carb settings for GTB

Moderators: 330GT, abrent

Post Reply
Jim Wickstead
Posts: 68
Joined: Mon Jan 13, 2003 12:41 am
Location: new jersey
Contact:

carb settings for GTB

Post by Jim Wickstead »

Does anyone have the correct (ie: official) carb settings for a 1966 275GTB/6C?

Carbs do not have a tag but are probably 40 DCN-3 (3 bolt attachment). I have recorded the present set-up but would like to have a more offical answer as to what is correct. Looking for the float setting, all jets, etc. I have received conflicting information and would like to nail this down.

Thanks in advance.

Jim W.
DWR46
Posts: 621
Joined: Tue Sep 22, 2009 8:23 pm

Re: carb settings for GTB

Post by DWR46 »

Jim: There were two different jetting combinations, one with 29 mm chokes and one with 32 mm chokes. Send me what you have and I will get you straightened out.
DWR46
Posts: 621
Joined: Tue Sep 22, 2009 8:23 pm

Re: carb settings for GTB

Post by DWR46 »

Also, the carb model is stamped on the rear, down low at the base, there are no "tags".
Jim Wickstead
Posts: 68
Joined: Mon Jan 13, 2003 12:41 am
Location: new jersey
Contact:

Re: carb settings for GTB

Post by Jim Wickstead »

The ventures are 32..... I will need to check the base of the carbs for a number. Had looked previously but no luck. I have not removed the carbs and am working with them installed to avoid other issues. Generally, after a careful tune and replacement of accelerator pumps the car runs well but with some flat spots during rapid acceleration. Air temp was around 88 so it may be running pretty rich. I have not done a plug cut but no sense of any loading up.

I appreciate you comments. Most helpful.

Jim
DWR46
Posts: 621
Joined: Tue Sep 22, 2009 8:23 pm

Re: carb settings for GTB

Post by DWR46 »

Jim: For the 32 mm setup:

Choke- 32 mm
Aux. Venturi 4.5
Mains 130
Airs 170
Idles 70
Pumps 45
Emulsion Tubes F25
Idle Airs 150
Pump Cam #26
Pump Stroke 3mm
N&S 175
Pump Del. Valve 100
Float Height 49.5mm (but 51 mm causes less spillover)
Float Drop 59.0mm

These settings should make the car run like a rocket.
Jim Wickstead
Posts: 68
Joined: Mon Jan 13, 2003 12:41 am
Location: new jersey
Contact:

Re: carb settings for GTB

Post by Jim Wickstead »

Dyke (do I have that right?),

Great information and very much appreciated. I had set the foats to 48mm but everything else seems pretty close. You are correct regarding marking on the back mounting flange. Very hard to get in there and see. I don't think it is identifying the carb. Appears to be a build number.
Will probably take of a distrubuter for a closer look. Will post the information at a later date.

Do you recall how many variients of the DCN ultimatel were used by the factory on the late series GTB's?

Another, wackier question: I had replaced the radiator electric fans on a 330 GTC using early E-Jag items. Apparantly, this is where Ferrari got them as original equipment. To my surprise they rotate the wrong direction and are not reversable by changing polarity. The cast aluminum fans cannot be put on backwards (to correct air flow) since they are counter sunk to match the motor shaft. Have you or anyone else on the forum every experienced this? Knew I should have just rebuilt the originals!

Regards,

Jim
DWR46
Posts: 621
Joined: Tue Sep 22, 2009 8:23 pm

Re: carb settings for GTB

Post by DWR46 »

Jim: You have the correct person. The model number and build number are BOTH on the rear, one on each side. You can see then on the rear carb most easily. Early six carb cars had DCN 3 and later had DCN 9. Both carbs came in LOW and HIGH Performance versions (29/32 chokes).

You have discovered the problem using Jag fan motors. However, a good electrical man CAN reverse the rotation inside the motor. I have had many done over the years.
Jim Wickstead
Posts: 68
Joined: Mon Jan 13, 2003 12:41 am
Location: new jersey
Contact:

Re: carb settings for GTB

Post by Jim Wickstead »

Dyke,

Thanks once again,

I will pull off a distributor to give better access to #6 carb's backside and confirm the model number. Regarding the fan motors, you have confirmed my suspicion and I do have an electrical guy just waiting for Ferrari electronics to mess with. So I guess I have another weekend project.

Regards,

Jim
Post Reply