Home » Public Forums » GMCnet » Sage Engine Tuning Advice Needed (new rebult engine low on power)
| Sage Engine Tuning Advice Needed [message #249490] |
Mon, 12 May 2014 11:14  |
Gary Carlton
Messages: 59
Registered: February 2014
Karma: 0
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I have just finished installing a new rebuilt long block 403 into my coach; rebuilt Patterson carb, new fuel pump, distributor cap and wires, etc. Got it up and running, no obvious leaks yet, good oil pressure, steady idle, timed to 12 degrees BTDC.
The issue I am having is that it is low on power under load. Going up hills will lead to slowing down or stalling the engine if more throttle is applied.
I'm guessing a vacuum leak or potentially my distributor vacuum advance has gone wonky but any advice of where you would look first is welcome.
Thank you in advance
gary
'78 Royale, "Road Grub"
Bellingham, WA
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| Re: Sage Engine Tuning Advice Needed [message #249496 is a reply to message #249490] |
Mon, 12 May 2014 11:34  |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Gary Carlton wrote on Mon, 12 May 2014 09:14I have just finished installing a new rebuilt long block 403 into my coach; rebuilt Patterson carb, new fuel pump, distributor cap and wires, etc. Got it up and running, no obvious leaks yet, good oil pressure, steady idle, timed to 12 degrees BTDC.
The issue I am having is that it is low on power under load. Going up hills will lead to slowing down or stalling the engine if more throttle is applied.
I'm guessing a vacuum leak or potentially my distributor vacuum advance has gone wonky but any advice of where you would look first is welcome.
Thank you in advance
gary
Going up a steep hill your vacuum advance should not have an effect. A Patterson distributor would be a help in power or a properly recurved stock one would be an improvement. Are the advance weights moving freely?Is your fuel filter in good shape? Did you put a high torque cam in the new engine? Did you set the lifter pre load to factory specs? The rockers aren't adjustable but you can shim the stanchions to allow for resurfaced heads. Are you still running the 3:08 gears a lower ratio would be a nice improvement. Are you running oversize tires?
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Sage Engine Tuning Advice Needed [message #249504 is a reply to message #249490] |
Mon, 12 May 2014 12:00 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Gary Carlton wrote on Mon, 12 May 2014 09:14I have just finished installing a new rebuilt long block 403 into my coach; rebuilt Patterson carb, new fuel pump, distributor cap and wires, etc. Got it up and running, no obvious leaks yet, good oil pressure, steady idle, timed to 12 degrees BTDC.
The issue I am having is that it is low on power under load. Going up hills will lead to slowing down or stalling the engine if more throttle is applied.
I'm guessing a vacuum leak or potentially my distributor vacuum advance has gone wonky but any advice of where you would look first is welcome.
Thank you in advance
gary
I agree with the fuel issue. Especially if you can stall it by giving it too much throttle. The open throttle is just letting in too much air and for some reason the fuel is not flowing. I am guessing that the stall happens when the secondaries start to open.
Fuel pump, filter/s, something wonky in the tanks. Also a crack in a gas hose somewhere between the pump and the tank will break the vacuum and keep the pump from being able to suck gas. Does switching tanks help?
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: Sage Engine Tuning Advice Needed [message #249520 is a reply to message #249504] |
Mon, 12 May 2014 13:42 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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George Beckman wrote on Mon, 12 May 2014 11:00Gary Carlton wrote on Mon, 12 May 2014 09:14I have just finished installing a new rebuilt long block 403 into my coach; rebuilt Patterson carb, new fuel pump, distributor cap and wires, etc. Got it up and running, no obvious leaks yet, good oil pressure, steady idle, timed to 12 degrees BTDC.
The issue I am having is that it is low on power under load. Going up hills will lead to slowing down or stalling the engine if more throttle is applied.
I'm guessing a vacuum leak or potentially my distributor vacuum advance has gone wonky but any advice of where you would look first is welcome.
Thank you in advance
gary
I agree with the fuel issue. Especially if you can stall it by giving it too much throttle. The open throttle is just letting in too much air and for some reason the fuel is not flowing. I am guessing that the stall happens when the secondaries start to open.
Fuel pump, filter/s, something wonky in the tanks. Also a crack in a gas hose somewhere between the pump and the tank will break the vacuum and keep the pump from being able to suck gas. Does switching tanks help?
Another possibility is that the upper butterfly's are opening too soon. They are spring loaded and reduce the secondary airflow until the engine can handle it. If they open too soon, the engine will bog instead of accelerate. They are adjustable. However, if it's a Patterson carb, it most likely is set up correctly.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Sage Engine Tuning Advice Needed [message #249539 is a reply to message #249490] |
Mon, 12 May 2014 18:17 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Senior Member |
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Gary Carlton wrote on Mon, 12 May 2014 11:14I have just finished installing a new rebuilt long block 403 into my coach; rebuilt Patterson carb, new fuel pump, distributor cap and wires, etc. Got it up and running, no obvious leaks yet, good oil pressure, steady idle, timed to 12 degrees BTDC.
The issue I am having is that it is low on power under load. Going up hills will lead to slowing down or stalling the engine if more throttle is applied.
I'm guessing a vacuum leak or potentially my distributor vacuum advance has gone wonky but any advice of where you would look first is welcome.
Thank you in advance
gary Start at this post and read all of Kerry's subsequent posts. His was a spanking new Paterson carb too.
http://gmc.mybirdfeeder.net/GMCforum/index.php?t=msg&goto=223197&rid=2083#msg_223197
Kerry said check the secondaries, but his short reply probably got buried too quick.
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| Re: Sage Engine Tuning Advice Needed [message #249546 is a reply to message #249539] |
Mon, 12 May 2014 19:51 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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A Hamilto wrote on Mon, 12 May 2014 17:17Gary Carlton wrote on Mon, 12 May 2014 11:14I have just finished installing a new rebuilt long block 403 into my coach; rebuilt Patterson carb, new fuel pump, distributor cap and wires, etc. Got it up and running, no obvious leaks yet, good oil pressure, steady idle, timed to 12 degrees BTDC.
The issue I am having is that it is low on power under load. Going up hills will lead to slowing down or stalling the engine if more throttle is applied.
I'm guessing a vacuum leak or potentially my distributor vacuum advance has gone wonky but any advice of where you would look first is welcome.
Thank you in advance
gary Start at this post and read all of Kerry's subsequent posts. His was a spanking new Paterson carb too.
http://gmc.mybirdfeeder.net/GMCforum/index.php?t=msg&goto=223197&rid=2083#msg_223197
Kerry said check the secondaries, but his short reply probably got buried too quick.
The significant part of the message is the comment about stalling the engine if more throttle is applied--that is a typical result of the upper butterfly's opening too soon. If the lower secondaries aren't opening, you won't get the bogging or stalling feel.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Sage Engine Tuning Advice Needed [message #249572 is a reply to message #249546] |
Tue, 13 May 2014 01:20 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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Senior Member |
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Paterson.
Todd Sullivan
Sully
77 royale
Seattle
> On May 12, 2014, at 5:51 PM, Bob de Kruyff wrote:
>
> A Hamilto wrote on Mon, 12 May 2014 17:17
>> Gary Carlton wrote on Mon, 12 May 2014 11:14
>>> I have just finished installing a new rebuilt long block 403 into my coach; rebuilt Patterson carb, new fuel pump, distributor cap and wires,
>>> etc. Got it up and running, no obvious leaks yet, good oil pressure, steady idle, timed to 12 degrees BTDC.
>>> The issue I am having is that it is low on power under load. Going up hills will lead to slowing down or stalling the engine if more throttle
>>> is applied.
>>> I'm guessing a vacuum leak or potentially my distributor vacuum advance has gone wonky but any advice of where you would look first is
>>> welcome.
>>> Thank you in advance
>>> gary
>> Start at this post and read all of Kerry's subsequent posts. His was a spanking new Paterson carb too.
>>
>> http://gmc.mybirdfeeder.net/GMCforum/index.php?t=msg&goto=223197&rid=2083#msg_223197
>>
>> Kerry said check the secondaries, but his short reply probably got buried too quick.
>
>
>
> The significant part of the message is the comment about stalling the engine if more throttle is applied--that is a typical result of the upper
> butterfly's opening too soon. If the lower secondaries aren't opening, you won't get the bogging or stalling feel.
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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