The 2150 carb has a vacuum port in the choke housing that continually draws heated/filtered fresh air through the housing, & into the intake manifold, keeping the spring hot & the choke open.
Mine is converted to a manual choke, which means the port is now sucking unfiltered air into the manifold.
I can easily block it off, but this will enrich the mix compared to the original set-up.

I'm wondering how much of a difference this would make to the mix?
I've removed the EGR previously, so maybe a slightly richer mix would be an advantage now anyway?

Thanks

 

The original 2150 on Dad's truck has both that hot air port as well as an electric choke heater. The hot air stuff was rotted out when I got the truck and the electric choke wasn't hooked up. In fact, it couldn't have been hooked up since there was no factory wiring for it, although the factory shop manual, the factory wiring diagrams, and the EVTM all show the wiring. So I hooked it up to the Stator terminal on the alternator, blocked the port that was drawing air, and it worked well.

I can't tell you if it actually made the mix any richer, but logic would say that it should. I didn't have to adjust the idle mix any, which is where it should be most noticable. But, I'm not confident that the EGR is working properly either, so...........

 

OK, thanks Gary.

Regarding the 2150 on Dad's truck, do you know what jets it had?

My original choke question was for the feedback carb on my truck, which is now running okay without the computer; but I've scored a rebuilt non-feedback 2150, free, with the correct venturis for my engine - 1.21 (the f/back carb is a 1.08 from the original 302 engine)......except it has 60F jets, which I thought may be a bit rich.

What do you think?

 

I will look to see what jets it has. But, with Bruno & Jason showing up in 30 minutes to work on the Bronco, and Marshall and friend showing up later to get the bed for body work, today looks to be a bit busy. And, I'm still having a cuppa.

 

I have run into this same problem, there is a lot of air introduced into the carb from different sources, and when you strip the emissions, you lose some of this air and I have had rich idle problems. What I have done is taken that port, or another convenient vacuum port, and hooked it straight to the nipple that hangs down underneath the aircleaner flange on the back of the carb(the original port where the choke hot air system drew air). This cleans up the exhaust smell that you sometimes get from these trucks, and also helps the idle on a older engine that is half wore out.

What I have also found is it lets you turn the idle stop screw back. This is important if you find you have a slight vacuum on your ported vacuum hook up going to the dist. If you have a slight vacuum on the dist, you will run into idle problems and such, but sometimes you can't close the butterflies in the carb enough to get rid of it. The intentional "vacuum leak" that you introduce will help this problem also.

Most of the time these small vacuum leaks do not affect the higher rpm operation. But in this day and age of overdrives and very low rpm cruising for high mpg, they canm have some affect when driving down the road and you are barely on the throttle.

 

I used a late 2100 1.14 venturi on my 351W jetted with 51's. For me it seemed about right. The plugs looked great and the tail pipe was nice and gray. It was a little cold shouldered, but not really seriously. With 3.55's and an NP435, I still was able to get 16.6+ mpg very consistently when driving reasonably 55 or so. (I know, but I'm not in a hurry these days)

I timed the diz by vacuum, and tuned the Idle air as well by vacuum.

I DID block the air leak, and used the stator post for choke. It wasn't my preference (I like manual) but it worked acceptably till I sold the truck.

I know the question was For Gary, I hope you didn't mind my recent experience.

 

No, not at all John - thanks for the insight. I've been combing the site for jetting info & experiences for the last day or so.

From what I've picked up............with a 1.21 venturi, no EGR, & being at sea level, maybe #60 jets won't be too far off. Or close enough for a good start anyway.

Thanks.

 

Thanks, Dave.
Vacuum/carburation is one of those areas that you just seem to keep learning something new in.

Right now the (feedback) carb with this open vacuum port is giving me white plugs, so I don't think it should be a problem blocking it off.

 

Well, I've just removed the feedback carb; drilled, tapped & plugged the open choke vacuum port, reassembled & took it for a drive.
The idle is smoother (it dropped about 100 rpm with the fix), & no more risk of dust entering the engine.

While I was in there, I checked the feedback solenoid, &, yes, they do shut off the air bleeds (so, a full-rich state) with the computer gone.
Also, I found this ex-302 carb has #50 jets, so the white plugs are maybe not that surprising.

I'll start to play with the non-feedback carb next. #60 jets might be a bit rich after all.

 

Tomorrow I'll check the 2150's jets off Dad's truck - I hope. If you respond your time I should see it in the morning my time and check.

 

Thanks Gary. Don't worry about it if you're short on time.

Blocking this port has given another slight vacuum lift - 18" @ idle now, with a mild RV cam; also 18" @ 55mph, empty, on a flat road.
I'm pretty happy with that.

I guess it could drop a bit going to a 1.21 venturi.

 

More vacuum is goodness. Less throttle begats more vacuum, all else being equal.

As for the jets in Dad's 2150, they didn't want to come out so I thought a picture would suffice. As far as I know it is the original carb for the '81 351M, but I wouldn't guarantee it. In any event it worked fine and will be back on it when the engine resides in Rusty in a few weeks. And, I'll expect the same MPG it got in Dad's truck - 10.25 on the highway. But, Dad said that's pretty much what it always got.

 

Hmm - #42's. Or is that #47?

Seems strange after all my reading in the the last few days; one site suggested that #56's were the stock jet for 1.21 venturi 2150's.

Thanks for the pic Gary

(Don't know how I'd fill in the weeks, if everything was straight forward )

 

I didn't check to see the venturi size on the carb, but will tomorrow.

 

I've forgotten - is this part of the venturi size?