Weber idle adjustments

[1QuickS]

I just finished up a project on a set of 46mm "American" Webers and noticed a machining error which is worthy of note to highlight idle adjustment procedure.

When at idle the progression circuit holes should be completely blocked by the throttle plates leaving only the mixture screw hole to provide fuel at idle. Both pictures are of the same carb, freshly remanufactured with new throttle bushings and new butterflies and taken after idle adjustments completed.




The next picture shows the same carb (different throttle plate) with the throttle plate closed but exposing the first progression hole due to location error during manufacturing. Note that the mixture screw tip is projecting into the bore effectively blocking fuel delivery.




Since air flows and mixtures were carefully set before I took this picture (I use a STE synchrometer and six Gunson Colortunes for getting idle mixtures spot-on) the final set-up is not ideal for progression circuit operation. This is due to fuel delivery for progression being provided by the holes of the progression circuit (seen under the large, brass screw in the side of the Weber throttle body) and by the fuel delivered from the idle mixture screw port. If you set idle mixture with the progression circuit activated (throttle plates opened too far) you will not have the same fuel delivery during progression as you would if the mixture screw was set properly; a lean progression.

Worn Webers have enough air leakage to keep the throttle plates closed enough during idle adjustments to avoid activation of the progression circuit. I recommend purposely opening idle air screws one turn as a starting point for idle adjustments to assure your throttle plates are as closed as possible to preclude progression leaness issues (which may lead one to installing a larger idle jet than required.)

Another comment: Use of 40mm Webers on large displacement engines will demand larger initial throttle openings at idle to provide enough air...obviously you will need to be careful to avoid opening the throttles too far. A remedy for this problem is to drill a small hole near the edge of the throttle plate adjacent to the progression holes to bleed more air.

[snbush67]

Paul,

Great tip, I visit your site often for tuning tips.

I have the Gunson Color tune as well which I have found exceptional for tuning. It definitely takes the guess work out of tuning, I have bad hearing and miss the subtleties of the changes in sounds, the visualization really helps. The Gunson Apparatus is a bit tedious to use however. Do you have any tips for using the color-tune? I only have one, six would be great!

I am thinking of designing a different style tube and mirror which is better adapted to the 911.

It would be great to have six synchrometers and six colortunes.

Shane

[1QuickS]

Hi Shane,

I use only one STE but since I tune so many Webers I decided that six Colortunes would pay for themselves, and it was a GOOD decision:-)

Colortune tips:

• I used a countersink to bore an internal taper into the tip that screws onto the threaded end of the Colortune; it really helps to guide it on
• I don't use the Piece of S... plastic tube with mirror; I use a mechanic's inspection mirror that has a swivel joint at the end
• if the tool falls out of your socket either use a magnetic pick-up tool of a set of long, curved forceps
• my socket has been embellished with a bit of tubing that stays inside the socket and has an ID that captures the insulator on the end of the tool so that I seldom drop the tool down that long, dark hole
• I clean the tool (soot from the inside eventually obscures a clear sighting) using MEK in a shaker jar filled with some BBs and then blow it out with compressed air. My shaker jar was a medical specimen jar until the plastic lid cracked and I now use an old Binks spray canister with a screw-on lid that I sealed the holes up on.

Cheers,

[snbush67]

Paul,

I appreciate the tips I have a great inspection mirror, I guess I will break it out and throw away the tubes.

From what it sounds like the only part of the kit needed is the colortune plug and the extension.

I use the extension to thread the tool, and then the stock spark plug tool to tighten.

The gunson is a really simple design I wish it wasn't 60 $, I would buy a few more. They cant cost more than 10$ to manufacture.

Thanks, Shane

[1976 TN Porsche]

Thanks for the TIPS Paul. I really need to buy a colortune. Good Catch on the Webers. Thanks.

[BK911]

Paul - Thanks for the tuning tips on your website. They were very helpful.

I am interested in purchasing a gunson colortune. What do I need to order? Just the standard 14mm kit will be good enough?

[1QuickS]

Hi BK911,

pm sent regarding Colortunes