| Engine stumbling running rough backfire through carb [message #277861] |
Fri, 15 May 2015 09:42  |
Tony Cook
Messages: 121
Registered: August 2014
Location: Torrance CA
Karma: 0
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Coach ran ok before parked for total brake overhaul had fuel issue which was a big part of my initial fuel starving problem when i first got the coach. Dealt with that for a while till i had tanks and fuel lines redone. Have changed out the Qjet filter so many times i could do it almost blind folded. Has been sitting bout a month . Test drove the last few days to test brakes out now new problem ( seems like one after another ) . Symptoms now it starts right up but hit the gas and has little power and seems like it wants to stall out but it does'nt tried to drive and its missing and backfiring through the carb . One thing when it backfired it seemed like somthing cleared and it had power and would accelerate well . That lasted a few minutes of driving and then back to stumble bumble. Replaced vacume hoses and checked for disconected or cracked vac hoses did'nt help. Plugs have been changed prior. I dont think at this point it is fuel but ? I am leaning towards ignition at this point . Not very savvy on this part of trouble shooting thinking changing parts on Distributer HEI stuff is still from PO that i did'nt replace per was running decent. What parts should i change on Distributor again not really knowledgable on the ignition components. Are the parts the same on a '76 Toro cap,rotor etc.? Thanks any help would be great. A little bummed out right now since i just spent the last 2 months on my back under the beast after work and on weekends doing brake lines . I know this is what to expect in some degree but talk about getting a punch to the gut. Thanks again Tony.
Tony Cook
77' Kingsley ' SuperSession 77 '
Torrance Beach,CA
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| Re: Engine stumbling running rough backfire through carb [message #277862 is a reply to message #277861] |
Fri, 15 May 2015 10:06  |
George B.
Messages: 213
Registered: February 2012
Karma: 1
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I had similar sounding problems and in my case it turned out to be a a worn out distributor. Had intermittent spark and when not firing fuel would build up and then when spark came back on would get the backfire. I had a points type distributor at the time.
George Butts
Las Vegas Nevada
73 "Custom 26' Q" & 76 23' Birchaven
71 Honda 600 Coupe & 01 Tracker Toads
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| Re: Engine stumbling running rough backfire through carb [message #277863 is a reply to message #277861] |
Fri, 15 May 2015 10:30 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Tony Cook wrote on Fri, 15 May 2015 07:42Coach ran ok before parked for total brake overhaul had fuel issue which was a big part of my initial fuel starving problem when i first got the coach. Dealt with that for a while till i had tanks and fuel lines redone. Have changed out the Qjet filter so many times i could do it almost blind folded. Has been sitting bout a month . Test drove the last few days to test brakes out now new problem ( seems like one after another ) . Symptoms now it starts right up but hit the gas and has little power and seems like it wants to stall out but it does'nt tried to drive and its missing and backfiring through the carb .Thanks any help would be great. A little bummed out right now since i just spent the last 2 months on my back under the beast after work and on weekends doing brake lines . I know this is what to expect in some degree but talk about getting a punch to the gut. Thanks again Tony.
Backfiring through the carb can be caused by running lean.(Lean mixtures take longer to get the fire going.) But because you have worked and reworked fuel, I agree with George and you that it could be ignition. Ignition can do the oddest things.
The fact that it starts well but hitting the gas causes the problem can be spark. When an engine is idling, the vacuum is high. High vacuum mean low compression. (No air to compress.) Spark has a harder time jumping in a dense medium than it does in a lighter medium. So when you press the gas, the engine gets air and the cylinders suddenly have more pressure and therefore a more dense mixture to jump across. And they will miss. You can pull a plug, ground it and watch spark jump just fine, only to have it miss when in the cylinder.
This usually is not a problem with HEI and more advanced systems, but I would try changing the module. It seems like I say that more and more, but as one of the fuel injection guys, we have chased so many "fuel" problems only to find out that the module was doing strange things. I am talking about new modules, made in USA, right out of the box that were bad.
If it ran well at the start and then failed at warmup I would look to coil as they can breakdown in heat. But modules can do the same thing. I saw an HEI that started fine in the morning, ran worse and worse as it warmed until it died and ran no more. Popping and sputtering... sounded like gas.
Never drive anywhere without a module tucked away.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] Engine stumbling running rough backfire through carb [message #277870 is a reply to message #277865] |
Fri, 15 May 2015 13:49 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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One other thing that I would like to add is a rule of thumb that I have used over the years. “If it is poping back thru the carb it is a fuel issue and if it is poping thru the exhaust then it is an ignition problem.”
JR Wright
78 Buskirk Stretch
75 Avion
Michigan
> On May 15, 2015, at 11:56 AM, Tony Cook wrote:
>
> Are 76 Toro part #'s same or are our coaches specific . Thanks Tony
> --
> Tony Cook
> 77' Kingsley ' SuperSession 77 '
> Torrance Beach,CA
> _______________________________________________
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Engine stumbling running rough backfire through carb [message #277871 is a reply to message #277865] |
Fri, 15 May 2015 13:46 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Tony,
In 1977, part of the year the coaches came with a 455 ending with coach# TZE167V101284 and now the 403 Starting in coach# TZE167V101285 in the motorhome, TZE337V101287 in the 23” Transmode and TZE367V101312 in the 26” transmode. Now if you have a 455 motor then using the 1975 or 76 Toro as a base for part is fine an if you have the 403 the use 77 or 78 model years of the toro. You will find a lot of the parts are the same for both engines.
JR Wright
78 Buskirk Stretch
75 Avion
Michigan
> On May 15, 2015, at 11:56 AM, Tony Cook wrote:
>
> Are 76 Toro part #'s same or are our coaches specific . Thanks Tony
> --
> Tony Cook
> 77' Kingsley ' SuperSession 77 '
> Torrance Beach,CA
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] wheels [message #277874 is a reply to message #277869] |
Fri, 15 May 2015 14:00 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Richard,
The wheels for our coaches are available from Jim K.
http://www.appliedgmc.com/prod.itml/icOid/623
http://www.appliedgmc.com/prod.itml/icOid/613
http://www.appliedgmc.com/prod.itml/icOid/1099
I you're thinking that you're going to find them on Ebay or another website then you're going to be waiting a long time. There are steel 16” wheel that will fit the coach, but they are hard to fine in the right configuration too. They must be the domed center hub and NOT the cone shaped center. I am at a loss of the actual years, but it is early to late 80’s chevy 1ton truck.
JR Wright
78 Buskirk Stretch
75 Avion
Michigan
> On May 15, 2015, at 1:02 PM, Richard Cockrell wrote:
>
> Hello:
>
> What is the prevail thought of the best 16" wheels for my GMC these day - I've been away for years. Model #?
>
> Thanks, rich
>
> Sent from my iPhone
>
>> On May 15, 2015, at 10:56 AM, Tony Cook wrote:
>>
>> Are 76 Toro part #'s same or are our coaches specific . Thanks Tony
>> --
>> Tony Cook
>> 77' Kingsley ' SuperSession 77 '
>> Torrance Beach,CA
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: Engine stumbling running rough backfire through carb [message #277876 is a reply to message #277861] |
Fri, 15 May 2015 14:38 |
Tony Cook
Messages: 121
Registered: August 2014
Location: Torrance CA
Karma: 0
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Coach is a early 77 Has the 455 . Hopefully when i get home from work i can tinker around a bit more . Replaced the Qjet filter again just because that was my achiles heal for some time and crossed my fingers and toes but that didnt do squat. Pulled a few plug wires just to see if any change but not really cept front cylinders when pulled it did want to stall seems like its not running on all cylinders but i am a little lame when it comes to engine diagnostics. So a loose vac line seems like the same conditions . Lets see where this adventure takes me ! HAHA
Tony Cook
77' Kingsley ' SuperSession 77 '
Torrance Beach,CA
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| Re: Engine stumbling running rough backfire through carb [message #277896 is a reply to message #277861] |
Fri, 15 May 2015 21:40 |
Tony Cook
Messages: 121
Registered: August 2014
Location: Torrance CA
Karma: 0
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Senior Member |
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So got home and did some snooping I am pretty sure it is a fuel issue. I had installed a glass see through filter just before mech.fuel pump and what i see is after driving and engine warms up fuel drains from line back to tanks as i can see whats doing through the in line glass filter ? Mech.Fuel pump is new and i also have installed a carter back up pusher pump off the Aux tank/selector switch to activate in case of VL. When i hit the pusher pump it does fill the line back with preaser. Is that normal for the mechanical fuel pump to allow the gas to slowly fade back to the tanks and build up/suck again ? I guess i can see how it does with just the pusher pump running and see if that clears anything up. Thinking maybe vent issues ? Hmmmm
Tony Cook
77' Kingsley ' SuperSession 77 '
Torrance Beach,CA
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| Re: Engine stumbling running rough backfire through carb [message #277911 is a reply to message #277861] |
Sat, 16 May 2015 11:05 |
Gadabout
Messages: 124
Registered: March 2013
Location: Edmonton
Karma: 2
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Hi Tony,
Backfires are usually caused by: Incorrect Air/Fuel Mixture or Incorrect spark timing.
" Symptoms now it starts right up but hit the gas and has little power and seems like it wants to stall out"
This symptom suggests a lean condition is developing as you apply throttle, the carb's accelerator pump should provide a squirt of fuel as throttle is applied,
you can observe this with the engine off , by looking in the carb and pulling back on the throttle.
A lean condition can also be caused by disconnected vacuum lines or faulty PCV Valve to eliminate the PCV just disconnect it and plug the line.
Remove the air-cleaner and check the following with the ignition off.
1. Firing order
2. Accelerator pump operation ( no squirt = lean)
3. All Vacuum Hoses
If you are experienced working on a running engine then have a fire extinguisher handy and make sure everything is clear from the belts and fan):
Start up the engine with the aircleaner off:
- Listen for Vacuum leaks
- While pressing the throttle observe the carb operation, you should see a initial squirt from the pump and fuel flow through the primary venturies as RPM increases. Do not over rev the engine, 1/4 throttle should indicate if a problem exists. (A backfire while doing this may require the use of a Defibulator on any observers  )
- Confirm ignition timing with timing light
Good luck and let us know what you find.
Carl Harr : Driver NASCAR Pro Series #2
1978 Gadabout-Restoring
1978 Palm Beach
1976 Glenbrook
Prevost Featherlite H3-45
[Updated on: Sat, 16 May 2015 11:09] Report message to a moderator |
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| Re: Engine stumbling running rough backfire through carb [message #277915 is a reply to message #277861] |
Sat, 16 May 2015 13:21 |
Tony Cook
Messages: 121
Registered: August 2014
Location: Torrance CA
Karma: 0
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I did the check for the squirts into the carb yesterday and it does but it was a little lacking on the right venturi at first i get full sguirts now but it seems lack of fuel preaser initially when hit the gas it will flatten /lean out there's enough gas in the floats to start right up but then i see gas in the clear filter start to fluctuate and literally disapears like it drains back to tanks and then picks up again. Very strange
Tony Cook
77' Kingsley ' SuperSession 77 '
Torrance Beach,CA
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