| Re: [GMCnet] losing power [message #220223] |
Wed, 28 August 2013 13:20  |
KB
Messages: 1262
Registered: September 2009
Karma: 0
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Senior Member |
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thanks guys. (sorry to hijack the thread)
Vac is about 15- at idle, used to be 18+ish on the old engine.
I've checked for vac leaks and can't find any (yes, I remembered
to goop the right rear bolt hole on the TBI gasket :-). I changed the dist
module and cleaned up the contacts and saw no change. I've double-checked
timing at 8 BTDC, but not sure how I'd tell if the timing mark is
wrong. It's the same balancer as was on the old engine and looked ok
(all this stuff was supposedly replaced only 12k miles ago). Intake is stock
in good condition with Dick P's block-off gaskets. No obvious problems
on the fit.
It runs ok with the computer in control, though the idle isn't
as smooth as I'd like. That could be because the fuel and spark tables
haven't been tuned yet. I went back to an earlier tune closer
to what the amazing Randy uses. On the old engine, I'd been backing
off more and more on the spark trying to reduce knock counts.
Turns out the "knocks" were probably the wrist pin or whatever
is ailing piston number 8, which we couldn't hear until it got really bad.
Current theory is the combination of new engine and RV cam is giving
us a lower vac reading. I noticed the IAC step counts were also
significantly higher than before (ie, has to open more to let in air),
which could also be due to the higher friction of a new engine.
So, I'll just check everything carefully, get the new fan clutch
and shroud installed, and we'll try a very gentle short trip to see what
happens. Fingers crossed... we really want to make Coos Bay.
thanks
Karen
1973 23'
1975 26'
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] losing power [message #220226 is a reply to message #220223] |
Wed, 28 August 2013 14:00  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Karen, what timing chain set did you use, and where did you time it.?
Jim Hupy
Salem, Or
78 Gmc Royale 403
On Aug 28, 2013 11:21 AM, "KB" <kab7@sonic.net> wrote:
> thanks guys. (sorry to hijack the thread)
>
> Vac is about 15- at idle, used to be 18+ish on the old engine.
> I've checked for vac leaks and can't find any (yes, I remembered
> to goop the right rear bolt hole on the TBI gasket :-). I changed the dist
> module and cleaned up the contacts and saw no change. I've double-checked
> timing at 8 BTDC, but not sure how I'd tell if the timing mark is
> wrong. It's the same balancer as was on the old engine and looked ok
> (all this stuff was supposedly replaced only 12k miles ago). Intake is
> stock
> in good condition with Dick P's block-off gaskets. No obvious problems
> on the fit.
>
> It runs ok with the computer in control, though the idle isn't
> as smooth as I'd like. That could be because the fuel and spark tables
> haven't been tuned yet. I went back to an earlier tune closer
> to what the amazing Randy uses. On the old engine, I'd been backing
> off more and more on the spark trying to reduce knock counts.
> Turns out the "knocks" were probably the wrist pin or whatever
> is ailing piston number 8, which we couldn't hear until it got really bad.
>
> Current theory is the combination of new engine and RV cam is giving
> us a lower vac reading. I noticed the IAC step counts were also
> significantly higher than before (ie, has to open more to let in air),
> which could also be due to the higher friction of a new engine.
>
> So, I'll just check everything carefully, get the new fan clutch
> and shroud installed, and we'll try a very gentle short trip to see what
> happens. Fingers crossed... we really want to make Coos Bay.
>
> thanks
> Karen
> 1973 23'
> 1975 26'
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] losing power [message #220231 is a reply to message #220223] |
Wed, 28 August 2013 15:31 |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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Senior Member |
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I installed a cloyes double roller on my Melling MTO-1 RV cam, straight up on the gear alignment dots, (some say you can advance one key space) rebuilt heads, bearings, rings, Honed, blocked crossovers, rebuilt carb, I'm getting 19" vacuum at idle. Carb throttle shaft nylon bushings added 1" alone. I would check your manifold for cracks or slipped turkey tray on install...try spraying carb cleaner around the edges an listen for smoother idle.
Sean and Stephanie
73 Ex-CanyonLands 26' #317 "Oliver"
Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD Honda 6500 inverter gen.
Colonial Travelers
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