75' F-250 2wd 390 4v C6 D61(3.07). This thing won't idle after it's been running for awhile at low/idle rpms. When I get frustrated about it and rev it to the floor for a few seconds a couple of times in neutral it idles just fine, until I take it out again and subject it to a long period of low/idle rpm operation. I'm blaming the gearing (3.07) and my driving for the low rpms.
Two, er three things I want advice on - possibly running hotter plugs and possibly advancing the timing (currently ~12-14 btdc). I should probably re-adjust the idle jets to run as lean as it will too, or should I?
Idle mixture should be adjusted for FASTEST rpm(or highest Vacuum reading). Anything less and it will want to stumble or not idle well.
How is the dizzy? Does the idle seem to slowly drift off to zero and stall? Maybe the advance plate is worn and allowing the timing to slip down as it idles, then going far enough to quit. Something to look at. Pull cap off and twist rotor to see how well it returns back. If it's sluggish/stiff, it could cause issues.
O.K. I'll try adjusting the idle mixture screws again. The carb is a new (well, less than 1 year old) edelbrock 600 4v that doesn't have a power valve. It will be 3-4 days before I can get to it.
Crank the two idle mixtures screws(in front of carb) all the way in, then turn each out 1 1/2 turns. Start truck, get it warm enough to idle, then slowly turn screw in til motor starts to slow down, then back it out 1/4 turn. Do each separately, but in the end they should end up about the same no. of turns out. Make sure the idle is slow enough to make idle mixture screws work. If turning them doesn't make any difference(like bottoming them down and it doesn't stall) then idle is too high to allow idle circuit to function.
I for one don't care for that style of carb, but they seem pretty popular. I'm a Holley guy, as three of my toys have TWO bolted on top of the engine.
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Last edited by Freightrain : 11-15-2007 at 01:24 AM.
I still have the stock holley 4v for that engine. I could have rebuilt it several times in the time I've spent monkeying with this edelbrock - always idle issues. At this point I'm glad I kept the holley and will most likely rebuild it this winter and change it out just to compare. But, for now I'll just focus on trying to adjust the EB so it will idle for long periods when its completely warmed up. Thanks for the instructions.
I would connect a timing light, and see it the timing returns to the same spot every time. This will give you an indication if the advanced is working properly. If stable then proceed with the carb adjustment. All indications is out of adj, or linkage is binding and not returning to the idle stop. I'm a holly guy and do not like the EB carbs.
Maybe I spoke too soon. Each of the last two times I drove the beast, it had trouble idling for a period. The first time I fiddled with the idle jets again, but I put them right back where they were (1 3/8 turns out) and it was fine then. The second time, I didn't let it warm up as long and it happened half-way to the lumber yard (three miles away). I revved the p _ _ _ out of it but that didn't help, it just died when I let off the throttle and stumbled on acceleration. So I held my foot on the pedal at the rest of the lights until I got there. After it sat for ten minutes, it started and idled just fine and carried the gravel without any hesitation all the way home.
It has an automatic choke, so I suppose another adjustment of that might help, but I doubt it. I've checked the timing with the light and it always returns to the same spot - when it is running O.K. I haven't figured out how to check it during the periods when it won't idle. I suppose I could start it cold and let it warm up in the driveway with the timing light hooked up and just let it idle until it exhibits the symptoms and try to see if the timing light provides any useful indications. The frustrating thing is that it doesn't seem to do this every time I drive it. Any other ideas what to check?
I agree with Freightrain, This isn't a plug issue but a carb issue. Idle miture set wrong or a blown power valve will do this.
Or a leaky float needle and seat.
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- art k. - Moderator for the Superduty, V10, and FE forums
'01 F250SD SC SB XLT V10 4x4 auto 3.73 Volant CAI, eBay headers and y-pipe
'97 Cougar XR7 30th Anniv Edition 4.6L
'74 F250 Highboy FE390 deceased! I've been wrong before, I'll be wrong again. Just wait and see.
Ah, didn't read that about the choke - Is it electric, and if so, where is it wired to? Alternator? Or key-on hot 12V? And when it does the poor idle/stumbing, is the choke fully open?
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- art k. - Moderator for the Superduty, V10, and FE forums
'01 F250SD SC SB XLT V10 4x4 auto 3.73 Volant CAI, eBay headers and y-pipe
'97 Cougar XR7 30th Anniv Edition 4.6L
'74 F250 Highboy FE390 deceased! I've been wrong before, I'll be wrong again. Just wait and see.
The choke should be wired to the stator on the alternator.
The connection with the black banding on back of alternator and casted on alternator with the letter "S".
The choke should be wired to the stator on the alternator.
The connection with the black banding on back of alternator and casted on alternator with the letter "S".
According to Holley:
WARNING: Correct polarity must be observed when connecting the electric choke wires. Connecting the (+) lead to
ground and the (-) lead to a 12V source will result in a direct short and could cause a fire. The 12V source
selected should be fused. If not, an inline fuse rated at 10 amps should be installed.
13. Connect the long wire from the kit to the positive choke cap to the terminal marked (+). Connect the other end of the wire to
an ignition activated 12V source. The choke cap should only get voltage when the engine is running. Check your voltage
source with a voltmeter.
NOTE: Holley does not recommend using the 12V side of the coil for your power source.
WARNING: Connecting the choke cap to the ignition coil will result in unacceptable choke operation, and could cause
engine misfiring, resulting in possible engine damage. Do not connect the choke wire to the coil!
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Built Ford Tuff With Good Ford Stuff
79 F-250 X-Cab 4x4 6.9 Turbo Diesel
64 Falcon X-Ram 428
55 FORD Truck 4-link Rides on air with X-Ram 428
67 Stang 351 C/J
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The choke should be wired to the stator on the alternator.
The connection with the black banding on back of alternator and casted on alternator with the letter "S".
Only if you have a less than 12 volt choke heater.
390 - Hotter plugs needed?
