This is a 1980 F150 4X4 302ci, manuf. in Calif. Has air pump, thermactors,
catalytic converter, etc., etc.
Carb is a Motocraft 2150, no tag, - engine calibration = EOTE-9C485-ADB.
It will try to idle if I crank the idle adjustment screws out 3 1/2+ turns each, but you have to stay on the throttle to even try to drive it. It will run fine on fast idle (choke closed) 1500+ RPM. When you finally get to the highway, it
will start flattening if you give it to much gas. If you tease the throttle, it will
get up and go. When this happens, the choke is open an the engine warmed up.

I removed the EGR vac. hose from carb, and capped the connection at carb.
The distributor is connected to vacuum port at left front of carb, along with
purge valve vac. port - purge output to carb has been removed and plugged.
PCV is connected to back of carb.
Choke stove air line is of course broken, hose is connected direct from carb horn to input on choke. Choke is controlled by 12v internal heater.
Tank internal, sender filter replace, fuel lines good, pump good del. and pres.
Filter at carb replaced with viewable filter to observe flow, and fuel cap is ok.
Timing is set at 8 degrees
Cylinders have good match in compression, about 125 each
When I can get it to idle, all warmed up, tongue held just right, etc., the
vacuum sits at 19" and is steady, no drift, running down hill with no throttle, 25".

I have done the following test: set both idle screws at one turn out, (about
where they should be), got it started, and held the idle at 1200 RPM. A helper sprayed short bursts of carb cleaner around gaskets to check for leaks. On the passenger side of carb, the RPM jumped up to 2000 RPM.
When I got ready to replace the gaskets, I tried the test again with me doing the bursts. I first adjusted the carb screws out 3 1/2 turns and tried the test again. I could not reproduce the jump to 2000 RPM. I turned the screws out
from 1 turn to 3 1/2 turns because my wife could not have kept it running at 1 turn out.

Folks, I have been messing with truck for ever, as time permits. I have had and tried bunches of suggestions, nothing seems to make a difference. I
replaced a 2150 rebuilt by Holley with a "yea it worked great" used carb because I could not tear down the rebuilt - small screws holding the throttle plates twisted off.

Thanks in advance - Ray

 

I had a similar problem and this is what happened:



EGR was leaking exhaust out, and letting unmetered air into the carb. Its the gasket underneath the EGR spacer on the manifold.

 

Thanks BOGGERTED for your information and trouble.

Once upon a time, I had the truck running on it's present carb. well enough to make a 60 mi round trip. At that time, I had to let it warm up to operating temperature to
avoid dying at intersections. At the end of the trip, while slowing for a stop light, it back-fired. It was all I could do to get it home (6 blocks).

Is it true that anytime you have a back-fire, it will take out the power valve in the
2150 carb? At anyrate, that back-fire could cause what you have shown above.

Ray

 

The back fire could take out the power valve, but when that happens it runs very rich. From your description of turning the screws way out, it sounds like you are running lean trying to overcome a vacuum leak somewhere. I would check on the gasket, and also check the egr valve. Just because you have the vacuum line off, doesn't mean it's sealed off inside. It could have a piece of carbon holding it open. You can make a temp block-off gasket it you want to experiment.

 

Thanks FRANKLIN2 - this is all beginning to make a lot of sense, explains the
original rebuilt carb. When I first test drove the truck, it back-fired violently
several times trying to start, had been sitting long time. The truck always
smelled rich. So I have swung from one side to the other.

I understand that you dare not use a sealant with the carb. stack gasgets.
How many times should you retighten the carb. hold-down nuts, and when, after
it cools back down, or while it is still at temperature?

Thanks
Ray

 

After it cools back down, you can check them, but they do not need to be too tight. You can warp the bottom of the carb if you get them really tight.

 

Thanks again Franklin2 - I'll check the casting to make sure it is not warped. I think I
used 12 ft/lbs (144 in lbs) of torque and a gradual diagonal pattern before, but I did not check it. I will be putting a blocking temporary test gasket in the EGR system to
make sure the EGR is not an issue. I will get that carb cleaned up and rebuilt before I
reinstall it.

Ray

 

I have rebuilt the 2150 carb, but do not have it on the truck yet. During the removal
of the carb I found no less than THREE vacuum leaks, the choke kick off had a blown
diaphram, a vacuum port that I did not know was on the carb, had a short OLD hose
on it with a coarse thread metal screw stuck in the end as a PLUG? And, the bolts
holding down the carb were not that snug, gasket leak previously noted makes sense.
Now, this 2150 is one of the later models with the open throttle mixture adjust to rich. I have six vacuum connections on this carb, ported to dist. ported to EGR, non
ported through choke from choke stove, choke kick off, non ported pcv at base carb, and dead center, just under the driver side ventura booster output is the sixth vacuum connection, this is the one that was plugged, what is it for. Also what is a good dry float setting on this 2150 - is 7/16 close or correct? Hope you enjoy the update.

Thanks to all
Ray

 

I've used copper spray gasket on carb and TB gaskets and never had a problem...also gives you some other security with leaks.....

JR

 

The kit should have a chart that tells you the float setting, as well as a little paper gauge to set it with.

 

Thanks JR and Dave F
JR I'll check out the gasket material immediately.

Dave F
Your right, the foot notes had me fooled. They use one column for both specs, and
foot notes for wet measurement. You caused me to go have another look, IT WORKED.

I got the needed gasket material for that EGR test gasket. Also, I found the vacuum
system had been changed to bypass the VCV, so instead of the EGR being pulled in
after warmup, it is dumping in on a cold engine above idle, nuts.

Both you folks have a good week.

Ray

 

If it's a paper gasket.....the stuff I'm talking about you just spray on...comes in a can...blah blah blah...works great and I've assembled engines with it.Luck

JR

 

This is the best yet, I checked the existing dry float setting and found it at little over 3/4 of an inch. I then pulled the float and upper valve assembly for measurements. What came out of the carb is identical to the new parts that went in. There was little room for the float to function before it shut off the fuel supply. In addition, there is a thin wire damper spring on the float, keeps it from bouncing around. I will set the dry at 31/64" smidge less than a half. Looks like the fuel level should be 7/8" at warmed idle, leaving 25/64" smidge more than 3/8" of reserve fuel. What an education!

Thanks for the help!
Ray