Carter-Weber jetting, etc.

[martybose]

I've decided that I want to know more about the jetting in my Carter-Webers. They are easily accessed, since all you have to do is remove the pin holding the air cleaner stud bridge and they are right there, no further carb disassembly required.

It turns out that the first issue is getting them out, as they use a damaged thread form of locking, and they are very tightly installed. The real issue about getting them out is that you need a tightly fitting screw driver that is 5/8" wide, and the shank has to be the same width to clear the carb body casting. After struggling for a while I hit the McMaster-Carr web site http://www.mcmaster.com and found the perfect screwdriver for this. It is part number 7297A22, described as a hollowed-tip screwdriver, 5/16" wide, .040 thickness tip, only $9.78 (plus shipping).

Once I had the proper tool I pulled all of the jets. It's quite a collection, as there are 4 jets for each throttle bore (main jet, idle jet, air corrector jet and emulsion tube), and the primary and secondary don't have any in common. The real surprise was that the two carbs, which were purchased new as a pair, had slightly different air correction jets in the primary bores. All of the others were identical. They are:

part name Primary Secondary

main jet 105 100

idle jet 065 060

air corrector jet 150/155 250

emulsion tube F53 F22

Interestingly, the tables I have don't even list an F53 emulsion tube for Weber DFTA carbs (their designation for these) but they do list an F53 for a closely related different model.

I'm now waiting for the back-ordered book on weber tuning theory so that I can work up a plan on what I want to change based on my driving symptoms. I've found a couple of sources for the component parts, I just need to decide what I want.

While I'm waiting for the book I'm working on new air cleaner bases and gaskets so they will be ready to reinstall.

Marty

Edited July 4, 2009 by martybose
tried to fix formatting of the table; didn't work!

[BeBop138]

Marty, keep us posted on what you find.........I am running a pair on my 265 and I am curious. Hope to pick up some tips as you get deeper into the tuning..........Thanks..........Lee

[martybose]

Thought I'd post an update on this. I stocked up on some idle and air corrector jets, and started experimenting.

I wound up with a 070 primary idle jet (one step richer than originally installed 065), and that seems to have completely eliminated the part-throttle pinging I was hearing.

The primary air corrector jetting was interesting. My two carbs weren't matched originally, one having a 150 and the other having 155. I started out with a pair of 155's, which is the leaner of the 2 sizes. It ran fine, but didn't seem to pull as well. So I switched to the pair of 150's, and it feels much better.

So the bottom line is that I'm now running a richer primary idle jet, which affects the bottom end primary-only running, and I'm running a slightly richer primary air corrector jet package, which affects the top-end of the primary only running until the progressive linkage starts to open up the secondaries. I haven't changed anything in the secondary jetting.

Now I'm starting to wonder if the heating up at freeway cruising speed and the detonation heard as it was starting to heat up were really indications of the primaries being too lean and not issues of too much ignition advance. So my next step will be to remove the tiewrap that is currently locking the centrifugal advance on my HEI and see what happens next.

Keep in mind that I am running an overbored 230 running 9 to 1 compression with 91 octane gas, cleaned up ports, Edmunds intake manifold and head, a mildly upgraded cam, an HEI ignition system and cast iron headers into a low restriction dual exhaust. The changes I have made may not be appropriate or necessary for a more stock engine.

Marty

Edited October 11, 2009 by martybose
fixing a few fat-finger typos.

[martybose]

This weekend I removed the tiewrap from the HEI centrifugal advance weights and went for a ride. In 80 degree weather it did not heat up on the freeway the way it used to, so apparently the problem was jetting all along. I did detect the slightest amount of pinging once. I've got a richer pair of idle jets in my collection, but I think I'll wait until I driven it more before I richen it up again.

Marty

[Normspeed]

Marty, are you running a stock distributor or an HEI? Where's your initial timing set at?

[martybose]

Marty, are you running a stock distributor or an HEI? Where's your initial timing set at?

I'm running a Langdon HEI with the initial timing set at 4 degrees BTDC and the vacuum advance running off of manifold vacuum (so that the vacuum advance is reduced when I stand on the gas).

Marty

[Powerhouse]

Made any progress on this yet? I am experiencing a too rich situation with my dual carter webers from langdons.

I don't know much about these carbs. All I see as far as jeting is the 250 and 150 next to each other on each carb. Are ther more jets under those? WHat do the screws without the numbers to the side of the jets do? Sorry for the dumbness.

[Powerhouse]

I sent an email over to Langdon's. He called me up and let me know a lot of helpfull tips on how these carbs work. VERY INFORMATIVE...as I have not much understanding of carbs. Just learned by doing really and that's only on the old single bbl. Anyway, I will try what he suggested. I just need to tune in that mixture and it should be fine. The jets are supposed to be just right.

[martybose]

I sent an email over to Langdon's. He called me up and let me know a lot of helpfull tips on how these carbs work. VERY INFORMATIVE...as I have not much understanding of carbs. Just learned by doing really and that's only on the old single bbl. Anyway, I will try what he suggested. I just need to tune in that mixture and it should be fine. The jets are supposed to be just right.

You must have caught him in a good mood; he won't talk to most of us.

Anyway, There are no less than 3 jets in each barrel of the Carter-Webers, and they don't match at all. I believed that the bottom end was too rich and the top end was too lean, so I bought some extra jets for it. I played around with the primary jetting after reading a couple of books on it, and about all I succeeded in doing was killing my freeway gas mileage, so I have temporarily returned to the original jetting. Well, sorta; it turns out the two carbs that I bought at the same time from Langdon didn't have identical jetting! So I picked one and made the other one match it. I was just about to start playing around again when I bent a valve with the compression tester adapter, so I'm waiting for parts to put it back together again.

Marty

[Powerhouse]

I checked the mix screws..both were the same distance out. I tried adjusting them leaner(closing)and it started to shudder. I took the jets out. They were the same on each carb. Except one of the f22 emulsion tubes had a piece of old metal stuck in one of the side holes. the jets were as follows:

secondary: 60 idle, 250 air corrector, F22 emulsion tube, 100 main.

primary: 65 idle, 150 air corrector, F53 emulsion tube, 105 main.

Edited July 14, 2010 by Powerhouse