two carbs or not two carbs...

[norrinradd]

Starter works, new Bosch sr71x ! Now, engine fired up instantly but rough idle. Air mix screws change idle on front carb; back carb does nothing. I suspect vacuum leak but can't find one. Brake booster line perhaps ? Front carb pulls 8kg on synchrometer, back carb pulls 3kg. Booster goes into #3

[Son of Marty]

If the balance screw between the 2 carbs can't bring them into sync yes the first step is to look for a vacuum leak, remove the booster line from the carb and plug the manifold if that doesn't fix it start to spray all the joints with carb cleaner or wd 40 or the like see if that improves things even for a second or two. 

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Edited August 22, 2021 by Son of Marty

[Chris_B]

I don't see a balance screw in your linkage. How do you balance your carbs?

[Son of Marty]

I don't know how that picture attached itself to the post, I use the factory linkage which is very much like Halboyles stuff. But on the linkage show in the picture each arm has a adjustment and can be shortened or lengthened to bring the cards into sync although he has 2 idle stop screws so who knows whats up with that.

[Chris_B]

I am not sure I understand what you are saying, but in my experience, balancing dual carbs without a balance screw connecting the linkage between the carbs is almost impossible because the dual linkage arm approach is just not precise enough. BTDT

[Son of Marty]

Exactly right the two arm system will go out of sync at will, where the single arm and screw will stay in sync until you take it apart. I sync mine literally once a decade or so, unless I change my jetting radically like when I rejet for the track/lapping days.

Edited August 23, 2021 by Son of Marty

[John76]

Wow....Carbe(s) Diem!

 

[norrinradd]

Well, blocked booster line with no change to idle. I removed rear carb to check o-rings for cracks or misalignments. When I reinstalled the idle got better. Maybe I tightened carb too tight ? Car will idle rough around 1000rpm but revs strong after that. Front carbs pull about 7kg on the syncro , rear carbs about 4kg so they are getting closer !  Should I mess with the air bypass screws get the numbers matching or just use the idle mix screws ?

[TobyB]

You should adjust the carbs to flow the same with the balance adjustment mechanism.

 

Then look at where the plates are at idle by removing the progression drilling covers.

 

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[halboyles]

Have you removed the screw that covers the progression holes to make sure the butterflies are at the same position when fully closed?  Back the idle speed screws out all the way, disconnect the linkage and check the location of the butterfly.  See pics for typical closed position.  If they are fully closed with the linkage off, put the linkage back on (idle speed screws still unengaged) and see if they remain in the closed position.

[norrinradd]

Balance adjustment mechanism ?  Huh ?  What am I looking for in the progression holes ? In your pic it looks like the edge of the butterfly plate thru the top hole. Thanks !

[halboyles]

When the throttle butterflies are fully closed you should be able to see just the top edge of the butterfly in the first hole.  On some DCOEs the edge might not even be visible.   The DCOEs run on the "idle circuit" when the butterflies are completely closed (see attached diagram).  If both sets of plates are not in the same position with the linkage either on or off, you will have a hard time synching the carbs.

The front carb should have a throttle lever with an arm that engages the balance lever on the second carb.  You use the adjustment screw on the balance lever to synch the carbs.  Attached is a pic of the two levers.

[Son of Marty]

Your going to always have trouble with the o ring mounts, IMO throw them in your neighbors pool, and use the phenolic spacers the factory used. Your showing a classic vacuum leak, make sure the rear of the carbs( choke housing) clear the manifold, some times they hit and the carb won't seat. 

 

 

 See how close the choke house is to the mani, they fit here but a thinner gasket and they hit. 

Edited August 29, 2021 by Son of Marty

[halboyles]

2 minutes ago, Son of Marty said:

use the phenolic spacers the factory used.  

What SoM said.  That is why they were used on the original 2002ti.  

[norrinradd]

You guys have convinced me to ditch the soft mounts. I have paper gaskets but, the choke housing will not clear the manifold ( seems like I just read that somewhere ).  I have choke block off plates coming as I cannot find the phenolic spacers ! Where to find that nifty set you just posted Halboyles ?