weber problems

[ckissick]

I'm on the last leg of my 3.0 transplant. I got everything running, but the carbs are messed up. It's a '78 3.0 with Webers and Bursch headers. It hesitates badly and misses when I give it gas under load. In neutral, it revs fine. It seems to be a basic fuel starvation problem. The carbs worked fine 6 months ago when they were on the 2.7, then I re-jetted, etc. them as per Bruce Anderson's book for a carbed 3.0 (F3 emulsion tubes, etc.) But it runs terrible. What's a good process to solve this? Is it clogged? Is a float sticking?

Charlie
Montara, CA
1970 911E 3.0 (almost)
1950 VW

[911pcars]

In a word, not enough fuel. Can be caused by:

1. fuel pump not supplying enough fuel
2. float level too low
3. accelerator pump stroke too short or not working

#3 is easiest to check. With the engine OFF, look down the carb throat(s) and watch for fuel spray as throttle is opened. The specs call for an exact amount measured with a small graduated tube.

#2 requires an external Weber float inspection tube. Try Pelican or PMO for that part.

If the engine works fine at high speed but not during acceleration, the fuel pump is probably okay - probably #2 or #3.

Hope this helps,
Sherwood

[RoninLB]

Originally posted by 911pcars

3. accelerator pump stroke too short or not working

ditto

or ignition

[ckissick]

#1, #2, and #3 have been eliminated as problems. The problem is with one carb not providing fuel. Somethings clogged? Any ideas?

Charlie

[911pcars]

One carb not receiving fuel is fairly drastic assessment for a hesitation under acceleration. Can you be a little more specific?

Sounds like the accelerator pump circuit might be blocked (if that's what you mean by "not receiving fuel"). If so, dissassemble carb and blow air or pressurized carb cleaner through the passages to see what's going on.

Sherwood

[RoninLB]

Originally posted by 911pcars

One carb not receiving fuel is fairly drastic assessment for a hesitation under acceleration.

there should be an accelerator pump circuit check valve in the bowl floor [to lazy to read in am] that can be replaced to tweak the flow. I guess it can also block the flow if clogged.

[Formerly Steve Wilkinson]

Are you saying one entire carburetor (three barrels) is not receiving fuel, or one barrel isn't?

Stephan

[ckissick]

I had my friend the Porsche mechanic test it out, and he seems to think one whole side is not getting fuel when accelerating. It does sound like the accelerator pump circuit, doesn't it? Thing is, the carbs worked great in the other engine. And the carbs were rebuilt about a year ago, so the diaphragm is new. It could only be a coincidence that it became clogged now. I'll let y'all know what the problem was when it is solved. As for now, my 911E 3.0 is slower off the line than my 1950 split-window.

This transplant has been quite an adventure. Someone should write a book. Oh yeah, someone has. (And I read it; good job, Formerly Steve)

Charlie
Montara, CA
1970 911E
1950 VW

[ckissick]

I promised I'd let y'all know what my Weber problems were when I sorted it out, so here goes. I installed one of the secondary venturis in backwards. Oops.

I bought Tomlinson's Weber book and starting teaching myself all about the Webers. As I read, I realized that my problem could have been with the secondary venturis, as I hadn't known it mattered which way they went in, et voila.

It still runs a little rough, and is in need of some tweeking, and possibly some re-jetting. Shouldn't be a problem.

Charlie