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RE: Do SU H6's wear out (TR3)?

To: triumphs@autox.team.net
Subject: RE: Do SU H6's wear out (TR3)?
From: Randall Young <ryoung@NAVCOMTECH.COM>
Date: Fri, 11 Oct 2002 13:54:29 -0700
> Listers,
> I've gone through the archive but it couldn't solve my problem.
> The lads at
> the workshop here say that my carbs are shot, leaking air through the
> throttle valve, usual story, recommend new ones. I tell them that you can
> rebush, get total refurbishing kits etc. They say - yes, we know all that,
> you can do all that, but these carbs are 45 years old and worn out, if I
> buy new I'll see a big difference compared with rebuilt, they'll be stable
> for years without any adjustment whatsoever.
>
> So - question. Any opinions? Do you agree with them?

In general, no.  Unless of course by "buy new" they mean to buy a different
design of carb.  It is of course possible for carbs to be damaged until it's
not economical to repair them, but just being 45 years old doesn't mean they
are damaged.  I've noticed that some shops like to install new carbs, IMO
it's just to hide that they have no clue how to examine/repair/rebuild them.

> Is a totally rebuilt
> unit of the kind offered by Apple Hydraulics (
> http://www.applehydraulics.com/carbs.htm), TRF and others more or less as
> good as a new unit, or do you eventually have to fork out for new ones?

My 59 daily driver is still wearing it's original carbs.  Might have to
change the throttle shaft bushings again in another 35 years, but I don't
expect to live long enough to actually have to replace the carbs ...

> PS is an H6 an H6 regardless of car. That is will an H6 from a
> Volvo, Rover
> or similar be identical to the unit found on the TR3?

No, they all vary considerably in the details.  Needles, springs, choke
linkages, throttle linkage, fuel attachment, mounting angle, etc.  Even
units from TR3/As are somewhat different for different years.  Burlen Fuel
Systems Ltd holds the rights to the SU design, you can find a good deal of
information by poking around on their website
http://www.burlen.co.uk

IMO we get spoiled by modern cars with their active feedback loops to hold
the idle speed rock solid.  Back in the 50's it just wasn't so important,
nor was it considered a problem to touch up the carb adjustments when the
seasons changed.  Later SUs of course sprouted all sorts of fixes,
thermostatically controlled jets and whatnot, but the H6 lacked any sort of
compensation for intake air temp, fuel temp, fuel composition (which now
changes noticeably between winter and summer in much of the US), etc.

Randall

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