| !977 Carb [message #340877] |
Sun, 10 February 2019 20:12  |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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I have a 1977 carb #17057254. Is this carb for the 403 or 455 or does it even matter.
I want to use it on a 455.
Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: [GMCnet] !977 Carb [message #340910 is a reply to message #340877] |
Mon, 11 February 2019 14:19  |
gmc-email-list
Messages: 124
Registered: February 2019
Karma: 2
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Senior Member |
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> On Feb 10, 2019, at 7:12 PM, Bruce Hart via Gmclist wrote:
>
> I have a 1977 carb #17057254. Is this carb for the 403 or 455 or does it even matter.
> I want to use it on a 455.
> --
> Bruce Hart
> 1976 Palm Beach
> Milliken, Co
Bruce
GM used seven different carbs for the GMC motorhome. 73 and 74 years had a carb #7043254
75 and 76 and early 77 had 7045254 except for California emission carbs which were 7045554
77 coaches with the 403 engine had 17057254 and California 17057559
78 had 17058254 and California 1758559
These carb numbers can be found on the left side of the carb, stamped on the flat surface close to the secondary throttle shaft.
There is also a date code (4 digits) stamped in the same area. 73 to 76 coaches had a number starting with 70
77 & 78 carbs start with 170.
Some parts for these carbs are quite different on the 170 from the 70. DO NOT INTERCHANGE parts between these two series.
One example is the primary metering rods. They are .080" shorter in the 170 series, they had a different taper to the rods and these carbs used different sizes of primary jets.
The rods for the 70 series carbs will be stamped D-50. (7046338) I am told that this was used ONLY in the GMC motorhome carbs. The 170 series are different. All GMC carbs used the same secondary metering rods. These will be stamped with a CJ. The primary jets for the GMC at your elevation should be .070". (7031970)
The proper power spring for the GMC is #7036019 which has an operating range from 4" to 8" of vacuum.
One problem that some people have had is the use of gaskets from an unknown kit. There are changes in the air passages in the carbs and it is easy to install a gasket that covers an air passage hole and that will make the carb perform improperly.
The Delco overhaul kit for the 73-74 is 7046812. For the 75-76 (non Calif) it is 17051886
I have quite a bit more information in my files about GMC carbs.
Emery Stora
77 Kingsley
Frederick, CO
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