Thanks to everyone who helped out with my Factory tach installation questions. Some great information received.

No here is one for the carb experts. I have two problems with my truck when it is cold. For reference it is an '83 F100 with a 302 2bbl 3spd auto bone stock.

1. Carb Icing - When it around freezing and damp out, I get severe carb icing. All the "carb pre-heat" stuff seems to be working fine... heat stove around manifold, vacum operated flap at end of air cleaner snorkle, etc.

Any thoughts on how to cure the problem?

2. Flooding symptom - When the truck is cold I have always snaped the gas pedal down to activate the choke and then started the engine. In the past it worked great... but lateley, when I turn the key the truck doesn't start. It acts like it is flooded and I have to depress the pedal almost to the floor and crank it until it fires up. When it does, it is just like starting a flooded vehicle... lots of black smoke and smell of gas. Once started and after 15 seconds or so, it runs fine.

I am suspecting the vacum operated unit on the carb that opens the choke flap a bit when the truck is started. It is supposed to open the flap to alow enough air in so flooding won't occur.

Comments?

 

I placed a manual choke cable on my carb and it works great. No more starting problems.

 

The diaphragm unit is called the "choke pull-off". True this could be bad, but when the problem happens is important. Usually if it's bad, the truck will fire right up, and then throw a fit. The choke pull-off only works once the engine is started and builds a little vacuum. If it won't start from the get-go, it might be something else.

It's easy enough to check it it's bad. See if the rod going to the diaphragm is pulled back when the engine is running. If not, and the hose is good, it must have a hole in it.

After a little checking, and you find it's not the problem, I would suspect a leaky float needle valve, or a leaky power valve. I would go ahead and put a kit in the carb. I have noticed too, that a carb running rich seems to have more of a freezing problem than a carb that is not. I wonder if it's the extra fuel evaporating?

 

Sounds like franky has the right idea. Gas evaps really fast taking away heat and allowing it to freeze. A good rebuild never hurt any carb. Any easier way to tell if the pull off is working is to use a vaccum pump or a long hose and provide human vaccum. You'll see it move if it is working.

 

Udate...

Seems a good choke cleaning and lubrication has fixed the starting problem. Starts and runs fine no.

The carb icing situation still a problem.

 

My hot air system is working correctly. I have noticed when the truck starts, and the flap in the aircleaner is shut, the metal hose to the exhaust manifold is warm, and after a few minutes, the aircleaner is warm to the touch.

 

i had a problem with the carb icing on my 80 300cid. there was a little vac leak which would not shut the damper all the way. so it was still pulling in some cold air. i replaced the vac line and now it works great.

 

My flap seems to be closed... at least when I check it at idle. Is it possible that it opens when I drive? Would it hurt if I stuck a rag in the end of the snorkle to make sure the flap stays closed all the time?

 

you want the flap to open when the hood tempture is at the the set range for the flap to open. that is what that disk does that is on top of the air cleaner with the vac hose on it. if you put a rag in the fresh air vent you maybe putting too hot of air from the manifold and start getting predetanation. i would think anyway. to see if the carb is really icing, if you shut the engine off for awhile (10 min) and start it then it runs good then i would say its a icing problem. if not it would be something else

 

The way I fix it is that I turn the engine off and wait 30 seconds and start it up again... it works fine then. I don't have to wait 10 minutes.