Subject: [TR] TR2/3 SU Carbs

From: Angelo Graham <[email-masked]>
Date: Fri, 20 Apr 2012 11:49:32 -0400

Hello List:
Need some of the collective wisdom of the List on this one. I have H4 SU 
carbs on my '2 and struggling with the common problems: leaking from the 
jet bodies, float levels, excessive richness, stiff choke actuation, 
etc. I installed kits in the winter & checked the throttle shafts and 
they were surprisingly a good fit.
I am contemplating having the carbs 'professionally' rebuilt to correct 
some of these issues and forking out the 4-5 hundred for the job. But 
before I commit, I am wondering if these early SU's can really be 
'fixed'. Given the design of the exposed jet SU can they really be made 
to be leak free? Even after a professional rebuild, will these carbs be 
good running and relatively leak free?
Just getting tired of the constant smell of gas in the shop and 
struggling with the carbs.
Thanks for any insight and advice on this one.
Angelo Graham

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From: "Randall" <[email-masked]>
Date: Fri, 20 Apr 2012 12:27:31 -0700

> Given the design of the exposed jet SU can they really be made
> to be leak free?

I believe so, yes.  However, they do require attention from time to time to
keep them that way.  My experience (with H6 that are basically identical in
the float and jet area) is that the original type seals only last about a
year before they start to leak.

Whether a "professional" rebuild will achieve that, I do not know.  I've
helped a local TR3B owner fix his carbs after they were professionally
rebuilt; the jets were not centered properly and the locking nuts had been
left loose.  My opinion, if you want it done right, do it yourself.

> leaking from the jet bodies,

Moss motors sells "improved" jet seals, which have worked very well for me.
It is also important IMO to polish the surface of the jet where the seal
rides.  This both reduces wear and improves the choke action.  I have also
seen replacement jets where the jet itself would leak!

> float levels

Use the standard type float valves (not Grose Jets), adjust them by the
book, check that the float doesn't have fuel inside and that the fuel
pressure is not too high.  If you are getting overflows, replace all the
soft lines and consider adding a (non-original) filter just before the carb
inlet to catch any crud that makes it past the screen and sediment bowl in
the pump.

> excessive richness

If this is at idle, it may be an indication that the jets and/or needles are
worn (from being run with the centering not quite right).  This is a
somewhat dangerous situation, as leaning out the idle will cause the cruise
mixture to also be lean; which can lead to overheating and even severe
engine damage.  (Which I once heard described as a "cloud of engine parts
chasing me down the highway.")

> stiff choke actuation,

As above, polish the surface of the jets until they shine.  Toothpaste and
your fingers will work fine (of course you have to clean out all traces of
toothpaste afterwards).  I also advocate replacing the springs both inside
the jets and the choke return springs.  They frequently get tweaked by
either old age, or previous owners trying to improve things.  Check that the
cable itself works freely and is the proper type (stranded center, not
solid).  Hook the linkage up following the photo in Practical Hints (or the
diagram in "More BS on TRs").  Don't worry that the pivots are
loosey-goosey, they are supposed to be that way.

-- Randall