On a 77ford351 *** can ii tell if the choke. Thermostat. Is bad

Tiny
JUMPINJERRY
  • MEMBER
  • 1977 FORD F-150
  • 15,000 MILES
After it warms up the chokewill not open.
Do you
have the same problem?
Yes
No
Sunday, October 2nd, 2011 AT 6:22 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
Thermostat has nothing to do with the choke. Look for a metal tube between the right exhaust manifold and choke spring housing that is rusted off. Air is heated in that tube then drawn through the housing to heat up the choke spring. Many years ago there were repair kits for that system. It involved drilling a really large hole in the manifold, inserting a special plug that a new pipe was attached to, and running that pipe to the choke housing. I haven't seen one of those kits for at least 25 years. You might have to fashion something by wrapping a length of steel brake line tubing around the manifold a bunch of times, then up to the housing.

There's also a small piston in the housing that uses engine vacuum to partially open the choke blade when the engine starts. If that isn't working, it could be plugged with carbon. That will make it run real rich for a few minutes until the heater opens the choke all the way. If the tube is the problem, the engine will run okay for the first two or three minutes, then run rich continuously after that.
Was this
answer
helpful?
Yes
No
Sunday, October 2nd, 2011 AT 6:52 PM
Tiny
JUMPINJERRY
  • MEMBER
Ok can the the spring in the choke. Housing go bad. N can I have put the spring in backwards. N what tube uses vacuum. Only have 2one to the choke. N one to the upper part of the carb. N can I heat the tube to see if the choke. Will. Open. The choke pull off opens it but. It stays running high unless I kick the throttle. Down. Then even. After it warms. Up shut. It down start it kkeeps running high unless I kick it down
Was this
answer
helpful?
Yes
No
Sunday, October 2nd, 2011 AT 7:21 PM
Tiny
CARADIODOC
  • EXPERT
What are all those "N"s? It's really hard to figure out what you're trying to say but I did get that there's two tubes. The supply tube starts inside the air cleaner housing because the heated air is going to end up in the engine. From the air cleaner, it goes down to the exhaust manifold where the air gets heated, then the tube continues up to the choke spring housing. Engine vacuum draws that air, now heated, across the thermostatic spring. As that spring warms up, it uncoils and the end pulls the linkage to pull the choke blade open.

When there's a break in the tube between the exhaust manifold and the choke spring housing, the air drawn in won't be heated, the choke won't open, and the carburetor will stay on fast idle.
Was this
answer
helpful?
Yes
No
Sunday, October 2nd, 2011 AT 8:40 PM

Please login or register to post a reply.

Recommended Guides