Carb Question
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Tuned
Joined: Aug 2003
Posts: 346
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From: Eastern Virginia
Carb Question
I'm finally getting around to tinkering with my '78 F250. 400 engine. Finally got the radiator issue resolved, and now i'm working on another minor problem that I have noticed since I have had the truck.
On cold start and drive-away the truck performs flawlessly. Starts up with a pump of the accelerator and runs smoothly at a high idle. Tap accelerator, idles down, put in drive, accelerates great. Fast-forward to warm engine. As soon as the choke opens up the truck seems to get sluggish on the highway, hills, etc. Off idle acceleration isn't bad. Sometimes a slight stumble off idle.
Seems to me the engine is starving for fuel after the choke opens. I have rebuilt the carb. No change. New filter, etc. Float is set at factory specs-wet. The closest I can find on the setting WET is 13/32.
Truck has 22,000 miles. Runs awesome with choke partially closed when cold. When warm the sluggishness appears and is accompanied by a slight hissing under the hood when accelerating. Recent tune-up, timing set to specs, EGR disconnected-no change. I think I was the first to rebuild the carb. I tried not to change any factory settings....good and bad maybe. Everything else underhood is pure factory.
Where do I look next?
On cold start and drive-away the truck performs flawlessly. Starts up with a pump of the accelerator and runs smoothly at a high idle. Tap accelerator, idles down, put in drive, accelerates great. Fast-forward to warm engine. As soon as the choke opens up the truck seems to get sluggish on the highway, hills, etc. Off idle acceleration isn't bad. Sometimes a slight stumble off idle.
Seems to me the engine is starving for fuel after the choke opens. I have rebuilt the carb. No change. New filter, etc. Float is set at factory specs-wet. The closest I can find on the setting WET is 13/32.
Truck has 22,000 miles. Runs awesome with choke partially closed when cold. When warm the sluggishness appears and is accompanied by a slight hissing under the hood when accelerating. Recent tune-up, timing set to specs, EGR disconnected-no change. I think I was the first to rebuild the carb. I tried not to change any factory settings....good and bad maybe. Everything else underhood is pure factory.
Where do I look next?
Thread Starter
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Tuned
Joined: Aug 2003
Posts: 346
Likes: 0
From: Eastern Virginia
Yes, thanks. I think it has been narrowed down to a vacuum leak. Now I just have to figure out where....The handle broke off my plastic MityVac pump, so I have to work it with pliers. Not fun. New metal pump should be in later this week.
Moderator
Joined: Dec 2001
Posts: 22,436
Likes: 17
From: Louisville,Ky.
Does it still have an egr valve? Verify that it isn't stuck open. I would take some carb cleaner and spray down along where the intake meets the heads and around the base of the carb when warm and see if the idle picks up.
Thread Starter
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Tuned
Joined: Aug 2003
Posts: 346
Likes: 0
From: Eastern Virginia
Thanks LxMan. I checked the EGR valve when I had the carb off. Actually it was plugged tight with carbon. I'm finding a mess of vacuum leaks. Even though the truck only has 22K miles, the vacuum components are shot.
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