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Fuel Switch on DRZ400

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Does anyone know what PRI means on the fuel switch of a DRZ400? And also what could happen if you ride the bike with the switch in that position for extended periods of time. Oh, yes... I am a beginner to this so detailed answers would be much appreciated. Thk. 😢

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The Pri setting allows fuel to free flow into the carb. It's normally only used when you've run the bike dry and need to get some fuel into the carb to start it.

One of the smarter guys will have to tell you if it causes damage. 😢

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The petcock on your bike is vacuum operated.. in the On and reserve position.. IOW it only allows fuel to flow in the ON and reserve position if engine vacuum is present. This keeps you from having to shut off the fuel when you park the bike.

As was already said,, the Pri or Prime position is not vac controlled, and used anytime you want flow with the motor running,,,like when you have run it out of gas,, and need to get some in the carb BEFORE it will start.....and produce vacuum.

If all things are working right,, running it in pri position will have no ill effect,, it's just suppling gas like the other two positions.. BUT,, in the Pri position,,,with fuel flow at all times,,, it could cause the carb to over fill when not in use,,, As in parked, or being trailered. hence the reason most off road bikes have an off position.. same principle on the DRZ S,, but it is an automatic off, via the vacuum operated petcock.

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Is that any different then the ON position on the same switch? 😢

the on and reserve positions of the fuel switch require vacuum pressure before fuel will flow. this is why you can remove the fuel tank with the switch in the on position and not have fuel all over the garage. the pri position just opens the valve like turning on the faucet.

hope it helps. 😢

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Does anyone know what PRI means on the fuel switch of a DRZ400? And also what could happen if you ride the bike with the switch in that position for extended periods of time. Oh, yes... I am a beginner to this so detailed answers would be much appreciated. Thk. 😢

Just curious, did you find any fuel leaking out with the fuel switch set on PRI for so long?

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Just curious, did you find any fuel leaking out with the fuel switch set on PRI for so long?

You won't have any fuel leak out while running it in the prime position, unless the float is screwed up or you lay the bike down. It's when the bike is off and the petcock is in prime that you have the potential for leakage.

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Here is a belated response that should help someone. On many bikes, the prime setting will of course fill the carb running or not. If you work the throttle at prime with the bike not running, it can add many shots of gas to the intake and fill the piston chamber because in prime it will refill always. Likewise on some bikes, you can use it like a choke to instead jet some fuel in the intake on a cold start. Old cars could flood on a hill or a full tank when children would pretend to drive and work the gas pedal.

 

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29 minutes ago, onoffroad said:

Here is a belated response that should help someone. On many bikes, the prime setting will of course fill the carb running or not. If you work the throttle at prime with the bike not running, it can add many shots of gas to the intake and fill the piston chamber because in prime it will refill always. Likewise on some bikes, you can use it like a choke to instead jet some fuel in the intake on a cold start. Old cars could flood on a hill or a full tank when children would pretend to drive and work the gas pedal.

 

There is no accelerator pump on a Mikuni bsr36 carburetor as it's a cv type carb and operates strictly on vacuum available.You can pump the throttle a million times and no fuel will ever be pumped into the cylinder.

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The biggest problem with the mikuni is if the float sticks and it overflows , that fuel is routed into the inlet not to the outside , and the engine will fill with fuel . This has caused many people trouble and can be hard to diagnose , greg

 

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On 12/7/2004 at 9:26 AM, jaydrz400s2004 said:

the on and reserve positions of the fuel switch require vacuum pressure before fuel will flow. this is why you can remove the fuel tank with the switch in the on position and not have fuel all over the garage. the pri position just opens the valve like turning on the faucet.

hope it helps. 😢

I did this and had fuel all over the garage. Is mine bad then? It's fine while connected (no flooding) but when I disconnected it to remove my tank, fuel just kept spilling out.

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2 hours ago, rbhudson said:

I did this and had fuel all over the garage. Is mine bad then? It's fine while connected (no flooding) but when I disconnected it to remove my tank, fuel just kept spilling out.

Did you turn the petcock to "ON" or "RES" ?If so then yes, the vacuum petcock is bad.It should not leak any fuel if left in either of those two positions.

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20 hours ago, bumtarder said:

Did you turn the petcock to "ON" or "RES" ?If so then yes, the vacuum petcock is bad.It should not leak any fuel if left in either of those two positions.

Thanks. Yes, I tried both "ON" an "RES" and fuel kept coming out. I'll either replace it with the OEM or go the WR400 non-vac version. 

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Depending upon which drz model you have the yamaha raptor petcock is not a direct bolt on item. There is a write up article in the drz faq forum on how to prepare one to install into a drz if you decide to go this route,but you will always have to turn the fuel on and off each time you ride the old school way or the engine will flood.K&L Supply and All Balls Racing market repair kits to enable you to rebuild the original vacuum unit.

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2 minutes ago, bumtarder said:

Depending upon which drz model you have the yamaha raptor petcock is not a direct bolt on item. There is a write up article in the drz faq forum on how to prepare one to install into a drz if you decide to go this route,but you will always have to turn the fuel on and off each time you ride the old school way or the engine will flood.K&L Supply and All Balls Racing market repair kits to enable you to rebuild the original vacuum unit.

Thanks! So far my motor has not flooded but fuel definitely kept coming out when I removed my tank. I've read that the petcock can fail on the fuel side or the vacuum side. My bike starts and runs fine and I don't think fuel is constantly going into the cylinder when not running. Which failure would this possibly suggest or should I play it safe and not even run it until repaired? Like I said, everything seemed normal until I disconnected the fuel line and fuel kept coming out.

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The only reason right now that the motor doesn't noticeably flood is because the float needle is sealing well against the seat. Check the motor oil carefully for fuel contamination often if you're not going to repair it right away. I wouldn't ride like that unless it was an emergency situation.

https://thumpertalk.com/forums/topic/1266056-raptor-petcock-on-a-drz-fit-yes-no-but-the-no-can-become-a-yes/

 

https://thumpertalk.com/forums/topic/1212995-mikuni-bsr36-float-valve-seat-needle-jet-o-rings/

 

Edited by bumtarder

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11 minutes ago, rbhudson said:

 or should I play it safe and not even run it until repaired? 

Run your bike as normal until you find a repair option. It's been doing ok so far....

I run a manual petcock sometimes, and I always forget to turn it off ! 🙂....just be aware

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