my 79 f250 4x4 with 400 2bbl has a hard time starting after it sit for several hours. it starts if i shoot carb clean in the bowl vent. could it be the float level is to low and the little fuel that is stored is not enough to start the engine. or maybe the float gasket is leaking? once it starts it runs great. any ideas?

 

anyone?

 

You should be posting the truck forum that relates to your truck.
This engine forum is for this series Engine specific questions.

ie: Stroke,size of pistons,measurements,Torque values.

That kind of stuff.

Your problem is more truck oriented not engine specific.

Dennis

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Take the air cleaner off, and with the engine off, push back on the throttle. You should see two streams of gas flowing into the carb throat. This should be enough to get it started. If you don't have any gas shooting in, I would suspect the accelerator pump system in the carb. Go ahead and rebuild the carb and see if it fixes it.

 

the accelerator pump does work fine. thats what makes me wonder. i am going to take the carb apart when i get time and repace all gaskets and float.

 

I was assuming the engine was starting on the cleaner because there was no fuel(I think you are too). But if it will squirt gas, then it is getting fuel, and there is fuel in the fuel bowel, because that's what feeds the accelerator pump. Might have to experiment a little more on this one.

 

[updated:LAST EDITED ON 09-Dec-02 AT 03:49 PM (EST)]Is the choke coming on? Is it cold where the truck is?

Does it turn over at the "normal" speed (IE not slow)

How long does it sit for? An hour, or over night?

Post back and I will try to help more,
-Brents

 

[updated:LAST EDITED ON 09-Dec-02 AT 09:16 PM (EST)]yes it is cold here in chicago. turns over good. it only does it somedays though. it started fine this morning, but when i got out of work 8 hours later it was hard to start again? once its warmed up its fine. ps. once its running it idles a ltlle rough and smells rich. otherwise the truck runs great. no hesistation or missing?

 

I sometimes have the same problem with my truck.

This is what happens to me:

After starting the truck when it is truly cold (IE after sitting for >10 hours, like overnight) it starts and runs fine. If I start the truck, let it warm up, then drive to work, all is OK.

Then at lunch time I go to the truck to go home (after 4 hours), and the choke comes on. It comes on when I touch the gas pedal. The problem, as I see it, is that the choke/carb is cold enough to come on (sometimes fully), yet the motor really isn't that cold because it's only been sitting for 4-5 hours (the motor has a very long thermal time constant).

This causes it to either not start, or if it does start it runs really rich.

So, if this is what you think is happening to you, put your foot to the floor when you try to start the truck. This will hold the choke open, and it may start a little easier.

Hope this helps,
-Brents

 

[updated:LAST EDITED ON 10-Dec-02 AT 11:43 AM (EST)]rustynuts, et al,

One of the more common problems with cold starting and cold-temp driveability is a faulty or misadjusted choke pull-down motor.

At cold temps, the choke should close completely, producing maximum air restriction and a very rich fuel/air mixture for easier cold starting. As soon as the engine begins to run, manifold vacuum supplied to the pull-down motor diaphragm opens the choke plate slightly to lean the choked mixture a little bit for idle warmup.

If the pull-down motor diaphragm is bad, it allows a vacuum leak, which leans out the mixture and causes idle quality and driveability problems.

If the pull-down is not adjusted properly, it will cause either over-rich or over-lean mixture during warmup. In general, idle quality and driveability problems are caused mostly by over-lean mixture.

BTW: Don't assume your problem is an over-rich mixture just because you can smell fuel in the exhaust. Lean misfire causes a lot of unburned hydrocarbons to go out the exhaust. The main symptom of an over-rich mixture is conspicuous black smoke (soot) in the exhaust.

On most later model Motorcraft 2150 2V carbs ('77-up), the pull-down motor is attached to the right rear of the carb body, just behind the choke mechanism on the side. The choke pull-down motor is labeled #2 in the following pic:

http://home.earthlink.net/~bubbaf250/graphics/2150/2150_rside_01S.jpg

The pull-down motor vacuum source is a port on the right rear of the carb, just above the bottom edge on the base flange. That port opens into the lower passages of the carb, below the throttle plates.

An adjustment screw on the back of the pull-down motor's diaphragm chamber allows you to adjust the amount that the motor opens the choke plate when vacuum is applied. It should pull the choke plate open by about 1/8" to 3/16" (as measured between the front edge of the choke plate and the inside surface of the choke tower).

For more explanation of choke and general carburetor function, check out this page:

http://home.earthlink.net/~bubbaf250/2150carb/carb02.html