Reserve tank issue

[gsatterw]

Ok. So more insight on my little fuel issue. My main tank is fine. When I hit reserve, the bike bogs like nothing else. She idles, but won't get the rpms past 5 k with out cutting out, cant ride when this happens.

So I was riding along with a full tank of gas, and decided to do a little experiment. I flipped to reserve while moving, and within seconds, the symptoms returned. I flipped back to main and the problem persisted. I was right around the corner from my house so i put her to prime hoping to fix the problem, ran home to grab starter fluid, ran back and blipped the throttle, problem still there. I put her back to main, and soaked both sides of the carbs around the boots while i whacked open the throttle. Doing this allowed me to get the rpm's past the 5 k bog spot and all the way to red line. After a few treatments, she was back in business like nothing happened. Bike runs very strong while on the main tank. I seem to have very poor gas mileage, but I ride her hard and have a lot of modifications that decrease fuel economy. But its really low.

Thoughts? Opinions?

Thanks, Graham

[knowles]

Whats low MPG's to you, what mods have you done?

[bombsquad83]

Knowles check his other thread for details on the MPG issue.  I wonder if you have junk in your reserve gas line that get thrown into your jets when you switch over.  Also, maybe your float needles are such that when you flip to reserve they get stuck open and make your mixture way too rich.  Do you get extra gas smell when you have the issue, or gas coming back into the airbox?  Maybe there is something wrong with your petcock that causes a leak into the vacuum tube when you switch over to reserve?  I would get a known good petcock, clean your jets, clean the needle valve seats, and check your float height with the tube from the carb drain method. 

This is all speculation at this point.

[gsatterw]

14t/41t sprockets (stock is 16/39), lunchbox, 22.5, 65, 145 jets, v&h full exhaust, and half the time i'm using the whole gear (usually pull to near redline). I think I'm getting like 30 mpg or something. I tend to do pretty fast starts too. I think there is probably a good amount of gunk in the line or in the petcock, it fits the symptoms...most of them at least. Anyone ever cleaned a frame petcock?

[bombsquad83]

I've personally never heard of cleaning the petcock.  A better scenario would be to replace it.  That rubber diaphragm in there could possibly be compromised, which would not be fixed with cleaning.

[gsatterw]

ok theory. So when i flip to reserve, a bunch of gunk gets shat into my carbs. its not a fuel starvation issue, because if it was, when I flip to prime and let the bowls fill up the problem should be solved, yet it persists. The bike will still idle fine because the idle jet sits higher in the fuel bowl and doesn't suck crap up. When i spray starting fluid, I get a really strong vacuum that blows all the crap through the jets, curing the problem.

Ehhh? Maybe?

[bombsquad83]

Maybe...so replace your fuel lines and petcock and see if the problem goes away.  Do you have a lot of rust in your tank?

[bombsquad83]

By the way you can take apart the diaphragm and check the rubber inside and try to clean it with some carb cleaner (once the rubber is taken out).  Inspect the rubber diaphragm for cracks and stiffness.

[gsatterw]

cool. I did notice a bit of rust in the tank when I was putting it on.

[bombsquad83]

That rust could be causing your issues.  It only makes sense that the rust would settle in the reserve line first since it sits lower in the tank.  You can use a POR-15 tank lining system to address this problem.  Several people on this forum have used this system, so just search for it to find the details.

Check your tank petcock filter for rips on the reserve side as well.  And clean your jets and float bowls out.

[bryan88]

Could be that the junk in the bottom of the tank has clogged up the reserve pick-up. It also seems (and this is just my humble/uninformed opinion) that these bikes need a good "head" of fuel to keep the pressure up?

[bombsquad83]

The bottom of the tank is always higher than the carb gas inlet.  If the petcock is functioning properly, you don't have a pinched gas line, and the carb vent is not blocked causing airlock in the float bowls, then fuel should flow as long as the level is high enough for the inlet on the tank petcock.

All this being said, I think there are very commonly issues with older petcocks due to underuse, age, and ethanol fuels because the diaphragm in the petcock becomes stiff or otherwise compromised.

One solution is to buy a new stock petcock.  As long as you don't have vacuum leak or clogged or pinched gas lines, this will work just fine. 

My solution was to buy a cheaper 2008 CRF250X petcock.  This does not require vacuum, and has an on, off, and reserve setting.  Installation of this petcock requires filing one edge of the petcock, making a spacer to make the petcock reachable while riding, and blocking off the vacuum port on the carb with a cap.  You can check out my build thread to see my implementation of this, or search the forum as others have posted instructions.  Using this petcock, you need to remember to turn off the petcock when you are done riding, or you risk flooding your airbox/engine with gas due to weak float needles (similar to leaving the stock petcock on prime).

I have had zero fuel flow issues with the CRF petcock, where as I found the old warn out stock petcock to be a pain.  This is not saying that a new stock petcock would not work great as well, just that my setup works too.

[bombsquad83]

The part number on that Honda petcock is 16950-KSC-003.  I got it from ronayers.com for $22.76.