On Thursday, August 05, 1999 1:07 PM, Rob Christopher [SMTP:robc@cisco.com]
wrote:
>
> I have a few questions, though, as you may have guessed.
>
> 1) My car has been converted to SU carbs (1 3/4 inch I think, not the 2
> inch) and the idle is now very low since replacing all these things (500
> rpm when warm). It was low before, 600-700, but now it dives down to
> ~300-400 any time I stop before recovering back to 500 rpm. Where do I
> adjust the idle on these to get it back to 800 rpm where it should be?
> There are three screws, one on each of the carbs attached to the linkage
> directly and a single one on an arm off the linkage and touching a cam
> type thing. I assume I turn the two nearest the carbs themselves. What
> is the other for?
The screws nearest the shaft are the idle adjustments, the one screw on the
long arm is for fast idle (the cam turns when you pull the choke, hits the
screw, opens the throttle).
> 2) All my references are for ZS carbs and say the dash pots should have
> enough fluid in them "to offer resistence when the threaded part is 1/4
> inch from the top of the dash pot". In my carbs (filled with ATF I'm
> guessing from the pink colour) I get resistence when the threads are
> over an inch from the top of the dash pot. Is this correct for SU
> carbs? Should I take some of the fluid back out? Is there anything
> wrong with having too much fluid in there, I know having no fluid is
> bad.
Your dashpots are a little overfull, but that's entirely OK. You are
supposed to fill them that full (I forget the exact measurement offhand)
every 6000 miles, so the excess oil can slowly run down between the piston
and the dome, to lubricate the sliding rod. It eventually gets sucked into
the engine, where it does absolutely no harm.
> 3) Plugs no 4, 5, and 6 were black (but not oily) when I removed them.
> 1, 2, and 3 were a nice tan colour as they should be. Where is the
> mixture adjustment on SU carbs? What do I measure to know the mixture
> is correct?
Depends on the carb model. On H6, as were used on TR3-early 4, there is a
brass nut on the bottom, right above where the choke linkage connects to
the jet. The jet rests against the nut when the choke is off, so
unscrewing the nut lowers the jet and richens the mixture.
HS6 (used on some TR4A) is similar, HIF6 (Jaguar ?), etc. are different.
The factory mixture setting procedure is to lift the pistons slightly (like
1/8", I forget the exact number) and observe the idle rpm (by ear). If it
rises slightly, then falls back, the mixture on that carb is right. If it
rises and stays up, the carb is too rich. If it immediately falls, the
carb is too lean.
You can either take off the air cleaners and use a small screwdriver to
lift the pistons, or there is supposed to be a small pin on the RH side of
the carb (near the fuel bowl) that will also do it. Another way is to get
the "SU tool kit" (Moss P/N 386-300, other vendors carry it too) and use
the tools that go into the center of the piston. The tool kit also
contains instructions, a mixture wrench, and the tools to synchronize the
carbs.
> 4) Can anyone guess the identity and /or origin of these carbs? The
> dash pot dampers have a brass hex head on them so someone at our local
> club said they are probably off of a TR4. They are NOT 2 inch SUs as
> another club member has them, and they are huge compared to mine. I'd
> like to identify mine so I can get more info on them in case I need to
> do further adjustments or I need to order parts.
How do the float bowls connect to the jets ? If the gas flows through a
stud/bolt, into the carb body and into the jet housing, they are probably
H6 as found on TR3-early4. If there is a separate plastic tube from the
float bowl to the jet, they are probably HS6 as found on some late TR4A.
I believe the HIF6 has a fairly rectangular bowl, that clamps to the carb
body with several screws.
You can download the Moss TR2-4A catalog from the web, at
http://mossmotors.com/cataloglayout/pdfs/tri/TRI.html
It has very nice diagrams of the H6 and HS6 carbs. (You'll probably only
want Section C).
SUs were also used on many other cars, including Nissan(Datsun) and even
some Harley Davidson motorcycles.
Randall
59 TR3A
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