OK, so I'm showing my age and maybe "infringing" on some copyright or
other, but here's a note from Jeff Jones from many years ago on this
list that may be pertinent. At the time, there was lots of talk
about getting SU's right. (Is Roger Garnett still on the list? - he
had a great set of instructions for getting them sync'd). Anyway -
FYI. Steve
---attached message---
Date: Tue, 6 Apr 93 17:24:39 EDT
From: jjones@angate.att.com
Subject: Re: Still can't get it right (MGB problems continue)
> if I hit the gas, it would sputter. I thought maybe I had
... stuff deleted
> College Station, the car was having problems with any kind of load other
> than minimal acceleration.
The above two comments are an indication of a too-lean acceleration mixture.
> for kicks, I bought another set of plugs and leaned the carbs just a little.
> Car sputtered on acceleration, unless I gave it some choke, and then it
> accelerated smoothly. So I put the carbs back where they had been (I did use
Ah-Ha!! You choke it and it accelerates smoothly. Again, an indication of a
too-lean mixture. Maybe you should have enriched the carbs. If we assume
that it IS a carburetion problem, then you might try the following:
SU carbs are pretty sensitive to the float-level setting. Set the level too
low and it requires more vacuum to suck the gas up out of the jet; it'll be
too lean. Set it too high and it sucks gas quite easily; it'll be too rich.
Also, SU carbs don't have accelerator pumps in them the way American carbs do.
Acceleration mixture is controlled by the rise of the large carb pistons, and
that rise needs to be damped with the oil in the dashpots. Without the oil,
the pistons rise almost instantaneously, greatly leaning out the mixture.
The oil does not come into play except at acceleration; idling, or steady
state, is not affected by the dashpot oil, or lack thereof.
I can duplicate your symptoms almost exactly by pouring the oil out of my
carb dashpots.
This may seem obvious but ... Take the air cleaners off and make sure the
carb pistons have full up/down travel AND that the dashpots in the top of
the carbs are filled with the proper oil, AND that the proper springs are
used. I've used ATF in the dashpots for 12 years. If that isn't it, THEN
check your float setting.
So much for clairvoyant troubleshooting.
Good luck. I'm interested in your final results and solution.
Jeffrey R. Jones
>
> >I have a Triumph GT6 running a pair of SU's taken from an MGB. The
>>installation was done two Previous Owners ago. With Joe Curto's help I've
>>done some work on the carbs (new jets, float bowl mounts, throttle shafts,
>>etc.). It is running much, much better but I'm not completely happy with
>>them yet. For example, they seem to require a slightly richer mixture
>>setting that I might have expected (perhaps 18 flats on the jets, though I
>>don't remember the exact number at this time). They also seem to require
> >some choke longer than I'd expect as it warms up.
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