| vacuum reading on 455 [message #255137] |
Sat, 12 July 2014 06:33  |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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I cannot find in the manual the proper readings for the vac lines. Any ideas on what is acceptable for an engine with 135k and a little upper half work? If the air cleaner is off should I block off the one in back that goes to the air cleaner housing? I heard 15 lbs steady for the main port and once I get to a certain rpm on the motor what should the vac advance read? Thanks in advance gentlemen. Another compression test today as well.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: vacuum reading on 455 [message #255169 is a reply to message #255137] |
Sat, 12 July 2014 13:25  |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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budworks521 wrote on Sat, 12 July 2014 05:33I cannot find in the manual the proper readings for the vac lines. Any ideas on what is acceptable for an engine with 135k and a little upper half work? If the air cleaner is off should I block off the one in back that goes to the air cleaner housing? I heard 15 lbs steady for the main port and once I get to a certain rpm on the motor what should the vac advance read? Thanks in advance gentlemen. Another compression test today as well.
At your elevation you should have 18 to 20" at idle at a manifold vacuum port--If you have any doubt which ports are what, I would tap into a fitting that screws directly into the manifold. Any other open port should be plugged. If you measure at the port that was designed for the distributer vacuum advance, you will see almost nothing at idle and a gradual rise to full vacuum as the throttle is opened. I'm suspecting you may have a vacuum leak somewhere. If there is one, it could be almost anywhere--brake booster line, brake booster leak, transmission modulator line, charcoal cannister line, HVAC vacuum system (although that would be a minimal leak) loose carburetor. One way to check is to pinch any vacuum hase you can find while running and monitoring the gage..
Bob de Kruyff
78 Eleganza
Chandler, AZ
[Updated on: Sat, 12 July 2014 13:26] Report message to a moderator |
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| Re: vacuum reading on 455 [message #255181 is a reply to message #255137] |
Sat, 12 July 2014 15:38 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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All my readings were 15/16 steady except the brake booster port. That needle was jumping from 15-18 back and forth. I tried the tranny, pcv valve, brake booster, small one next to it, back one for air cleaner, etc. I think I am ok? I even tried all the readings with the vapor line off the carb and plugged. Pretty much same readings. Thanks, I must have some carb issues....
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: [GMCnet] vacuum reading on 455 [message #256626 is a reply to message #255181] |
Sat, 26 July 2014 16:42 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Spray some WD 40 on the carb shafts. You might find after 135k miles that
the shafts have worn and allow for a vacuum leak at idle.
On Sat, Jul 12, 2014 at 2:38 PM, Lawrence Harrison
wrote:
> All my readings were 15/16 steady except the brake booster port. That
> needle was jumping from 15-18 back and forth. I tried the tranny, pcv valve,
> brake booster, small one next to it, back one for air cleaner, etc. I
> think I am ok? I even tried all the readings with the vapor line off the
> carb
> and plugged. Pretty much same readings. Thanks, I must have some carb
> issues....
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: vacuum reading on 455 [message #256670 is a reply to message #255137] |
Sun, 27 July 2014 07:00 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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I have tried cleaning the carb throughout and still have some minor popping in the carb at idle. Goes away at throttling and not very pronounced. Thinking of pulling carb and inspecting for gas leaks and float concerns. Thanks for the input.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: vacuum reading on 455 [message #256728 is a reply to message #255137] |
Sun, 27 July 2014 17:26 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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I already did a block off kit with Dick Paterson gasket set. All this happened after no issues after original repairs. I am posting a new question concerning a lean carb and how much fuel should be spilling out of the primary jets at idle. I notice that the primary jets are healthy squirters at throttling but when idling one of the two jets does not have a constant drip of gas into the carb. sometimes they alternate at dripping. New post now! Thanks for the input.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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