The idle mixture screws affect the mixture fed through the tiny ports swept by the throttle valves. The idle screws affect little more than the idle. If your carb is running way too rich at speeds well above idle and the choke plate is in the full vertical position, there is probably something more complex wrong with this particular carburetor.
Help Needed For Fast Idle Adjustment For a Motorcraft 2150 Carburetor
- Thread starter Bellavita
- Start date
Thanks to all of you for your help! The choke plate would never reach full vertical postion and even when I'd put it there manually it was still running rich. Upon removing it, there was fuel leaking from the bottom side of the carb because everything was wet with gas. It has been removed, drained, dried and returned.
This post is to thank all of you for your tips on getting the 2150 set. The third carburetor I got was installed yesterday and was able to get it adjusted! 
To make it possible to adjust the fast idle, I slipped a piece of fuel hose over the screw to create a handle adjustment. This allowed me to dial it in easily. The other item is the mixture screws are out about 3 turns to get maximum vacuum and smooth idle. I got it idling per spec right at 700 rpm @ at nice 20" of vacuum. I took it for a short trip and so far it is working good.
Again many thanks for all your help.
To make it possible to adjust the fast idle, I slipped a piece of fuel hose over the screw to create a handle adjustment. This allowed me to dial it in easily. The other item is the mixture screws are out about 3 turns to get maximum vacuum and smooth idle. I got it idling per spec right at 700 rpm @ at nice 20" of vacuum. I took it for a short trip and so far it is working good.
Again many thanks for all your help.
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Great job! I usually tune the idle mixture for greatest vacuum and then take it a hair richer for easiest starting and good idle in cold weather.
I may do that. Is a hair richer an 1/8 of a turn out? Thank you for the tip!
That would be totally reasonable
Hello Everyone,
I'm writing to share with you I have my first mileage check with the new Motorcraft 2150. I got 19.75 MPG! This was with mostly highway driving at 55 mph with some city mixed in.
The best I ever achieved with the Motorcraft 2100 was only 16 mpg so my mpg has increased a whopping 23.4%!
Both carburetors start and idled excellent and both had idling vacuums of >20 in of Hg with no engine vibration, smooth as silk.
The only difference is with the 2100 there was almost instant response to the gas pedal. With the 2150 I have to press the gas pedal more. The 2150 wants me shifting out of the gears very quickly.
A number of you are experts on the Motorcraft carburetors and was wondering if this improvement over the 2100 was through engineering improvements. I know the 2150's were better for emissions.
Thank you!
I'm writing to share with you I have my first mileage check with the new Motorcraft 2150. I got 19.75 MPG! This was with mostly highway driving at 55 mph with some city mixed in.
The best I ever achieved with the Motorcraft 2100 was only 16 mpg so my mpg has increased a whopping 23.4%!
Both carburetors start and idled excellent and both had idling vacuums of >20 in of Hg with no engine vibration, smooth as silk.
The only difference is with the 2100 there was almost instant response to the gas pedal. With the 2150 I have to press the gas pedal more. The 2150 wants me shifting out of the gears very quickly.
A number of you are experts on the Motorcraft carburetors and was wondering if this improvement over the 2100 was through engineering improvements. I know the 2150's were better for emissions.
Thank you!
Definitely not an expert, but it sounds like your new carb is calibrated leaner than the old one, hence the better MPG and the loss of power. Does the engine surge at all? Do you hear more pinging than before? How do the spark plugs look after driving it a while?
Awesome questions ripcord. I'd say it surges a little when warming up but is fine when at temp. There is no pinging. I'll check the plugs after I've racked up a few more miles. I just changed two of the six so I'll look at those.
Thank you for your insights.
Ripchord, question for you. When you say calibrated are you referring to the size of the jets?
Jets are part of it. Also the total CFM, ventri sizes, possibley vacuum setting of the power valve.
If your 2150 came from a different application than AMC, it might be good to see what jets and power valve AMC used in CJs.
If your 2150 came from a different application than AMC, it might be good to see what jets and power valve AMC used in CJs.
Jets are part of it. Also the total CFM, ventri sizes, possibley vacuum setting of the power valve.
If your CJ, I would expect it to run best with around #45 to #47 jets, 1.08 ventries, and an 8.5 lb power valve.
If your CJ, I would expect it to run best with around #45 to #47 jets, 1.08 ventries, and an 8.5 lb power valve.
Great info. I'm going to look up the specs of my 2100 and compare to those of the new 2150.
I'm very grateful for the precise detail you provided, thank you.
Hi Everyone,
I found the root cause as to why my CJ7 lacked easy acceleration - a worn out 37 year old vacuum advance. I don't know how it entered my mind to replace it but I did and the change was huge in starting and acceleration. Instant starts, immediate rise to cold idle and when driving it takes little force on the gas pedal to accelerate to shift through the gears. Spirited driving has returned!
I found the root cause as to why my CJ7 lacked easy acceleration - a worn out 37 year old vacuum advance. I don't know how it entered my mind to replace it but I did and the change was huge in starting and acceleration. Instant starts, immediate rise to cold idle and when driving it takes little force on the gas pedal to accelerate to shift through the gears. Spirited driving has returned!
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Excellent! Great job! You'll no doubt see improved fuel economy, too.
Good Morning Ripcord,
You were right. I just measured my fuel economy today. With a mix of 80% highway, 20% city, I got 20.14 mpg! The new 2150 carb got me to 19.75 mpg and the new vacuum advance added another .39mpg! A 2% improvement.
In 1986, the CJ7 was rated at 15 city, 20 hwy. and 17 mixed. My 37 year old CJ is running as good as new!
