Idle Issues

[dmplatt]

Stock 302, 2150 carb (pretty sure...)

Two symptoms, not sure if they are related:
1. On cold startup, the truck settles into a very low idle speed immediately
2. Under acceleration and partial throttle runs nice and smooth, but at idle and every stoplight it surges pretty badly and wants to stall.

Is this a vacuum leak issue? Are they related? Where do I start!?

 

[DuctTape]

If it is a stock carb and new to you, I'd start with a good cleaning. If you don't get improvement check vacuum, then timing. If you haven't already, do a tuneup, including replacing spark plug wires. If none of that does it it is carb rebuild or new carb time.


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[DirtDonk]

Checking the tune-up settings is key. You need to know if the ignition timing is correct, and if the carburetor adjustments are correct, and basically if everything is performing up to snuff.
Vacuum leaks always worth checking for. Could be any number of areas on an old carb'ed motor.

Do you know if it's points ignition or electronic?
What year truck?
Automatic or manual trans?
Modified exhaust or stock?
Generally in good condition, or just so so?
Vacuum advance hoses hooked up?

Are you familiar with old cars and how they work? Not a silly question really, as it's been a long time since a carburetor was put on a new vehicle and I don't know your specifics.
When you start it up cold, are you pushing on the throttle pedal to set the choke before engaging the starter?
If you are doing that, do you feel the clicking associated with that function?
Have you pulled the air cleaner off to see if the choke plate is closing down over most of the carb opening?

And as DT was asking, you had this very long and know what kind of mileage on it since it's last tune-up?

Good luck. Keep the questions coming, but put a lot of extra info about your truck too please.

Paul

 

[jckkys]

The symptoms are actually minor. First the choke seems to be doing nothing and likely needs no more than an adjustment. The idle probably just needs a simple mixture and speed adjustment too. A rebuild kit is the best source of set up and adjustment instructions for your 2150, the OE carb on '76 Broncos. That's assuming your public profile is correct. A few tools make these adjustments possible. Any parts store will have an engine analyzer that includes a tachometer, volt meter, ammeter,etc. These are only about 15-20 bucks. Next a simple vacuum gauge. An inexpensive timing light and spark plug feeler gauge will let you do simple tuneups. Mike's Carburetor has a lot of tune up and adjustment videos to let you see how and where the adjustments are made. The rebuilt kit has great illustrations and diagrams, but most importantly the specifications for your carb. The parts needed to perform a rebuild are a bonus. Vacuum leaks are possible but not the first place to look. A local classic Mustang club is a good place to find people who understand Ford carbs and know how to get them running well.