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Re: [GMCnet] A couple 'issues' I'd like some advice on. [message #270931 is a reply to message #270914] Sat, 31 January 2015 23:17 Go to previous messageGo to previous message
James Hupy is currently offline  James Hupy   United States
Messages: 6806
Registered: May 2010
Karma:
Senior Member
Kerry, I have a great deal of experience with cam timing. If you advance
the timing, you should notice the vacuum will be higher at a slightly lower
rpm. If you retard it, you should notice the vacuum higher at a slightly
higher one. The maximum vacuum should not be any higher than it would be
with the timing straight up. Unless you have a camshaft that is quite a bit
different than the stock Olds cam. I am just guessing here because I don't
know what cam you indeed have. If you know the spec's, it would help me be
more exact.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Jan 31, 2015 9:02 PM, "Kosier" wrote:

> Kerry,
>
> I think your hot idle mixture is way too rich. I would turn the idle
> mixture screws in, while watching the vacuum gauge to see if
> that won't improve things. Also, I'm not criticizing. but is it possible
> you got distracted and set the timing chain to the
> retarded position instead of advanced. Don't ask why I know this is
> possible.
>
> Gary Kosier
> 77PB w/500 Cad
> Newark, Oh
>
> -----Original Message----- From: Kerry Pinkerton
> Sent: Saturday, January 31, 2015 8:56 PM
> To: gmclist@temp.gmcnet.org
> Subject: [GMCnet] A couple 'issues' I'd like some advice on.
>
> I've got a couple things going on and I'd appreciate some wisdom from the
> brain trust. I have some ideas but I'm scratching my head.
>
> Some history and then some facts.
>
> 77 403 26' pull a Saturn toad and have a Powerdrive and a 3.21 which ends
> up as a 3.66 final drive ratio. 65mph is about 3000 RPM.
>
> Motor was rebuilt about 5000 miles back, As of yesterday, compression is
> 150-165. All but 1 cylinder (#4) is between 165-160. Patterson carb and
> distributor with his plugs and wires replace when the engine done. All
> electric fuel pumps. Two pumps outside the tanks, filters before each pump,
> another filter before the engine, and the carb filter. Switching to the
> other tank changes which fuel pump is on.
>
> A couple months back, I replaced the timing gears with a 4 degree advanced
> set. At the same time, I changed my vacuum gauge from an elcheapo gauge
> that had a range from 10 to 2 o'clock, to a S&W guage that sweeps from 7
> to 5 o'clock. Readings on the vacuum match a large old mechanics vacuum
> gauge that was my Dad's back in the late 30's and has always been very
> accurate.
>
> When I first started the engine after replacing the timing chains, it had
> been sitting for a couple months while I replaced the tranny. The motor
> idled like crap. Rough, popping through the carb. It would smooth out as
> it warmed up but still ran a bit rough. Yes, the modulator vacuum hose is on
> and functioning correctly. I talked to Dick Patterson and went through
> the timing, dead on 12 degrees with the vacuum adv off and plugged.
> Verified
> the mechanical advance is working, also verified the vacuum advance is
> working. Dinked with it a bit over a couple days and things got better as
> far
> as the idle was concerned but never really changed anything. I moved the
> timing a degree or two but was at 12 when I started and ended up at 11.
> Backed out the idle screws about 1/4 turn. About this time I drove the
> coach and noticed the vacuum seemed a bit low. 55 mph steady and level was
> about 10 inches of mercury. Hot idle was about 16.
>
> Talked to Dick again wondering if the advancing the cam timing 4 degrees
> would effect the vacuum. He said no and thought it was a vacuum leak. I
> dinked with the timing and got it up to about 12 at 55 mph steady and
> level road. I've checked everything I can for vacuum leaks. New PVC valve,
> removed the booster vac line and plugged it. No change on vacuum gauge.
> Carb bolts are tight, modulator is hooked up. Everything is capped. The
> fact that I've got 18 at hot idle makes me think it's not a vacuum leak
> because I'd THINK that a big vacuum leak would show up more at idle than at
> higher RPM?????
>
> Problem #1 is the vacuum level. The coach runs fine. Pulls stronger than
> before. BUT at 65mph on a level road just pulling against the wind and
> maintaining speed, my vacuum is 7-8. I watched it all the way to Tampa
> and back. Runs fine, just lower vacuum than I thought it was before. At
> 55,
> level and steady, I read 12-13. At 65, level and steady but obviously a
> heavier wind load (don't forget I'm towing too), I'm at 7-8. Btw the toad
> brakes and coach Ebrake are clear and rolling free.
>
> So the question is, what kind of vacuum do you get a 65 level and steady?
> Dick said since the coach was running fine, I should put a piece of
> electrical tape on the vacuum gauge and just drive it. He might be right
> but I THINK it was about 5 inches higher before I advanced the cam timing.
> I don't THINK advancing the cam timing should effect the vacuum much if
> any. If I set the timing for max vacuum, I can get hot idle vacuum up near
> 18-19 but the timing mark is almost out of sight...probably 25-30 degrees
> of advance and that's with vacuum off and 700 RPM.
>
> Problem #2 is a "cough". Not a backfire, just a 'chu'. Happened a couple
> times on the way to Tampa and 6-10 more on the way home. Its not much,
> just enough that the wife sometimes asks, "What was that?"
>
> Remember the rough running that seemed to go away right after I got it
> running again.
>
> One more data point. On the way home, we stopped for lunch and I started
> the Onan. Ran like crap. Wouldn't come to speed and stabilize enough for
> the automatic transfer switch to turn on the 120. Turned it off and came
> on home. Now it starts and runs BETTER but still rough, it will at least
> trip the transfer switch on. My buddy Beau thought it was crap in the
> carb.
>
> I'm wondering if it is water in the tanks? This trip had 1600 miles of
> buying today's ethanol laced crap. Other than one tank starting out, and a
> stop at a big Shell in Florida (Ken and Stick also filled up there and
> have reported no problems) all the gas was purchased at big truck stops,
> Flying
> J, Petro, etc. I'd have thought that any water would have been flushed
> out,
>
> I've thought about plugged fuel filters. Wide open throttle is no problem
> and I'd think it would be if there was a partially blocked filter.
>
> It's not repeatable. 10 times in 1600 miles. It SEEMS to happen when I'm
> transitioning from a level pull or downhill to more throttle at about 2600
> rpm. Just a little 'chuu'. Not a bang, not a pop, not loud, literally
> sounds like a muffled cough.
>
> So today, I checked the timing again with TWO timing lights. 12 degrees.
>
> Ken Henderson loaned me a wide band O2 sensor and I welded a bung up close
> to the engine and hooked it up.
> At cold idle (700 rpm) with the choke about closed it read 10.4
> warm idle with half choke was 12.1
> hot idle (hot enough that the oil cooler fan was on so the oil temp was >
> 180), the ratio was 12.4 climbing to 13.2 as it ran a bit more.
>
> IN PARK (it was getting late and I did not drive it today)
> 700 RPM 13.2
> 1300 RPM 12.0
> 2000 RPM 14.6
> 2500 RPM 15.7
> 3000 RPM 15.9
>
> That's all the data I have.
>
> In summary, I have two issues. They might or might not be related:
>
> 1- Low vacuum? (or perhaps it's just fine???)
> 2- The cough? Water?? Add a couple bottles of denatured alcohol??
>
> Your thoughts, advice, etc are solicited. Please try not to hijack this
> thread. If you want to talk about something else, please start another
> thread.
> --
> Kerry Pinkerton
>
> North Alabama, near Huntsville,
>
> 77 Eleganza II, "The Lady", 403CI, Manny Brakes, 1 ton, tranny also a 76
> Eleganza to be re-bodied as an Art Deco car hauler
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