Home » Public Forums » GMCnet » Got home safely...some questions
| Got home safely...some questions [message #289412] |
Sun, 25 October 2015 19:19  |
thorndike
Messages: 406
Registered: January 2011
Location: Conifer, Colorado
Karma: 0
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Thanks to everyone giving me an on the road education, I was able to make it home safely. As shown here: http://imgur.com/DIgWn7E
I do have a question. When I was about halfway around Denver, I noticed that the engine was beginning to run a little rougher with less umph. I attributed it to the altitude as it got worse as I got higher. My current home is at about 7200 feet and I was barely able to make it there. By the time I got to the driveway I had it floored and was going about 12 mph. Unfortunately, our new home is about 1000 feet higher and I can guarantee that it won't make it there running like it is.
So, short of installing fuel injection (which IS on the list, but the new home purchase has to come first) what can I do to the carb/engine to get it running a bit better at altitude?
Bob
Robert Peesel
1976 Royale 26'
Side Dry Bath
Conifer, Colorado
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| Re: [GMCnet] Got home safely...some questions [message #289414 is a reply to message #289412] |
Sun, 25 October 2015 19:28  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Remove your air cleaner and make sure your choke is fully opened. Sounds
like the problem to me. If not, you are way too rich in jetting for your
present altitude. Fuel injection sure will help with that. If you know your
way around quadrajets, they can be re jetted to run there. Glad you made it.
Jim Hupy
Salem, Or.
On Oct 25, 2015 5:20 PM, "Robert Peesel" wrote:
> Thanks to everyone giving me an on the road education, I was able to make
> it home safely. As shown here: http://imgur.com/DIgWn7E
>
> I do have a question. When I was about halfway around Denver, I noticed
> that the engine was beginning to run a little rougher with less umph. I
> attributed it to the altitude as it got worse as I got higher. My current
> home is at about 7200 feet and I was barely able to make it there. By the
> time I got to the driveway I had it floored and was going about 12 mph.
> Unfortunately, our new home is about 1000 feet higher and I can guarantee
> that it won't make it there running like it is.
>
> So, short of installing fuel injection (which IS on the list, but the new
> home purchase has to come first) what can I do to the carb/engine to get it
> running a bit better at altitude?
>
> Bob
> --
> Robert Peesel
>
> 1976 Royale 26'
>
> Side Dry Bath
>
> Morrison, Colorado
>
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> GMCnet mailing list
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| Re: [GMCnet] Got home safely...some questions [message #289417 is a reply to message #289414] |
Sun, 25 October 2015 20:32 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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> I do have a question. When I was about halfway around Denver, I noticed
> that the engine was beginning to run a little rougher with less umph. I
> attributed it to the altitude as it got worse as I got higher. My current
> home is at about 7200 feet and I was barely able to make it there. By the
> time I got to the driveway I had it floored and was going about 12 mph.
> Unfortunately, our new home is about 1000 feet higher and I can guarantee
> that it won't make it there running like it is.
>
> So, short of installing fuel injection (which IS on the list, but the new
> home purchase has to come first) what can I do to the carb/engine to get it
> running a bit better at altitude?
>
Having lived in Colorado at about your altitude with old iron in the 1970s, I can tell you we got more oomph out of our engines by advancing the static timing by from 5 to 8 degrees (additional) before top dead center. However, I'm with Jim in that any lack of advance adjustment shouldn't affect performance to the degree it seems to be doing. Frozen advance weights, bad vacuum advance, other things, get the brain trust to help.
If the engine was advanced so far that in starting, the engine kicked back from excessive advance while cranking, it was time to moderate the advance. Just what we used to do. Some changed the main jets, but on your coach, not a good idea to do because you would drive it back down the mountain some time. Bad, bad, bad to run too lean on these. Also, you would court engine knock with the added advance at sea level. I've talked myself out of trying that advance trick. Emery Stora lives at altitude now. I am sure he would have some good advice for you. Emery?
There are aftermarket devices that allow you to vary advance from the instrument panel. Maybe after you get the engine running right, you can find one of them. If I had a 455 or 403 in otherwise good shape that blubbered, and no choke problems, or sunken float problems, I would get a Dick Paterson carb, and a Paterson distributor if it checked out so far as compression was concerned. It would run better than new if the engine was otherwise in good shape, but you must remember that possibly one reason it was sold to you is because it had some problems that resisted the seller's best efforts (if any efforts) to repair. Maybe the previous owner got an expensive diagnosis and decided to have you repair the problems. If you had a cracked manifold problem, it might run better when relatively cool.
With your new house coming, hang around on the forum until you get settled advice on what to check and in what order. That is the cheapest way, if not the easiest or time-efficient way.
Congratulations on your maiden voyage. She got you home.
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
[Updated on: Sun, 25 October 2015 21:43] Report message to a moderator |
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| Re: [GMCnet] Got home safely...some questions [message #289424 is a reply to message #289417] |
Sun, 25 October 2015 21:27 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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As most gasoline powered piston aircraft pilots can tell you, running at higher altitudes we have to lean out the mixture to get maximum performance. That is hard to do on a fixed mixture automotive carburetor so computer controlled FI is a solution there.
Why do we advance the timing at higher altitudes? Because driving higher altitude is like driving at 1/2 or 3/4 throttle at sea level. The amount of air reaching the cylinders is less so higher advance settings can be used. The vacuum advance on the distributor is suppose to take care of this for you, but who knows what vacuum advance is currently installed on your distributor and if it is working correctly? Also the stock vacuum advances used by GM were for best emissions and not for maximum power and mpg.
I would look at both FI and a replacement re-curved distributor from Dick Paterson. Also tell him about your higher altitude concern when you order it. He might modify the vacuum advance slightly (if necessary). You might put a vacuum gauge on the line going to the advance and see what numbers you have. Then move it to any vacuum port on the manifold and see what you have there. They will be similar but not the same.
No matter what you do you are going to take a hit on performance running at that altitude. Outside air temperature also have a great performance hit. So hot weather will also reduce your maximum power.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Got home safely...some questions [message #289435 is a reply to message #289424] |
Mon, 26 October 2015 00:57 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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You will certainly have less power at that altitude . Your mechanical advance should be around 34 degrees total. For mountain driving a lower final drive ratio would be a big help. Mine is a 370 ratio which is a big help.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Got home safely...some questions [message #289440 is a reply to message #289412] |
Mon, 26 October 2015 08:21 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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I have driven a couple carb engines in the mountains, but maybe not at 7000 feet.
Even with a incorrectly jetted carb for that altitude, he should be able to get the gmc to go faster then 12 MPH??? there has to be something else wrong I would believe. But I am a flatlander...
If you live at 8200 feet, I would think Fuel injection would have to be in your future. Must be a nice view, post some pictures showing you coach overlooking the land.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Got home safely...some questions [message #289471 is a reply to message #289440] |
Mon, 26 October 2015 15:59 |
thorndike
Messages: 406
Registered: January 2011
Location: Conifer, Colorado
Karma: 0
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The views are fantastic! If I can get the coach there, I will certainly take some photos!
lqqkatjon wrote on Mon, 26 October 2015 07:21I have driven a couple carb engines in the mountains, but maybe not at 7000 feet.
Even with a incorrectly jetted carb for that altitude, he should be able to get the gmc to go faster then 12 MPH??? there has to be something else wrong I would believe. But I am a flatlander...
If you live at 8200 feet, I would think Fuel injection would have to be in your future. Must be a nice view, post some pictures showing you coach overlooking the land.
Robert Peesel
1976 Royale 26'
Side Dry Bath
Conifer, Colorado
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| Re: Got home safely...some questions [message #289489 is a reply to message #289412] |
Mon, 26 October 2015 22:14 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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Bob,
I looked at the previous posts in your adventure and found you had some trouble with the coil and ignition module back on the plains. You received good advice and some anecdotes about the damage and electrical stress on the module resulting from plugs being over-gapped. Take them down to .038" or so, might as well plan on replacing them as long as you have them out. Heck, due to deferred maintenance they could be at .090". If you are fully financially stressed because of the new house, at least regap them close to right. New Autolite AP85 plugs, platinum, I found locally at O'Reilly (might still be Checker in Colorado) Auto Parts, for $2.99 each with $1 mail in rebate making $1.99. They cross to the more desirable, recommended by Dick Paterson, NGK XR5IX plugs but I can't find a NGK rebate and they are $7.99 each. The platinum plug should last better than stock plugs which you might get cheaper. Sounds like you are ready to not worry about ignition problems for some time.
The reason I suggest this is that your new module may have been overstressed in the trip back to Colorado because the plugs may still be overgapped and the module is getting ready to head west. Also, the module hasn't been proven, either, and those not of Delco manufacture have been seen to be failure-prone.
I am sure you decided to buy an additional spare module, and with your recent practice, not too hard to replace it with your spare. If it runs the same, you have a tested module now as a spare and a new one in the engine. Use the dielectric grease.
Note, Bob, this is contrary to the advice I gave you about the carburetor and distributor, because I assumed that you were running rich. Take this advice with a grain of salt, if you wish. If it does make sense, you might be able to get out really cheaply.
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
[Updated on: Mon, 26 October 2015 22:48] Report message to a moderator |
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| Re: Got home safely...some questions [message #289532 is a reply to message #289489] |
Tue, 27 October 2015 13:29 |
thorndike
Messages: 406
Registered: January 2011
Location: Conifer, Colorado
Karma: 0
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Senior Member |
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Carey,
Thanks for the suggestions. I am definitely pulling the plugs and replacing as I don't know when the PO replaced them and at $2/per the price is right!
Bob
cbryan wrote on Mon, 26 October 2015 21:14Bob,
I looked at the previous posts in your adventure and found you had some trouble with the coil and ignition module back on the plains. You received good advice and some anecdotes about the damage and electrical stress on the module resulting from plugs being over-gapped. Take them down to .038" or so, might as well plan on replacing them as long as you have them out. Heck, due to deferred maintenance they could be at .090". If you are fully financially stressed because of the new house, at least regap them close to right. New Autolite AP85 plugs, platinum, I found locally at O'Reilly (might still be Checker in Colorado) Auto Parts, for $2.99 each with $1 mail in rebate making $1.99. They cross to the more desirable, recommended by Dick Paterson, NGK XR5IX plugs but I can't find a NGK rebate and they are $7.99 each. The platinum plug should last better than stock plugs which you might get cheaper. Sounds like you are ready to not worry about ignition problems for some time.
The reason I suggest this is that your new module may have been overstressed in the trip back to Colorado because the plugs may still be overgapped and the module is getting ready to head west. Also, the module hasn't been proven, either, and those not of Delco manufacture have been seen to be failure-prone.
I am sure you decided to buy an additional spare module, and with your recent practice, not too hard to replace it with your spare. If it runs the same, you have a tested module now as a spare and a new one in the engine. Use the dielectric grease.
Note, Bob, this is contrary to the advice I gave you about the carburetor and distributor, because I assumed that you were running rich. Take this advice with a grain of salt, if you wish. If it does make sense, you might be able to get out really cheaply.
Carey
Robert Peesel
1976 Royale 26'
Side Dry Bath
Conifer, Colorado
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