Weber jetting question
 

I just rebuilt my Weber's and installed ,F7 Emulsion tubes
55 idle jets, 130 mains, 200 air correction
and 32mm venturis. I have a 1750 cc engine on my 68. It finally is not running lean as it did before the switch, but it really doesn't idle without the mixture screws all the way in. I switched back to the 50 idle jets and now it idles OK, but the mixture adjustment cant be out more then 1/2 turn before it starts dieing. Should I go to a 47.5 idle jet ?, try to fuss with the air mix?. I've read all the archives, but that's where I came up with the new jetting installed

I ran 55's for along time with limited success, a fellow 912 guy suggested trying 65's and bingo, no more popping and cold idle problems. I am at basic sea level though.
Chas.
69/912

I'M not sure I understand. I was running too rich with the mixture screws in almost all the way. When I switched from the 55's to the 50's it improved but left little room for tuning. I think if I went to the 65's the problem would be amplified. Unless there is something else I need to be tweaking.

There is controversy on this subject but fuel pressure in my opinion can contribute to rich running Webers, I run a rotary elect. pump with a regulator built in, 3 lbs psi I think. My richness went away then the jetting adventure started. I went to 50's at first but that made things worse so I returned to 55's and as I said before, finally got 65's which majorly improved my situation, popping and cold idle problems. It is my understanding that the idle circuit runs the carb up to around 3500 rpms, then the mains kick in, I run 135 mains. Are you running 40 idf's ?
Chas.
69/912

Yes, 40 IDF's. IM using a Carter 4070 rotary fuel pump, high volume low pressure. Recommended by webercarbs.com.
I'll play around with it, it seems to be doing OK with the 50's but I wish I had more latitude with the mixture adjustment.

how hard was it to replace the venturis?

Cobra-6, or anyone? Do you need to run a fuel return line to the tank or is this carter pump a simple inline pump?

Thanks

Craig

No need for a regulator or return line. It's a great pump.

Guys, I am interested in this discussion as I recently bought a
69 912 stock 1600cc with twin webers 40 idfs . I must admit that I have very little knowledge of carbs, but my friend Brian has been helping me out. We balanced the carbs and set the float levels, and checked the timing etc, but still very hard to tune, and the mixture screws are screwed all the way in before you start mixture.

The jets are mains 115, air correction 200, idle 45 and F11 emulsion tubes. I think venturies are 28mm.

We changed idle jets to 52 without any noticable difference. Seems to be running very rich and heavy on fuel.

Can someone give me a baseline jetting for 40 idfs and maybe advise on what may be the problem.

Thanks for you help... this is my first post.

j.d.

Hey Cobra-6 just got the new pump hooked up, this made a huge difference on my engine, My engine would always run great when first started up then as it got hot it would loose its carb settings and you could feel it. My gauge on the carb showed a drop in pressure to about 1.5 when it was hot, cold it was at 4. This pump took care of that and its holds its adjustment PERFECT. Now, how good are these pumps, do you have a back up?? I was thinking about leaving the orginal in place?I left the lines all the same so I could plug them back in if needed?

Craig

It does make a huge difference as well, great upgrade. Carter pumps have been around a long time and are extremely reliable. I pulled my stock pump and cut a block-off plate.

Here's a little blurb about electric pumps.

Fuel pumps and Weber's