Weber 40 IDA 3C accelerator pump inlet

[p400]

I am looking to eliminate flat spots or hesitation with quick throttle application using 40IDA3C Webers. I think I see .50 pump jets and .50 inlet/ bleeds are the standard sizes?
1) is there any technical, in any manual, about jet size and bleed size choices or alterations?
2) anyone using no bleed inlet valves?
thanks
Craig
i realize i could consider many other things to resolve this, but i really only want help with inlet /bleed sizing in a Weber 3C.
thank you

[74er]

http://www.pmocarb.com/bulletins.htm

It might not be of much help but see section 4 of link.

[p400]

Thanks 74er, Good tip on inlet bleed. I have skimmed those bulletins before, but not well enough.

"4. Reducing Injection Quantity- We have found that race engines often need varying levels of injection quantity. Coming out of a turn, too much injection quantity can actually cause bogging. PMO has different float bowl check valves to adjust the injection quantity up or down. Rob King at S-Car-Go has cut the injection quantity down to almost nothing with excellent results. The normally installed float bowl check valves have a .5 mm side hole for bleed back. The larger the bleed back hole the less injection quantity. The valves come in increments of .1 mm up to 1 mm. We have 1.5 mm valves for people who want to almost eliminate injection quantity but still start the engine."
copied from PMO website.

So, based on this injection quantity control explanation(accelerator pump jet quantity) from PMO, Porsche Weber people are varying their inlet bleeds to get proper pump quantity out of an acceleration jet? I have never read this before. No doubt i must be out of touch. I have not used the little vials for quantity check.

Is this correct, when you use the little measure vials, find quantity off, you purchase and install smaller or larger bleeds?
Craig

[ValveFloat]

Do you know if you are going lean or rich with quick throttle opening?

One thing I have found is that having the idle mixture too lean will result in hesitation on quick throttle opening. I suppose this could be alleviated with a larger accel pump injection, but richening the idle mixture (larger idle jet) works well. And the engine seems to run smoother at cruise also.

[p400]

Thanks Joe, i would say you are correct, there seems to be other methods of rich/lean adjustment, instead of looking at the inlet valve. However, my real intent with this thread is to get a better or full understanding of why the inlet/bleed circuit exists.
if i am at 1/3 throttle and jam on full throttle leaving a turn and i seem to be going lean with a hesitation......and everything else is perfect ....... is this the point where accelerator pump quantity is important? and the only way to get more is a bigger jet or a smaller bleed?
Maybe there are not that many jet sizes to choose from, maybe the jets are all oversized as normally fitted, and the way to get more (and accurately) is smaller bleeds, yes, maybe , no?
Craig

[kucharskimb]

hah!! perfect timing. i just replaced my diaphrams tonight thinking they were leaking... not the case...

my problem is this:
if i rotate the throttle shaft, it takes 1/8-1/6 of a turn to get the accel pumps to activate. there is no slop in my linkage. i can duplicate the lag by manually operating the arm on the accel pump body. this has also been duplicated on an LM-1 A/F ratio meter, showing a lean spike before the accel pump catches up.

so, tonight i have been looking up info on the internet. again. this time i stumbled upon the same info that you have discovered--the check valve.

i just had my check valves out and, honestly, don't remember seeing a hole on the side. i'll have to look at mine again. i know there was a calibration on the squirter hold down screws, which also have check balls in them.

it is my understanding that upon accel pump activation, the check ball in the bottom of the float bowl closes, and the individual check balls in the squirter hold down screws open. at the end of the squirt, the squirter check balls close and the float bowl check valve opens, creating a vacuum to draw fuel into the accel pump housing, where it awaits the next activation.

one guy said that he simply soldered the little holes closed, and it got rid of the problem. my question is this:

you can vary the intensity of the shot with the squirter nozzle size. you can vary the volume of shot with the accel pump linkage length. why, then, is there a seemingly redundant volume adjustment with the check ball orifice size?

i know there should be absolutely no hesitation in the squirters as evident with all holley carbs. you can breath on the throttle spindle and fuel will drip out.

on the little vial check, it only determines total quantity of the squirt. adjusting the threaded rod can only adjust this so much. so i can see that the rod could be fine adjustment and the jet could be used for making bigger adjustments.

is this similar to your problem? if you look down the carb with the engine off and the fuel pump running, and then activate the throttle, do the squirters activate immediately, or is there a lag? if they activate immediately, i would suggest it is the volume. if they are slow to react as i have described above, then... well, i've been searching for the answer to this for 5 years...

[kucharskimb]

here's a pretty comprehensive site

http://www.huskyclub.com/tav16.html

and... looking through my manual, it has this bleed back valve valued at "none" for every stock 911 application, except on the 904, where it was .4.

i guess i need to look at mine again...

[ValveFloat]

and... looking through my manual, it has this bleed back valve valued at "none" for every stock 911 application, except on the 904, where it was .4.

In my carbs those check valves are marked 0, zero.

[p400]

thanks Matt and Joe, for help with this subject of accelerator pieces on a 3C Weber.

Mat sounds like the ball checks in either 71 or 72 would be the culprit, but could be just one little gasket 69 that is the problem.
Joe you are correct , i wish i had done more homework on this, all Porsche have 000, or closed, or none on the bleed back valve. This tells me Porsche is set up rather heavy on squirt volume.
It would be wonderful if we could see a scan of the cam lever associated with #42. Any chance someone has a carb apart and they could scan the side view of this part. I would like to add it to a webpage so others can compare and assure theirs has not been ground.

I am happy with a better understanding on the bleed , i would like a better feel for the cam profile on the accelerator circuit.
kinda crazy huh
seems to me you could adjust your cam too far and end up with less squirt, or someone could grind it off trying to adjust and you dont know it.

[kucharskimb]

talked with PMO today. Richard says the small actuating lever on the accel pump should just be touching (ie, no slop/backlash) the metal button on the diaphram. that's great, but why then would you go on to measure the squirt volume with the vials?

i have some more questions regarding the reaction spring. but i'll post a more complete parts diagram.

p400, is that your site that i referenced. you have some great info there. i've been doing some testing with an LM-1 AF monitor. you can see some of my results here:

Weber Tuning. LM-1 and Dyno. Database, Information, Troubleshooting, Graphs.

feel free to use the stuff i've gathered.

[p400]

yes my site with info , thanks, hope it helps.
how do you talk with Richard , i thought fax only.
i dont have one yet , but the AF monitior looks great!

i dont know how to combine these engine rebuilding and tech threads on Weber, help.

[dvkk]

Originally posted by kucharskimb
one guy said that he simply soldered the little holes closed, and it got rid of the problem.

I tried that once. Then I discovered that the little check ball inside is plastic......

[kucharskimb]

craig
sent you a PM.

dvkk
yeah, i think he made mention of that in his article. it was for a 12 cylinder setup

[p400]

Hi Matt, in looking for a reason for delayed hydraulic reaction, the biggest classical reason is trapped air. i am noticing the Weber 40 IDA 3C rebuild kit diaphram is made out of several layers, which could easily trap a critical, small amount of air between layers by design, a very poor design for a low flow diaphram because of this very fact.

maybe there is a kit with with a single layer pump diaphram?

[kucharskimb]

you must have an old rebuild kit, because they moved away from the black double layer diaphram around 2001. the ones you get from PMO now are single layer and red.

i guess it could be like a brake caliper, but then, you would think there would be a bleeder plug on top of the accel pump.

i understand the concept, with air being compressible and fluid being almost incompressible. so lets say there is an air pocket inside the pump body. the only way i could conceive to bleed off air would be to loosen the two top nuts slightly. slowly depress the actuating lever. hold it down. tighten all nuts, then release slowly, to draw in more fuel. repeat.

got any better ideas?...

[p400]

well, just a thought about trapped air. Could it be you just dont have enough pump cycles on the accel pumps, and there is trapped air that would be purged out. Seems like this would happen pretty quick, but just another thought. so maybe the ball checks or gaskets at one end or the other are leaking.