Need advice on Weber tuning

[bemumford]

I tried tuning my new Weber 40IDF's today with limited success. Using the directions in Bob Tomlinson's Weber book, I syncronized them successfully but I had trouble getting the idle mixture adjustment right. The idle jets are .55's. The car seems to idle best when the idle mixture screws are about 1 turn open instead of 2 1/2 turns. Even with all mixture screws open 1 turn, I can't change idle speed much by closing any one mixture scew, and I can't induce a lean backfire by closing any one mixture screw. There's a fair amount of exhaust smoke, and the idle is somewhat uneven, so I suspect it's still too rich. Off-idle performance is great. The car drives better than it ever did with the old Solexes, and I haven't detected any flat spots. Do these symptoms suggest smaller idle jets are in order -- perhaps .50's?

Answers to other questions you might ask:

Stock cam, 1720 cc big bore kit, recently adjusted valves, new 050 distributor with Pertronix ignition and 5 degree advance at 850 rpm, main jets are 1.30.

Ed Mumford

[Dieselfitter]

Ed, You should probably change your Idle jets to 50s or 45s you can then have better control of your idle adjustment. My car is set up simular . You might try setting your timing to 30 degrees advance at 3000 rpm. Seems to work the best for me. See ya Mike

[bemumford]

Thanks, Mike! I'll give the smaller jet a try. I'll also look again at timing. I remember wanting to check timing at 3000 last fall, but I don't recall actually doing it.

Ed

[craign]

Ed,

I found with my 050/pertronix I got better results if I timed it at 30 deg at 3,000 rpm and ignored the idle setting.

It does take a few more minutes to warm up but I get better response at speed this way.

Here is another weber adjustment procedure, don't know if it will help but at least you can compare to what you are doing now.

http://912sig.pca.org/Weberadj.pdf

Craig

[bemumford]

Craig,

Thanks for your post and the Weber adjustment procedure link you attached. It's a nice day in Iowa today, so this afternoon I'll try re-timing the ignition and try this adjustment procedure. If that doesn't do the trick, I guess I'll order smaller jets and hope that gets me a little more adjustment range.

Ed

[C. Clark]

I just went from 55 to 50 idle jets, the engine idles at cold start up much better and does not load up as it did before the change. Jets are cheap, it's worth the effort.
Chas.
69/912

[bemumford]

Chas,

Thanks for your post. Is there room enough to replace idle jets with the carbs installed, or do they have to come off the car?

Ed

[C. Clark]

Ed,
There's room....that said I have become aquainted with thinking tight and small when working on my cars. I used a short, "stubby" screw driver to loosen / remove the jets. I also used a mirror so I could see exactly what was going on and of course a good light, trouble lite worked for me. Be careful though, there's a rubber O ring that seals the jet screw to the carb body, on 3 of the 4 jets it stayed in the hole but one came out with the jet and a I could see it being lost. The jets are a two part system mine came out in one piece I gently pulled the actual jet out of the screw part with pliers. The jets have a split in the end which holds it to the screw part, I had to carefully spread the split to insure a snug fit. It's easy really, took me about 20 minutes but I've done it before, just take your time and think it through.
Good luck,
Chas.
69/912

[bemumford]

Chas,

Thanks for this additional information and for your encouragement. I had hoped earlier this week to retime the distributor and try an alternative tuning procedure as others have suggested. However, I'm now thinking I'll order new jets and do the whole thing at once.

Ed