Weber carbs tuning

[Colin Cooper]

Hi Guys,

Who is the 'go to' man for tuning twin Webers in the Southampton / Portsmouth area?
Cheers,

Col

[oilyhands]

He is a little north of you, but Tom Airey in New Cheriton used to be pretty good at them..

He may be retired but I think the business is still going..

Oily

[Duckpit]

Its very easy to do yourself, providing you do not have a problem with the carbs

Balance the carbs, probably by ear and a hose pipe, then adjust slow running jets at circa 1200 RPM so that you get max revs on each jet, ie screw in or screw out each jet approx 1/2 turn each time to get max revs. Or purchase a color tune

Lots of info on the web on how to do it

[Stridey]

Another one here for DIY.

the synchrometer is about £38.

remove the air filters,(a dab of loctite on the nuts when you re-assemble.) it can be a faff to reach the head of long bolts to rear of filters. 

plenty of YouTube videos on what to adjust. All done with a screwdriver.

good luck! 

[John Vine]

the synchrometer is about £38.

Or borrow one via the equipment-for-loan register.

JV

[oilyhands]

Extract from my website..

 

Setting the Idle and slow running

Rough running and idle is normally down to the idle mixture and balance settings being incorrect, below is a technique to establish a clean idle and progression. Before adjusting the carbs in this manner you must make sure that the following conditions are met.

i) The engine is at normal operating temperature
ii) That the throttle return spring/mechanism is working OK
iii) That the engine has sufficient advance at the idle speed (between 12 and 16 degrees)
iv) That an accurate rev counter is connected.
v) That there are no air leaks or electrical faults.

A reasonable idle speed for a modified engine on Webers is between 900 and 1100 RPM.

If you are adjusting the idle for a set of carbs already fitted then progress to the second stage, if the carbs are being fitted for the first time, screw all of the idle mixture adjustment screws fully home and then out 2.5 turns. If you are using DCO/SP carbs then start at one turn out. Start the engine and let it reach normal operating temperature. This may mean adjusting the idle speed as the engine warms up. Spitting back through the back of the carburettor normally indicates that the mixture is too weak, or the timing is hopelessly retarded. If this happens when the engine is warm and you know that the timing is OK, then the mixture will need trimming richer on that cylinder. Set the idle as near as you can to 900RPM.

Using an airflow meter or carb synchroniser adjust the balance mechanism between the carbs to balance the airflow between them, if the rearmost carb is drawing less air than the front, turn the balance screw in a clockwise direction to correct this. If it is drawing more air, then turn the balance screw anti-clockwise. If the Idle speed varies at this point, adjust it back to 900 RPM, to decrease idle speed screw in an anti-clockwise direction, to increase, screw in a clockwise direction.

When you are sure that the carbs are drawing the same volume of air, visit each idle mixture screw, turn the screw counter clockwise (richening) in small increments (quarter of a turn), allowing a good 5 - 10 seconds for the engine to settle after each adjustment. Note whether engine speed increases or decreases, if it increases continue turning in that direction and checking for engine speed, then the moment that engine speed starts to fall, back off a quarter of a turn. If the engine speed goes well over 1000RPM, then trim it down using the idle speed screw, and re-adjust the idle mixture screw. If engine speed decreases then turn the mixture screw clockwise (weakening) in small increments, again if engine speed continues to rise, continue in that direction, then the moment it starts to fall, back off a quarter a turn. The mixture is correct when a quarter of a turn in either direction causes the engine speed to fall. If that barrel is spitting back then the mixture is too weak, so start turning in an anti-clockwise direction to richen. During this procedure, the idle speed may become unacceptably high, so re-adjust it and repeat the procedure for each carb barrel.

After all the mixture screws have been set, the idle should be fairly even with no discernible 'rocking' of the engine, if the engine is pulsing, spitting or hunting then the mixture screws will need further adjustment. If the engine is rocking or shaking then the balance is out, so revisit with the airflow meter/ carb synchroniser. No amount of adjustment will give a good idle if the throttle spindles are bent or leaking air or the linkages are loose on the spindles!

That’s all there is to it.

HTH

Oily

[Tim S]

Tom Airey is very good. Not cheap but he achieves very good results, has masses of parts on the shelf and his rolling road is useful.

[Colin Cooper]

Thanks all.

I've been to Tom before, but a around £300.00 he is a bit expensive.

I've also had a bash at doing it myself, and already have a sync-meter, but don't seem to have the 'touch' somehow. Looks like I'm going to have to have another go!

Cheers,

Col

[Garf]

That may well be the going rate now.

For my Mini Cooper S with twin carbs I've had 2 garages quote this week £100 per hour and they said it would be 2-3 hours time depending on how much adjustment is required.

Both are with the famed A series guru Pete Baldwin on rolling roads.

[Nick T]

When i had my crossflow, the pervious owner had drilled and tapped a couple of fittings for the 2nd/3rd cylinders of the inlet manifold for brake bleed nipples. You can then use a motorbike carb balancing tool which just plugs in without all of that faff or removing filters. Took about 2 minutes to balance the carbs when hot.

 

Cheers

 

Nick