TR2/3/3A Guide for SU Rebuilding

[PatGalvin]

Hello everyone

Well, my H6 SU's are weeping some fuel from the lower jet assembly. This may be the time to disassemble and renew the gaskets/seals on the lower end. The carbs were rebuilt a few years ago (Jeff at Paltech) but I can't seem to stop the weeping of fuel. I need for these to be leak free for sure.

Any thoughts on what manual or guide you all like best for supporting the carb disassembly and reassembly?

Thanks for any tips.

Pat

 

[TR3driver]

There are two sets of seals in that area, both of which seem to have very short lives. The cork seals that the jets ride in never lasted more than a year or two for me; but nitrile O-rings seem to hold up much better. Polishing the surface of the jet may help, too. (It definitely improves choke operation.) Someone (I forget who offhand) showed a support added to help reduce stress on the float bowl mounts, which I may try the next time they start to leak. But I'm curious to see how much the heat shield will help, so I haven't done it yet.

The TR2-4 Haynes manual has better diagrams of the TR3A carbs; but I wouldn't buy one just for that. It's pretty obvious once you get into them, and the factory manual has the right information, it just illustrates the earlier carbs.

 

[Brinkerhoff]

The jets need to be free of any nicks and polished esp. around the fuel inlet hole which can nick the lower seal as you assemble the jet. The o rings work for a long time. A little oil helps to assemble.

 

[poolboy]

https://www.teglerizer.com/sucarbs/techtip6.htm
https://sucarb.co.uk/technical

There's a couple of links that might help..You'll find other stuff by doing an online search... google or bing..

 

[Geo Hahn]

Many years ago Moss had an exchange program wherein you sent them your SUs and they sent you a set of rebuilts. Was pretty reasonable at the time, sounds cheap now (about $150 for the pair IIRC).

I do not know what they did or what they used but 30 years later those carbs are still leak free. I don't dare touch them to do any more than simple adjustment.

 

[Brinkerhoff]

Not to poke fun at anybody but if you are planning a trip out of town in a British car you need to be able to strip, clean and reseal an SU on the side of the road. They are as simple as a flush toilet. $ 9 gasket kit and basic tools is all you'll need . Best way to learn how an SU works ? Take apart one that is working properly and clean it thoroughly. Carb problems are often misdiagnosed and way too many parts get replaced unnecessarily.

 

[TR3driver]

Not to poke fun at anybody but if you are planning a trip out of town in a British car you need to be able to strip, clean and reseal an SU on the side of the road. They are as simple as a flush toilet. $ 9 gasket kit and basic tools is all you'll need . Best way to learn how an SU works ? Take apart one that is working properly and clean it thoroughly. Carb problems are often misdiagnosed and way too many parts get replaced unnecessarily.

I disagree on two points:
1) A small leak won't keep you from driving home. I've covered literally thousands of miles with the seals dripping a little. Yes, there is a small risk from the fuel dripping onto the exhaust, but it is very small. Gasoline won't burn unless it is mixed in fairly specific proportions with air, and also has a high temperature ignition source. It scared me badly the first time I saw a red hot manifold turning black as each drop of fuel fell onto it (obviously the engine had other issues); but driving another 200 miles or so didn't hurt anything at all. Although I definitely don't recommend trying it, I have seen someone literally put out a lit cigarette in a pan of liquid gasoline! Those explosions you see on TV are done with dynamite...

2) Every nut on an H6 SU is a British Standard size, not SAE or metric. In some cases there is a substitute that will work (eg a 6-point 1/4 socket will turn the nuts on the throttle linkage clamps) but even they are usually obscure.

I actually carry a set of BS wrenches with me, but don't bother carrying carb seals & gaskets. Of course I've also never been more than about 1000 miles from home; but even when I (hopefully) drive old Route 66 from end to end, I won't bother carrying carb gaskets. What's in the carbs will get me there and back again.

 

[vivdownunder]

Years ago a line of TR's with their hoods up at a show nearly always had at least one leaking carby. Fires usually resulted from a failed rubber fuel line, although fuel from the front carby leaking down onto the generator near the brushes would get my attention.

Usually it's failed cork jet seals AUC2120. Be careful when replacing them with either cork seals or O rings to get the cupped keeper washers right way up. Once or twice I've seen a jet leaking where the choke fork attaches. Took a while to fathom that one out after a new seal kit didn't help.

Occasionally its the large cork seal AUC2118 at the top of the jet drying out and shrinking. Leaks from under a 1.75" SU carby body are usually the rubber "top hat" seals that help insulate the fuel bowl and leave it slightly flexible. (1.5" TR2 fuel bowls were hard mounted). While there it's worth checking that the dizzy vacuum pipe connection under the front carby is airtight.

Viv

 

[SteveBones]

I about 1.5 years ago I rebuilt my TR3A carbs. It had been over 15 years since the last time I tried rebuilding.

The best guide I had was what came with the SU rebuilt kit I received from Moss Motors. I recall the kit included everything for rebuilding except the throttle shafts that I ordered separately. If you are interested, I can scan a copy of the directions, and email them to you. The directions showed both exploded diagrams and the step by step sequence for taking apart and reassembly. I am not great about checking my messages but will keep an eye out if you are interested.

One of the best and most helpful was the guideline on the number of turns to use for setting the fuel mixture. It was really close to right on and required very little adjustment or tuning.

Steve