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Re: [GMCnet] Carb / Vacuum issue [message #288583 is a reply to message #288553] Mon, 12 October 2015 15:36 Go to previous messageGo to previous message
USAussie is currently offline  USAussie   United States
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma:
Senior Member
Brian,

Have you considered sending the carb to Dick Paterson for a rebuild? If you do make sure you contact him before you send it so he
can tell you what to check to make sure it is a good core.

http://www.paterson-gmc.com/

Regards,
Rob M.
The Pedantic Mechanic


-----Original Message-----
From: Brian Pimm

I'm starting a new thread to continue this discussion, was vacuum question. I was loaned a known good carb from a local GMC'er to
test mine against.
At idle mine was developing 16" of vacuum, dribbling fuel out of the primaries and running mostly in the 10-12 AFM area. After
switching carbs idle now developing 19" of vacuum, not dribbling out of the primaries and operating in the 11-15 AFM area plus it
runs a great deal better. the replacement carb is a little lean coming off idle and into the primaries under load it can bog a bit
if you don't feather the throttle so it's not perfect but it is much better. it is idling at 14 to 1 and doesn't load up if it idles
for an extended period.

So now we know that the carb is the problem. what should I be looking for on the tear down. History is carb was rebuilt by me 2
years ago but I had fuel problems, gunk in the tanks plugging the filter, this has been resolved by cleaning the tanks and replacing
all the fuel lines, including hard lines. I had the top off of the carb a few weeks ago to check the float level and everything
looked clean inside but I didn't tear it down any
further.

Problems are low vacuum, fuel dribbling out of the primaries and little or no effect from the idle screws, which is probably from
the excess fuel being pulled from the primaries.

I'm not a carb expert although I have rebuilt and tuned a few through the years, mainly Weber side drafts.

any and all help is appreciated.
--
Brian


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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

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