Dave,
I don't know whether you have received responses from List members who
didn't "reply all", so I may be redundant here.
To me the most telling
statement you made "I do not know the history...there is no telling the last
time they were rebuilt or serviced." In my mind there is no point in trying
to figure out whether you have mixture problems, fuel level problems, throttle
shaft leakage or what ever until you've been through the carbs and made sure
they're set to specs to the best of your ability.
I have a '66 1600 with a
'69 U20 (SU) motor. At one point in time, it would pull above about 4500 -
5000 rpm period. I found that if I pulled the "choke" out a couple of
notches, effectively enriching the mixture, it would pull it's heart out. It
was too lean at higher rpm, as a result of keeping the mixture lean enough at
idle so it would idle. (If I set the idle mixture rich enough to eliminate
the "4500 rpm barrier", the car would load up and quit after idling for a
maybe 30 seconds.) Turns out the throttle shafts were leaking past the teflon
bushings. After going through the agony of putting new bushings in those
carbs without effecting much improvement, I bought a set of brand new throttle
bodies, which were $350 for the pair at the time. That solved the problem.
So, make sure the carbs are mechanically correct: fuel level correct in the
float bowls, float needles and seats not leaking, float bowl inlet filters
clear, nozzles properly centered in the throttle bodies (pistons drop smoothly
with a light "thunk"), no apparent wear between the jet needles and nozzles,
choke actuating levers set properly, throttle butterflies opening fully at
wide-open throttle, throttle butterflies closing when the accelerator pedal is
lifted, no binding in the throttle cable or linkage, carbs are balanced and
mixture set at idle, and carbs are balanced at ~2,000 rpm (separate screw on
the linkage).
I check the float needles and seats by removing the float bowl
cover, inverting the cover so only the weight of the float is bearing on the
needle and seat assembly, and trying to blow air past the seat with a "Mighty
Vac" which works in both vacuum and pressure mode and gives an indication of
leakdown. A cheaper procedure is to make sure the fuel is out of the float
bowl inlet, invert as above, pull a vacuum on the fuel inlet nipple with your
mouth and stick your tongue over the end of the nipple. If the needle and
seat are leaking, the seal between your tongue and the nipple won't hold.
That said, I seriously doubt the float needle and seat are your problem, or
you'd likely have fuel coming out the overflows.
I set the choke actuators by
pulling the choke out slightly, then securing the choke wires to the linkage
so there is no movement in the nozzles at that point. As you pull the choke
out further, the nozzles should begin to drop and the linkage should begin to
open the throttles slightly.
This all presumes you have satisfied yourself
that the ignition system is performing properly across the rpm range. No
point in trying to solve performance problems unless you know the ignition is
right.
Hope this is helpful.
Gary
________________________________
From:
dave n <dave@ranteer.com>
To: Datsun <datsun-roadsters@autox.team.net>
Sent:
Friday, August 8, 2014 10:59 PM
Subject: [Roadsters] carb problems?
two
issues Ibm having with an early 67 roadster
1. typically, until you run the
car for 15 or 20 minutes, it doesnbt like
to go above 4500 rpm. tonight I
took it out on the freeway, and after about
15 minutes at 65 I could get it to
run over 4500 or 5000. up until then, it
just hit a wall (so to speak).
2.
after running for about 30 minutes at 60 to 75, I pulled it into a large
parking garage. wasnbt cold, but was not as hot as outside. turned it off,
did a few things, then it wouldnbt start. no biggie as that is where it
currently lives. back on July 4th in the evening I had gone to get it, drove
it home, and then it wouldnbt start. later it started up and ran just fine.
always starts right up when cold. Ibm sure it will start in the morning.
Ibm
thinking I have carb issues? newly rebuilt/refurbished dizzy with
pertronix,
good solid coil, electric fuel pump (which, btw, is in the engine
compartment).
I do not know the history of these carbs; there is no telling
the last time
they were rebuilt or serviced. Ibve had the car since 2006 and
its been
mostly apart since then or sitting. does not get driven much,
especially now
that I have to be careful about taking it somewhere.
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