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Re: TR3A (carb) tuning problems

To:, triumphs@Autox.Team.Net
Subject: Re: TR3A (carb) tuning problems
Date: Wed, 16 Apr 1997 10:42:16 -0400 (EDT)
In a message dated 97-04-16 00:36:48 EDT, you write:

<<  The car has Stromberg 175CD carbs

Well, MJ, I think I see a problem right off, here!  I can't imagine why you
would use Strombergs, when the SU's (standard equipment for a 59 TR3) work so
well, and tune so easily!

<< and will not run smoothly at speed  without the choke pulled way out.
 It will idle fine with the choke in once it warms up, but put any load on it
and it sputters, backfires and generally is not happy.
 It would seem to be starving at high speed or at least under load.  Can you
run at a sustained high speed, and then it just sputters when you
accellerate, or the motor comes under load?  If so, check out the enrichment
mechanism.  Do the pistons give immediate resistance when lifted, or do they
lift 1/4 inch before giving resistance? (Also, are you sure your timing is
right, your Vaccuum advance works, and there aren't any vaccuum leaks?) Are
you using heavy enough oil in the dashpots?  If you can't get sustained high
speed, even when not under load, then I would check: Float level adjustment;
fuel pressure from pump:  make sure any fuel filters aren't clogged or too
<<I disassembled the carbs, put new gaskets, needle valves and the like out
 of a carb rebuild kit about a month or so ago.

Did it work OK before this? :-)

<<  The mounts to the intake manifold are good, there do not seem to be any
air leaks there.  Fuel filter is fine and gas tank does not appear to have
water or other
 contaminants in the fuel.

Well, that shoots a few of the above theories.  Can you get a pressure test
of the fuel line at the carb, or at least make sure you are getting a good
strong spurt if you disconnect the fuel line at the rear carb and shoot the
fuel into a can? (you might not wan't to smoke while doing this.)

<< The Haynes manual describes the tuning of the Stromberg carbs as setting
 initially and then lifting the piston about 1/32 of an inch, with a stall
 indicating rich (or Lean, I don't have the book in front of me) 

(Lean, of course)

<<and an increase in idle indicating lean (or rich, see above).  When I try
 tuning approach, I get no difference in idle, suggesting the setting is
 correct, but I know that not to be the case.
In my opinion, it suggests more that it's not a very precise test.  The only
time that test has worked on my SU's is when they were completely re-built,
including throttle shafts, and on a nice tight engine.  What would make your
life a WHOLE lot easier here is a Colortune tool, available at Moss TRF, or
any of the others.  I have 2, and use one on the front cylinder and one on
the rear, so I can tune both carbs at once, and know I'm in balance.  This
way, you can see exactly what is happening to the fuel mixture and spark
inside the cylinder, when you induce the problem to occur)  The Unisysn tool,
available from both sources, is also very good.

<<Any suggestions, or is the TR3A just very cold natured and I may not have
 let it run long enough to really get warm - even though the temp gauge
 works up to 160-170 when I do these tests.

That's a good place for the temp guage to be. 

 <<Any help would be appreciated.
I'm not sure where you live, but the ISOA has a tune-up clinic coming up soon
in Chicago, and lots of other Triumph clubs have them in the spring.  Two (or
ten) heads are often better than one, at least before the first case of beer
is gone.


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