Home » Public Forums » GMCnet » Carb versus timing
| Carb versus timing [message #312148] |
Mon, 16 January 2017 09:53  |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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Senior Member |
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A year or so ago I started a thread regarding problems I was having after a carb cleaning and rebuild and would like to offer a followup now that I've resolved my issues.
The backstory is that like happens so often, the coach sat too long and the carb was fairly gummed up from old fuel. I pulled it, gave it a good soaking and then reassembled with fresh parts. I also had taken the opportunity to remove the intake and perform all the tasks related to that plus drained and refilled the tanks with fresh fuel.
As part of the intake R&R, wires and hoses were disconnected and the distributor removed. The distributor got a new rotor and wires and the engine got new plugs. After putting it all back together, the engine ran terrible. It was hard to start and it stalled with the slightest of throttle. I went through all the obvious items, checking hose connections, vacuum, linkage, timing, accel pump, float level, etc and even replaced the fuel pump at some point.
Everything seemed to point to the carb but I couldn't discern that anything was wrong with it. No settings were changed, only confirmed as correct and reassembled with new gaskets, filter, accel pump etc. I also confirmed it was the correct carb for this coach. The coach was relatively new to us before being parked for too long but we drove it enough to know it ran fine previously.
Ater searching the internet for some insight and ending up on a Olds 442 forum, I read where several posters talked about how the 403 motors preferred lots of initial timing advance. So I started advancing the initial timing and as I approached 20 degrees, it began to respond better! I knew that couldn't be correct because in theory there would be too much total advance. I had already cleaned and lubed the advance weights in the distributor as well as confirmed that the vacuum advance worked so I dug deeper and mapped the advance curve, both mechanical and vacuum. It was then I determined that someone had replaced the distributor at some point with one that was not close to correct for this application.
Whoever had done that obviously set the initial timing at a point where it worked for that advance curve and the coach ran okay. But when I pulled everything apart, I wasn't aware of that so I naturally went back to the specs for this application. I'm lucky I didn't wear out the threads on the carb before finding the true source of the problem!
I ordered the correct weights and center piece and secured a correct vacuum advance can and put it all back together. Now it runs like it's supposed to!
The moral? Besides the obvious about don't assume anything, always double check the timing, both static and dynamic when troubleshooting a sluggish engine.
1978 Eleganza II
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| Re: [GMCnet] Carb versus timing [message #312163 is a reply to message #312154] |
Mon, 16 January 2017 14:07  |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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Senior Member |
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Rob:
I’ve always tracked the mileage as an indicator of overall efficiency, and as an early indicator when things are going wrong.
My .02……
Dolph
DE AD0LF
Wheeling, West Virginia
1977 26’ ex-PalmBeach
1-Ton, Sullybilt Bags, Reaction Arms, 3.70 LSD, Manny Transmission, EV-6010
“The Aluminum and Fiberglass Mistress"
> On Jan 16, 2017, at 3:03 PM, Rob Mueller wrote:
>
> Ken,
>
> When I bought Double Trouble it had a spread bore Holley on it which a PO
> had installed in an attempt to get better gas mileage. I don't know if that
> was successful or not because I replaced it with a Q-Jet from Dick Patterson
> within a month or so after buying the coach. I did that because it couldn't
> get out of its own way! The carb improved things quite a bit.
>
> I decided that I'd install one of his custom curved distributors as well to
> see what effect that would have.
>
> To my surprise the distributor made a bigger improvement than the carb!
>
> BTW I still don't know what my gas mileage is as I've never checked it. I
> don't care.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> USAussie - Downunder
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
> USA '77 Kingsley - TZE 267V100808
>
>
> -----Original Message-----
> From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Ken
> Harland
> Sent: Tuesday, January 17, 2017 2:54 AM
> To: gmclist@list.gmcnet.org
> Subject: [GMCnet] Carb versus timing
>
> A year or so ago I started a thread regarding problems I was having after a
> carb cleaning and rebuild and would like to offer a followup now that I've
> resolved my issues.
>
> The backstory is that like happens so often, the coach sat too long and the
> carb was fairly gummed up from old fuel. I pulled it, gave it a good
> soaking and then reassembled with fresh parts. I also had taken the
> opportunity to remove the intake and perform all the tasks related to that
> plus
> drained and refilled the tanks with fresh fuel.
>
> As part of the intake R&R, wires and hoses were disconnected and the
> distributor removed. The distributor got a new rotor and wires and the
> engine
> got new plugs. After putting it all back together, the engine ran terrible.
> It was hard to start and it stalled with the slightest of throttle. I
> went through all the obvious items, checking hose connections, vacuum,
> linkage, timing, accel pump, float level, etc and even replaced the fuel
> pump
> at some point.
>
> Everything seemed to point to the carb but I couldn't discern that anything
> was wrong with it. No settings were changed, only confirmed as correct
> and reassembled with new gaskets, filter, accel pump etc. I also confirmed
> it was the correct carb for this coach. The coach was relatively new to
> us before being parked for too long but we drove it enough to know it ran
> fine previously.
>
> Ater searching the internet for some insight and ending up on a Olds 442
> forum, I read where several posters talked about how the 403 motors
> preferred
> lots of initial timing advance. So I started advancing the initial timing
> and as I approached 20 degrees, it began to respond better! I knew that
> couldn't be correct because in theory there would be too much total advance.
> I had already cleaned and lubed the advance weights in the distributor
> as well as confirmed that the vacuum advance worked so I dug deeper and
> mapped the advance curve, both mechanical and vacuum. It was then I
> determined that someone had replaced the distributor at some point with one
> that was not close to correct for this application.
>
> Whoever had done that obviously set the initial timing at a point where it
> worked for that advance curve and the coach ran okay. But when I pulled
> everything apart, I wasn't aware of that so I naturally went back to the
> specs for this application. I'm lucky I didn't wear out the threads on the
> carb before finding the true source of the problem!
>
> I ordered the correct weights and center piece and secured a correct vacuum
> advance can and put it all back together. Now it runs like it's supposed
> to!
>
> The moral? Besides the obvious about don't assume anything, always double
> check the timing, both static and dynamic when troubleshooting a sluggish
> engine.
> --
> 1978 Eleganza II
>
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| Re: [GMCnet] Carb versus timing [message #312164 is a reply to message #312148] |
Mon, 16 January 2017 14:03 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Ken,
When I bought Double Trouble it had a spread bore Holley on it which a PO
had installed in an attempt to get better gas mileage. I don't know if that
was successful or not because I replaced it with a Q-Jet from Dick Patterson
within a month or so after buying the coach. I did that because it couldn't
get out of its own way! The carb improved things quite a bit.
I decided that I'd install one of his custom curved distributors as well to
see what effect that would have.
To my surprise the distributor made a bigger improvement than the carb!
BTW I still don't know what my gas mileage is as I've never checked it. I
don't care.
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Ken
Harland
Sent: Tuesday, January 17, 2017 2:54 AM
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Carb versus timing
A year or so ago I started a thread regarding problems I was having after a
carb cleaning and rebuild and would like to offer a followup now that I've
resolved my issues.
The backstory is that like happens so often, the coach sat too long and the
carb was fairly gummed up from old fuel. I pulled it, gave it a good
soaking and then reassembled with fresh parts. I also had taken the
opportunity to remove the intake and perform all the tasks related to that
plus
drained and refilled the tanks with fresh fuel.
As part of the intake R&R, wires and hoses were disconnected and the
distributor removed. The distributor got a new rotor and wires and the
engine
got new plugs. After putting it all back together, the engine ran terrible.
It was hard to start and it stalled with the slightest of throttle. I
went through all the obvious items, checking hose connections, vacuum,
linkage, timing, accel pump, float level, etc and even replaced the fuel
pump
at some point.
Everything seemed to point to the carb but I couldn't discern that anything
was wrong with it. No settings were changed, only confirmed as correct
and reassembled with new gaskets, filter, accel pump etc. I also confirmed
it was the correct carb for this coach. The coach was relatively new to
us before being parked for too long but we drove it enough to know it ran
fine previously.
Ater searching the internet for some insight and ending up on a Olds 442
forum, I read where several posters talked about how the 403 motors
preferred
lots of initial timing advance. So I started advancing the initial timing
and as I approached 20 degrees, it began to respond better! I knew that
couldn't be correct because in theory there would be too much total advance.
I had already cleaned and lubed the advance weights in the distributor
as well as confirmed that the vacuum advance worked so I dug deeper and
mapped the advance curve, both mechanical and vacuum. It was then I
determined that someone had replaced the distributor at some point with one
that was not close to correct for this application.
Whoever had done that obviously set the initial timing at a point where it
worked for that advance curve and the coach ran okay. But when I pulled
everything apart, I wasn't aware of that so I naturally went back to the
specs for this application. I'm lucky I didn't wear out the threads on the
carb before finding the true source of the problem!
I ordered the correct weights and center piece and secured a correct vacuum
advance can and put it all back together. Now it runs like it's supposed
to!
The moral? Besides the obvious about don't assume anything, always double
check the timing, both static and dynamic when troubleshooting a sluggish
engine.
--
1978 Eleganza II
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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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| Re: Carb versus timing [message #312183 is a reply to message #312148] |
Mon, 16 January 2017 20:51 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Spread bore Holley has small primaries / large secondaries like the Qjet, hence the name. The Holleys are easiier to rejet from the outside. They don't run bettter and the Q jet has lots of design details thst make it capable of better economy.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Carb versus timing [message #312185 is a reply to message #312183] |
Mon, 16 January 2017 21:05 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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Senior Member |
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JohnL455 wrote on Mon, 16 January 2017 21:51Spread bore Holley has small primaries / large secondaries like the Qjet, hence the name. The Holleys are easiier to rejet from the outside. They don't run bettter and the Q jet has lots of design details thst make it capable of better economy. I apparently was thinking of a different version Holley, disregard my ealier comments.
1978 Eleganza II
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