The high idle/choke all work fine. But once the choke opens (the engine is warm, thermostat open) the truck wont idle. Sometimes it will, most times not. I even have the idle stop screw all of the way in, and adjusting the idle air screws doesn't help.

Perhaps this is related, maybe not. But when in high idle mode, the idle speed screw doesnt even touch the cam, and still the idle is very fast, the only way I can adjust the high idle speed is with the pull-off valve. Air leak I was thinking, but can't find it. And then why would it need MORE air to stay idling when warm?

I was having trouble with it barely running at all today and then found a clogged jet, but still it only barely idles, when warm, with the idle stop screw all of the way in.

Any ideas?

 

My F250 (400) is not idling either.... well it does, but not all the time, and definitely not when it is cold. I have not adjusted the idle screw yet, as I plan to change the fuel filter to see if that helps. It won't idle right if it is not getting gas! (Does fine on the road, though.) You might want to look at your fuel filter as well if adjusting your idle and carb renders no results.

 

Mine was like that and I finally gave up and took it to a shop. The guy told me the carb was gone because of pitting in where the mixture screws go and some other stuff I don't remember. I bit the bullet and bought a brand new Holley from summit and it has run great from the second I bolted it on.(knock on wood)

The carb just may be gone?? Good luck with it. Let us know what you find out.

 

it did idle okay for a while (since i got the truck running again after 10 years), this seems to be a new problem.

 

Okay, I was checking the vacuum lines and the PO had them hooked up all wrong. The spark advance was hooked up to manifold vacuum, so it was always advanced. I connected that to the ported vacuum at the side of the carb, and tee'd it with the egr valve through the PVS and seemed to have fixed my high idle problem.

Also it does idle better once the engine is warm, but is still very rough and the idle stop screw has to be all of the way in. I disconnected the egr vacuum, no difference. If I lift up on the egr diaphragm it'll stall out, so that seems to be in working order. If I close the choke part way by hand the idle smooths out nice, so I must have an air leak. I sprayed carb cleaner around and the only place it effected the idle was around the throttle bushing (bummer), but I have to spray quite a bit, i.e. that much air cant be getting in. Do they always leak a little, or this more than likely my problem?

 

I took the carb to a local carb repair shop and he said the throttle play was fine, he even said putting bushings in it wont do any good. He suggested the EGR spacer might be leaking so I took everything off. The gaskets are in fine shape, no tears or signs of blow-by. However the carb spacer to intake manifold gasket looks like it is leaking. So I made a new one (I have the proper gasket material) and hopefully that'll do the trick. I'll know tomorrow when I put everything else back together.

 

Sounds like a vacuum leak. For the carb-to-manifold spacer gasket, I recommend using a steel-woven gasket from Fel-Pro which you can still buy. I've made them out of header gasket material before, it's not easy to get right. EGR spacers are prone to failure. Up until about 1977 or so, they were made out of aluminum and burnt out very easily. After 1977 they were made out of cast iron and were available as a replacement for the early-style aluminum spacers. However, even the cast iron ones warp\burn out\rust over time. It needs to be checked for flatness with a flat bar and a feeler gauge.

 

It has the iron spacer and there is no burn through on the carb spacer either. I'll check the egr spacer for flatness, thats a good idea. I've done so much work on this truck and I just want it to run reliably. No matter what happens I am learning a ton. Thanks for the help!

 

Finally! What ever I did (new gaskets, new vacuum lines, completely disassembling the carb, whatever) it idles at all temp and the idle is controllable too. It could be smoother, but perhaps I am asking a little much from a 30 year old truck that hasn't been run in 10 years.

 

hey what type of vacuum routing you have on your 302? my 78 has a 302 and the only vacuum lines that are hooked up goes to the spark advance at the distributer, im needing to know what all goes were on it so i can hook it up right.

 

Here is the link to a very informative post about, among many other things, idle issues.
https://www.ford-trucks.com/forums/7...ml#post6422219 FMC400 made a vacuum diagram (a couple posts down) that I used to route things right. My set-up doesn't have any pollution controls (except egr), so really the only thing controlled by vacuum is the egr and vacuum advance. Also his diagram shows two separate sources for ported (controlled by the carb) vacuum, and my carb only has one. I just used a tee to go to the vacuum advance and then to the egr through the PVS valve.
One important thing I learned is the difference between the two vacuum sources. Manifold vacuum comes from the "tree" , where the brake booster gets its vacuum, and is full blast all the time. Ported vacuum comes from the carb, where the vacuum increases as the carb is opened more, so that should control your egr and spark advance.
Hope this helps

 

https://www.ford-trucks.com/forums/7...ml#post6422219

sorry here is the link