Thanks for all the replys to my tuning problem. I had a great w/end
planned, including spending several hours trying to finish debugging my 2L
carbs. The majority of the time, however, was spent trimming out and laying
carpet in my folks newly remodeled family room. I can't complain though as
they allow free storage of two roadsters and my stash of parts in their
garage!
I used the remaining 45 minutes of daylight to the fullest (old crotchety
neighbors). I readjusted both carbs, and also rebalanced them with the
Unisyn. I found part of my problem in the bent center linkage (the previous
owers were not nice to this car). This by itself helped the car incredibly
as this bent linkage would not allow the carbs to remain balanced through
the rpm range. Next time I will check the float level and gross gets as you
have recommended. The car still have *some* hesitation at medium throttle.
It goes away at higher revs-- I think some minor adjustments will take care
of this.
I've only been driving through the alley which limits me to 30mph before I
run out of road. I have plates and its insured so the next time out will
hopefully involve some road travel so I can see how it responds in 4th and
5th. Still not quite legal without exhaust and bumpers. One thing that
continues to surprise me is the high gearing! I tend to shift to soon out
of habit from driving my MX-6 (geared WAY low). I'm sure I'll find some way
to adjust. ;-)
Thanks again.
Nathan
> Hey all!
>
> I'm back to tuning my roadster this weekend. Thanks to your last insight,
> I was able to determine one of my HUGE problems. I had ordered and
> installed rebuilt carbs from Z-therapy (nice looking carbs). After
> assembling, I was unable to get the car to idle. I followed all your
> recommnedations, setting and rechecking timing and valves, updated
> distributor to an early non-smog, replaced plugs/wires/coil. After all
> this, still the same result. Apparently either the throttle shaft bearing
> were sent without grease or my car backfired and blew out the grease (most
> likely the latter). This resulted in a huge vacuum leak, not allowing my
> car to idle or run smoothly at all. Scott at Z-therapy was great. He
> repacked the bearings and installed new seals and even expressed the carbs
> back!
>
> Now, fast forward to the future (always wanted to say that! <g>).
> These are my current symptoms and what I have checked. I'll be the first
> to admit, I am learing as I go, so I may have missed a crucial step.
>
> Problem:
> Car falls on it's face (almost like you shut off the key) under medium
> acceleration or above 2000rpm. If you keep your foot on the gas, it
> hesitates (long), pops and misses. While not under a load, it revs freely
> and idles smoothly-sounds healthy. Using a timing light, I can see that
> both my distributor advance are working.
>
> The carbs have been set with a Uni-Syn and the mixture is at 2 1/2 turns
> out. I have tried to set mixture using a vacuum gauge on the manifold.
> Vacuum or idle doesn't seem to respond to adjusting the mixture (it did
when
> I had the massive vacuum leak)-am I all wet on this one?
>
> Other stats-maybe useless.
> Stock SU cam
> Manifold vacuum is at 21pounds at idle.
> Idle set at 700rpm.
> Vaccum advance starts opening at 3 pounds and is open fully at 10.
> Carbs vacuum appears to work, going as high as 15 pounds if the throttle
is
> "blipped" to 3000 rpm.
> Timing set a 16BTDC (appears to advance to almost 30BTDC when both
advances
> are open)
> Cylinder compression 190+ on all cylinders.
>
> What else it there? I'm sure I could hire somebody to tune it, BUT I am
> planning on driving the U20 for extended distances (like the all Datsun
meet
> <g>) and want to be able to know whats going on if trouble arises on the
> road. Sorry about the length of this post. If anyone has the "miracle
> cure" or even any sage advice, I am game. Even after driving it in it's
> current condition, I'm excited about the what lay ahead. The body of the
> car is being worked along with the interior and chrome. It should all
come
> together soon.
>
> Thanks in advance!
> Nathan
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