SU H6 Carb Jets

[Dandydog]

I’m in the process of tuning my ‘62 TR-4, and have found that I can’t adjust the carb mixture properly: Starting from 12 flats open, I’ve screwed the jet adjusting nut on each carb all the way up (1 or 2 flats at a time), and the RPMs still rise quite a bit when each piston is lifted slightly. (The timing is set at 4* BTDC, plugs are new and gapped correctly, points same; the carb linkage has been released, the choke disconnected, the piston clicks when dropped and the idle air intake has been equalized with a Unisyn.)

I’m guessing that the jets and/or needles are worn (they’ve never been replaced), but I’m open to other interpretations of my problem. Suggestions are welcome and all reasonable ones will be acted on. (I’d also appreciate experience-grounded information on SU parts suppliers.)

Thanks for your help!

[RobH]

Welcome to the forum. Can we know your name?

 

How are the needles set in the carb pistons?  The shoulder on the needle should be at the same level as the base of the piston.  If they are set too far up, the result will be as you describe. 

Best source of parts has to be Burlen since they make SUs. 

 

 

 

Edited September 25, 2021 by RobH

[stuart]

Direct link https://burlen.co.uk/

Stuart.

[rcreweread]

On 9/25/2021 at 11:16 PM, Dandydog said:

I’m in the process of tuning my ‘62 TR-4, and have found that I can’t adjust the carb mixture properly: Starting from 12 flats open, I’ve screwed the jet adjusting nut on each carb all the way up (1 or 2 flats at a time), and the RPMs still rise quite a bit when each piston is lifted slightly. (The timing is set at 4* BTDC, plugs are new and gapped correctly, points same; the carb linkage has been released, the choke disconnected, the piston clicks when dropped and the idle air intake has been equalized with a Unisyn.)

I’m guessing that the jets and/or needles are worn (they’ve never been replaced), but I’m open to other interpretations of my problem. Suggestions are welcome and all reasonable ones will be acted on. (I’d also appreciate experience-grounded information on SU parts suppliers.)

Thanks for your help!

Hi - I've sent you a PM (Personal message - go to envelope icon at top of page, click on it, and it opens your forum mailbox and you will see my message/contact details) - I can see you haven't read it yet - I may be able to help you.

Cheers Rich