TR2/3/3A Running rich SUs.

[steveg]

The dirty little secrete on SU carbs is that different cams ,pistons and valves WILL require
a trip to a professional tuner. He will select from the dozens and dozens of available needles
a profile that gets you into the ballpark where you can THEN fine tune it to your driving needs.
All else is guess work and will NEVER get you where you need to be. This should be done on a chassis
dyno for optimum results......

With patience, needle reprofiling can be done off the dyno with a series of road tests (I never got into it). Des Hammill explains how. This book is interesting reading for anyone who wants to super-tune their SUs or understand them better - available from Moss or Amazon:



The second book available from the same sources has step-by-step instructions for rebuilding the various SU series, as well as good chapters on function.

FWIW - my Healey runs HD8s with a 278 degree fast road cam, high-lift rockers, some porting and .060" overbore forged pistons with dual O2 meters and a dual exhaust-temp gauge*. Originally I went to the Moss rich needles, but went back to the standard needles. The car still shows air/fuel ratios in the 12s for power and the 13s for cruising. This is in line with what Hammill recommends.

*So I like science projects.

Soon, I'll be installing O2 meters on the TR6 - want to see how the ZS carbs read before switching to the SU HD6s.**

**Don't take this wrong - I don't actually think they're going to give a power increase over the ZS carbs. I have them on the shelf from the Healey and think it would be interesting and easy to install them and see how they run. Another science project.

 

[sp53]

Tom thanks for the post and all the thoughtful writing. WOW. So I am not crazy. I arrived at what you are saying the hard way after much gasoline soaking of the hands, and then doubted myself. Right Now, I am not sure what I have in there for thickness or if I have ruined the sealing quality of the washers. I do have a collection of that stuff from over the years. If I were to remove the jet assembly, as a whole to swap out the washer, would a slightly thinker washer cause problems? I can see how that could push the jet down a fuss, but perhaps not a problem. I say this because the numbers I am dealing with are small, like 1/32. Moreover, when you remove a whole assembly, do you leave the carb on the car and then pull the jet assembly out, and then put it back on the bottom of carb with upward pressure always being careful not to strip the carb body or would you remove the carb.

thanks Steve
Steve

 

[karls59tr]

Karl I know nothing about unstock cams, but I would say if your idle is high, you are probably pulling air in from a second source. Like throttle shafts or manifold leak. Spray some carb cleaner on the shafts and or manifold; if the idles goes up faster, the shafts are letting in too much air. Advanced timing will raise idle also and incorrect dwell compensated by advanced timing will also. Probably throttle shafts--- they are the moving part that wears out. A distributor with incorrect weights or sloppy something will advance the timing and raise the idle also because it pulls forward to easy.

steve

Thanks for the input Steve. I suspect worn shafts so I'll do the test in the Spring when the weather breaks up here. Is there a typical place on a Tr3 where a manifold leak occurs? Also ...do you know what the correct dwell should be?

Karl

 

[sp53]

The dwell should between 50 and 60 degrees. I set the points with a feeler gauge at 14 and put the dwell meter on to see. These numbers are small to deal with and it is not like a Chev with a door on the cap. You will probably need to fiddle it around to say 50 55 60 with trial and error and then set timing--- always dwell first then timing.

If the manifold is leaking, it will be right at the head and you would probably hear that hiss.

 

[Tom Bryant]

<snip> Right Now, I am not sure what I have in there for thickness or if I have ruined the sealing quality of the washers. I do have a collection of that stuff from over the years. If I were to remove the jet assembly, as a whole to swap out the washer, would a slightly thinker washer cause problems? I can see how that could push the jet down a fuss, but perhaps not a problem. I say this because the numbers I am dealing with are small, like 1/32. Moreover, when you remove a whole assembly, do you leave the carb on the car and then pull the jet assembly out, and then put it back on the bottom of carb with upward pressure always being careful not to strip the carb body or would you remove the carb.

Steve,

As a rule, those copper sealing washers can be reused innumerable times without any problems. There can be exceptions, but unless there's visible damage, there should be no issues with reusing them. As I said before, they're supposed to be 1/32" (0.031") thick. Thinner is likely to cause leakage, slightly thicker will not be an issue. Yes, it will push the jet bearing downward a bit, but there should be plenty of adjustment available in the nut to compensate.

As I indicated earlier, if you turn the jet adjustment nut all the way to the top and it fetches up at that point, such that will turn no more, even with a wrench, then your jet bearing is tight enough, and your washer is thick enough. And if you can keep turning that adjustment nut, then you have a problem that needs to be addressed.

I sometimes remove a jet assembly with the carburetors still on the engine, especially if I expect only minor tweaking. Since I only use Teflon o-rings for the jet seals, I'm also able to simply pull out just the jet and then re-insert it, while leaving the jet bearings and seals still in place. You can't do that with cork seals. Frankly, I just can't understand why everyone hasn't thrown those cork seals into the dustbin of history and moved on to the far superior Teflon.

Tom Bryant

 

[sp53]

Thanks Tom much appreciated. I tried many years ago to use the black rubber ones from Moss, bit it leaked worse. I only had one on each cup. Using 2 and the newer Thelon, I can see how that would work; it probably helps with choking also, easier to pull out. I will get some. Yes the carbs are cleaned very clean, so I will see after I try your bottoming out test which way to go. I can visualize that it should work. Yes I have tried to fish some jets back into cork seals at about 50% effective; the kits came with those synthetic something that kinda feels like high quality cork that I soaked in oil over night, but they do leak a fuss.

Thanks Steve