carb tuning, fast idle

Reply Subscribe

Thread Tools

Search this Thread

May 10, 2012 | 08:35 AM

siloketh

Thread Starter

Senior User

Joined: Jan 2012

Posts: 331

Likes: 0

From: Redneck Paradise

carb tuning, fast idle

Recently my truck started idling a bit higher than normal over the weekend so I didn't think much about until I noticed a slight decrese in mileage. I dont know what caused the idle to change but its getting on my nerves. The only way i can describe the rpm change is using v8 idle range which 500rpm is normal but I would compare it to 1200rpm at idle on my truck.

My truck is equipped with a single barrel wiend carb electric choke. Is there something wrong in the electronics or do I need to adjust the carb to idle lower when warm? By the way, I dont know how to adjust a carb and all my buddies are fuel-injected...figured I should add that bit in there.

I've had this truck since december and never had this hiccup before. Any help is greatly appreciated. Thanks once again guys

May 10, 2012 | 09:37 AM

Harte3

Postmaster

Joined: Dec 2006

Posts: 3,603

Likes: 10

From: Spokane, WA

Check for vacuum leaks first. If there is one or more you will end up chasing your tail trying to adjust the carb.

May 10, 2012 | 10:18 AM

1986F150six

Lead Driver

Joined: Jul 2009

Posts: 6,477

Likes: 19

From: Sheffield, AL

Quote:

Originally Posted by siloketh

As Hart3 said, check for vacuum leaks. The 1 barrel carburetor is held down by two bolts which tend to vibrate loose. See if you can move the carburetor or air cleaner assembly back and forth. If it moves, they are loose. Take a 1/2" wrench and gently snug them. Check all of the screws which hold the top of the carburetor. There are 4 screws on the bottom of the carburetor, but the carburetor has to be removed to access these.

This engine really acts up when vacuum leaks are present, so check all vacuum hoses and ports. There are ports [often times capped off] on the intake manifold tree and on the firewall [passenger side]. These caps can get brittle and crack or fall off. Some of the vacuum lines are originally plastic and get old and crack. They can be replaced with rubber vacuum hose [do one at a time so they do not get crossed up].

Check the throttle shaft for excessive play and try disconnecting the throttle cable to see if the cable is binding.

May 10, 2012 | 10:31 AM

siloketh

Thread Starter

Senior User

Joined: Jan 2012

Posts: 331

Likes: 0

From: Redneck Paradise

Thanks once again ya'll. I will check for the vac leaks and loosened bolts and go from there

May 10, 2012 | 11:19 AM

arctic y block

Post Fiend

Joined: Sep 2006

Posts: 14,325

Likes: 14

From: Island Southeast Alaska

1986F150six has said it all. And said it very well. Vacuum leak and or throttle plate bore worn are where to look first.

When this is eliminated come on back and we can help you adjust it if need be.

May 14, 2012 | 10:58 AM

siloketh

Thread Starter

Senior User

Joined: Jan 2012

Posts: 331

Likes: 0

From: Redneck Paradise

The bolts came loose over time. Snugged them down to spec in my haynes manual. The idle improved but was still a little high, so i adjusted the idle just a touch & now she purrs like a kitten sittin at the red light

thanks everyone once again for your help/advice