Carl;
Thanks for the ego stroke there. But, I learned the long way when I was
in
collage 20 yrs ago trying to get my modified spitfire to work right (with
no aditional funds). I ruined lots of stock needles learning.BTW, Ive found
that .0005 to .001 off the #2 and 3 position on the Volvo B18 (ZH?)
stock needles works much better. It does cost ~2MPG. The KD needles work OK
on the low end but are way to rich on the top end. On my resent project ,
(the 165 hp TR6) I adapted su needles to work in my ZS carbs as per the
CPM(competition prep manual) and used the leanest of the 3 available
choices (RF?) (again, my notes are sill in my old shop 400 mi away). The
bottom end was still to lean, so I took .001 off the #2,3 positions
(tapering into the #5) and got great results. It took some fiddeling to
center the needle, but it seems to work great. I cannot stress enough
though that the carbs MUST be in great shape before deviating from stock
needle profiles. The stock clearance on the suction chamber / piston shaft
is .0005 according to what Ive read. The best way to measure it would be to
slide the (spotlessly clean and DRY) piston into the chamber about the same
distance it would be at idle.The piston/suction chamber must be "clocked"
the same way it is on the car! Measure the rocking clearance with a dial
indicator and go from there. Visually, you can also see significant wear on
the male shaft(piston) . if you can get a mike on the shaft, or set it up
in Vee blocks and use a dial test indicator, you can check out of
roundness.(All the wear wil occur on the throttle shaft side down in the
piston, and on the AF side at the top of the shaft. the wear will be worse
down in the piston.) Put it this way, you probably can't feel any play at
.0005. The more wobble you can feel, the less chance you'll have of
getting a consistant low speed mixture(sticky piston=random lean condition)
. Mind you , you'll never see it when you are twiddleing the mixture,
because it only happens when the engine vacume is applying side trust to
the piston. You can see the piston come to rest in different places after
revving the engine in bad cases of shaft wear. If so , use Carroll Smiths
way of dealing with bad bolts. He takes them off the car, then beats them
with a hammer so he's never tempted to put them back on. He he he...
Don Boyd
----------
> From: CarlSereda@aol.com
> To: dbji@whidbey.net
> Subject: Re: Re: SUs & Carbs
> Date: Monday, August 03, 1998 10:11 PM
>
> man you must know your carburettors to be able to alter taper with sand
paper
> to adjust mixture! For now I will stick with ATF for dampers like I have
for
> last 24 years and work on fixing the loose throttle shafts.
> I may have asked already - but can you tell me what specifically to
measure to
> determine if airvalve on the guide tube is ok? - and tolerable clearance
> between piston and guide tube?
> Carl
|