| [GMCnet] Newfound Power... [message #89236] |
Sat, 19 June 2010 14:06  |
kelvin
Messages: 608
Registered: February 2004
Location: Eugene, OR
Karma:
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Senior Member |
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I'm a happy camper this morning...
Just to set the stage...
A '73 230 with the 455. This coach had a '76 vintage Caddy Q-jet on it
when I got it 9 years ago. It worked but certainly not well. It had
been upgraded to HEI at some point but that was probably from the same
Caddy. One of the first things I did was install a Patersen HEI. Nice
improvement in how it ran right there.
I then tried to find the correct Q-jet (after I learned they were
special) but only came up with a warped one. I ended up buying an
Autozone rebuild and swapping as many GMC parts into it as possible. It
worked better and the mileage went from 5-6 to 7-9. Got 10mpg two times
with a pretty stead tailwind. Pretty much what everyone says to expect
from a GMC.
The motorhome has always had lousy secondary actuation. Falls on it's
face really bad and just seems to be less than optimal across the
board. Not great at pulling hills by any means and I know it should
work better. Merging into freeway traffic is slow and painful. Really,
really need a rebuildable GMC Q-jet but they just aren't out there.
A new friend of mine knows Q-Jets pretty well. He'd never got to sit
on the step of a "rolling dyno" GMC and watch the carb work and was
excited to try it. He came over this morning and we took it for a
spin. Him playing with the carb while I floored it told him a few things.
So we took the top off the carb and fiddled around with various piece.
He didn't like how the metering rods were moving (not getting open fast
enough) and a couple other things. We also changed the spring rate on
the Secondary Air doors and replace the GMC metering rod "lifter" with
the one that came off the Autozone carb. He liked the location of some
holes in that better.
I gotta tell you. I think we have it pretty close to right. The coach
just gets up and goes when I floor it. And it's actually better over
the whole range of operation even though nothing we did should have
improved the Primary circuit. It's truly night and day from just a few
hours ago.
And for the first time in EVER I can break a tire loose from a
standstill. A motorhome that can burn rubber is freakin' awesome.
There goes the fuel mileage...
Later,
Kelvin
'73 23' in Eugene, OR
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