New to 48IDA's - Accelerator Pump Adjustment Thursday, 30-Mar-2000 17:47:47 This may be a stupid question, but how do you adjust the accelerator pump on 48's? I am comfortable with jet selections, have adjusted the floats etc. but don't know how to adjust the acc. pump. I thought I read that there is a screw on the side of the carb which adjusts it, but I can't seem to find it for the life me. Thanks for your input. John E.

Message thread:

John E.: New to 48IDA's - Accelerator Pump Adjustment (30-Mar-2000 17:47:47)

Bruce Tweddle: There isn't an adjustment (30-Mar-2000 20:28:54)

Tobias Bylund: 44 IDFs same problem... or? (31-Mar-2000 12:25:23)

Bruce Tweddle: different animal (31-Mar-2000 13:14:31)

Rich Gromer: Re: different animal, valve job? (31-Mar-2000 20:07:02)

Bruce Tweddle: Its some kind of a vacuum feedback thing (31-Mar-2000 21:58:14)

Craig Merrow: Had a similar problem with Kadrons... (01-Apr-2000 07:00:58)

Rich Gromer: Re: Thanks, All! (01-Apr-2000 12:56:43)

Gary Berg: Re: New to 48IDA's - Accelerator Pump Adjustment (01-Apr-2000 01:45:22)


There isn't an adjustment

Thursday, 30-Mar-2000 20:28:54

the only thing you can do to the acc pump is change the output nozzle jet. Most common is a 50.

I think Berg makes a new adjustable acc pump cam. The only adjustability is the position of the cam on the shaft. The reason you might want this is that the drag racers typically have their idle speed over 2000 rpm. To get this, the idle position of the throttle shaft is held open more than if set for street. This puts the pump cam part way up the ramp. The adjustability is to back it off so the pump isn't depressed at idle.

Bruce Tweddle


m having the same problem on my carbs, the engine seems to be overly-rich at idle and low rpms and i read that this could be of the acc-pump. is there any adjustability to the idfs??

Tobias Bylund


different animal

Friday, 31-Mar-2000 13:14:31

The accelerator pump should only deliver fuel when the throttle shaft is in motion. With your engine idling, remove your aircleaner and look at the pump nozzles. If droplets of fuel are comming out of the nozzles at idle, then you need a valve job.

Bruce Tweddle


Re: different animal, valve job?

Friday, 31-Mar-2000 20:07:02

Hey Bruce, tell me more! How do dripping Acc pump jets indicate the need for a valve job?

Rich Gromer


Its some kind of a vacuum feedback thing

Friday, 31-Mar-2000 21:58:14

When I typed "different animal", I was thinking of the adjustability of the pushrod that actuates the pump diaphragm, then remembered the dripping pump nozzles. When I first dialed in my 40 IDFs to pass the smog numbers for my 75 Beetle (think about that, 75 = FI), I ended up going full circle on the main jets, air corrector jets, and idle jets. I was all over the place with the three types of jets, and the final was exactly where I started with the exception of the idle jet. It was a 47 instead of a 50. A local road racer who drove my car (I wanted his advice on handling), noticed a slight flat spot in the transition (2500). To me, it wasn't there. Anyway, one year later, my car flunked the smog numbers badly. How can this be? It runs good and I haven't changed anything. I ended up cheating (the stock DP in my 72 super passes the numbers for my 75) and continued to try to figure it out. Then someone said "Oh, you've got the drippy IDF pump nozzles problem. Its your valves." I didn't believe him, so I proceded to try to stop the leaking. I took out the check valve and tried to fix that. I eventually pulled the heads and did the valves, problem solved. I'm sure the valves are in horrible shape now, but 48IDAs don't care. The 40 IDFs are for sale, and I've got a pair of 40 Dells that I will use instead of the IDFs for this exact reason.

ATTENTION all 40-44 IDF owners: Take your aircleaners off and look down the throats at the nozzles. If they are dripping at idle, report back here.

See ya Monday

Bruce Tweddle


Had a similar problem with Kadrons...

Saturday, 01-Apr-2000 07:00:58

I had an over-rich condition that came and went, and it took awhile to find the cause. The accelerator nozzles would stream fuel whenever the throttle was opened, and would continue to do so even after the initial shot from the accelerator pump. After much head-scratching I found out the problem was the little check valve under a brass plug in the float's a cheap plastic piece with a tooling hole in the top, and it had an air bubble in it and cause it to float rather than seat. I replaced these with 7/32" steel ball bearings from my local hardware store, and solved the problem. The car ran a lot better after that.

Craig Merrow



Re: New to 48IDA's - Accelerator Pump Adjustment

Saturday, 01-Apr-2000 01:45:22

There are accelerator ramps made by Berg for the 48IDAs that are adjustable. They come stock on the Berg carb. Amust for the serious tuner. As far as the weeping from the nozzles at idle could also be the design of the cam, over lap etc, and how far are your idle adjustment are open. The engine will pulse, causing the butterfly to flutter, thus making the accelector pump opening and closing at idle. The adjustable ramps allow you to create a gap between the ramp and the roller wheel, solving the problem at idle. For non adjustable ramps I have ground clearance between the wheel and ramp, about a .015 to .025 gap following the contour of the ramp making it smooth and persice. There are many mods you can do to the 40s and 44 IDF carbs to make them idle clean and run smooth remember these carbs where not designed to work on VWs and need help. Anyway thats my 2cents for the night

Gary Berg

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