question on vacuum operated fuel valves - Motorcycle-Journal Forums

tlpotts · 09-12-2008, 08:49 PM

I have a 150cc chinese bike that has an engine vacuum operated fuel valve. Do these types of valves operate as just a valve or is there some fuel pumping action also?

My valve leaked gas so while I'm waiting for the part I installed a manual shut off valve. (I did leave the vacuum line attached to the old valve to hopefully prevent problems with a vacuum leak). However the bike cuts out when going up hill (about a 5% grade) and won't immediately restart. But when I let set for about 10 - 20 seconds it starts right up and is able to go downhill and on straightaway with no problem. But I don't trust the bike to go too far so I'm not sure if it would happen on the level road at continuous highway speed. The gas tank is mounted in the rear, higher than the engine and I thought it was a gravity-feed system.

The engine is based on the honda gy6 engine technology.
Any help would be appreciated.

2005GZ250 · 09-12-2008, 09:37 PM

There is no "pumping" from the fuel valve, so you are right about it being gravity feed system. If the bike ran ok with the org fuel valve then I would think that your manual valve is not letting enough fuel to flow to the carb, but the problem only happens when going uphill is strange.

Blade · 09-12-2008, 09:48 PM

Quote:

Originally Posted by 2005GZ250

There is no "pumping" from the fuel valve, so you are right about it being gravity feed system. If the bike ran ok with the org fuel valve then I would think that your manual valve is not letting enough fuel to flow to the carb, but the problem only happens when going uphill is strange.

Plus 1 to this, check the fuel flow and make sure it is enough to fill the carb. Another problem could be the float level may not be right an could be shuting off the fuel flow when you go uphill.

falcon · 09-12-2008, 10:27 PM

In my limited experience with the fuel taps. Vaccum operated fuel taps function is to open to allow fuel to flow while the engine is running (opens and closes a small amount while starting). The problem you describe is usually caused by too small a internal diameter fuel tap or a kinked hose.

Mydlyfkryzis · 09-12-2008, 11:38 PM

Or the original petcock is not working correctly. If it is not shutting off completely, it may also be not opening completely.

09-12-2008, 08:49 PM	#1 (permalink)
tlpotts Newbie Joined: Sep 2008 Posts: 1	question on vacuum operated fuel valves I have a 150cc chinese bike that has an engine vacuum operated fuel valve. Do these types of valves operate as just a valve or is there some fuel pumping action also? My valve leaked gas so while I'm waiting for the part I installed a manual shut off valve. (I did leave the vacuum line attached to the old valve to hopefully prevent problems with a vacuum leak). However the bike cuts out when going up hill (about a 5% grade) and won't immediately restart. But when I let set for about 10 - 20 seconds it starts right up and is able to go downhill and on straightaway with no problem. But I don't trust the bike to go too far so I'm not sure if it would happen on the level road at continuous highway speed. The gas tank is mounted in the rear, higher than the engine and I thought it was a gravity-feed system. The engine is based on the honda gy6 engine technology. Any help would be appreciated.

09-12-2008, 09:37 PM	#2 (permalink)
2005GZ250 Fender Buffer Joined: Sep 2005 Bike: 2005 GZ250 1973 "heavyoldandslow" GT750 Location: Roland, AR Posts: 439	There is no "pumping" from the fuel valve, so you are right about it being gravity feed system. If the bike ran ok with the org fuel valve then I would think that your manual valve is not letting enough fuel to flow to the carb, but the problem only happens when going uphill is strange. __________________ I only ride 'em. I don't know what makes 'em work. Oddball: Donald Sutherland, Kelly's Heroes 1970

09-12-2008, 10:27 PM	#4 (permalink)
falcon In Training Joined: Dec 2007 Bike: 07 Suzuki Boulevard M50 Location: Brisbane Australia Posts: 135	In my limited experience with the fuel taps. Vaccum operated fuel taps function is to open to allow fuel to flow while the engine is running (opens and closes a small amount while starting). The problem you describe is usually caused by too small a internal diameter fuel tap or a kinked hose. __________________ Growing OLD is Mandatory, Growing UP is Optional I'm the most responsible person around......anything goes wrong I'm responsible.

09-12-2008, 11:38 PM	#5 (permalink)
Mydlyfkryzis Seat Tester Joined: Oct 2006 Bike: 1991 Honda Nighthawk 750 Location: Northern NJ Posts: 69	Or the original petcock is not working correctly. If it is not shutting off completely, it may also be not opening completely. __________________ Richard C. 1991 Honda NH750 1976 Honda CB360t

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