Home » Public Forums » GMCnet » [GMCnet] Connecting and Adjusting the Choke
| [GMCnet] Connecting and Adjusting the Choke [message #176152] |
Mon, 09 July 2012 15:28  |
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Steve[3]
Messages: 13
Registered: September 2011
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Can someone point me to a picture or diagram
of the choke side of a Rochester carburetor for a 78 w/403. I don't have something connected correctly so the choke is not working and it has a very hard time starting. It could be that its wildly out of adjustment, but if it's not put together correctly, well...you know.
Thanks
Steve
78 Eleganza
Santa Cruz, CA
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| Re: [GMCnet] Connecting and Adjusting the Choke [message #176201 is a reply to message #176186] |
Tue, 10 July 2012 02:08  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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I do not have a picture but there is one steel tube running from the choke to the heater mounted in the intake manifold. There is a second tube from the heater running to the top rear of the carburetor. Jim K. had these parts available on this web site. Please check that the heater in the manifold has a good gasket. I have seen several of these go bad and this gasket is what started my engine fire.
I now have an electric choke and the heater has been removed. I have a block off plate covering the heater hole in the intake manifold.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Connecting and Adjusting the Choke [message #176250 is a reply to message #176236] |
Tue, 10 July 2012 19:56 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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It works OK and is easy to install. My went to electrically operated chokes on carb engines in years after our GMCs were built. I have an electric choke because I have the intake manifold crossover's blocked. When you block them, there is no exhaust heat going through the intake manifold to warm up the choke heater. So you are down to using an heat alternate source. The electric choke is my preferred way to do that. Another approach is to wrap some copper tubing around an exhaust manifold and hook it to OEM bi-metal choke assembly.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Connecting and Adjusting the Choke [message #176278 is a reply to message #176152] |
Tue, 10 July 2012 22:57 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| Steve[3 |
wrote on Mon, 09 July 2012 14:28]Can someone point me to a picture or diagram
of the choke side of a Rochester carburetor for a 78 w/403. I don't have something connected correctly so the choke is not working and it has a very hard time starting. It could be that its wildly out of adjustment, but if it's not put together correctly, well...you know.
Thanks
Steve
78 Eleganza
Santa Cruz, CA
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Steve--I see most people have directed you to an approach you really didn't ask for. The original design works very well and if your coach is un-molested, the original choke is by far the best way to go and stay with. You need to download the available shop manual on Bdubs site which has very clear diagrams of the choke linkage.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Connecting and Adjusting the Choke [message #176287 is a reply to message #176278] |
Wed, 11 July 2012 00:13 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| Bob de Kruyff wrote on Tue, 10 July 2012 22:57 |
| Steve[3 |
wrote on Mon, 09 July 2012 14:28]Can someone point me to a picture or diagram
of the choke side of a Rochester carburetor for a 78 w/403. I don't have something connected correctly so the choke is not working and it has a very hard time starting. It could be that its wildly out of adjustment, but if it's not put together correctly, well...you know.
Thanks
Steve
78 Eleganza
Santa Cruz, CA
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Steve--I see most people have directed you to an approach you really didn't ask for. The original design works very well and if your coach is un-molested, the original choke is by far the best way to go and stay with. You need to download the available shop manual on Bdubs site which has very clear diagrams of the choke linkage.
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Bob, It was not my intention to direct him to change to electric. I wanted to let him know this was an option if he does not have the parts to put the manifold hot air one back together. Those parts are expensive and if he ever blocks the crossovers he will be re-addressing the problem a second time. If he has all of the parts then why change at this point. He can just check the heater gasket and put it all back together again.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Connecting and Adjusting the Choke [message #176443 is a reply to message #176152] |
Thu, 12 July 2012 10:34 |
Steve[3]
Messages: 13
Registered: September 2011
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Thanks Bob, I cant believe I haven't been using Bdub's site. Its great, but I still can't find the picture or drawing that I need (which doesn't mean its not there).
Ken and Bill bring up a good point about the tube and an alternative to stock equipment that may or may not be working. One of my fears is that the choke assembly was damaged and something bent when it was shipped to me on the carburetor.
Anyway, what I'm hoping to see in a drawing or picture, is actually behind the choke housing. There is flat bar coming out of the vacuum break/diaphragm that, in addition to actuating the air valve lever, has an adjustable tang on it. I believe this tang should contact the tang on the fast idle cam on the intermediate choke shaft. My question is: should the tang on the fast idle cam be on the high/left or the low/right side of the adjustable vacuum actuated tang (as you look directly at the choke side of the carb). It seems to me that it should be on the high/left because in this position, the engine starts beautifully, but as the engine warms up, idle becomes very rough and it dies. If I leave it on the lower/right, it does not appear as though the tangs never meet. In this position, the engine is very hard to start, but once warmed up, idles smoothly on its own.
Another issue (and part of the reason I suspect there may have been damage in shipping) is that the fast idle lever occasionally gets snagged on the secondary lockout lever when I go to full throttle. It's easily unsnagged with a tap on the peddle, but still very scary.
I do have GMC manual X-7725 but still cant seem to figure it out.
Any advice is welcome.
Steve Thomas
78 Eleganza
Santa Cruz CA
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| Re: [GMCnet] Connecting and Adjusting the Choke [message #176503 is a reply to message #176443] |
Thu, 12 July 2012 16:42 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Sir: Maybe this will help.
http://www.gmcmhphotos.com/photos/g6120-q-jet.html
| Steve[3 |
wrote on Thu, 12 July 2012 11:34]Thanks Bob, I cant believe I haven't been using Bdub's site. Its great, but I still can't find the picture or drawing that I need (which doesn't mean its not there).
Ken and Bill bring up a good point about the tube and an alternative to stock equipment that may or may not be working. One of my fears is that the choke assembly was damaged and something bent when it was shipped to me on the carburetor.
Anyway, what I'm hoping to see in a drawing or picture, is actually behind the choke housing. There is flat bar coming out of the vacuum break/diaphragm that, in addition to actuating the air valve lever, has an adjustable tang on it. I believe this tang should contact the tang on the fast idle cam on the intermediate choke shaft. My question is: should the tang on the fast idle cam be on the high/left or the low/right side of the adjustable vacuum actuated tang (as you look directly at the choke side of the carb). It seems to me that it should be on the high/left because in this position, the engine starts beautifully, but as the engine warms up, idle becomes very rough and it dies. If I leave it on the lower/right, it does not appear as though the tangs never meet. In this position, the engine is very hard to start, but once warmed up, idles smoothly on its own.
Another issue (and part of the reason I suspect there may have been damage in shipping) is that the fast idle lever occasionally gets snagged on the secondary lockout lever when I go to full throttle. It's easily unsnagged with a tap on the peddle, but still very scary.
I do have GMC manual X-7725 but still cant seem to figure it out.
Any advice is welcome.
Steve Thomas
78 Eleganza
Santa Cruz CA
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C. Boyd
76 Crestmont
East Tennessee
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| Re: [GMCnet] Connecting and Adjusting the Choke [message #176515 is a reply to message #176503] |
Thu, 12 July 2012 18:13 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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Charles that is great info. I will use this this weekend.
On Thu, Jul 12, 2012 at 3:42 PM, Charles Boyd <covered-wagon@comcast.net>wrote:
>
>
> Sir: Maybe this will help.
> http://www.gmcmhphotos.com/photos/g6120-q-jet.html
>
>
>
>
>
>
>
>
> Steve[3
> > wrote on Thu, 12 July 2012 11:34]Thanks Bob, I cant believe I haven't
> been using Bdub's site. Its great, but I still can't find the picture or
> drawing that I need (which doesn't mean its not there).
> >
> > Ken and Bill bring up a good point about the tube and an alternative to
> stock equipment that may or may not be working. One of my fears is that the
> choke assembly was damaged and something bent when it was shipped to me on
> the carburetor.
> >
> > Anyway, what I'm hoping to see in a drawing or picture, is actually
> behind the choke housing. There is flat bar coming out of the vacuum
> break/diaphragm that, in addition to actuating the air valve lever, has an
> adjustable tang on it. I believe this tang should contact the tang on the
> fast idle cam on the intermediate choke shaft. My question is: should the
> tang on the fast idle cam be on the high/left or the low/right side of the
> adjustable vacuum actuated tang (as you look directly at the choke side of
> the carb). It seems to me that it should be on the high/left because in
> this position, the engine starts beautifully, but as the engine warms up,
> idle becomes very rough and it dies. If I leave it on the lower/right, it
> does not appear as though the tangs never meet. In this position, the
> engine is very hard to start, but once warmed up, idles smoothly on its own.
> >
> > Another issue (and part of the reason I suspect there may have been
> damage in shipping) is that the fast idle lever occasionally gets snagged
> on the secondary lockout lever when I go to full throttle. It's easily
> unsnagged with a tap on the peddle, but still very scary.
> >
> > I do have GMC manual X-7725 but still cant seem to figure it out.
> >
> > Any advice is welcome.
> >
> > Steve Thomas
> > 78 Eleganza
> > Santa Cruz CA
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
>
> --
> C. Boyd
> 76 Crestmont by Midas
> East Tennessee
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
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: [GMCnet] Connecting and Adjusting the Choke [message #176875 is a reply to message #176152] |
Sun, 15 July 2012 22:53 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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If your cross-over is totaly blocked off, the hot air tube won't do much for signal. So maybe they de-adjusted the choke. If not the case and if you have all the linkages on in the right order and orientation, then you can rotate the bimetalic adjustment so it is just closed on a cold (95 outside) engine so it is not too rich. Start there and adjust accordingly. Be sure the unloader tang is bent correctly so with the choke closed, and engine off, when you floor it and hold it there it opens the choke about 3/16. There are a whole list of specs to initial set everything to on a Q-jet on the bench, just don't have them here right now.
John Lebetski
Woodstock, IL
77 Eleganza II
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