Choosing correct power valve
Moderator
Joined: Jan 2001
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From: Virginia
Once you really get into carbs, it's when you realize the aftermarket carb people are really sticking their neck out, they have no idea what their carb is going to be installed on. So you can be pretty much guaranteed the aftermarket carb you are using is a compromise to fit most engines.
It also brings to realization that the factory spent a lot of time tuning and calibrating their carbs to each specfic engine setup, and when you start messing with anything, even the exhaust system, you are messing up the calibration of the carb.
It also brings to realization that the factory spent a lot of time tuning and calibrating their carbs to each specfic engine setup, and when you start messing with anything, even the exhaust system, you are messing up the calibration of the carb.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
Luckily the naturally-aspirated gasoline engine has a pretty consistent A/F requirement regardless of brand. And, it is very tolerant of variations in the ratio - as long as you aren't requiring its exhaust to be squeaky clean. Or, if you aren't looking for the last MPG or HP. Yep, carbs are a compromise.
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Cargo Master
Joined: Aug 2007
Posts: 2,560
Likes: 69
From: New Zealand
One more query.............
The 2150 that I'm re-kitting has emulsion tubes with 8 holes each near the top.
I have a spare parts carb (also a 1.21, 2150 but the tag is missing) that has rows of vertical holes down the length of the tubes, & I've heard this was the better design - is that correct?
If so, will the whole booster assembly swap satisfactorily, or am I better to stay with the original parts?
The 2150 that I'm re-kitting has emulsion tubes with 8 holes each near the top.
I have a spare parts carb (also a 1.21, 2150 but the tag is missing) that has rows of vertical holes down the length of the tubes, & I've heard this was the better design - is that correct?
If so, will the whole booster assembly swap satisfactorily, or am I better to stay with the original parts?
Old School Hot Rodder
Joined: Feb 2006
Posts: 6,472
Likes: 11
From: Exmore, VA
Ken, from my experience with Weber, Zenith and Solex carbs, the larger number of holes in the emulsion tubes aids in throttle response and will actually make it run richer.
Specific example, 1972 Mercedes-Benz 250C (2.8L SOHC with dual Zenith 35-40 INAT progressive 2bbls.) The primary emulsion tubes had 2 holes mid-way up. I found a set of Weber emulsion tubes from a bunch of scrap Pinto Holley-Webers with maybe 10 holes in them, the main jets had to go down 3 or 4 sizes it ran so rich.
Specific example, 1972 Mercedes-Benz 250C (2.8L SOHC with dual Zenith 35-40 INAT progressive 2bbls.) The primary emulsion tubes had 2 holes mid-way up. I found a set of Weber emulsion tubes from a bunch of scrap Pinto Holley-Webers with maybe 10 holes in them, the main jets had to go down 3 or 4 sizes it ran so rich.
Moderator
Joined: Jan 2001
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From: Virginia
I would compare jet sizes and all the other little air bleed hole sizes. The different design may require a difference in some other part of the carb, you never know. But that piece is easily changed if you wanted to experiment correct?
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
I agree - check all the various bleeds and restrictions. I don't know about the 2150's, but many carbs have restrictions built into the passages which limit the amount of air or fuel flow regardless of the bleed or jet size. I've seen instances where a main jet or PV change gained nothing due to a restriction.
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Cargo Master
Joined: Aug 2007
Posts: 2,560
Likes: 69
From: New Zealand
Ken, from my experience with Weber, Zenith and Solex carbs, the larger number of holes in the emulsion tubes aids in throttle response and will actually make it run richer.
Specific example, 1972 Mercedes-Benz 250C (2.8L SOHC with dual Zenith 35-40 INAT progressive 2bbls.) The primary emulsion tubes had 2 holes mid-way up. I found a set of Weber emulsion tubes from a bunch of scrap Pinto Holley-Webers with maybe 10 holes in them, the main jets had to go down 3 or 4 sizes it ran so rich.
Specific example, 1972 Mercedes-Benz 250C (2.8L SOHC with dual Zenith 35-40 INAT progressive 2bbls.) The primary emulsion tubes had 2 holes mid-way up. I found a set of Weber emulsion tubes from a bunch of scrap Pinto Holley-Webers with maybe 10 holes in them, the main jets had to go down 3 or 4 sizes it ran so rich.
I agree - check all the various bleeds and restrictions. I don't know about the 2150's, but many carbs have restrictions built into the passages which limit the amount of air or fuel flow regardless of the bleed or jet size. I've seen instances where a main jet or PV change gained nothing due to a restriction.
OK, thanks all.......I'll leave everything as original for now. Yes, it can be swapped easily later, Dave.
I'm optimistic that this carb is going to be good - it's not butchered up, has almost no throttle shaft or other wear, is still tagged, & is surprisingly a full match for the year & engine of my truck.
It was thrown behind the seat of a parts truck I bought.....the PO said it was 'just a piece of junk', but he had tried to run it with the jets missing & given up in disgust.
You've gotta be lucky sometimes
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Wow! Running a carb w/o jets has got to be ..... interesting. It should idle, but would probably bog down very quickly if you cracked the throttle. Bill - Surely one of your guys tried that? (Not you, I'm sure.)
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