Home » Public Forums » GMCnet » Trip to Kansas and carb? problems
| Trip to Kansas and carb? problems [message #95482] |
Thu, 12 August 2010 10:00  |
docsdad
Messages: 32
Registered: May 2008
Karma: 0
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Took trip from Thomson, Georgia to Pittsburg, Kansas this past week. Have made it back to my son's house in Murphysboro, Illinois. During trip, experienced following conditions. Early morning temps in high 70's with noon time temps in high 90's with some 100 days. MH is a 75 455 carb engine with 138000 miles. The engine appears to be a early replacement by GM dealer with first owner.. In early morning, runs great can travel 65 and 70 if necessary, Normal running speed 60 MPH. As temperature of day increases and about 2 or 3 hours of driving time, it starts to experience missing and faltering when going up hills and slight rises. With the cruise on it would be at full throttle and it would sputter and almost die. Also in town after it starts acting up, I experience same faltering when accelerating from a stop. Removing the cruise control, and using judicious minimum amount of throttle, it kept running but would slow significantly going up hills. Into low 40's and in Tennessee going up Mt Eagle, down to 20MPh. Never quit but put some additional gray hair on an old man.
I need some good advice on where to look. I have changed filters out to kazoo, replaced the ignition module twice, have a new coil to install, but think the problem is with the carb. Do not have the blocking plates in. If I can not get the carb to work, if that is the problem, then I think I will get a new aluminum manifold and fuel injection. I hate to go to this expense, however if it is not just the carb. I have rebuilt carb and for short trips under 2 hours, the unit runs like a dream. Note I was also towing a Tracker this time, but even when I was not towing, had the wife drive the towd, but when it was hot, it still experienced these same problems. Used only premium gas or no alcohol regular when I could find it. Last time I changed the ignition module, I put in new plugs, gap set to .045. The old plugs were way over .060. So put your heads together and give me some ideas. I am a shade tree mechanic and retired engineer so I think I can fix any thing, but not having a lot of luck with this problem. Also I have an electric fuel pump on this unit feeding into a large filter and it does not seem to help. It almost seemed to add to the problem when I would turn on and so I quit using it. Filters I took off showed a small amount of rust particles, but none were clogged and like I said above, when cool the next morning, It ran fine. I was limited to driving about 4 hours a day which does not make for good travel planning. Any thoughts will be appreciated. I am leaving the MH in Illinois so I can come to GMCMI convention in September but plan to work on it between now and then and if its not fixed the maybe you guys can solve my problem. PS I have never heard my fan run like everyone talks about so this week installed a new fan clutch and have heard it run only a few times never heard the old one run.
Jim Thompson 75 Avion GA
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| Re: Trip to Kansas and carb? problems [message #95522 is a reply to message #95482] |
Thu, 12 August 2010 11:51  |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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| docsdad wrote on Thu, 12 August 2010 11:00 |
Took trip from Thomson, Georgia to Pittsburg, Kansas this past week. Have made it back to my son's house in Murphysboro, Illinois. During trip, experienced following conditions. Early morning temps in high 70's with noon time temps in high 90's with some 100 days. MH is a 75 455 carb engine with 138000 miles. The engine appears to be a early replacement by GM dealer with first owner.. In early morning, runs great can travel 65 and 70 if necessary, Normal running speed 60 MPH. As temperature of day increases and about 2 or 3 hours of driving time, it starts to experience missing and faltering when going up hills and slight rises. With the cruise on it would be at full throttle and it would sputter and almost die. Also in town after it starts acting up, I experience same faltering when accelerating from a stop. Removing the cruise control, and using judicious minimum amount of throttle, it kept running but would slow significantly going up hills. Into low 40's and in Tennessee going up Mt Eagle, down to 20MPh. Never quit but put some additional gray hair on an old man.
I need some good advice on where to look. I have changed filters out to kazoo, replaced the ignition module twice, have a new coil to install, but think the problem is with the carb. Do not have the blocking plates in. If I can not get the carb to work, if that is the problem, then I think I will get a new aluminum manifold and fuel injection. I hate to go to this expense, however if it is not just the carb. I have rebuilt carb and for short trips under 2 hours, the unit runs like a dream. Note I was also towing a Tracker this time, but even when I was not towing, had the wife drive the towd, but when it was hot, it still experienced these same problems. Used only premium gas or no alcohol regular when I could find it. Last time I changed the ignition module, I put in new plugs, gap set to .045. The old plugs were way over .060. So put your heads together and give me some ideas. I am a shade tree mechanic and retired engineer so I think I can fix any thing, but not having a lot of luck with this problem. Also I have an electric fuel pump on this unit feeding into a large filter and it does not seem to help. It almost seemed to add to the problem when I would turn on and so I quit using it. Filters I took off showed a small amount of rust particles, but none were clogged and like I said above, when cool the next morning, It ran fine. I was limited to driving about 4 hours a day which does not make for good travel planning. Any thoughts will be appreciated. I am leaving the MH in Illinois so I can come to GMCMI convention in September but plan to work on it between now and then and if its not fixed the maybe you guys can solve my problem. PS I have never heard my fan run like everyone talks about so this week installed a new fan clutch and have heard it run only a few times never heard the old one run.
Jim Thompson 75 Avion GA
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Sir: I also have had these issues. What helped me was to blow shop air back thru the fuel lines into the tank (with the gas cap off) then switch to reserve and blow thru the 2nd tank. This will clear the rust and debree from the pick up "socks" and maybe if you are lucky it will blow them off. I also added an inline dispossable filter in front of the switching valve. When the filter shows signs of needing replacing I blow shop air back thru the tanks while changing the filter. It don`t cost nothing and just takes a few minutes more. I have a quick disconnect on my coach air tank and I carry a air hose in case I need to do it in a rest area. Comes in handy for airing up tires also...
Good Luck.. hope this helps..
C. Boyd
76 Crestmont
East Tennessee
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| Re: Trip to Kansas and carb? problems [message #95529 is a reply to message #95482] |
Thu, 12 August 2010 12:24 |
jknezek
Messages: 1057
Registered: December 2007
Karma: 5
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Senior Member |
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Except for the engine stumbling I'd say it's the intake manifolds. Had similar problems with a FL trip. Was definitely the intake manifolds for me. When it was cold they held together ok, but when the engine got hot the cracks expanded and I lost power. Of course, my engine wasn't stumbling, it just had no vacuum.
Thanks,
Jeremy Knezek
1976 Glenbrook
Birmingham, AL
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| Re: Trip to Kansas and carb? problems [message #95802 is a reply to message #95482] |
Sat, 14 August 2010 11:04 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
Karma: 0
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Senior Member |
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Hi there
I had an incredibly bad experience with something like this only mine happened when cool and starting in the morning as well. Sometimes it had to warm up a couple minutes but it was there.
In the end, based on any contaminants found, which were none, I can only point to two, things.
First - My fuel pump showed signs of weeping gas from the air holes, this would mean the membrane was failing or about to. we replaced that but no fix.
We also ran from a gas can to the fuel pump, in my case no fix so everything from the fuel tanks, to the fuel pump was good.
Second - My carborator was judged as bad. Even though as we adjussted things and could actually get up to 70 mph at one point by nursing the gas, the median high speed was usually around 32 mph. When it all started, I was nursing the gas trying to get speed up downhill so I could make it over the next hill....
there was a controversy on the carb findings but was sent another rebuilt Non GMC MOTORHOME carb. At this point, so far, I have not had a reoccurance yet.
_____
It seems you have not had the problem before and it seems heat related.
I am a backyard mechanic so I am relying a lot on what Ihave seen and heard as well as my own experience.
If your carb is rebuilt, before I spent a lot of money, you could try some of the things I mention above. I did also rebuild the electronic ign as mine was found to be arcing at the power wire due to a missing ground strap on the coil.
One of our members added a air duct, scoops from the front and ducts ( dryer duct ) up by the engine top to cool the carb. I believe he has said he has not had a problem.
Another thought brought up on another thread, if it happens, try adding fuel to cool the fuel in the tank down. If this stops the problem, you are picking up heat, either at the tank, the fuel line going forward or where the fuel passes by the headers if you have them and of course up by the manifold at the carb.
I have also wondered if the fuel bowl can pick up heat from the manifold and if a heat shield between the carb fuel bowl and the manifold would be helpful.
Bob had mentioned that these GMC were built identical and to engineer standards. The heat problems are showing up now in days of alcohol polluted fuel and mods that have been done on the GMCs with problems showing up later and many times during high heat periods.
My problem took a very very long time to find the CURRENT fix, I hope your fix is fast and permanent.
LarC ( Nothing worse than nursing the gas to get over the next hill )
Gatsbys' CRUISER  08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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