Sync Webbers

[protex1]

Well I have the 3.0 with MSD ignition and Webber carbs. How it has been sofar. The car sputters like the rev limiter is cutting in at the 4000-5500 range when hard on the throttle. Sputters and pops thru the exhaust and pops at the carb at random. I did valve adjustments checked the plugs and an oil change last weekend. checked the timing and with my cheep light it looks like idle is at 5 btdc and at about 5800RPM about 32 advanced. I got a sync tool today and looked at the webbers. Here are the results. #6 is sucking about 8 on the meter and the air screw and mixture will not make and change. #5 is close to the same and measures 6 on the meter, #1,2,3,4 are all at 4 to 4.5 on the meter. the air screa on 6543 makes little change. I gave up for now. I noticed the fuel spray from the top of 1 and 2 when reving hard. May need larger idle jets? I also need new gasket for left bank accl pump. Any ideas to get em in the right direction. Thanks Pelican.

[snbush67]

It sounds like your number six idle jet may be plugged, I think you can pull it and blow some air through it to clear it out.

Once you determine that the jets are all clear, then you should synch the carbs.

If you continue to have problems it is likely you have some debris floating around and plugging the jets.

Start the car and warm the engine, then shut it off

Turn all the 6 air screws in so that they are gently seated, leave the nuts loose

Turn all of the 6 idles mixtures in till they seat then back out 2 and 1/2 turns

Turn the 2 main idle screws of each carb out and then in until they touch, then another 1/4 turn

Start the car, you can turn the main idles in a bit to idle around 950 rpms

Then unhook the short arms on the linkage to each carb

Use the synchro to check the pull of each carb

Find the one that is pulling the most air and using the air screw adjust the other two carbs in that bank to equal the one pulling the most air.

Now go to the opposite bank of carbs and find the carb that is pulling the most air on that bank and adjust the other two to it.

So now you have to synch each bank to each other, do this by determining the bank that is pulling less and turn the main idle screw of that bank slightly to even them out.

Now hook the short arms back up and check balance again, it shouldn't have changed but if it did it is likely that you may have to adjust the arms so that they are equal length.

Now adjust the idle screws to steady the rpms at 950-1000 while checking the balance, if you turn the left in a little you need to do the same on the right. It's a dance.

Next is to lean the mix out.

First you want to rev the engine a few times to clear it out, when the idle steadys pick a carb and turn the idle mix screw in slowly about 1/8th of a turn, repeat in 1/8 increments until the engine slows, you have to listen closely, once you do it a couple of times you will be able to tell when it starts to bog. When it starts to bog turn the screws back out until it runs smooth, usually about an 1/8 of a turn back out does the trick.

Now repeat for each individual carburetor.

Check the air draw with your synch on each carb, and adjust to equal.

Tighten the air screws and replace the air cleaner and go for a drive.

Good luck!

[protex1]

Wow thanks for the detailed description on this. There are a few things I did not notice in what I was reading when I wad working on the car that you added. I will print this out and reply when I get back to the carbs Monday after work I hope. Thanks again!

[1QuickS]

Cylinders #3 and #6 have a single throttle plate mounted to the throttle shaft while cylinders 1 & 2 and 4 & 5 have two throttle plates per shaft. The long shaft and the short shaft are connected for rotation using a shaft coupling which is either a cylindrical one or for the earliest Webers a "folded spring". If the shaft coupling is broken or loose or has been "adjusted" by a previous owner then there is the real possibility that your #6 throttle plate is mechanically too far open to be adjusted with air correction screws.

Typically when "Lean Best" idle mixtures have been achieved you will see a STE reading of 4.5 to 5.0. Larger air flow readings indicate a rich mixture that requires more air flow to allow combustion.

Your air flow reading on #6 is large (8 per your posting) and your other cylinders are at 4.5 (6 @ #5 isn't that far off) so I'd check for a throttle plate that isn't closing at #6. Closing the idle air correction screw decreases the air flow at idle speeds.

Check out this site for another version of basic tuning procedure: Weber Carbs Technical