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View Full Version : Carbs w/ high altitude adjusters?


ceswanson
11-30-2004, 08:11 PM
While reading stuff on the Motorcraft 2150 that some here have talked about, I saw that some of the later ones came with an "altitude aneroid" (sp?) that would allow for some automatic altitude adjustment as one drives to higher altitude. The posts talked about an extra circuit that allowed x-tra air at higher elevations, but I haven't seen to much else about it. And I'm a still learning, so maybe I saw the answer but didn't realize it was right in from of my nose. So...

Does this really help? (I'm in Denver, so it's easy to have a 5000 ft elevation change with 30 minutes of driving) If so, do the later 2150s still bolt up to a 2bbl 345? Any other carbs that try to do the same thing that work well with the SV? Really curious. I know FI would answer the problem, but 1) too much money right now and 2) I want to learn about carbs. Thanks.

Charles

GreatScout
11-30-2004, 10:42 PM
I'm not familiar with this set up myself, but I'd like to learn more about it!! I'm in the same locality and I've yet tried to take my Scout up to anything higher than 5400'. I got a Holley/Motorcraft 2bbl too (don't know what model though), and I got her tuned to where she'll run quite well at this elevation, but at 7000 or 8000'?? I dunno...

Gary Billings
12-01-2004, 10:08 AM
Charles,

I have the Motorcraft 2100 currently on 2 of my Scout 800's, both with 345's. I live up at almost 9000 feet here in Conifer. These carbs are pretty versatile even without the altitude adjuster. I can run up to 13,000 feet on above-treeline trails, and as low as 700 feet without any carb problems. I have size 54 jets in one of them which is a tad bit rich for my altitude. I thought I had size 47 jets in the other one, but I could be wrong. Ideally, I'd like to get size 50 or 51 jet for my altitude.

Pull-N-Save (http://www.pullnsave.com) out in Aurora usually has some older Ford's there with the MC2100 for $17.99 + $3 core. Rebuild kits are $15-20. So, for $40, you can have a really great running, great starting, great idling motor. Just make sure you pick up a carb with the short accelerator pump housing (the long one will hit the thermostat housing)
& a "1.21" moulded into the side of the carb. This is the venturi size.

-Gary

Baradium
12-01-2004, 11:13 AM
Anyone know of a 2bbl carb with provisions for a mixture control?

Thomas
12-01-2004, 11:24 AM
Anyone know of a 2bbl carb with provisions for a mixture control?---If you are using a 2300 with #64 and above jet, yes, but not if you are using what came stock in "Scout" carburetors. The 2300 has the ability for you to use the adjust-a-jet from holley, but it has been written here in the past that the minumum jet size is equal to a #64. The adjust-a-jet goes on the 2300 between the fuel bowl and carb main body and replaces the metering plate.

Doug Shailor
12-01-2004, 12:16 PM
While reading stuff on the Motorcraft 2150 that some here have talked about, I saw that some of the later ones came with an "altitude aneroid" (sp?) that would allow for some automatic altitude adjustment as one drives to higher altitude. The posts talked about an extra circuit that allowed x-tra air at higher elevations, but I haven't seen to much else about it. And I'm a still learning, so maybe I saw the answer but didn't realize it was right in from of my nose. So...

Does this really help? (I'm in Denver, so it's easy to have a 5000 ft elevation change with 30 minutes of driving) If so, do the later 2150s still bolt up to a 2bbl 345? Any other carbs that try to do the same thing that work well with the SV? Really curious. I know FI would answer the problem, but 1) too much money right now and 2) I want to learn about carbs. Thanks.

Charles

GM (Rochester Div) tried much the same thing back in the late '70's with the Q-jet but they only made the carb of a couple of years because: a) it really didn't work all that well and b) FI was on the horizon.

Yes, FI is the best answer for IH SV engines. Someone was working on a MPI solution on an SV intake a few years ago and posted some pics then but I don't remember ever seeing anything about a finished project.

http://pic5.picturetrail.com/VOL94/159721/3925001/75232197.jpg

http://pic5.picturetrail.com/VOL94/159721/3925001/75232226.jpg

79Indy
12-01-2004, 06:06 PM
I have a 2150 on a Grand Wagoneer that has the compensator. I can't tell that it works all that well at altitude. I live at sea level and when I take it to 8-9000 feet, it puffs a bit of black smoke. I've had other vehicles do alot worse, but the 2150 doesn't completely compensate for the altitude.

I think it would bolt onto the manifold just fine. The linkage may be another story.

ceswanson
12-01-2004, 06:14 PM
79Indy,

Do you think that the compensator helps? Or is just kinda "gimmicky"? What year is your Grand Wagoneer? Thanks.

Charles

79Indy
12-01-2004, 07:58 PM
My GW is a '90, but all the 80's models had them too. There's usually always one at the yards. The aneriod model has an extra little rectangular choke chamber behind the normal choke plate. Also, the mechanism itself hangs off the back of the carb body and is about three inches wide, two and a half inches front to back, and maybe about an inch and a half top to bottom.

As to how well it works, I can't really say. It definately is not as good as fuel injection, but it doesn't get tempermental at altitude like some carbs. Like I said, it still seems to run a little rich.

You may want to play with jets. I always take a big flat blade screwdriver with me to the yards and take the jets from any 2100/2150 I see, which are usually very plentyful in the Ford areas. The jets all seem to interchange, eventhough the variations of the 2100/2150 are numerous. I've found everything between #52 to #62's. The GW, which has a 360, has #56 jets from the factory.

Good Luck.

M. Mayben
12-01-2004, 08:40 PM
The "altitude compensating" carbs were intended to be a workaround for OEM emissions certification on vehicles sold NEW by NEW vehicle DEALERS, back in the late 70's>late 80's.

Vehicles off the line were emissions certified at roughly "sea level" operating conditions. If the same vehicle was sold/delivered say by a dealer in the Denver area or Cheyenne, or Helena (just examples), then the fuel delivery system (carb) was SUPPOSED to be "tweeked" PRIOR to delivery, per explicit Technical Service Bulletin information using EXPLICITLY spelled out service parts. This "maintained" the vehicle as being in emissions compliance at the point of delivery and in essence, the selling dealer became a "manufacturer" under the law.

The "compensating" carb concept was really an effort for the OEMs to be able to maintain emissions compliance in ALL vehicle markets, WITHOUT having to pay a dealer (warranty claim) to bring the vehicle into compliance by reworking the carb.

It was NEVER meant to be "compensating" in the sense that most of you are thinking (the be-all and end-all perfect carb for any operational elevation). The advent of EFI took care of this issue and carbs in general began to disappear from the scene in the mid-80's and were pretty much gone by 1991 (U.S. domestic market).

GreatScout
12-01-2004, 09:29 PM
Well I know I for one have learned a lot from this thread. Thanks a bunch guys!

ceswanson
12-02-2004, 10:31 AM
Absolutely. Learning alot already. So another question (or several). Elsewhere I saw that the MC2150 compensating carbs were on vehicles shipped to dealers above 4000 ft. Which jives with Michael's explanation. Did they really do what they were designed to do? Or did they suffer like the TQ that Doug was talking about? (i.e. If I go to find a used 2150 to play with/rebuild, should I look for or avoid the compensator model?) Was it design with a preset altitude that switched it on, or was it more of a gradual operation as altitude increased? If its an on/off type operation, can it be recalibrated to switch at a higher altitude? I understand Michael's explanation about why it was done originally, but is there some reason that we can't utilize that operation to improve the carb's operation? Am I just giving my self newbie braindamage? Many thanks to all that have replied.

Charles

M. Mayben
12-02-2004, 12:27 PM
OK now...you boys are making me reach WAAAAY BAAAACK into the hard drive between the ears here.

I'm still unpacking my library from moving into the shophouse a few months back. Did manage to find one of the textbooks I used in one of my former careers as a post-secondary automotive/industrial engine technology educator(14 years). It has a little info contained therein regarding APT (factory-adjusted part throttle) carbs and Altitude Compensation circuitry. These "workaround" circuits kinda go hand-in-hand.

Unfortunately the examples used are a Rochester (GM subsidiary) "explanation", not Holley/Motorcraft.

The textbook is an EXCELLENT basic automotive technology reference because it was written/published/revised during the "IH Light Line" era and covers the transition from the "old stuff" through the beginnings of "pooter-control" on light duty motor vehicles. Title is:

"Automotive Mechanics" (8th edition)
William H. Crouse
ISBN: 0-07-014820-1

Copyright stretches back to 1946 and has been revised MANY times so you can find MANY editions through used book outlets.

I would say that this textbook would be an excellent addition to anyone's technical library and is a great companion to the OEM service manual.

I had the pleasure of knowing Mr. Crouse and actually performed "technical reviews" during pre-publication trials conducted by the publisher (McGraw-Hill). I also worked on many projects with his "favorite nephew" who was a mobile HVAC systems design engineer for Diesel KiKI/ZEXEL (our former employer).

This info is too extensive to paraphrase here, If anyone would like this info, send a request for a copy of the 2 pages as an email to:

RodeLizrd@aol.com

I'll send out the 2 pages as an email attachment on 12/3/04 as a return from your email (no spam/no virus, I'm on a mission to eliminate those "originators" from the gene pool).

As to the "effectiveness" of this carb design, I can't/won't comment on that as I DO NOT have any hands on experience working with them. However, they had to "work" (at least for 50,000 miles) in accomplishing their design task or they would not have been "certified" for use in their intended vehicle sales/delivery markets.

In my OPINION (not backed up by facts/experience), I THINK they do what they were intended to do (maintain emissions levels and drivability at "higher" altitudes). They can't make up for "decreased" performance due to lack of air density, only a forced-air induction system will do that.

In a practical sense, I think that finding a servicable carb (not previously butchered), and performing a "correct" freshening of the same (finding the proper "kit" and internal parts may be a challenge), and then calibrating it for the IH SV engine operating characteristics AT THE INTENDED OPERATING ALTITUDE may be a real challenge!!!! This would be a project for someone with a considerable background in carb work and drivability issues.

79Indy
12-02-2004, 01:31 PM
Michael - I had heard that the aneroid was to be adjusted by the dealer when new. The factory manual supposedly has instructions for this. I don't have the manual, unfortunately.

There is an allen adjuster on the back, but I don't know anyone that's fiddled with it. When I've rebuilt this carb, I just unbolt the unit and bolt it back on when I'm done with everything else. I think everybody else does this, too. From the front, there is just a spring loaded plunger that allow air to go through that rectangular channel I was talking about.

Charles - I also have a '79 F150 that has a 2150 that I've had up in Flagstaff, which is about 7000 feet, and it does just as well. Remember, there are several things you can play with like jets, power valve calibrations, and accelerator pump settings.

M. Mayben
12-02-2004, 01:56 PM
79...

You are CORRECT regarding "dealer adjustment".

Back in the day when this guapo was "current", the dealership service term "Pre-Delivery Inspection" (PDI) actually MEANT something (money in the pocket of the mechanic/technician). Part of the PDI procedure was to make the neccessary "adjustments" based on the "delivery market" of the subject vehicle when sold (based on physical address of the vehicle registration). Remember, you're dealing with "legalbeagle" stuff here with MAJOR financial penalties for NOT doing it as specified by the OEM!

Today, PDI don't mean squat in my book (I'm an old MECHANIC!), it means making sure the doors close/lock and the paint film protector is removed (most of it anyway). In some cases, PDI is actually performed at the point of manufacture because the OEM doesn't "trust" their own dealership personnel to do it CORRECTLY!

This work had to be performed using a 4 gas analyzer (5 gas hadn't come along yet, IIRC 5 gas was introduced to the marketplace in '91), a VERY expensive piece of equipment (same guts as any "approved" emissions test unit).

This "adjustment procedure" was distinctly different from the earlier process which involved carb R&R and parts replacement, followed up by adjustment using a 4 gas unit.

Thanks for mentioning that, as I said, this stuff is coming back now as a flood of memories from a FULL hard drive!

79Indy
12-02-2004, 03:15 PM
Michael - that's interesting to hear about the ways things used to be done. I believe it. I helped my mother pick up a new car recently that was just off the truck. Essentially they did a quick check over and then detailed it. The detail took longer than the check over.

I notice I didn't mention that the 2150 on the F150 I've driven up in Flagstaff does NOT have the aneroid.

ceswanson
12-03-2004, 11:30 AM
Just wanted to say thanks to everyone for all their replies. I'm a little bit smarter now.

Charles