78 Ford F-250

[WVRampage]

The truck is a 78 with the 400M thats bored .060,with a summit cam lifter set in it(.484 intake .512 exhaust)Holly street dominator intake and a eldebrock 600 carb. So hers the problem it has a very irratic Idle,it didnt have this problem it just showed up. I normaly idles right on 1100 and latly it has been droping off to 500 or just starting to die,so I cleaned the carb out,ran some dry gas in it and messed with the idle,now it Idles at 1500 with the choke part way on but with the choke off it goes back and forth from 1500 to 800 and back like our cars do with the AIS messed up.Do you thing that the vacume advance could be messed up and causing this as nothing on the truck was changed other than the oil and a heater hose that broke over the alternator possibly geting the distibuter wet.I figure you guys could help me out thamks very much for all the help on other things.

[dr_amx]

Sounds like an issue with the choke or the high idle circuit. to check the vacum advance you can use vaccum gauge or just use a hose and suck a vacuum and make sure it holds. Is the idle scew touching its base? 1500 rpm to me is way to high.

[jre97]

Check for vacuum leaks, especially your bolts where the intake bolts down to the heads my old ford was terrible about the bolts coming loose. You might have to play around with your float level if it's a little to high you'll be drizzling gas in making an erratic idle. It should start out around 1200-1500 when you first start it at fast idle then tap the gas and it should fall off to about 800. If your distributor was wet it would be misfiring alot so that's probably not the case.

[METZ]

I agree with a vacuum leak. Also check the EGR plate for leaks or faulty EGR valve.

[Vigo]

if you cant find a real obvious vacuum leak, check the bottom or the carb for flatness by filing it. i know the carb 2.2s were bad about that.

otherwise i have no experience on carbs... i do have a 75 360FE f-150 tho, i bet mine was beaten with a bigger ugly stick then yours! hah that showed you..

[turbovanman²]

VAcuum leaks, plugged fuel filter, carb needs overhauling.

[Tony Hanna]

If no vacuum leaks are found, then +1 for the carb overhaul. With some wear, they'll start sucking air around the throttle shafts and cause the idle to hunt like that. Also, check your throttle return spring. I've seen a weak spring cause the same problem because the throttle doesn't return against the idle speed screw every time.

[Anonymous_User]

First is the vacuum leak as mentioned.

The carb COULD need a rebuild, but being an Edelbrock carb, they are pretty sturdy and should last quite some time. I doubt if the carb is 20 years old!

Since you can choke it and get it to idle, its sucking air from somewhere. I've had numerous problems with intake manifolds sealing on these motors - well, clevelands, which are basically the same thing.

[moparzrule]

anonymous user beat me to it, this is not a holley carb this is an edelbrock. And the part about the intake sealing was my next thought. For some reason these engines don't take well to aluminum intakes. My brother ran a Weiand Action Plus manifold on his 400 with no issues though, which I think is made by holley anyway. I believe he put some kind of goop on the manifold gasket for extra sealing though. I don't know he used to be a machinest and engine builder so he knows all the little tricks about engines.

I run edelbrocks on all my carb engines with great success and they are extremely easy to tune. I do not believe the issue is with the carb. I would also check out the vacuum advance. Are you running the stock distributor or aftermarket?

[WVRampage]

This is an intermitent problem now and when its acting up nothing now helps it so Im leaning twards the fuel pump is messed up and a few people up here with jeeps have had the same problem and the fuel pump was it.

[Anonymous_User]

I only use Fel Pro Printoseal intake manifold gaskets on my Cleve. Best sealing gasket I've found and I've tried LOTS of them.


Most Fel-Pro Performance intake-manifold gaskets have Printoseal construction, which puts beads of special elastomers around the ports for extra sealing power. They also feature a non-metallic, rubber-fiber base material that resists gasoline and alcohol, while allowing engine builders to precision-trim around the intake ports.

There is a metal valley pan gasket for the Cleve's, probably one for the M's also. I tried it, ain't worth a ----.

As for the fuel pump, without a gauge, it's just a parts swap and cross your fingers type thing. I haven't run a mechanical pump for a LONG time. Do you have a filter between the pump and the carb? What is it's condition? I'd check the float setting also. Been a while, do the Edel. carbs have a float level sight?

And, just for the helluvit... my cleve (older pic)

http://www.geocities.com/screamincleveland/Engine.html

[WVRampage]

The other day when it was acting up and I was trying a few things under teh hood I hit the linkage to rev it up and s bunch of air apeared in the fuel filter and it stumbled so thats what made me think it was the pump.

[moparzrule]

Well it might not be the pump sucking air (although it is very possible), before you go changing your pump I'd check all the fuel line for pin holes. Just feel around if the line is wet at all. I had this problem with my 77' power wagon, was sucking air but I had a hole in the metal line. I replaced the whole metal line with rubber line. It might not be a bad idea to do anyway to replace the line, and then replace the pump if it still does it.

[moparzrule]

Oh and the performer carbs don't have a float sight.

[WVRampage]

The problem comes and goes alot is why I dont think its a line,as I said it could go weeks with no problem and then just not run very well at all and when it does run its just as powerful as ever.

[moparzrule]

What ignition system do you have on it?

[moparzrule]

Check your plugs to see if a lean or rich condition is happening.

[WVRampage]

it still has the factory ignition on it,with a new duraspark box,the only thing I havent replaced under the hood nice geting it out of a feild and rebuilding the engine is the alternator,fuel pump and Distibuter.It sat for about 4 years with a blown engine and then It took me a few months to get the body and engine back in working order.

[moparzrule]

Oh that duraspark box it probably your problem, i've seen them go bad intermittently like that before. Thats why I asked about the ignition.
The fuel pump should probably be replaced anyway since it's original.

BTW my brother had less cam on his 400 but ran a 750 edelbrock, something you might want to look into for a few extra ponies. Do you have headers?
Here's his setup, can't remember what he had for ignition-
.030 over
Weiand Action plus intake
202/208 duration@.050'' cam (can't remember lift)
edelbrock 750 carb
Headers with dual side exit 2.5'' with bullet mufflers (extremely loud at WOT, very raspy).
Made enough torque to snap the input shaft on the tranny and blow out 3 dana 60 rear-ends. He had 6'' skyjacker lift and 39.5'' Super Swampers when he sold the truck, body was rotted real bad.

[WVRampage]

I like the power curve with the 600 on it,also for what I use it for not much more power is needed.I need to make som ladder bars for the rear so I can get rid of wheel hop.I do what to put one of those HEI distributers on there someday but I just havent got around to it yet.Also it doesnt have headers.I use it to haul with and do anything with at the property my family got,so it sees action as a log skider from time to time.Over all I wouldnt trade it for any other kind of truck.

[jre97]

The metal valley pan is the intake gasket on the 351/400m block and I don't think there are any others available. If you don't find any loose bolts on your intake it might be worth it to pull the intake and replace the valley pan/gasket. alot of times people reuse them and the sealing bead is smashed in and it really presents itself escpecially with an aluminun intake because they expand and contract so much with heating and cooling.

[turbovanman²]

You have to use the Perma-Tex spray or some form of sealer in the intake gasket, the metal just isn't enough, :(

Air in the fuel filter is fine, remember, the system isn't pressurized and will replenish the carb when it goes down.

[moparzrule]

You have to use the Perma-Tex spray or some form of sealer in the intake gasket, the metal just isn't enough, :(

Air in the fuel filter is fine, remember, the system isn't pressurized and will replenish the carb when it goes down.

I agree with the first part, diasagree on the second. The system is pressurized, 6-8 PSI actually. You must be use to using holley's, but edelbrocks don't like air in the system very much. Mine starting popping and missing at WOT, perhaps I had a good bit of air in the system but still the patching of the pinhole in the line fixed it!

[moparzrule]

I like the power curve with the 600 on it,also for what I use it for not much more power is needed.I need to make som ladder bars for the rear so I can get rid of wheel hop.I do what to put one of those HEI distributers on there someday but I just havent got around to it yet.Also it doesnt have headers.I use it to haul with and do anything with at the property my family got,so it sees action as a log skider from time to time.Over all I wouldnt trade it for any other kind of truck.

Thats the beauty of an edelbrock, you won't loose any low end with a 750 :thumb:
The secondaries are mechanical yes, but they have air doors on top. They open more if the engine demands more and meter fuel depending on how much they open. So, at low RPM's the engine won't demand as much so the air doors will stay closed even if you floor it so it won't flog it out. Trust me my brother's truck had NO lack of low end power, thing was insane. And I am used to driving big block V8's and other hi-po V8's, heck my first car had a 440 LOL, and my second a chevy 383 stroker. But that 400 had more torque than both hands down. I'm sure the headers helped alot though, but my point is a 750 doesn't flog out the engine. Oh yeah the 383 chevy had a 750 carb on it too :amen:

[Anonymous_User]

The metal valley pan is the intake gasket on the 351/400m block and I don't think there are any others available.

Summit part number FPP-1240 is the Printoseal intake manifold gasket kit for 351/400M.

[jre97]

Summit part number FPP-1240 is the Printoseal intake manifold gasket kit for 351/400M.

Good call it's been 12 years since I've done a 351/400 ford.:thumb:

[mech1nxh]

The problem comes and goes alot is why I dont think its a line,as I said it could go weeks with no problem and then just not run very well at all and when it does run its just as powerful as ever.

have you taken a fuel sample?......

[85lebaront2]

Damn, I guess a Ford guy needs to get in on his one. Edelbrock carbs are Carter AFB or AVS series carbs. Try your idle mixture screws, if only one effects the idle, then ther is a problem in the circuits on the other one. The tiniest piece of dirt can plug the idle jet. It is the skinny tube under the primary clusters, the jet is the small orifice on the bottom. Air leaks can cause wierd problems also, use a propane torch, not lit, to probe around joints with it running, if you hit the leak, it will speed up and smooth out. Vacuum advance - should be ported on a Ford, not direct. If you have to idle at 1100 rpm, you may have vacuum on it all the time. DurasparkII, either works or it doesn't, will not cause erratic idle. I have had two trucks with DurasparkII ignition,each time one failed it was backfiring, cutting off or just not starting. BTW, I had a 1977 F150 with the FE 390, .030 over, stock iron 4V intake, factory 600 cfm Holley, home designed duals and running the 77 DurasparkII ignition. Carried a heavy 11ft slide in camper and towed my 30ft 5th wheel at first. Would turn low 13s in the quarter with 3:25 gears.