Holley 390 problem
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5th Wheeling
Joined: Apr 2003
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From: Earth
Holley 390 problem
Just last week I installed a Offy intake manifold, Pacer headers and a Holley 4160 (390 cfm) carb on my '83 Ford F-150 4x4. The performance and acceleration improvement is great! That is until I disconnected the electric choke to see how it would run. With the choke unplugged from it's 12 volt source, the truck ran rough for about a mile. I then pulled over and turned the ignition off so I could reconnect the electric choke. When I turned the ignition switch off I got a very loud SWOSH out of the carb that lasted a couple of seconds. It sounded like the carburetor had an implosion. It scared the crap out of me because I thought I had severely damaged the truck. After reconnecting the electric choke, the truck started right up but idles very rough and hesitates severely on acceleration. Had to increase the curb idle from 600 to 750 rpm just to keep it running. Once I got up to speed on the highway it ran fine but when taking off and momentarily after upshifting I have a bad hesitation. I strongly suspect I blew my accelerator pump and may have damaged something else. Would appreciate some advice from any Holly 4160 (390 cfm) carb experts out there.
Jerry....Springfield, MO
Jerry....Springfield, MO
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Joined: Mar 2003
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From: Colorado
Holley 390 problem
... but from my new experiences, I'd guess you may need to rejet. What is your average altitude in Springfield? The instruction sheet that came with my Holley said to drop the jet size by one for every (approx.) 2000 feet above sea level. I've found that 46's are the best for my Bronco at 6,000'. Springfield ought to put you AROUND 48's - 50's. My 390 came with 51's. Check plugs and visible (black) exhaust for indications of a rich mixture. Mine ran great at WOT with the rich jetting while I waited for smaller jets. The plugs became carbon fouled (black powder coat) in a matter of days. The tailpipe did too.
I removed my electric choke as soon as I got to adjusting the vac /sec spring. Being electric, the choke has a plate that has to heat up every time the engine is off for more than a couple of minutes - even when the engine is warm and the weather is too. Removing the 12 volt source would leave the choke permanently "on" unless you wired it open.
I've had the "swoosh" a time or two - don't know what it is but it hasn't been anything but alarming so far. I believe it may have been "run on" from rich running/carbon deposits. I haven't had it since I got the mixture leaned down.
I removed my electric choke as soon as I got to adjusting the vac /sec spring. Being electric, the choke has a plate that has to heat up every time the engine is off for more than a couple of minutes - even when the engine is warm and the weather is too. Removing the 12 volt source would leave the choke permanently "on" unless you wired it open.
I've had the "swoosh" a time or two - don't know what it is but it hasn't been anything but alarming so far. I believe it may have been "run on" from rich running/carbon deposits. I haven't had it since I got the mixture leaned down.
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5th Wheeling
Joined: Apr 2003
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From: Earth
Holley 390 problem
Broncr....Thanks for your help. I'm going to pull the carb off tomorrow and thoughly inspect it for any obvious defect. Probably blew a gasket or maybe even the power valve. It acts like a vacuum leak but manifold vacuum is reading about 16 hg...the same as before. No vacuum leaks detected. The electric choke is good in cold weather but during the summer months I'd like to try what you did. You said the choke plate can be "wired" open. Any special technique there? How do I know what size jets my Holley 390 came with? Altitude here in Springfield is about 1300 feet.
I lived in Colorado for 15 years until my job transferred me to Missouri about 3 years ago. I lived in Aurora and worked in Englewood. Where are you at?
I lived in Colorado for 15 years until my job transferred me to Missouri about 3 years ago. I lived in Aurora and worked in Englewood. Where are you at?
Hotshot
Joined: Oct 2002
Posts: 18,488
Likes: 22
From: The Big, Oregon
Holley 390 problem
Jerry- what you did was drive with the choke closed. Modern Holleys have power valve blowout protection, so I wouldn't wory about that . Just change your plugs, and see what it does. And make sure you keep the electric choke hooked up- It's the only thing that keeps the choke open when the engine is warm.
Elder User
Joined: Mar 2003
Posts: 628
Likes: 0
From: Colorado
Holley 390 problem
... unless you're willing to undo it on the side of the road somewhere. I'm not proud, I'd just drive my Bronco to the end of the road tomorrow - without any unusual concerns.
I used a piece of "bailing wire" to hold the choke open - just worked the choke/throttle and did the obvious - wrapped the wire around the butterfly lingage and attached it to something so it COULDN'T CLOSE.... Right now it's warm and I've been tuning the vacuum secondaries - so I don't even have the choke on. When it does goes back on, the choke will be a manual I have from an old Holley 600 cfm 4150. I've never had an automatic choke that didn't give me some kind of trouble eventually.
As for YOUR jets, the only way to be certain is to pop the front float bowl and look at one. They're screwed into the metering block which is between the float bowl and the carb body. Use a LARGE standard screwdriver to remove one/them - try not to "nick" the inside of the jet. They've got a number/size stamped on the outside.
I've seen recommendations that you shouldn't change more than
one jet size at a time, but I dropped three as soon as I could and ended up two lower than that.
I grew up in Colo. Springs and now live in Castle Rock.
I used a piece of "bailing wire" to hold the choke open - just worked the choke/throttle and did the obvious - wrapped the wire around the butterfly lingage and attached it to something so it COULDN'T CLOSE.... Right now it's warm and I've been tuning the vacuum secondaries - so I don't even have the choke on. When it does goes back on, the choke will be a manual I have from an old Holley 600 cfm 4150. I've never had an automatic choke that didn't give me some kind of trouble eventually.
As for YOUR jets, the only way to be certain is to pop the front float bowl and look at one. They're screwed into the metering block which is between the float bowl and the carb body. Use a LARGE standard screwdriver to remove one/them - try not to "nick" the inside of the jet. They've got a number/size stamped on the outside.
I've seen recommendations that you shouldn't change more than
one jet size at a time, but I dropped three as soon as I could and ended up two lower than that.
I grew up in Colo. Springs and now live in Castle Rock.
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