hot. A couple of the suggestions were to get a phenolic carb spacer, or replace the carb with a Holley 2bbl. I chose the latter, because I ended up with a free holley. I was still having problems with the autolite, and i waited until I had the time and money to rebuild the Holley. The Holley was a problem in its own right. Its number 7508-1 was almost impossible to find a kit for, and I happened upon the #3-888 renew kit in a Bronco forum. I bought the kit, and on monday I rebuilt the carb. When rebuilding, the accelerator pump discharge needle disappeared. Luckily I had a 650 4bbl, and I pulled the accelerator pump discharge to rob the needle. It didn't have a needle, it had to metal balls in it, one a tad bit smaller than the other. I put them in the two barrel. I the adjusted the carb according to the instructions, mounted the carb, and started the truck. It ran like a champ. I took it for a drive, and it ran great. On the way home when it ran hot, it started acting up again. I followed the advice and replace the condenser and points. ran worse. tested the coil, appeared to be bad. replaced it. The truck would not even start, sounded like misfiring , or no spark at all. We checked the timing, and set it to 10 btdc. checked all of the spark plug gaps-.035., plugs all clean, no foul. set the point gap at .023. checked fire on all spark plug wires- all fired. put the holley carb on after checking my rebuild job, and manually set the float. started the truck and it ran great for 15-20 seconds. Then it started missing, and running like crap again. This problem has left my dad and myself befuddled. My dad is the reason I have a bumpside anyway. When I was growing up, we had a 72 custom with a 360, and a 65 custom cab with a 428CJ that my dad built with his own hands. He could always just listen to the trucks and tell you what was wrong with them, but in this case he is at a loss. I know that this appears at first to be a novel, but I felt if I truly needed the help, the least I could do is lay it all out on the table. I am now leaving it up to fate, and a few good men at FORDification. I really appreciate all of the help you give. thanks.

Darken7

P.S. If there is any additional info that I could acquire to help in a diagnosis, please message me. I will not get to work on it again until the weekend, but I could give more details.

[thebannister8]

is the new carb dialed in

[darken7]

what do you mean by dialed in? If you mean setting the air/fuel mixture, setting the float, and all that yes I have dialed it in. Now I am not sure about the size of the jets, but they worked for a couple of days. Does that help?

Darken7

[peanutman]

I might make a suggestion. Was having a very simular problem with mine. Rebuilt carb and done a complete tune up the works. Rough idle and cutting out at a steady rpm, found out the vac advance was bad replaced it, still ran bad. Rebuilt the carb again, still the same. Checked for vac leaks -none
Changed the points and condenser again and replaced the coil, during that process found a bare spot on points feed wire fixed that. Ran better but not much, so at this point i was ready to take a 16lb sledge to it.
Called an old ford guy, described what all i had done and what it was doing,he said right off a bad dizzy. Bought a rebuilt dizzy $ 69.00 and it fixed it
I guess the bad carb was masking the bad vac advance and dizzy, i had went through the works like you re-adjusting points, timing, carb etc... Found out the plates that the points site on and mechinizems under those were wore out and i had a short in the dizzzy

[darken7]

Once again I owe much appreciation to the people at Fordification.com
Owing much to Peanutman's advice, I replaced the distributor and the truck started running again. Now I am having what appears to be carb trouble. I put a 2 barrel holley #7508-1 on that I had recently rebuilt. The problem is that the carb runs great until the choke starts to let off. Then it runs rough and dies. I tried adjusting the mixture screws, nothing happens. I took the screws out and nothing happens. The only way to keep the carb running is to choke it. Is it possible that there is a problem in the casting of the carb? Can i try a different distributing block in the carb from a 4 barrel? I am also keeping an eye on an original 2 barrel holley on auction to replace it. I also did a vacuum test on the intake and the reading was around 18 but the needle was moving very rapidly back and forth about one mark on either side of 18. I am not really that good with diagnosing the vacuum test, but I think that says something wrong with the mixture. Any help would be appreciated. Again Thanks to Peanutman for the dizzy post. Another question: If I am running a stock engine, does my timing need to be set at 6 btdc, or is the advised 10-12 btdc OK? it is currently set at 10 btdc. I set it there after the new distributor. Before the new dist. it was at 6 btdc. I appreciate it.

Darken7 http://www.fordification.com/forum/post ... =3&t=39972#

[swinn]

My thought is that if it runs OK with the choke on, but not with it off, that indicates a vacuum leak somewhere. The intake is getting extra air from somewhere else besides the carb throat . When you open the choke, you have too much air. Could be a leak at the base of the carb, leak on the intake itself, bad brake booster (if you have one) letting air in through the booster vacuum feed (you can plug the booster vacuum feed to eliminate that one). Try some carb cleaner spray around the base while it is running with the choke on to check the base. If spraying the base doesn't have an effect on it it's sealed.

On the other side of that if you don't have any air leaks it could be lack of fuel. With the choke engaged you need less fuel to achieve a proper Air/Fuel mixture. When you open the choke, more air is coming in so you'll need more fuel, if the carb can't deliver enough fuel it would die. I don't know enough about carbs to know where to look for that type of a problem though.

You probably already knew all that, but those were my thoughts. Good luck!

[peanutman]

Hey darken7 thanks for the kudos, i don't deserve it. I was lost until i talked with the old ford guy. I don't know much about holley carbs, but something ant right if it will run at all with the air screws out. Someone will be along to help you on that. My truck seems to run better at 10-12 btdc vs 6 as the book states and that's with a new timing set, dizzy ect.. so not sure why but my 302 is too sluggish at the factory setting. What your running shouldn't hurt anything unless your running hot at that setting or pinging.
On the carb it sounds like something is missing out of the carb, iv'e never had good luck w/holleys but most on here like them and have a lot of knowledge on there operation. Good luck! I will chime in if i can help.

[fordman]

i agree a vacuum leak is the possible problem. use the cabr cleaner and spray it around. if the engine revs up or tries to die from too much carb cleaner in one place then you found your vacuum leak. do you have a power brake booster? when the eninge is running and you press on the brake pedal how does the engine run? the same or almost die?