911R tribute Webers and distributors

[jordanpryce]

I'm having a hell of a time rejetting the webers for sea level since acquiring Axle. It's a 1967 with a 2.7, e cams, stock CDI and ignition and Weber 40mm IDTP carbs.

Current jetting:

Main 145
Idle 60
Air correction 180
Main venturis (chokes) 34
Emulsion tubes F3

She's popping on acceleration and backfiring with the occasional backfire out of the carbs as well.
I've tried setting warm idle to 1,000 and adjusting the idle air screws out to best idle, but even screwed in to 1 turn or out to 3 turns I'm not getting much of a response. I'm thinking I need to go up on the mains and maybe down on the air correction jets.

Another thing I was wondering about was the distributor. It's a later one with a vacuum advance (although nothing is connected). I have no idea what the curve is, or if it was recurved. I'm not sure where I should go with this one...

[jordanpryce]

What's a dizzy?

I don't know what you're talking about. But thanks in advance for the help.

[edmayo]

It sounds like you're saying it ran okay at a higher altitude and you just need to jet for sea level now. If that's the case main jet sizes change about 2% per thousand feet, calculate the change based on the altitude change and your original main jet size that worked okay at your previous altitude.

[jordanpryce]

Thanks Ed. It was jetted for above Denver at 8,100ft. So if I get your math, that's 16%. 125 mains X 116% = 145 which is where I'm jetted now, but still seems lean with the popping and backfiring. Any thoughts on reducing the air correction jets?


Mains 125
Idles 50
Air correction 180
Chokes 30
Emulsion tubes not sure..

Now jetted at

[edmayo]

Your jetting sounds "in the ballpark" but I also notice you went up to 34mm venturis. There is a certain feel to adjusting carburetors which of course, I don't know if you're doing right or not. There is also the possibility that when you switched venturis that you may have gotten one of the booster venturis in backwards, that can cause the backfires since it isn't drawing fuel. Also float levels of course.

[62S-R-S]

You can't do much better than this fella in comprehending 911 webers.

2/3 of way thru the booster venturi problem is highlighted. Hope this helps.

youtube.com/watch?v=vtuMFT3ylEM

[jordanpryce]

Great video. I'll pull the carbs off again and check my work and report back. Ed, I paid extra attention to the direction of the booster venturis when reinstalling them, but no one is perfect. Thanks for the reminder.

[jordanpryce]

Ed was right. Dispite my careful assembly, the number six cylinder booster Venturi was backwards. FYI, it's easy to check with a mirror and light or Iphone.

[edmayo]

Glad to hear you got your issues solved, thanks for letting us know