View original topic: Accelerator pump adjustment
K9Torro Fri Nov 03, 2006 11:27 am

I am trying to follow a write up I found on this site to adjust my Web 40 IDF's , it says to adjust the accelerator pump nuts/rod , I can't see them on the carb and the book I have does not show any pic's of them either can anyone help me out, are they inside the carb ? or are they outside and a part of the linkage ?

thanks in advance,


RockNbus Fri Nov 03, 2006 11:47 am

Go to this link:

Look at the square plate in the lower middle portion of the carb. Just below it, you will see the small rod with the nut on it. That is what you need to adjust.

K9Torro Fri Nov 03, 2006 12:03 pm

Hi and thank for the post , I got a problem my accelerator pumps do not have an adjustment rod like the one pictured , the arm coming out of the diafram cover has a pin connection to a piece of linkage that goes back under the carb and hooks to the same rod that moves the throttle plates when you step on the gas, I can't see anyplace to adjust it there ?


RIS Fri Nov 03, 2006 12:51 pm

You have the earlier IDF's, you have a choice of two pin locations to adjust the accelerator pump volume/duration.

What symptoms are you experiencing that have you thinking it's the accelerator pump adjustment?

K9Torro Sat Nov 04, 2006 10:58 am

Hi Rich,

I just got a new (to me) Weber book from Ebay and it looks like you are exactly right , this book covers carbs produced prior to 1979 and it shows an older version of the IDF's that is identical to the ones I have that use a linked roller cam set up on the accel pump.

I will look for the second pin hole, WHICH ONE IS USED TO PUSH LESS GAS ? WHERE IS THE HOLE ? I believe that the carbs are running way too rich or pumping to much gas when I push down the throttle. The exhaust which is new is very sooty and when you punch it you see puffs of smoke.

The engine is a newly rebuilt 1835 using a AE dual relief block, aligned bored, machined german crank, new rod/main and cam bearings, rods were weight balanced, 12.5 lb flywheel, engle 100 cam with new gear and bolts, 92mm Kolbenschmidt pistons and cylinders with new rings/pins and clips, high vol febi oil pump and new strainer, magnum big valve cylinder heads with new push rods and tubes, new bosch wires and plugs, type 009 dist with electronic module, bosch blue coil, rebuilt weber idf 40's.


The car starts and idel's fine , if you baby the throttle and do not make any sudden change it pulls to red line , but if you jump on the throttle from any position it bogs down really bad, it eventually recovers itself if you let off a little and then re-apply the throttle. This happens both under load and sitting still in neutral. I am thinking it is the accel pumps.


K9Torro Sat Nov 04, 2006 11:00 am

Rich -

I am using 4 inch billet air cleaners with oiled K/N filters , do you think that going to a velocity stack set up instead will cure this problem without messing with the carbs ?


gerg Sat Nov 04, 2006 11:01 am

Sounds like you need to go through the proper jetting / float height / fuel pressure checks & processes.

The Weber books generally avaialble are OK but the Weber Tuning Manual (by Weber) is the SH*T. A fairly easy read, and you will have a GREAT starting point for understanding how they really work.

It would benefit anyone here trying to help you to know what your mains / E tubes / idles / air correction / and venturis are.

K9Torro Sat Nov 04, 2006 11:15 am

Hey G -

I am a Weber " newbie " , how can I get this info, do I have to take the carbs apart to read some numbers on the parts ?


SkrapMetal Sat Nov 04, 2006 11:20 am

I'm a carb newbie also, and that link was a great help

gerg Sat Nov 04, 2006 12:13 pm

I am still fairly new at it too - but John C and mharney will not steer you wrong if you read any of the posts that they have commented in.

You can get most of the info by removing the jet stack - all that is required for that is to remove the air cleaner.

The venturis are usually marked in the casting unless you get some that are cut on a lathe and not marked. Look down each barell and you will see the venturi. The numberreferes to the narrowest cross section of the venturi in mm.

This is not the best photo, but the arrow points to the venturi. Keep in mind that the carb top is removed here. There is a set screw with lock nut holding the venturi in place. Once removed, along with the squirter and secondary venturi / crossbar, the venturi should lift right out.

That leaves the idle jets. Looking at the outside of each carb, there are 2 brass caps that unscrew from the holes indicated below. These brass caps are holders for the idle jets.

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