Jetting Advice - Weber's on a 2.2T

[keitho64]

All,

I am looking for a recommendation from the experts on jet size. I adjusted the carbs this weekend and with the mixture adjustment 4 turns out I still get occasional popping at idle. I have the air bleeds out a max of 1/8 turn. The jets are 52’s. Should I go up one or two sizes? Or am I missing anything else? The rest of the performance seems good but I have not put many miles on it yet.

The engine is a 70 2.2T but I have no knowledge of what cams are in it.

Thanks

[T Bird]

Keith
The general rule of thumb is that if the mixture screws are out more than 3.5 turns, you need to bump up a size in the idle jets. .52 idle jets do not sound too far off for a 2.2 T. However, before you go changing idle jets to .55, do you have these carbs balanced? I wonder because of your reference to the idle air correction screws. It doesn't matter how many turns open or closed those screws are. What counts in the end is that each barrel is pulling equal vacuum and that vacuum balances side-to-side at idle and at 3000 rpm.

With the linkage disconnected, you use the idle air correction screws to get each barrel of a carb to pull equal vacuum at idle speed. Generally, you start your adjustments with each idle air correction screw open 1/8 of a turn. Although, I personally prefer to start with each screw turned in all the way (fully closed). Using an STE or unisyn, you find the barrel that pulls the most vacuum with the idle air correction screws turned in all the way. Lock the jam nut on that screw. Then you open up the other two idle air correction screws (one at a time) until those barrels pull vacuum equal to the barrel that has the idle air correction screw turned in all the way. Lock down the jam nuts on the screws when you get vacuum in those barrels to equalize. Now, vacuum is balanced on that carb. Then you repeat the process for the other carb.

Next you balance side-to side vacuum at idle with the idle stop screws. That is, you get each carb to pull equal vacuum at idle speed by turning the idle stop screws in/out. When you have each side pulling equal vacuum at idle speed, you reconnect the linkage and check again to make sure that the linkage has not exerted preload on the throttles and upset the balance at idle. If it has, adjust the length of the press rods to remove the preload.

Next, speed the engine to 3000 rpm and check side-to-side balance. THIS IS CRITICAL. Do not speed the engine by pressing on the crossbar. Have an assistant in the car apply pressure to the gas pedal. If balance is off @3000, you have to lengthen or shorten the press rods to achieve balance. Once you accomplish this and attain balance at 3000 rpm, you must recheck idle speed balance. Lengthening or shortening the pressrods can upset idle speed balance. You must balance at both idle speed and at 3000 rpm. Keep at it until you are balanced.

When you have vacuum balanced, then AND ONLY THEN, do you adjust mixture. If you can't tame the popping with the mixture screws out no more than 3.5 turns, then consider bumping up the idle jets a size.

I posted step-by-step Weber set-up instructions last week in response to a post by Cerbin. They are based on my experience in tuning these carbs over the last 15 years. They may not be perfect and others may disagree with them, but they have worked for me. You may want to review those. I'll post a link if a get a chance.

Good luck.

[T Bird]

Keith
Here's the link.

Weber rebuild

[keitho64]

John

Thanks for the advice. I actually used your procedure this weekend. I found it to be the most comprehensive and easy to follow. You should consider publishing that.

I did perform the balance at 3,000 and had it correct. (or so I thought) This is only the third or fourth time I have tried this on Weber’s. I will recheck them one more time. My reasoning for going up a jet size was based on your write up. The car does run very good and steady mid range RPM is smooth as is acceleration.

From what I have found on Pelican it seems that .55 might be a place to start. However, I am concerned that may be too rich for my setup. I will run through the adjustments another time and see if I end up with the same result. Outside of the occasional popping at idle everything else seems to be on the money.

[T Bird]

Keith
How about balance at idle? Are all barrels pulling equal vacuum at idle speed? If your vacuum balances and you're still popping and the idle screws are out 4+ turns, go for the .55s. Remember to get new O rings and oil them up so that they don't get pulled into the threads and break.

Glad to hear that the set-up instructions were helpful.

Good luck!

[keitho64]

John

I am thinking that I may have messed up and need to redo the adjustments again. After driving the car I have the number six cylinder pulling very little air at idle while the other 5 are all equal. I did not recheck at 3,000 but I will check that before I run through the adjustments another time. I was thinking it may be dirt in the carb. Since the car seems to run good I planned to leave it alone for a while and start driving it to see what happens. The car idles at 900 and is very smooth. I get the occasional popping out the exhaust but no more spitting out the top of the carbs.

From your experience do you have any suggestions as to why the one cylinder is pulling less air than the other five? I am assuming I need to go through the adjustment again.

Thanks for all of the help.

[T Bird]

Keith
Sorry it took so long to reply, but I was out of town and away from the internet since Monday morning.

I don't quite understand the problem. Did you get vacuum balanced originally, but now it's off? Are you using an STE or a unisyn? Are you sure that you have a good, tight seal with the STE or unisyn around the throat of barrel #6? Any gaps here will produce low vacuum readings on the STE or unisyn.

If that's not it, what I would do is disconnect the right and left press rods and measure vacuum. If #6 is still off, the linkage is not at fault. Readjust vacuum on this carb. That means, screw in the three idle air correction screws all the way and start over. Find the barrel on that carb that pulls the most vacuum and lock down the nut. Adjust the other two to match, as outlined above and in my instructions. Then balance side-to-side at idle with the idle stop screws. Reconnect linkages and recheck side-to-side at both idle and 3000. Then readjust mixture and test drive.

These instructions must be followed precisely. You can't skip a step. You are mixing air and fuel here and must get the air and fuel portions equal for every cylinder.

Vacuum at idle measures how much air is slipping by the throttle plate and through the idle air bypass. If your problem is not faulty adjustment on your part, it could mean that something is wrong with the engine, and specifically, #6 cylinder causing it to draw significantly less vacuum than the other cylinders. That could mean poorly adjusted valves, or a burned valve, for example. Webers should be set up only after ensuring properly adjusted valves, clean air filter, and correct ignition timing. The only other thought is that something could be wrong with the throttle plate for barrel #6. Usually, when these carbs wear out, the clearance between the throttle plate and bore increases causing excessive vacuum readings, not insufficient vacuum as you seem to be experiencing. When this occurs, it becomes impossible to balance vacuum because even with the idle air correction screw open all the way, you can't equalize vacuum with the barrel that is worn out.

Good luck. Keep us posted.

[si2t3m]

The instructions that John posted a while is really helping me in my search of ZEN with my Webers! Thanks a bunch. Yes one needs the ear of a musician.

Just to mention that each bank of carbs has 2 throttle shafts. #3 and #6 are attached the the other part of throttle shafts with some small allen bolts in a coupler.

It might be a good idea to check in that barrel (with the engine off) if the throttle plate is in sync with the 2 others. Had forgot to tighten on side on mine so it would never open.

It's a WAG but worth to check!

HTH

Marc-Andre
914-6 conversion 3.0L

[keitho64]

<<>>

AHa! This is what I was wondering. I plan to take the carb off this weekend and check that out.

Thanks for all of the input.