B2200, orig. carb:

This here truck won't come off of high idle when its cold outside (below 35 d. approx.).

Choke Unloader (more commonly known as Choke Thermostat):
(I assume that's what the 2" dia. round thing is on the back of the carb. that is electrically powered).

Things I've checked:

Voltage to the choke unloader - Meas. 7.5 v with eng. running and checked metal ground
on unloader to ground (good connection).

This problem goes away after I fool with the carb. and run it a bit. Makes me wonder if the unloader is bad/quits
working only when very cold? Sticking linkages maybe? Linkages seem to move freely though.

I don't know at this point. I'm thinking of trying a new choke unloader. Anyone know where I can buy this part?

Any other ideas or troubleshooting suggestions are greatly appreciated!

 

Is the choke plate closed with power to it? Can you manually open choke plate, and slow down the idle? That thing should move linear with the voltage applied, at 7.5 it should be 3/4 way or so open.

 

"Is the choke plate closed with power to it? Can you manually open choke plate, and slow down the idle? That thing should move linear with the voltage applied, at 7.5 it should be 3/4 way or so open."

Sometimes. When really cold choke plate don't open hardly at all.
Then sometimes you can see choke plate slowly go open after I start 'er up. She runs/idles fine when this happens. Just doesn't happen often enough.

The basic symptoms: Will not come off high idle on really cold days and choke is visibly not opening.

 

My "guess" is the coil in the electric choke is bad, you are spot on in replacing it.

 

thanks Kevin.

Ya, that seems like about the only thing it could be.
Now, where to get a replacement?

Follow up: OK! for those needing the Choke Thermostat (as it is commonly called) I called
NationalCarburetors dotcom. and they do have 'em. The guy quoted me $25 plus $3 to ship. That's
a heck of a deal if you need one.

But, I still wasn't quite convinced mine was bad, so this morning (nice and cold out in the garage)
I went out to have another look. I took the C.T. (choke therm.) off one more time to check the
electrical connections in this fricker.

1) I disconnected the power lead from the alternator (it powers this thing)

2) Meas. the resistance (continuity check) from the power term. to inside the CT housing.
1.5 M ohms (1.5 mil ohms). Virtual open circuit. AHA!
The culprit is revealed! This is why the choke was not opening on cold days.

3) At this point I didn't know if this part was available, so I attempted to fix it.
There is a rivet that joins the outside connector to the inside piece of metal
that goes to the heating coil. I set the C.T. up on the valve cover with a hex wrench
underneath said rivet and gave it a rap with hammer and punch from the other side.
Measured again. Near 0 ohms. FIXED!

Started her up and choke slowly opened (and carb came of Hi-idle) after a couple minutes
of running. Hallelujah!

Hope this helps anyone else with this type of problem.

Good Luck with Yours

Additional troubleshooting info:

Measured about 8 ohms from power connection on outside of C.T. housing to
ground plate also on outside of housing (after fixed). I assume this is normal
for a good one. (This was with power wire unplugged from Alternator).