Appie,
Not to start a pissing contest here, but this has been discussed several times over the years that I have been on the GMCnet. There are differences between the motorhome carbs and the non-motorhome carbs. I don't know what they all are, but you should contact Dick Paterson. He is the recognized expert on the GMC motorhome carbs. I have run his carb on our 403 and it ran great along with his distributor too.

http://www.springfield-ignition.com/gmc-motorhome/carburation/

You can send him an email if you go to the contact tab on the website.

J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 Buskirk 30' Stretch
1975 Avion (Under Reconstruction)
Michigan

> On Mar 5, 2015, at 5:05 AM, Espen Heitmann wrote:
>
> Well, then I think it is time for the ones that say there is any internal or external differences from what I list below to come forward and state
> it.
>
> On the 7043252 you will have to :
>
> Enlarge the small hole in it primary butterflies to 1/8"
> Change the primary rods and jets
> Change the power valve spring
> Change the secondary rod hanger
> Block the extra external vacuum ports
> There is a minimal difference in the original air valve dashpot opening time, if/when the dashpot is replaced they will be identical.
> Set it up to 7043254 specs
>
> Other than that they are identical down to the internal air bleeds, same casting # etc, that there should be any differences in the internal passages
> is a statement that I can not take seriously as there is just NO reason for it or possibilities in the carb castings to re route anything from the
> original design.
>
> Please prove me wrong, I have just spent the last week going through the carburetors i question tearing them completely down and measured every
> opening, bleed and lenght that it is possible to measure.
> --
> 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Mean Green Machine,
> And just sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
> in Norway
>
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The rods are not straight, they are tapered. If you use straight rods you will not get the correct mixture. I am not at home right now but I will be there later so I can look up the information. And get back to you.

Emery Stora

> On Mar 5, 2015, at 3:43 PM, Espen Heitmann wrote:
>
> Ok here we go for the jet and rod....
>
> So we know for sure that the 7043252 in the primary circuit had # 70 jets and 50D rods, this is our starting point, we have to
> compare and do some math.
> How much will this combination flow is the question and the answer, the 50D rods with the 0.036 tip is the clue, remember that all
> other rods have a 0.026 tip.
>
> I will not take everything now but in short what I did find out is that the open area with a :
> # 70 jet and a 0.036 tip is 0.00283057
> # 70 jet and a 0.026 tip is 0.00331752
> That gives a difference of 0.00048695
> To give you an idea of how large the difference is we will try to find a jet size that will flow the same as the # 70/0.036 but with
> the standard 0.026 tip.
> I did some more research and did find a combination that would flow 0.00289027, just a tiny bit more with a 0.026 tip, it was jet
> size # 66
>
> The above is with the rod at WOT, so what about at idle ?
>
> Well we know the diameter for the 50D rod, it is 0.050, this has a flow with the # 70 jet at 0.00188496.
> So since I did find out that a# 66 jet with a 0.026 rod did flow about the same as the #70/0.036 combo I just have to find a rod
> with a diameter that gives the same, the # 44 rod flows 0.00190066 with the #66 Jet and that is pretty darn close to the # 70/0.050
> combo
>
> So now I know that the closest jet/rod combination to the # 70/50D is #66/44 and that is way to lean for a 455 on idle..
>
> BUT remember in the post above I said the primary butterflies had a larger 1/8" home in them ? well there is your answer to why the 455 can run on the
> lean rod and jet combo, the hole is directly over the idle mixture screws, get it ?.
>
>
> --
> 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Mean Green Machine,
> And just sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
> in Norway
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Espen, please remember that the jets and needles were sized when gasoline
was formulated to be used in a carb equipped engine. Today's gasoline is
formulated for use in fuel injected engines under high pressure, not less
than atmospheric pressure. Jet and needle sizes that you are using are
probably a good starting point. I do not know if European gasolines are
blended with alcohol, or what percentage it might be. Altogether confusing
for sure.
Jim Hupy
Salem, Oregon
78 GMC ROYALE 403
On Mar 5, 2015 3:11 PM, "Espen Heitmann" wrote:

> Thanks
>
> I have a rod and jet combination that is very close to the flow of the
> original setup, there will of course be a small difference in the middle
> stage
> since it is not a 3 stage rod, but again so do I not think anyone will
> feel the difference.
>
> I have to go through my paperwork so I will post the number tomorrow, had
> a long day and are dead tired.
>
> Pffft... the value of the US $ has gone up 30% in 6 months, gas prices are
> the same and we have not heard a word from the US ambassador
> --
> 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Mean Green Machine,
> And just sold my 1973 26'-2 # 581 White Canyon lands under the name
> Dobbelt trøbbel
> in Norway
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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As some of you know so have I been messing around trying to find a similar Rochester to the early coaches using the 7043254 carb.

From a early point I did see that the 7043252 from a toronado ( Not many of them out there, but easy to get hold of compared to the 7043254 )was pretty similar but as I did not have the original carb I had no way to know for sure except that I did rebuild and used one last summer that was set up as close as I could get to the 7043254 specs.

Well now I have a 7043254 at my shop being rebuilt and I had a 7043252 on the shelf and it was not hard to find out the differences between them.

Is it possible to use the Toronado carb ? Yes and it will be close to identical to the GMC carb except for the 50D primary rods.

I got home and found the information on my computer.
This information was emailed to me by Bob Drewes back in 2006. It is below between the lines.
------------------------------------------------------
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.
---------------------------------------------------------------------------------------------------- --

Notice in his discussion of the primary metering rods he discusses the "different taper" between the series 70 and the series 170 carbs.

Emery Stora

> On Mar 5, 2015, at 4:40 PM, Espen Heitmann wrote:
>
> The primary rods in question are straight ( I had them in my hand 8 hours ago ), but the special 50D has three steps on it, the middle step will give
> a little leaner condition in the 1000 to 1500 rpm range, not a problem on the 455 and I will bet that you will not notice the difference.
>
> The secondary rods are identical on both carbs
>
>
> emerystora wrote on Fri, 06 March 2015 00:18
>> The rods are not straight, they are tapered. If you use straight rods you will not get the correct mixture. I am not at home right now but I will
>> be there later so I can look up the information. And get back to you.
>>
>> Emery Stora
>>
>>> On Mar 5, 2015, at 3:43 PM, Espen Heitmann wrote:
>>>
>>> Ok here we go for the jet and rod....
>>>
>>> So we know for sure that the 7043252 in the primary circuit had # 70 jets and 50D rods, this is our starting point, we have to
>>> compare and do some math.
>>> How much will this combination flow is the question and the answer, the 50D rods with the 0.036 tip is the clue, remember that all
>>> other rods have a 0.026 tip.
>>>
>>> I will not take everything now but in short what I did find out is that the open area with a :
>>> # 70 jet and a 0.036 tip is 0.00283057
>>> # 70 jet and a 0.026 tip is 0.00331752
>>> That gives a difference of 0.00048695
>>> To give you an idea of how large the difference is we will try to find a jet size that will flow the same as the # 70/0.036 but with
>>> the standard 0.026 tip.
>>> I did some more research and did find a combination that would flow 0.00289027, just a tiny bit more with a 0.026 tip, it was jet
>>> size # 66
>>>
>>> The above is with the rod at WOT, so what about at idle ?
>>>
>>> Well we know the diameter for the 50D rod, it is 0.050, this has a flow with the # 70 jet at 0.00188496.
>>> So since I did find out that a# 66 jet with a 0.026 rod did flow about the same as the #70/0.036 combo I just have to find a rod
>>> with a diameter that gives the same, the # 44 rod flows 0.00190066 with the #66 Jet and that is pretty darn close to the # 70/0.050
>>> combo
>>>
>>> So now I know that the closest jet/rod combination to the # 70/50D is #66/44 and that is way to lean for a 455 on idle..
>>>
>>> BUT remember in the post above I said the primary butterflies had a larger 1/8" home in them ? well there is your answer to why the 455 can
>>> run on the
>>> lean rod and jet combo, the hole is directly over the idle mixture screws, get it ?.
>>>
>>>
>>> --
>>> 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Mean Green Machine,
>>> And just sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
>>> in Norway
>>>
>>> _______________________________________________

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Loffen wrote on Wed, 04 March 2015 18:34

As some of you know so have I been messing around trying to find a similar Rochester to the early coaches using the 7043254 carb.

From a early point I did see that the 7043252 from a toronado ( Not many of them out there, but easy to get hold of compared to the 7043254 )was pretty similar but as I did not have the original carb I had no way to know for sure except that I did rebuild and used one last summer that was set up as close as I could get to the 7043254 specs.

Well now I have a 7043254 at my shop being rebuilt and I had a 7043252 on the shelf and it was not hard to find out the differences between them.

Is it possible to use the Toronado carb ? Yes and it will be close to identical to the GMC carb except for the 50D primary rods.

Espen

Here is a message posted in 2009 by T Maki -- I will repost since the 2009 threads are no longer in the search archive.

QUOTE

I could go into a long, boring recitation of detail about
how I accomplished this, but suffice it to say that I've
built my own carburetor from three usable cores, reference
material from all the GMC 'net resources I could find, Doug
Roe's book, several hundred pages of tips, tricks, data,
tables, and many hours in junk yards (plus the many hours
and miles going between them).

I now have a carburetor that doesn't leak, works pretty much
like a new one, and in which I have confidence. (We'll see
about that on the San Diego swap meet trip later this month.)

Quick synopsis:

Three cores - two 7043250, 7043252 (this was on coach)


Super Kit from Carburetor Doctor #SK23a

Tossed air horn and float bowl from 7043252 due to severe
warpage

Kept throttle body from 7043252 so as not to have to modify
linkage (shafts and plates are in good shape).

Rejetted to: .073/53 giving 5% rich primary over OEM 70/50;
DG secondary rods with K hanger giving 2.64% rich secondary
(I've collected 70, 73, and 74 primary jets; 48, 49B, 53C
primary rods; F, G, H, K, L, M, N, O, P, R, S, V secondary
hangers; and CG, CH, CT, DA, DD, DG, DP, and DR secondary
rods so I can change to many different combinations.)

New power piston spring. I went with the 6" rather than the
8" (7036019) as suggested. It's easy enough to change later.

Correct power piston. The one in the carb on the coach was
incorrect (appeared to be an aftermarket thing), was not to
specification, and had been "snipped". I had one in the
collection that was correct.

Everything thoroughly cleaned, bowl wells sealed, a little
light machining of several surfaces that needed it.

Adjusted to the book, torqued correctly to the manifold.

All new vacuum hoses.

Filled bowl from electric pump. Engine started on the first
turn, set idle down to spec, 20-21" of vacuum.

Took it out for a test run, and other than a little problem
with the accelerator cable (now fixed), I'm pleased with the
effort.

The cable problem kept the primaries from opening
completely. When the top of the engine caught fire back in
November, the plastic sleeve melted a bit and left a drop of
hardened plastic inside the outer steel sleeve, and a drip
around the end of the plastic sleeve near the cable bracket.
The inner cable couldn't get past the blockage. I trimmed
the drip away, and melted out the plastic in the sleeve.
Works perfectly now.

I wouldn't necessarily recommend all of this to anyone, but
I've learned more about Quadrajets than I ever expected. And
learning is at least half the fun.

END QUOTE

15 Nok / 7.8 (USD equivalent) = 1.932 USD/liter.

3.78 (liters per gallon) x 1.932 = 7.27 USD per gallon!

OUCH!

That's the price of total socialism, I'd wager.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~~ k2gkk + hotmail dot com ~~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
______________
|[ ]~~~[][ ][]\
"--OO--[]---O-"


> Date: Thu, 5 Mar 2015 15:30:20 -0700
> To: gmclist@temp.gmcnet.org
> From: bimet@online.no
> Subject: Re: [GMCnet] Replacement carb again 7043254 vs 704525
>
> Carey, please do the math for me, $ 1 is now 7.8 Nok and we pay 15 Nok give or take a little for 1 liter of gas
>
> --
> 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Mean Green Machine,
> And just sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
> in Norway

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