| Vapor lock? [message #361102] |
Thu, 24 December 2020 13:15  |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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OK! I have been sitting around too long. So here goes.... iF you have a Transmode or any GMC Motorhome with fuel line tapped into main fuel line behind the switching valve and behind any electric fuel pump that might have been added, and IF the generator does not have a shutoff solenoid, and IF the fuel dries up in the generator carb bowl and the float drops and opens the inlet needle and IF the fuel in the line siphoned back into the tank and left an air filled, open ended line into the float bowl vent that is tied to the fuel line going to motorhome engine couldn’t the main engine fuel pump or inline electric fuel pump suck air thru this line and mimic Vapor Lock or fuel starvation? If this senerio Could happen you could check and temporarily repair by trying to start generator or activate prime button if equipped to fill generator fuel line till float bowl inlet closed?
Delete, flame, or comment.
C. Boyd
76 Crestmont
East Tennessee
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| Re: Vapor lock? [message #361103 is a reply to message #361102] |
Thu, 24 December 2020 13:29  |
94nubble
Messages: 275
Registered: July 2011
Location: Chesapeake VA
Karma: 3
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I would say yes. If you do have an electric fuel pump, it should make some noise as it tries to prime the carb. As the bowl in the carb fills and closes the bowl valve, the sound of the pump should change. If the sound doesn't change, I would pull the fuel line off the generator and plug it. Then try it again and/or try to start the engine to see if the fuel comes up in the carb.
Tom McManus
1977 Royale
Chesapeake VA
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| Re: Vapor lock? [message #361105 is a reply to message #361102] |
Thu, 24 December 2020 15:39 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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C Boyd wrote on Thu, 24 December 2020 14:15OK! I have been sitting around too long. So here goes....
IF you have a Transmode or any GMC Motorhome with fuel line tapped into main fuel line behind the switching valve and behind any electric fuel pump that might have been added,
and IF the generator does not have a shutoff solenoid, and IF the fuel dries up in the generator carb bowl and the float drops and opens the inlet needle
and IF the fuel in the line siphoned back into the tank and left an air filled, open ended line into the float bowl vent that is tied to the fuel line going to motorhome engine couldn’t the main engine fuel pump or inline electric fuel pump suck air thru this line and mimic Vapor Lock or fuel starvation?
If this senerio Could happen you could check and temporarily repair by trying to start generator or activate prime button if equipped to fill generator fuel line till float bowl inlet closed?
Delete, flame, or comment.
Chuck,
Your scenario could happen, but it might even be more possible if that solenoid valve that GMCs didn't need was removed. Those old Bendix pumps always leak down. Whether the open needle as seat could leak enough air to look like vapor lock, I am not sure because I don't know how much air that might take. If the coach had only the mechanical pump, I bet it could screw it up pretty fast.
Judging by the priming time my Onan usually requires, I would have to guess that the needle is usually off the seat when the machine has been shut down for even a short time.
And, if the operator was careless enough to leave the auxiliary tank just about empty and then run the roof A/C (at 0.45gph) long enough, he could get stuck if not right where he stopped, real close to same. This is even more likely if the tank selector valve is OE and so leaks all possible directions.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Vapor lock? [message #361106 is a reply to message #361102] |
Thu, 24 December 2020 16:42 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Thanks as always for your thoughts Matt and Merry Christmas to EVERYONE.. I would think if you were lucky enough to be parked level you should still have the ~7 gallon reserve left but by the time you got it started and moved out of the parking spot some would be migrated to main and it would be a trick to get somewhere to get gas.
It started snowing here in Knoxville about 3 this afternoon and we got about 6” easy and still snowing. First White Christmas in 16 years I think? We got to video call with Great Grand Kids. Ms Lyza Beth Boyd (2 yr old) danced and squealed at her Frozen Castle doll house. Just about the best Christmas ever..
C. Boyd
76 Crestmont
East Tennessee
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| Re: Vapor lock? [message #361107 is a reply to message #361102] |
Thu, 24 December 2020 16:46 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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C Boyd wrote on Thu, 24 December 2020 12:15OK! I have been sitting around too long. So here goes.... iF you have a Transmode or any GMC Motorhome with fuel line tapped into main fuel line behind the switching valve and behind any electric fuel pump that might have been added, and IF the generator does not have a shutoff solenoid, and IF the fuel dries up in the generator carb bowl and the float drops and opens the inlet needle and IF the fuel in the line siphoned back into the tank and left an air filled, open ended line into the float bowl vent that is tied to the fuel line going to motorhome engine couldn’t the main engine fuel pump or inline electric fuel pump suck air thru this line and mimic Vapor Lock or fuel starvation? If this senerio Could happen you could check and temporarily repair by trying to start generator or activate prime button if equipped to fill generator fuel line till float bowl inlet closed?
Delete, flame, or comment.
That sounds absolutely logical to me. Yet another thing to check IF you have the generator fuel line hooked up as you state.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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