• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Tips
Tips

TR6 Help with SU Carbs on TR6

Share this page

71TR6

71TR6

Jedi Hopeful
Country flag
Offline
Hello All,
After a year of trying to get the ZS carbs to run right on my TR6, I broke down and purchased a set of SUs off Ebay after hearing good reports on them.

Well, I installed the SU carbs today and while the car will run, the idle won't come down. I've got the idle screws jacked all the way out and it still "idles" at around 1500-2000rpm. This is driving me buggy and I can't seem to find the reason why. There is no binding in the linkage anywhere.

Does anyone have any suggestions on what to check?

Ron W
 
You may want to check the fast idle adjusting screws to make sure that they're not rotating the fast idle cam. You should back them off, and with the throttle fully closed adjust them so they're just almost touching the cam.
 
Thanks for the quick responses. the fast idle screws are backed completely away from the cam so there should be no interference. Checked for air leaks with a propane torch with the valve cracked open- no change in idle speed as I went along the different joints.

I'm learning more about these carbs than I care to. I just got off the phone with Joe Curto- what a resource! He indicated it is probably the bypass valve that is in the throttle butterfly that is causing the high idle. The bypass valve causes a constant air leak and should be soldered shut or replaced with a solid butterfly for a TR6. He further indicated that based on the BCY needles that were in the carbs, the carbs appear to be off a TR2000 and as a result will be running very lean on a TR6. As a result, the needles are going to be changed from the BCY to a BDM (recommended by SU for the TR6). While I had the carbs apart, I also noticed the two piston spring heights were different so they're being changed as well.

We'll see what happens after I get the parts.

RonW
71TR6
 
Ron,

I put a set of SU's on my TR6. No issue with a bypass but needed to plug a few vacuum ports. The engine idled high until I did that. Also had to play with several needle types until we landed on one that did not starve a fast road cam. After all was sorted out, it was worth the effort!

John
 
Check to make sure the butterflies are seated properly as well. I just changed from SU H6 to HS6 on my 4a. When we first installed them, the car tried to idle at 5000 rpm! The butterfly was half open on the front carb. We had to remove it and readjust it so it was seated properly in its bore. We put one hand over each carb to see which one was the culprit.

Good luck - it will take awhile to get all the issues ironed out. I am still working on getting the right needles for my "D" cam.
 
Back
Top