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The applied vacuum to the petcock is only during the intake stroke of the piston when the intake valve is open.

Starter motor cranking speed is about 300 rpm, vacuum only being applied 25% of the time.

There are THREE more cycles of the 4 stroke engine when there is No Vacuum being applied to the petcock diaphragm.
There is a very tiny vacuum orifice in the cap of the petcock diaphragm, to help retain the previously applied vacuum.

At 7500rpm there is a more continuous vacuum in the intake port, even if a lesser value. Worst fuel mileage I've ever gotten on my KLR was 35mpg @ 90mph so it needs to only flow about 3 gallon per hr. I will suggest that the KLR petcock is capable of flowing about 5 gallons in 20 minutes.
 
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I’m with you 100% on keeping the vacuum petcock. I also agree that having a prime position is problematic. I was suggesting a normally closed push button primer. It would only prime if held in and would spring back to its normally closed position as soon as finger pressure was released. The only way to flood the engine would be to hold it open for a long time with a stuck float. Seems an unlikely confluence of circumstances.
The only problem with vacuum petcocks I've seen is lots of people tend to never use the off position. I had a buddy (Harley guy) who for 10+ years never used the valve on his. His float needle never leaked, but one day he ran low on gas and destroyed the rubber inside when he finally tried to move from on to reserve.. At least with the old standard types you're forced to move it from time to time avoiding that catastrophe.
This thread reminds me of a bike I had when I was 12 yrs old. a 60's vintage 124cc Sears. You HAD to turn the gas off on that one "before" you shut it down or within a minute you had a crankcase full of gas. I don't think the carb even had a float system, but that was nearly 50 years ago so I can't remember.
 

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...And the 'On' stand pipe is taller than the Yamaha Raptor manual petcock, so as to give a little more reasonable reserve range...
This is an often-mentioned concern with the Raptor petcock that I just don't get.

I have tracked fuel economy on my KLR for a bit less than 40K miles and know that it gets 44 mpg with a low of 40. Up hill, down hill, rain. shine, fast, slow, it gets 40-45mpg. I got 56 once, but it was downhill with a tail wind...

I know how big my tank is; it holds pert nar 7 gallon. 40 times 7 is 280 miles. There's seldom a gas station that isn't within 40 miles, so when it gets to 220 miles I go look for a gas station. I never even go on reserve.

Seems to me that the same sort of two-digit math can be applied to a 6-gallon tank and a different MPG range.

Do people really need to run out of gas to be told to go look for a gas station and that's why they need a 40-50 mile reserve range, plus tipping the damn thing over to get more gas out of the right wing? Do people think that having less reserve means there is less fuel, overall, in the tank? Is this a mystical concept?

I tell ya, I just don't get all the concern over reserve range. Is knowing how far you can go, and how far you've come, some sort of a lost skill like shutting off the petcock? My BMW is the first bike I ever had that didn't have a petcock, and the KLR the first one that had a vacuum petcock (for a while).
 

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Discussion Starter · #24 ·
This is an often-mentioned concern with the Raptor petcock that I just don't get.

I have tracked fuel economy on my KLR for a bit less than 40K miles and know that it gets 44 mpg with a low of 40. Up hill, down hill, rain. shine, fast, slow, it gets 40-45mpg. I got 56 once, but it was downhill with a tail wind...

I know how big my tank is; it holds pert nar 7 gallon. 40 times 7 is 280 miles. There's seldom a gas station that isn't within 40 miles, so when it gets to 220 miles I go look for a gas station. I never even go on reserve.

Seems to me that the same sort of two-digit math can be applied to a 6-gallon tank and a different MPG range.

Do people really need to run out of gas to be told to go look for a gas station and that's why they need a 40-50 mile reserve range, plus tipping the damn thing over to get more gas out of the right wing? Do people think that having less reserve means there is less fuel, overall, in the tank? Is this a mystical concept?

I tell ya, I just don't get all the concern over reserve range. Is knowing how far you can go, and how far you've come, some sort of a lost skill like shutting off the petcock? My BMW is the first bike I ever had that didn't have a petcock, and the KLR the first one that had a vacuum petcock (for a while).
Well, let me tell you about the highway between Rufus, OR and Madras, OR. It is 94 miles give or take. There was a gas station in Rufus, but I still had a third of a tank (showing 84 miles to empty on the big LT) and figured there had to be a gas station before Madras. My wife wasn’t happy when we sputtered to a stop going up a hill 12 miles shy of our hotel in Madras as it was getting dark...
 

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It doesn't matter whether it is an automatic or a manual fuel valve, if the available positions are not used occasionally it will become a problem eventually.

There is nothing more to 'force' one to use the selector handle of a manual valve vs an automatic valve.

The KLR runs perfectly fine on the top 4.5 - 5.0 gallons, many riders apparently attempt to re-fill before ever needing Reserve to reduce hazzard on busy freeways.

The rubber selector disc of either type of valve can be torn by eventually being forced to turn to reserve. The tid-bit of rubber can then flow down the fuel hose & jam the float valve. The Automatic fuel valve still has a fair chance of closing the fuel supply when the engine is Not cranking nor running.

Most manual fuel valves will continue to leak after being injured & have no secondary fuel control.
 

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Many people have wished for a fuel gauge on the KLR.

I absolutely hate most motorcycle fuel gauges, be they on carbureted or fuel injected bikes because most of them start flashing their "LOW FUEL" warning with 1 - 1.5 gallons of fuel remaining. Due to the odd shapes of most motorcycle fuel tanks, most of the fuel gauges are Wildly in-accurate, side stand vs rolling, up-grade vs down grade.
I'd rather have a manual reserve of reasonable quantity, even on under seat fuel tank, fuel pump equipped motorcycles, atvs, side x sides. (But that ain't gonna' happen.)

Therefore I for one have always appreciated a one gallon reserve on street legal bikes, Tom.
 

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I’m with you 100% on keeping the vacuum petcock. I also agree that having a prime position is problematic. I was suggesting a normally closed push button primer. It would only prime if held in and would spring back to its normally closed position as soon as finger pressure was released. The only way to flood the engine would be to hold it open for a long time with a stuck float. Seems an unlikely confluence of circumstances.
Following notion has no experiential nor reference basis:

I think the "PRIME" positions on fuel systems so configured merely provide raw fuel to the carburetor venturi when activated; absent the greater finesse of the KLR's starting enricher, a component mixing BOTH air and fuel, as described in pictures and text above. I'd imagine a combustible mixture upon starting more likely from the KLR starting enricher, than from a prime-type system in that position.

Maybe not. Maybe my perception is never fulfilled, or only sometimes valid.
 

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Following notion has no experiential nor reference basis:

I think the "PRIME" positions on fuel systems so configured merely provide raw fuel to the carburetor venturi when activated; absent the greater finesse of the KLR's starting enricher, a component mixing BOTH air and fuel, as described in pictures and text above. I'd imagine a combustible mixture upon starting more likely from the KLR starting enricher, than from a prime-type system in that position.

Maybe not. Maybe my perception is never fulfilled, or only sometimes valid.
the petcock has no way of affecting the carb other than allowing fuel to flow; prime just allows fuel to flow without the engine cranking/running (or vacuum source)

Dave
 

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I've recently read that the Suzuki DR650 uses a vacuum operated petcock which does have a 'Prime' position instead of the 'Off' position and will fit the KLR650.
And the 'On' stand pipe is taller than the Yamaha Raptor manual petcock, so as to give a little more reasonable reserve range.

Numerous older Kawasaki models used the 'Prime' position petcocks, I don't recall which models. But even a 'Prime' position petcock can accidentally be left On Prime and can then allow a drippy float needle to flood the cylinder & crankcase with gasoline.

In my 10 years of involvement on KLR650 internet forums I've seen numerous KLR pistons which became fairly sudden oil burners, which upon tear-down had broken ring lands. Many people always suggest detonation to be the probable cause, but I have never seen any evidence of detonation on any of the piston crowns which could be seen in their supplied pics.
I therefore suggest that an equally possible cause of broken ring lands is from hydro-locking of the piston against a partially flooded cylinder.
I believe that this is part of the reasoning that Kawasaki mostly dis-continued the use of 'Prime' position petcocks. And it is the reason that I dis-courage the use of manual petcocks.

It's a matter of risk managment IMO. In order to dump fuel into the engine, you need to forget to turn a manual petcock on and off and you need a float valve problem. (If Kawi had put a proper overflow tube in place, it'd be a non-issue). I'm also not sure that the bike will drain fuel into the cylinder unless it's sitting just right. The flip side is that the vacuum petcock isn't ethanol compatible and is a fairly regular failure point - even Kawi added the little filter at the carb, presumeably to address this......though just making a new, ethanol proof diaphragm would seem to be a better fix. I see the possibility of hydrolocking the cyl with fuel but I doubt it's a common thing.

Seeing as how the vast majority of my 41 bikes have had manual petcocks, I've become pretty accustomed to turning them on and off as necessary and believe that the Yamaha petcock replacement has simplified and improved my KLR's......combined with my IMS tank (and gas cap), I believe I've eliminated several of the common KLR problem areas.

Paul, you mentioned once a CVK float bowl that has the overflow tube in it; retrofitting that might add staples to the belt and suspenders!

YMMV,

Dave
 

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Discussion Starter · #31 ·
Many people have wished for a fuel gauge on the KLR.

I absolutely hate most motorcycle fuel gauges, be they on carbureted or fuel injected bikes because most of them start flashing their "LOW FUEL" warning with 1 - 1.5 gallons of fuel remaining. Due to the odd shapes of most motorcycle fuel tanks, most of the fuel gauges are Wildly in-accurate, side stand vs rolling, up-grade vs down grade.
I'd rather have a manual reserve of reasonable quantity, even on under seat fuel tank, fuel pump equipped motorcycles, atvs, side x sides. (But that ain't gonna' happen.)

Therefore I for one have always appreciated a one gallon reserve on street legal bikes, Tom.
My BMW flashes with about 1.2 gallons left. The fuel gauge and the DTE function of the trip computer are uncannily accurate. I have only run it out one time, but it died within 2 miles of what the DTE had been saying on average and the last bar of the LCD display had just went out before the engine died. I ran it down to the last LCD bar one time before (the display has very small bars, I would guess at least 50 between empty and full) and it took 6.15 gallons to fill the 6.2 gallon tank so I would say it is pretty darn accurate. When it says you have 14 miles to empty, it ain’t kidding.

I much prefer an accurate fuel gauge to the reserve petcock, but I can live with either.
 

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It's a matter of risk managment IMO. In order to dump fuel into the engine, you need to forget to turn a manual petcock on and off and you need a float valve problem. (If Kawi had put a proper overflow tube in place, it'd be a non-issue). I'm also not sure that the bike will drain fuel into the cylinder unless it's sitting just right. The flip side is that the vacuum petcock isn't ethanol compatible and is a fairly regular failure point - even Kawi added the little filter at the carb, presumeably to address this......though just making a new, ethanol proof diaphragm would seem to be a better fix. I see the possibility of hydrolocking the cyl with fuel but I doubt it's a common thing.

Paul, you mentioned once a CVK float bowl that has the overflow tube in it; retrofitting that might add staples to the belt and suspenders!

YMMV,

Dave
The USA EPA is who required the removal of the float bowl overflow pipes from street legal motorcycle carburetors. It not just a Kawasaki thing.

The carburetor and intake port are angled slightly forward. Slightly over-flowing fuel will tend to seep out thru the pilot mixture screw and the 3 low speed pilot outlets under the edge of the throttle plate before it seeps out of the pilot air or main air jets in the throat of the intake bell mouth of the carb.
Even setting on a center stand, I believe the carb is angled 'down-hill'.

In 32 years of dealing with KLR650 vacuum operated fuel taps, I have Never seen any parts of the fuel tap vacuum diaphragm or its sealing o-ring jammed in the carburetor float needle.
I have seen plenty of crumbs from the selector discs. Even more crumbs from the selector discs used on the manual fuel taps of the seasonally used ATV's.

There is currently only one fuel station in this town which sells a non-ethanol #91 premium priced, premium grade fuel. So even I have used many hundreds of gallons of ethanol laced #87 gasoline thru my personal KLR650 in the past 20 years.

It is a mystery to me how that 'tiny little duck-bill screen fuel filter' in the 2011 & up permanent fuel inlet nipples can flow enough fuel to allow 35-40 mpg at 90 mph in a head wind and some of the larger in-line fuel filters might not!

Mark Gardiner & Ian Hopkin on one or two of the KLR FB groups said that the KLR600, 650-A & 650-C models in the UK had overflow stand pipes in the float bowls.
 

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Paul,

Yes, I'm aware that it's an EPA thing......yet another compromise unfortunately. regarding the vacuum petcock; I'm aware of both your opinion and your luck with the stock petcock but as you know, petcock failure is an exceedingly common problem - you don't have to spend too many years on these forums to see that....and, of course, EM wouldn't have a market for the manual ones if people weren't interested in swapping. I'd suggest that ethanol is far more of a problem if a bike sits for any period of time - if run regularly, it appears to be fine according to many (yourself and GoMotor for eg.)

I may try to source a bowl with the stand pipe as I believe that's the ultimate insurance.

Cheers,
Dave
 

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I put in Star Brite StarTron and fire the girls up when I get a chance. No problems with the bikes and their fuel for years.
Without it... it's a carb cleaning after a couple months sitting with these ethanol fuels.
It's the best fuel additive going.
 
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