Need Weber Carb Technical Help!!!

vntgspd · 05:45 PM

Okay, I have been working on a carb rebuild and tuning for a couple of months now and have learned alot as I had intended.

I have done the searches and read the books but need some input from the experts here.

Carbs are 40IDA Webers
170 Air correction jets
60 Idle jets
125 Main jets
F3 Emmulsion tubes
50 Accelerator pump jets
Engine is 2.4L with 2.2S pistons and E cams

The car idles well and pulls well from about 4K up (on main jets I assume). In my search to balance the cylinders and clean up the low speed circuit, I have encountered two issues that are troubling:

1. The center choke on one of the carbs won't adjust idle mixture. The cylinder is dead but plugs, wires, compression all check out and runs well on main jets. I disassembled carburetor and cleaned again and did get a good size chunk of white debris out. Upon reassembly the same problem still exists. All jets are clear and carb cleaner and air flow through ports with no issues. Seat inside mixture screw bore looks okay and screw is a new one purchased from PMO. What could I be missing?

2. Accelerator Pump jets do not flow the same within a carb. I am finding that some chokes may be around .4cc while others are at .6cc on the same carb. I have disassembled and cleaned again and checked for free flow through all ports and jets. I suspect it may just be a difference in the jets. Before I go and replace them, is this difference something I should be concerned with? I would think that this amount of fuel must be balanced to get good driveability.
Also, Wayne's book says to measure after two "pumps" of the throttle and PMO suggests measurement after one "pump" of the throttle yet both suggest the same amount of fuel should be administered during this process. Can anyone clarify what amount of fuel I should be targeting with either method?

Sorry so long - hopefully I have provided the necessary details for the experts. I look forward to your responses (and getting the car back on track!).

David

911quest · 11-11-2006, 08:39 PM

when you rebuilt these did you just use carb cleaner in the can or did you dip them for a couple of hours in carb cleaner sounds like that one cly, has a clogged idle jet or the progression holes are clogged

Walt Fricke · 11-11-2006, 09:37 PM

Here are my thoughts until an expert chimes in.

1) I make some assumptions:

a) the hole is dead, as in pulling the spark plug wire at idle causes no change in RPM? But doing the same at a higher speed does?

b) you unscrewed the progression hole cover as part of assuring yourself that the passages from the bottom of the affected float bowl up to the idle jet and back down to the adjusting screw, and then on to where the idle mixture squirts into the choke are indeed really clear? Carb cleaner blows through each of these? Or applying suction to each of these where you can access it externally will suck a fluid out of the float bowl? White debris suspicious.

But if things are patent, then what? My next suspicion would be an air leak somewhere along the way, though I don't have any good ideas on where. I can't imagine a progression hole would be enlarged, or that a slightly bad seal on the idle jet holder would let in enough air so you got no fuel (I have reused my the copper seal washers on my various jets over and over and over). Ditto with the adjusting screw.

There is a brass insert with a hole in it right above the idle jet ("calibrated bush" Haynes calls it). It acts like the air corrector in the main circuit. Hard to see how it could get larger. Or that it would fall out (it is pressed in, I think). Or even that, if blocked, it would prevent any fuel from getting in, or make the mixture so rich it would not fire. Hmm - if you run only on idle, and turn off the engine, is that plug the slightest bit wet?

If you had a big air leak in the gaskets below the carb, maybe that might affect things? The general rule seems to be that small air leaks (say along throttle shafts) affect idle but don't much affect high speed running. On the other hand, these affect things by leaning out due to excess air, not because of inadequate vacuum I think.

Have you used a Unisyn or other device to measure the relative vacuums through the chokes?

2. Are all six accelerator pump jets really the same size? I don't suppose you have a jet gauge to check to see if the stamped numbers are what the jet actually is? A long shot, but my only other thought is perhaps more of that white stuff somewhere, which doubtless occurred to you when you flushed some and you redid things again and got no more.

There wouldn't be a Porsche spec for the engine you built. Since the pumps are adjustable, maybe there really isn't much of a spec to go by.

Porsche gives 0.5 +/-1 cc per stroke for the 2 liters with the Weber. For the Zeniths they say the same, and say you should pump it once or twice before measuring. Of course you could capture two strokes and divide the result.

On my race motors w/40s and 46s I cranked the pump way down so it hardly spit anything - just enough that a lot of pumping would get a cold engine running. Otherwise I had bad bogging coming out of corners due to over richness. So I figure it is something you need to adjust while driving the car hard. But someone who wrote it down will come through with what works for them, no doubt, as your high compression 2.4 with carbs is a popular setup.

Walt

vntgspd · 11-12-2006, 07:06 AM

Thanks for the input.

911quest - the carbs were dipped and cleaned well, or so I think.
The idle jets and progression holes are all clean and clear.

Walt - yes I removed the plugs and jets to verify that all passages are clear and carb cleaner flows freely. The brass plug on top also appears to be fine. I did not try vacuum to see if it pulls fuel so maybe I'll give that a shot. I'll also have to get some vacuum leak detector to see if there are any issues there. I did try sparing shots of carb cleaner to look for vacuum leaks and nothing was evident.

I did notice that the IDTPs used an oring to seal the idle jet holder but the IDA I got did not. The IDA also does not have the relief machined to accept the oring. I put them on anyway but they split after a week or so. Now there is no seal on them but they don't seem to leak. I'll have to go back and look at my parts diagram to see if there should be some sort of seal there (the idle jet holder screws DO NOT bottom out on the carb body to ensure the jet seals properly I assume so I would think any seal in this area must be soft like an oring to allow the idle jet to seat).

It should be noted that this same setup ran well on this engine with the IDTP carbs I took off. They had slightly worn shafts and so I was looking to put a better set of carbs on the engine. Now I wish I left it alone! Worst case I will put all of the jets back into the IDTPs and see how that works.

Thanks!

David

2.7RACER · 06:21 PM

Two things: What is the size of the venturi's? 32mm would be right, pull all of the venturi's and measure. They may be stamped on the side, still measure.
The 60 idles are too big for this engine. closer to 50 or 52.
I'd get O-rings for the idle jets. Stops air leaks.
The 125 mains are on the small side. I run 145's on my 2.7 at 5000 ft. Solex cams and 9.5 JE pistons.
I'd try 140 or 145's.

Walt Fricke · 11-12-2006, 06:21 PM

David

An evil thought: have you done a leak down on the hole that doesn't fire at idle as well as at least one other which does as a standard?

60 idle jets might be a bit large, but I'd think that hole would still fire. And the others do. Doesn't the A/F ratio have to get way way off in either direction from stoich in order for the mixture to fail to ignite? You could try a smaller jet in that hole just to see - a smaller jet should be a stronger signal (easy for me to say, since I made up a jet box with 6 of more sizes than I need, though I set it up for both 40s and 46s). I'm not sure that some expedient like somehow fixing a small wire in the jet would emulate a smaller jet if you don't have a smaller one lying around.

Swap your spark plugs around?

Walt (just pondering this puzzlement)

kucharskimb · 06:40 PM

squirters giving you uneven amounts...
occassionally, the check balls in the hollow brass screws that secure each squirt stem will stick. you can clean the brass assemblies in vinegar. yes, they should be equal amounts. start with about 1/4 of threaded actuating rod exposed after the nut as a starting point.

dead cylinder...
odd that it is the center barrel. when i have had a cylinder that would not adjust with the mixture screw, it was one of the following:
1. plugged idle jet--sounds like you have evaluated.
2. float bowl overflowing and fuel pouring through secondary venturi. is the plug wet or dry? --with a flashlight and inspection mirror with the car running and aircleaners removed. if it is dripping, it is too much fuel.
3. clogged air corrector (on top, not air corrector screws on the sides) some of the top plate gasket material could have fallen into the hole, or something else. you can also spray cleaner into this top air corrector port and see if it comes out the idle jet hole and the mixture screw hole.
4. also, each screw will be set differently. have you tried opening it further to see if the cylinder wil come on?

you need the o-rings on the idle jets. that allows the system to create the low pressure (vacuum) to suck out the fuel.

i agree with the 32mm venturies. 55 or 60 on the idle is close. 125 mains will probably end up being small. but let's stick to the problems at hand.

vntgspd · 11-12-2006, 07:35 PM

Great input everyone! I will try out the suggestions tomorrow if possible and report back with findings.

At this point I am hesitant to change any jets because the car ran very well with this set up before, with the exception of a very slight flat spot from 4500-5000 rpm.

Matt - I don't recall backing out the mixture screw more than 2 or 2.5 turns!

I will try that to see if it comes to life. I should be so lucky as to have this be a simple brain fade.

Thanks again.

David

vntgspd · 11-27-2006, 04:09 PM

Quick Update - FINALLY!

I made sure all air jets and mixture screws have proper o-rings.

I made sure the idle passage was clear - I can spray cleaner into the idle jet hole and it comes out the mixture screw hole and the idle air jet on top.

I double checked the spark plug. It is dry, DOES NOT fire at idle but DOES fire at high speed. Also fires at idle with a quick shot of carb cleaner down the venturi.

Tried opening the mixture screw more than 2 turns - no change.

Tried vacuum on mixture port but was unable to pull any fuel from the float bowl. Could be the mickey-mouse vacuum arrangement.

Checked a couple spare hollow brass bolts for the accel. pump jets and did not see any check balls. I have yet to check the screws on the carbs. Could there be some with check balls and some without??? This would seemingly cause a variance in fuel flow.

After all of this, there is still no change. The car will sit and idle perfectly for an hour and also seems to run well at high speed. It just hesitates through all of the midrange and is also sometimes slow to return to idle speed.

BTW, double checked all of the venturis with the Synchrometer and all are even (within one needle width on the Synch). Also appear to be even at 3000rpm although marks are closer together at that vacuum level so variance could be higher.

Once again - any thoughts??

The carbs are currently back on my bench and I am considering a complete teardown again and removal of the lead plugs to ensure 100% cleanliness. I just hesitate as I don't want to create any new issues considering the passages APPEAR to be clean already.

Thanks!

David

T77911S · 11-28-2006, 04:34 AM

if u pulled "white stuff" out of the carb, re-soak it for a day or two, then blow it out with an air compressor.

Early_S_Man · 11-28-2006, 07:22 AM

David,

Have you checked your spark plug wires for ene-to-end continuity lately? 3000 - 4000 Ohms is normal, depending on whether the distributor ends have 1000 Ohm resistors or not. If an 'open' is found, unscrew the Beru spark plug connector and replace it.

kucharskimb · 11-28-2006, 08:57 AM

accel pump check balls: pull all six out and soak them in vinegar--i prefer balsamic as it is stronger... if you can't hear the little balls inside moving when you shake them gently, they are jammed or corroded.

for the cruise circuit, i think a picture might help you here:

you have to ensure that the air/fuel flow is uniterrupted between 24 and 19. you also have to ensure that the fuel delivery from the bowls/emulsion tubes 22 is uniterrupted. this can be done with compressed air or spray cleaner. if you are going to use air, either use a can with a straw (cleaning computers), or a low pressure from you compressor with a straw attachment. since the carbs are on your bench, you can orient them differently to get the cleaner to run in the direction you are troubleshooting.

ensure that the butterfly on the dead cylinder rests against the side of the bore in the same position as the other two cylinders. you can check by looking at the relative position to the progression/idle feed holes.

a final check might be the seat of the idle jet on that cylinder. try swapping jets to see if it is warped, damaged. also, look inside at the idle jet seat. if either are damaged, you will not develop the correct vacuum. the jet seats against the the carb body inside. the holder sits in the threads and the o-rings basically seal up the threads.

the fact that everything is dry in that cylinder is telling me that you are not getting fuel.

vntgspd · 12-30-2006, 06:02 PM

Solved the last of the issues today!

Thanks to all on this board for your input and suggestions.

Here's what I found:

The dead cylinder was a result of a clogged idle passage down by the main jet. It would flow carb cleaner and air but would apparently clog up under light vacuum. I removed the lead plugs, cleaned the circuits and all was well for that cylinder.

Once the idle circuits were adjusted, the car idled and ran well at low speeds. However, I had an issue with the accelerator pumps that was not resolved. One carb was spraying significantly less fuel than the other. I chased this down to jets with slightly different hole sizes and one stuck check ball on the screw for the pump jet. After resolving these issues, the accelerator pump jets were better but still not right. I was still getting a moderate hesitation at throttle tip-in.

After some time dealing with this, I found the culprit today. I did not realize that the brass screw in the bottom of the float bowl also had a check ball in it. Sure enough, one of them was blocked and therefore letting fuel back into the float bowl instead of forcing it out the accelerator pump jets. I replaced the faulty check valve with a spare and now it runs great!

Special thanks to the following:

Larry @ Oil analysis
Richard @ PMO
Dan @ Scott's Independant (who helped diagnose the final issue this morning over coffee!! Thanks.)

THANKS!

David

azasadny · azasadny's Garage

David,
Great news! I'm glad you've got it figured out. I've only had my Webers since 12/20, but I absolutely love them and the sounds/throttle response I get from them!!