Question about Yamaha YZ 125 Motorcycles

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Regarding the fuel stopcock of yamaha chappy, it has three settings: on, reserve and PRI, what is the neaning of PRI?, thanks...

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You have a vacuum operated petcock....so that when engine starts and draws vacuum...a diaphragm lifts in the petcock to supply fuel to carb. When the engine shuts off...vacuum is lost and the petcock closes.
If you run the tank empty....in order to get fuel into the carb and get the bike started initially....you can open the petcock without engine vacuum by rotating petcock to the PRIME position. Once started return the petcock to the ON position. If you leave it on prime....with engine off...fuel may leak into carb and run into engine and contaminate crankcase oil with fuel.

Posted on Mar 23, 2011

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1 Answer

Gas tank


no...Full is on...res is reserve...Pri is Prime.
Do not leave it on prime !!! This is for re-filling the carbs when they have been emptied.
It is a vacuum operated tap, when switched to full or reserve, fuel only flows when the engine turns over...prime flows fuel all of the time.
The tap should be set to full unless fuel is running low.
Leaving it on prime when not running can lead to serious engine damage !!!

Mar 26, 2014 | 2008 Keeway Supershadow 250

1 Answer

2008 Keeway Super Shadow


Full is on...res is reserve...Pri is Prime.
Do not leave it on prime !!! This is for re-filling the carbs when they have been emptied.
It is a vacuum operated tap, when switched to full or reserve, fuelicon1.png only flows when the engine turns over...prime flows fuel all of the time.
The tap should be set to full unless fuel is running low.
Leaving it on prime when not running can lead to serious engine damage !!!

Mar 26, 2014 | 2008 Keeway Supershadow 250

1 Answer

Petrol tap on / reserve position


Hi, Andrewjoh128 your fuel valve positions are as follows with the long end of the lever pointing:
1. Forward=off
2. Down=on
3. Up=reserve
For more information about your issue and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day.
1998 Yamaha XVS 650 Dragstar Petrol tap on reserve position Google Search
Stupi rookie question ON Reserve or PRI motorcycles
Yamaha XVS650 Service Manual
OEM parts for Yamaha
YAMAHA XVS650 Owner Manual

Oct 12, 2012 | 1998 Yamaha XVS 650 Dragstar

1 Answer

I have a 1983 Yamaha Virago 500 and I really need to know what RES and PRI mean on the fuel-**** and how I should use these functions


Those are your PRImary and REServe tanks, although it's actually just two valve openings at different levels in the same fuel tank.

The idea is to use the primary tank all the time and if the fuel level falls below the primary inlet the bike will stop as a warning that you're running out of gas. You can then use the reserve setting to get to a gas station.

Jun 23, 2011 | Yamaha Vino Motorcycles

1 Answer

As soon as I put gas in the tank it all drains out, presumably passing through the carbs and out of the air intake. bike's a 1980 yamaha maxim 650cc.


they have a vacumn opperated fuel tap, should only allow fuel to pass when the engine is running, unless you have it on pri(prime) if it runs out with the tap on run(on) or res(reserve) the tap need a kit.
unless the fuel and vacumn hoses have been mixed up

Apr 05, 2011 | 1980 Yamaha XJ 650

1 Answer

Positions "Reserveswitch"


The On position is where you run the bike after filling the tank. The Res position is when you are almost out of fuel and the motor stutters you turn the switch it it and that will give you about 1/2 a gallon of gas left in the tank to get to a gas station and refill. Pri is for priming the carbs only. If you have ran out of gas after using the reserve fuel you switch it to this position to fill the float bowls with fuel. Do this for only 30 seconds and switch it back to On position.

Oct 01, 2009 | 1996 kawasaki GPZ 1100

1 Answer

Fuel Reserve switch


Typically there are three positions to choose from. On means you are using the main tank. Reserve means reserve tank and off means no fuel available from either tank. the off setting is used when trailering your bike.

Aug 13, 2009 | 2000 Yamaha V Star 1100 Classic

2 Answers

Erratic Sputtering...


Three years with that few miles sounds like a good candidate for bad gas. I would start by taking the carb off and cleaning it really well with carb cleaner.

May 24, 2009 | 2006 Yamaha V Star 1100 Silverado

1 Answer

CANT START


Hi,

Most bikes (and gasoline feed engines for that matter) would require two crucial elements to start/run: 1) fuel and 2) ignition. A hard starting engine then could be caused by:
1. fuel starvation - there is no fuel in the carbs (or high pressure fuel pump for injected). This could be brought about by the fuel tank's valve which will only allow fuel to flow through if there is a vacuum, the engine is already running. In some models, there is a setting on the fuel valve ON, RES and PRI. On is just that one but requires the vacuum from the intake manifold, RES is for reserve, same as ON except that it the inlet sits lower inside the tank but also requires vacuum. PRI is ON and will allow fuel to flow even without vacuum. Before starting the bike, moved the fuel valve control to PRI if the Yamaha has one. Additional on cold start, putting on CHOKE to about 3/4 up would also enrich the fuel/air mixture making an easier start.

2. Ignition - At every engine start, the battery supplies power to the starter motor and to the ignition system. In some instances when the battery is going weak, the starter motor will gobble up most if not all of the power output of the battery leaving nothing for the ignition system to use. This is especially evident if the bike was used at night with the lights open and the bike did not have a chance to re-charge its battery before switched off. Starting on the next morning would be on a bike with its battery partially depleted. In some instances, the charging system may be at fault if and when it fails to deliver sufficient charging to the battery. Often causes are corroded or loose connection or even a a partially defective voltage regulator.

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

Thank you for using FixYa.

May 30, 2008 | Yamaha RX-V661 Receiver

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