3 Mixture Screws In And No Idle Change??

cameron.arnott · 09-06-2006, 04:36 AM

Another question for the 'Oracle'..... Some may know I've had some 'issues' with a high idle for a while.

More playing tonight and I have found that I can screw all three mixtures screws all the way in on my right hand carb with no effect on the idle.

Any ideas on this one please? Its sounds like time to pull it off and take it apart again......Bloody Hell I'm getting frustrated

Love the car though

ruf-porsche · ruf-porsche's Garage

If the idle is to high, you are no longer using the idle jet to control the mixture. What was the rpm that the engine was turning when you fiddle with the mixture screws?

cameron.arnott · 09-06-2006, 02:03 PM

RUF,

Idle was sitting at about 11-1200 at the time. The left hand side idle screws would affect the idle but not the right hand side....

Cheers

madmmac · madmmac's Garage

Vacumn/intake leak on the right side maybe?

ruf-porsche · ruf-porsche's Garage

Do you have a uni-synch for synchronizing carbs? One carb maybe drawing more air than the other carb.

If you don't have a uni-synch get a piece of rubber hose and listen to the air entering the carbs. Do they both sound the same?

avendlerdp · avendlerdp's Garage

Yow! Let's start at the beginning. First off, disconnect the left/right throttle linkage so both carbs are on their throttle stops. If you have a sync tool, set both sides to pull the same air and THEN set mixtures and you are done. If you don't have a snyc tool, open the mixture screws on the trouble carb to about 2 turns out and then start backing out the throttle stop screw until the whole bank of cylinders cuts out. Now open it up until it runs at a low, solid idle noting the number of turns out that is. Next, do the same to the other side and get it to idle with the two throttle screws set the same number of turns out from that "dead" level. This will be a close setup and then you can turn each mixture screw until it's corresponding cylinder runs the best. Once you have the mixtures close, turn down the throttle stop screws together to reach your desired idle. Finally, hook up the linkage and go win the big race.

Alex

cameron.arnott · 09-07-2006, 03:03 AM

Tonights progress....

Warmed up car and ran it at 900 idle. Problem still the same. Both carbs are synched. I can't set the mixtures because the aren't having any effect on this carb!

Peered down thoats whilst running, throttle plates fully closed. No sign of fuel in throat at all. I pulled the top of the carb off and the floats look good.

Any more ideas before I pull them apart?

Cheers

Avery · 09-07-2006, 05:52 AM

You could have worn out throttle body butterfly shafts. So much air is getting by the shafts such that cranking in the air bypass screws have no effect. Try spraying WD40 on the T/B shafts while the cars is running. The WD40 will temporarily seal the shafts from air leakage. If you notice a temporary drop in idle speed, you MAY have worn our T/B shafts. Don't give up on adjusting that linkage though until you are convinced its not the rod adjustments. Have you tried disconnecting ALL the rods on the T/B to see if that has affect on idle.

Thomas Owen · 09-07-2006, 06:34 AM

Sure sounds like air/vacuum leaks.
Good luck -

avendlerdp · avendlerdp's Garage

Can you kill the motor by lowering the idle set screws? Looking down the throats may not tell you if the plates are fully closed and clearing the progression ports. Try lowering the idle to something like 500 rpm and then see if you can get the mixtures to respond.

alex