fuel shut off valve - Suzuki Z400 Forum : Z400 Forums
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post #1 of 11 (permalink) Old 03-29-2011, 11:24 AM Thread Starter
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Question fuel shut off valve

just got an 05 z400 and wonder what is the fuel shut off position on the valve? it has a ON , RES, and PRIM but nothing for off, and what is PRIM for?
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post #2 of 11 (permalink) Old 03-29-2011, 11:40 AM
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On is off......
It is a vacuum fed carb. That gas will not flow in the on position but will flow in the prime position.

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post #3 of 11 (permalink) Old 03-29-2011, 11:49 AM
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As spize said on is off but that is only true while the engine is off. "Prime'' will feed fuel to the carb only while the engine is off. Once it starts it will stop flowing fuel while on ''prime'' and you will have to switch it to "on"

I think that is how it works at least, some one correct me if I'm wrong.

If you happen to have bought the bike with an FCR carb installed then "prime'' will fuel flow all the time and "off" or "res" will not flow fuel weather the engine is on or off.

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Last edited by chinoduca; 03-29-2011 at 11:54 AM.
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post #4 of 11 (permalink) Old 03-29-2011, 11:57 AM
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Buy a raptor 660 Petcock - the stock one sucks!

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post #5 of 11 (permalink) Old 03-29-2011, 12:07 PM
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X2 on the raptor valve, I do think it's a better flow to run on prime all the time, I'm not sure now either?

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post #6 of 11 (permalink) Old 03-29-2011, 01:04 PM
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Buy the raptor 660 Petcock and just avoid any of the problems that arise from the stocker.

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post #7 of 11 (permalink) Old 03-29-2011, 10:23 PM
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In simple terms always run in on, if you run out of gas turn it to prime for 20 seconds then to res restart. then make hay for more gas. Prime is only ment to fill an empty carb.
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post #8 of 11 (permalink) Old 03-30-2011, 01:21 AM
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worst fuel petcock design ever bar none.....raptor unit 20 bucks off ebay new

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post #9 of 11 (permalink) Old 03-30-2011, 01:47 AM
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My stocker ran better on prime all the time- it may have been malfunctioned but no longer matters- raptor petcock and fcr. when I would run in the on position it seemed to sputter like it was starving for fuel. didn't do that in the prime position. it did stop the flow when engine was off so i dunno? but i agree with the others with or without a fcr carb- cap off that vacuum port and get a raptor petcock. bolts right in- is cheap- and much more reliable.

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post #10 of 11 (permalink) Old 03-30-2011, 01:55 AM
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Please do some searching this has been covered multiple times.

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post #11 of 11 (permalink) Old 03-30-2011, 02:18 AM
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You can run on prime all you want, I dont get why you guys are saying not to, it's not any different than the reserve setting on a normal style petcock. The only downfall is that when your out of fuel, your pushing or walking

The stock petcock is controled by engine vacuum. When it is in the "on" or "res" settings, fuel won't flow until the engine is turning over, or running. The prime position is the same exact thing as "res" would be on a normal petcock. If you run on prime, it will flow fuel to the carb no matter weather it is running or not. This is not a problem unless your carb has problems.

Like said several times, the stock petcock is a quirky piece of crap that is malfunction prone. There really is no reason for it to shut the fuel flow off when the engine is not running. As long as your needle valve in the carb is good, you will never have a problem from that. In my experience, the stock petcock does not always shut the fuel off when the engine shuts down, and some people have had diaphram problems, and had fuel flowing through the vacuum line flooding the engine and even the crank case.

The raptor 660 petcock is a direct bolt on replacement which is your typical on, off, reserve, style petcock. It also flows fuel faster than the stock one. This becomes very important with big bores and strokers... and big bore strokers.
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