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  1. Note: While this article has a significant focus on vacuum petcocks, it also has some important information if you are considering changing out your OEM fuel tank or replacing your Petcock: see “Factors to consider” further on in the article. The biggest issue: The OEM petcock on the S and SM (and maybe the E in other parts of the world) uses engine vacuum to open and close the petcock valve and thus control the fuel flow from the tank. It has known failures whereby it fails to shut off fuel flow when the bike is off, which can flood the engine with fuel over time, filling the crankcase with fuel, and completely diluting the engine oil, etc. (bad outcome). Alternatively, it has failure modes where it will not allow fuel to flow in ON or RES. Background detail on the OEM petcock: The S and SM OEM petcock has three positions: ON, RES, and PRI. (See the "comparison" photo below) It has two hoses connected: one carries fuel from the petcock to the carb and one brings engine vacuum from the engine. In the ON and RES positions, fuel flows from the petcock to the carb only when the engine is running. Normally, there is sufficient fuel in the carb float bowl for the engine to start. The PRI position allows fuel to flow continuously, without vacuum, and is normally used to "prime" the carb float bowl after carb removal, as the float bowl would be dry, unable to start, and thus wouldn't create enough vacuum. Failure One: No fuel or inadequate fuel in ON and RES, runs fine in PRI: From the description of the valve function you just read you can probably figure this one out: either there is no vacuum getting to the valve to open it when the engine is running, or the petcock has failed internally and the vacuum is not opening the valve. You can test by pulling the vacuum line off at the nipple between the carb and the engine, and pulling the fuel line off at the carb. Apply slight vacuum to the vacuum line (if you are sucking…make sure you put the correct line to your lips…ha) and see if fuel flows. If so, then the vacuum port between the carb and the engine must be blocked. If not then replace the vacuum line with another line and repeat, to see if the hose is blocked (or cracked/split). If it still fails, then the petcock is not opening the valve with vacuum and needs to be rebuilt or replaced. Failure TWO: Petcock fails to stop fuel flow when engine off and engine floods with fuel, diluting the engine oil: This petcock failure can occur in two ways: first, it can fail so that fuel always flows to the carb. This is initially not so bad, as the float in the carb float bowl floats up when the float bowl fills, and has a valve that closes against an o-ring when full, UNLESS it fails to close; then the float bowl overfills, fuel runs down the carb throat into the engine, leaks past the piston, and fills the engine oil sump. Second failure mode: the diaphragm in the OEM petcock can fail, which allows fuel to flow through the petcock and into the vacuum line, which runs directly to the carb throat on the engine side, and takes the shortcut to filling the engine with fuel again. Summary: The OEM vacuum petcock can be rebuilt, and many riders have never had an issue. It is super convenient to simply turn off the bike and walk away, without the need to remember the fuel shutoff. However, sufficient numbers of riders have experienced the "engine full of gas" failure to make replacing it with a manual petcock worth considering. Rebuild kits: I could not source one from Suzuki, but found two that look like they would work: Moose racing 0705-0352, and K&L kit 18-5038. The Manual Petcock option: A commonly installed solution is to install a manual petcock, which requires the operator to switch the fuel OFF every time they leave the bike. There are a number of useable manual petcocks, which by definition, are not vacuum operated. These petcocks have three positions: ON, RES, and OFF. (See the comparison photos below) There is no vacuum line connected to the petcock, and fuel always flows to the carb in ON or RES. The advantage of these petcocks is that their bases are identical to the OEM and thus mate easily with the tank. The disadvantage of putting a manual petcock on your S or SM, is that when bike falls over and stalls, fuel will continue to flow to your carb. Factors To Consider: Nothing is ever easy, there are a couple of things to consider when selecting a replacement petcock, AND WHEN REPLACING THE FUEL TANK with a different one (Stock to large plastic, or vice versa), besides quality of the product. A: Reserve quantity: The main fuel inlet in the tank is the one at the top of the brass standpipe on the petcock. When the fuel level drops below this point, the engine starves and you select reserve, which draws fuel from the other inlet at the very bottom of the tank. With any change of tank or petcock you will have to factor in/measure the impact on your reserve. Have another look at the comparison photo and you will note the very short standpipe on the ATV Raptor petcock: it has virtually NO reserve. I will discuss how to address this later in this article. B: Interference between petcock selection lever and tank lip: With the OEM tank (metal) there is a lip at the edge of the tank that hangs down. This lip can interfere with the movement of the selector lever to the straight up position, which is RES on most manual petcocks. The solution from Suzuki for the OEM petcock was to simply put a spacer between the petcock and the tank, and to design their petcock so that the selector is not required to be set pointing upwards. You have two basic ways to deal with this issue if you use a metal tank and wish to substitute the petcock: use the OEM spacer that came with the OEM petcock (see image below), and/or remove the tip of the selector lever so that it can be turned straight up without contacting the lip. This issue does not arise with plastic tanks. C Fuel line routing and interference with choke operation: replacement petcocks frequently have the fuel line nipple out the right side, instead of the bottom as on the OEM petcock. In addition, alternative fuel tanks frequently have the petcock physically located lower than when on the OEM steel tank. This can create two challenges: how to route the fuel line to the carb, and in some cases how to address problems with interference with the choke control. D: Vacuum line from Carb: If you install a manual petcock, you need to block the vacuum line from the carb. Either cut a small piece of the vacuum line and put a screw into it and push it on the vacuum nipple between the carb and the engine, or get a rubber cap and push this on. E: Mounting bolt length: depending on the tank and petcock and use/not use of spacer you will likely need to replace the mounting bolts with ones that are longer/shorter to avoid bottoming them out or not having enough threads engaged. Alternative Petcocks: There are quite a number of manual and vacuum petcocks on the market, and each has to be considered for the install challenges it may create. I will specifically discuss the OEM "E" petcock, the Raptor petcock, and the Pingle. Here are some comparison photos: note the orientation and location of the fuel outlets, and the length of the reserve standpipe. Note also that I have placed the Pringle petcock, with images, after this section. OPTION ONE: The Suzuki OEM petcock for the DRZ400 “E” in North America: The Suzuki OEM petcock for the DRZ400E appears to have the same reserve standpipe as the OEM petcock for the S or SM, and it is not vacuum operated, and might be the easiest/best solution as you would not have to alter the reserve standpipe to address the reserve quantity issue as you will with the Raptor. It does have the fuel line nipple out the bottom but is oriented to the right side, so that may present some challenges or advantages, depending on the tank/carb combo you are putting it on. Additionally, it may require the spacer or tab modification to get the selector lever to clear the lip on a stock steel tank. OPTION TWO: The ATV Raptor Petcock: How to adapt the Raptor for use: Once again, nothing is EVER easy: First, the Raptor fuel nipple is on the right side, and the OEM on the bottom, as in the "comparison" photo, so you will have to assess the fuel line routing and petcock position for interference with the choke. Note that the Clarke 3.9 tank and the Raptor petcock seem to fortuitously be made for each other....ha ha...the fuel outlet on the Raptor lines up perfectly with the fuel inlet to the carb so a short straight hose is all that is needed, AND the choke operates perfectly. See photo that follows. If you are considering the Raptor for an OEM Steel tank then you will have issues with the choke and fuel line. Eri Marquez has proposed a method to modify the Raptor petcock to solve this: Raptor Petcock and Steel Tank Mod Second Issue: The Raptor has a very tiny reserve. The Raptor petcock from Yamaha, which fits on the stock tank or on the plastic tank just fine however it is designed for use on ATV's, which have big flat tanks, rather than the upright tanks that we have on bikes. As a result, the Raptor petcock comes with a very short brass standpipe on the main intake. So, with the stock Raptor standpipe, you will have a very tiny amount of fuel remaining in the tank at that point, thus you will have virtually NO RESERVE. I have fixed this relatively easily, read on. To fix the reserve issue, I got some 7mm (no SAE equivalent size) brass tube at a model store, twisted the old reserve standpipe out (it is a press fit) , cut a 4.5 inch (11.5cm) length of the new tube, used a hacksaw to carefully make a slight kerf around the end of the replacement pipe to hold the lip of the OEM fuel filter on, rounded and emery clothed the end I was inserting into the petcock, froze the tube, and pushed it into the new Raptor petcock. This was superb, and resulted in a standpipe that is 4.1 inches (10.5 cm) above the flat mount face of the raptor petcock. It gives me a 1.5 Litre (0.4 US Gal) (30km/20mi) reserve on a Clarke 3.9 gal tank. (Note: tube is measured by outside diameter, pipe by inside diameter: you need exactly 7mm outside diameter to get this new tube to press fit into the petcock and seal and stay, thus the need for "tube" and not "pipe") By the way, the Clarke 3.9 US gal tank is an honest measure: the tank dispenses 14.7L (3.9US gal) of fuel to dry tank......but still has 1.7L (0.45 US Gal) of fuel in the right lobe. (tank actually holds 16.5L (4.4 US Gal) of fuel) If you lay the bike on the left side, pick up the front wheel and tip it to past level, this fuel crosses and is usable. So: with a 4.1inch (10.5cm) standpipe on the raptor petcock on the Clarke 3.9US Gal tank, you get 13.2L (3.5 US Gal) in the ON, 1.5L (0.4 US Gal) in RES, and a further 1.7L (0.45 US Gal)avail in the right lobe. The Pingel petcock option: Some folks have used the Pingel valve, which is a slightly higher cost, but apparently higher quality solution. Issues mentioned include: the valve must be assembled before mounting to the bottom of the tank on steel tanks as the tank lip does not allow for the manufacturers valve assembly instructions to be followed, and apparently the reserve standpipe is quite short, so the reserve fuel is very limited. 6191-AH61AV DRZ all years With a reserve Have fun!!
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