DRZ 400 Carb Vent and Bogging

[scottbc]

This past Sunday I rode the Whipsaw Trail. Those who have done this know that therecan bedeep mud and deep puddles. I found that the bike would bog and loose power just when I needed it to blast out ofthe water or mud. I think that this is because the carb vent is under water when this happens.

Has anyone else experienced this? What's the answer? Do I add a T vent to the hose?And if I do where is the best place to run the vent hoes to?

Thanks, Scott

 

[snackdaddy]

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I too have a drz 400 and do the whipsaw at least once a year.

My DRZ always bogs down on the whipsaw. It is a very high trail and above 1800 meters my carb starts to poop out.

Does not help you much but that is my .02

 

[Farp]

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If you have the carb jetted for sea level and are at 1800 meters the bike will be running too rich. You need to put in a smaller main jet and lower the needle to run at that altitude. That's probably what's causing it to bog at wide open throttle. Sorry I can't be more specific re main jet size and amount of needle drop, you'll just have to go by trial and error - or live with it.

 

[scottbc]

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I have ridden at some pretty high altitudes and have never had a bogging problem, some power loss but not bogging. It seems that whenever I get into a deep water situation is when the bogging occurs.

Scott

 

[ruskin]

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I, too experience similar symtoms. At the first sign of bog I changethe filter skin. With the heavy dust right now it is getting dirty enough to affect air intake only after a 100 kms or less even. Filter skins don't seem to take it.


I also experimented with the vent hosebecause I was concerned about water intake. I found that even lengthening the hose 6'' (to vent into the air box) caused the engine to cut out at higher rpms. This was evenbefore I plugged it into the airbox.





I'm slipping the clutch alot more these days.

Ruskinrider

 

[Farp]

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Could be a combination of things. A bike jetted for sea level will be too rich at 1800 meters, pretty sure about that. When you're in a deep water/mud situation the bike can't accelerate and increase the rpm as fast as it normally would so the air velocity through the venturi is slower to develop. Maybe this combined with a rich mixture is causing the problem.

I think you've got a CV carb on that bike so the throttle slide is actually opened by the difference in pressure between the venturi and the outside atmosphere (venturi pressure is routed to the top of the slide diaphragm while the bottom of the diaphragm is open to the atmosphere). The venturi vacuum is developed by the velocity of the air rushing through it so if the bike is experiencing a lot of rear wheel resistance it can't rev as fast and the air rushing through the venturi is reduced, and the throttle slide won't open as fast as it normally would when you've got the butterfly held wide open.

Without doing a whole lot of testing it's hard to determine what's causing your problem. If the bike only bogs under extreme load try slipping the clutch a little to let it rev more freely and see if that helps. Other than that I don't know what to advise.

Maybe some of the others on this forum have experienced the same thing and found out how to fix it. An ounce of experience is worth a pound of speculation. Good luck

 

[scottbc]

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Good points all. I hadn't really thought about the added load not allowing the engine to spin up as fast as usual.

The filter skin is definatly getting pretty dirty. The thing is thatI only have had this problem when exiting a creek or bog. This has happened at various elevations. Slipping the clutch may be the easy soulution.

Scott

 

[old trials guy]

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I have seen many instances of over oiled air filters.I think the average air filter calls for a couple of ounces of filter oil. I have seen them almost totally saturated and dripping.

Excessive oil means less air which means rich mixture. Add some water to further slow the air flow and you have a super rich condition which gets worse with elevation.

The oil is not intended to make your filter waterproof butto yield a light film of oil on the open cell construction of the filter whichis tacky and captures the dust particles.

Clean your filter (I highly recommend No-Toil products) and re oil making sure you use just enough to make the filter slightly tacky to the touch. Make the mixture screw accessible for adjustment if you haven't already done that and try adjusting it when you are at higher elevations to get best throttle response.

The average Japanese dual sport is usually jetted so lean from the factory they generally run better at elevation so that is why I suspect the air filter.

One last comment, I found my DRZ was prone to stalling regardless of the carb tweaking and slipping the clutch to keep the engine above stall speed is a good technique.

otg

 

[scottbc]

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I am already using No Toil, love the stuff, and am really carefull when oiling the filter and skins. Add a little oil and work it it about. I don't think that I was getting water into the air box, it wasn't seat deep.

OTG you say that your DRZ would regularly stall, mine never stalls unlessI screw up. This was a first, and at an inconvienient moment. I have always been amazed at the bikes ability to just lug through things.

Scott

 

[old trials guy]

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The DRZ is a great bike but I was never happy with the carburation at low speed. I am sure with some effort it could have been sorted out but I had decided to get the Sherco which is injected. Hopefully the Japanese will get on the ball and start building injected bikes for Canada.

It might be worthwhile checking valve clearances if you haven't done so recently. A tight valve and hot engine could result in poor low speed performance.

Good luck sorting it out.

otg