The early 46IDA3C Webers used same cam levers as the 40IDA3C and used the fixed length, non-adjustable pump rods, squirt amount was reduced by use of the bleed hole size in the inlet check valve, pictures of various inlet valves below, size markings on back side but holes are obvious:

http://forums.pelicanparts.com/uploa...1434563601.jpg


Also, 46IDA3C Webers, both early versions and later ones used the same discharge jet ("nozzle or squirter") and all had 0.50mm orifices in their tips.

Later 46IDA3C Webers came to use the adjustable pump rods but this began in 1968 along with their use in production cars. It is interesting to note that the 46IDA3C Webers used for race applications in 1968 (911R & Sports Purpose applications) used the earlier pump rods and cam levers, presumably due to an abundance of inventory of the earlier version Webers.

If you pursue the "hatchets" from Chris then you will need to be aware that unless those have been changed from OEM they will have a hole for the 4.5mm dia stud on the boss of the later version, adjustable pump rod design vs. the 3mm diameter, fixed-length pump rod you have.

Your webber jetting looks like you're starving your engine.

OK getting the picture regarding check valves and nozzles now. Seems it may be worth buying two bigger check valves before the hatchets in case it's a pure volume of fuel issue. I will have a harder look at the valves tommorow to see what number they are. I can say they have the hori zontal bar across to hold the ball in. Do you know the number sequence and size to application or cylinder capacity.

I totally confident in the jetting its just the acceleration enrichment which has been proven by the "back off" and roll on tests and the improvement gained by getting the available fuel volume in as fast as possible to improve matters by at least 90%.

Just tuning the solution now.

You want the inlet check valves (pictured in my last post) without any hole in the side which is what I believe you already have. The side holes allow gas to be pumped back into the float bowl during acceleration demand; without the hole, all fuel sucked into the accelerator pump would be directed to the discharge nozzles. This assumes that the check ball in the inlet valve closes and does not leak during acceleration demand. The picture shows inlet check valves with holes so you know what to look for, again, you do not want ANY holes. All check valves have the same inlet (top hole in the valve where the screw driver slot is) and discharge hole (bottom hole with keeper bar pressed into it).

Paul is quite correct I have looked at all of the discharge valves I have out of 40IDAs at present (around 30) and one of them have any holes.

The same valve is used in a 40 or 45 DCOE and they normally are either a 40 or a 60.

I am happy to let you have a couple hatchet blanks and can enlarge the hole if needed.

I don't need money as the information about the change they make is worthwhile knowledge.

Chris, many thanks I'll call you as discussed next week when the blanks are in. I'm happy to drill them to ensure they fit my old type rods and pivot unless you are totally happy to do so and have the sizes ?

Thanks again.


Andy

Had time today for some tuning and adjustment, took the trouble to de bung and clean all idle circuit drillings including the hidden one, reset fuel pressure at 3.5 psi , re set floats to top mark on level tool, set best lean idle using Pauls listening method. The idle screws are on average 2 1/2 turns out

The problem is still there under hard acceleration but better with improved driveability at small throttle openings.

I have yet to pester Chris for the hatchet pump cams to try but do wonder if the idle jets are a bit small, they are 60's and by my thinking if the idle screws are so wide on tickover the jet may not be keeping up with demand through the transition to the main circuit?


What do you guys think ?

Andy

Hi Bob, not sure I understand, my jetting is ballpark / same as most other 2.8 twin plug motors.
Plug chops have always shown evidence on the side of rich for higher rpm. The AFR was declared ok at the rolling road ( being gentle with a new motor) .
This stutter or flat spot is I agree caused by a temporary lean condition under conditions not routinely used , it works fine with roll on throttle so a burned piston is not a major risk in my mind.
I could lift the pump pressure to 4 psi though.
I should say my carbs are the early circa '69 ones so have a fixed air inlet size to the idle circuit not sure if this is contributory?

Thanks for the inputSmileWavySmileWavy

If you can't get bigger jets, then I would suggest a similar sized set of jets and ream/drill them to slightly larger bore, trial an error until you flat spot is eliminated.

Bumping the fuel pressure may help if it is easy enough. Most standard pumps are 5psi with an inline dial restrictor is that how yours is set up?

BTW, people have been fighting Weber flat spots since they first came out.

Yep, easy to dial in more pressure with my set up. Question is , is it the right thing to do.

I know these flat spots are the bane of modified engine carburation. :(

We'l get there with so much help around SmileWavy

Mixture for transition is best analyzed by slow but steady acceleration from 2000RPM through 4500RPM in 3rd gear, take 60 seconds to do this and note AFR readings or engine response. This test is best performed on an inclined road to provide more realistic operational conditions. Idle air bleeds can be changed to tuneable versions which I have a kit for. The air correction allows for "tilting" the mixture delivery as RPMs rise without up-sizing idle jet.

I thought we were working a sudden acceleration issue and not a normal running issue.

Floats are there to provide a method for maintaining fuel level constant in the bowl which is important to make the main circuits work correctly. Up[ping fuel pressure is OK but not more than 4psi, the needles are not designed for that. However, I am just in the process of making Viton tipped needle valves which can withstand 7 psi and are not affected by ethanol. Your fuel flow would be critical at WOT, not at mid-RPM, sudden acceleration.

Did you say you have IDTP Webers vs IDA? This makes a BIG difference for your application.

Hi Paul yes sudden acceleration, normal driving no issues. We are still on track. They are early webers I need to get the numbers off the bowls don't I . . I can confirm early accel rods, hatchets etc, early fixed size idle air inlet made of brass and lead plugs in all galleries rather than brass.

Edit.They are not IDT's which I now understand are the ones with emission control factors , these are much earlier .

Good they are not IDTPs, makes life easier for transition tuning. Tuneable idle air correction jets are very useful for that issue.

Get the hatchets and see where you are. You might also look at making some longer pump rods for testing. The OEM ones position the roller so that it does not have full lift potential of the cam-lever. Also, I imagine your pump rods are worn as well as the hole in the lever arm mounted on the throttle shaft and therefore have "lost motion" and do not provide as much squirt as new ones would.

You will need to get the adjustable pump rods and the square boss that attaches to the hatchet to install the hatchets.

Thanks Paul will do. The existing pump rods and arms are in perfect condition I resized all the holes and rods when I originally re furbed the carbs.