I just rebuilt my carbs for my six. I got the car warmed up and started tuning them.
First when I turned the mixture screws on one of the carbs the idle did not change unless I just about turned them all the way in. The other carb did not change much
at all when I turned the in or out. When I tried to adjust the air correction screws on both carbs I could not get them to all read the same on the sync tool. I was geeting a lot of backfiring thru thru the carbs. What is my problem here???????

Hey man
Put the "6cyl" in the title heading and you will get some
really good help. Most guys would fall over for a set.
But I can't help
Cheers
Joe

It could be a variety of things. Since you rebuilt the carbs I'll guess that you got ALL the crap out of the passages that feed the idle circuit because it doesn't take much to plug a jet and mess up the idle.

How are the bushings for the butterfly valves? Try spraying a little carb cleaner around the ends of the throttle shafts to see if the idle smooths out any. If it does then you've got worn bushings and air leakage.

Also, try the carb cleaner trick around the bases of the carbs and look for the same result. Again, vacuum leaks will really cause problems with carbs.

All the carb gaskets are good?

Backfiring or spitting through the throttle bodies usually indicates that the carbs are lean. Back out the idle mixture screws some and it should settle down.

What is are the specs of the idle jets, air correctors, mains, etc? Were these changed from stock? Is this a stock engine with stock cams?

If you're not getting a change by adjusting the air bypass screws and the engine is giving you a "lean spit", it seems to me that you've got vacuum leaks.

You need to make sure the fuel pressure is about 3.5#, if much higher it'll flood. How is the float level? If you do not have a PMO gauge you'll need to buy one (I bought two so I can do one side at a time) so the floats are not to high or too low. If too low the engine will run too lean, too high and it will get too rich. Since I imagine you preset the mixture screws correctly that you had to turn them all the way in makes me think that side is flooding. Did you unhook the crossbar linkage and do the carbs seperate? If connected it will be hard to get them to match up. The spitting through the car can be from a lean cylinder unless you have 906 cams which have a lot of overlap and they spit no matter what usually. You can have one cylinder on a side be rich, one lean and one right on and never know which is which. I use my pyrometer to measure the exhaust from the cylinders to see if their temp is close, if one is low, it is too rich, etc. Good luck.

It sounds as if they are reacting just about as they should.

If you feel the need, PM me and I'll give you my ph #.

The Weber dance is too long for me to type at my advanced age.

Guru Help...score

cheers
Joe

Thanks for the help.I will check for vacum leaks and I do have a pmo gauge and the
floats were fine.All the gaskets are new. All the jets are stock for weber 40's.I made sure all the passages were clean when I rebuilt them.All linkage was disconnected
when I made adjustments.I did notice when I had the sync gauge on one carb it
would balance fine at around 4 to 4.5 and the other carb would get one barrel to a maximum of 4.5 and the other 2 barrels I could not get any lower than 6 no matter what I did with the air corr. screws.
Anyway JP I will PM you for help.

Here's a copy of my post from 9/22/04

Assumptions: the carbs have the optimum jet and venturi package (good luck on this one), the float level in the carbs is correct, the cams are correctly timed, the valves are properly adjusted, the ignition timing is dead on, you have the proper spark plugs for your engine, the linkage is good, the fuel is good, the engine is good.

Remember that the mixture and air bypass adjustment screws are precision needle valves, not head gaskets. Use your fingers to tighten them, not your fist.
Start and warm up the engine.
Make sure the two drop links for the throttle linkage are exactly the same length, and disconnected. You can use a 8mm thin igntion wrench to snap them off.
Turn the mixture screws all the way in and then 5 half turns out.
Turn the air bypass screws all the way in.
Turn the idle speed screws out til it just touches, and then in 5 half turns.
Put on your hearing protection and start the car.
Use your STE and find the barrel that pulls the most. We'll call this one baseline.
Balance the barrel in the other carb that pulls the most with the idle speed screw. (if you have a Uni-syn, give it to someone you don't like and purchase a STE airflow meter)
Go back to the other carb, with the baseline barrel. You will have one all the way in, then use the air bypass screws and balance the other two barrels.
Go to the other carb and do the same thing.
Snug the jamb nuts on the air bypass screws.
All six barrels should pull the same amount of air at this point, if not repeat air adjustment proceedure.
Snap the throttle linkage drop links back on the carbs. If the idle changes then you need to barely adjust the linkage mounts so snapping the drop links on, doesn't change the side to side idle balance.
Use the hand throttle or a vice grip and rag to lock the linkage between 1400 and 1800 rpm.
Start back at the baseline barrel and adjust the mixture screw in or out, to get the smoothest running and highest idle, then turn it in 1/4 turn.
Do the same with the five other mixture screws.
If you have to turn the mixture screws more than two turns either way, you've got the wrong jets.
Recheck side to side and individual air balance, adjust as needed.
Road test the car.
If you get snapping and poping out the intake, it's generally a lean condition.
If you get heavy exhaust fumes, or pboofing out the exhaust it's probably too rich.
If you get a flat spot or popping out the intake at between 2800 and 3200 rpm, you probably need larger idle jets.

That's a rough, five minute draft of my carb tuning proceedure, hope it helps!

If it goes good it should take about 45 minutes, if not about three years.

PK

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Make sure you don't have the idle mixture screws and air bypass screws exchanged, this will give you trouble for sure!

Here's a great test to see if your idle jets are working properly. If you back out the idle jet carrier just a little bit (1/4-1 turn) and the idle drops then that jet is working, if nothing happens, that jet or it's circuit is clogged.

I just did this and found that "much" of what you're talking about can be cured with new vacuum lines all around. Mine still had all the factory braided cloth stuff. Next use the carb cleaner method mentioned above. You're popping does sound like a lean condition. After 35 years, you'll probably need to have new shaft bushings. I recommend Harry Beiker at:

www.biekerengineering.com

There is also a factory fix for the shaft bushing (has a factory number and all), it's a special tape precut that wraps around the shaft. I may have one laying around somewhere with the part number.

All of these are good points, however I would like to mention the overall condition of the engine, the engine will act exactly as you are describing if the valves are tight. Please check your valve clearance and compression then tackle your carb problem if that is what it is.

Erik Madsen