Run it out of gas after every ride?

8 replies to this topic
  • Sanch

Posted October 02, 2001 - 03:50 AM


I just purchased a '99 YZ400F for myself and an '02 TT-R90 for my son. To sum it up, we love them! My question is that when I bought the YZ400, the previous owner said to turn off the fuel and run it until it dies after every time out. Wouldn't leaning it out like this be bad for the motor?

  • Guest_Guest_*

Posted October 02, 2001 - 03:55 AM


This is not an outboard motor. If you are going to store it for the winter you might want to do that, but I don't know, we don't have winter here.

  • mcarp

Posted October 02, 2001 - 04:01 AM


The reason he said that was that when you trailer the bike, fuel can slosh around in the carb into the engine. This makes it hard to start and possibly foul a plug the next time you ride it. At least that is my experience.

Will it be lean, yes, for a brief moment it will pop and backfire before it dies. I don't mind this, I would rather have a temporary lean condition than a fouled plug.

BTW, there are some arguements out there that draining the carb could change the float height. I have not found this to be true with my '00 WR despite running the gas out each ride for the last 18 months. I just checked it last week in fact when doing the BK mod. But it could affect other bikes, dunno.

But I do know I was having starting problems when I ignored this advice. I've consistenly been doing this step and have NOT fouled a plug since-even with 4-5 different jetting settings-some of which were rich and should have fouled (ie did foul in the past).

Also, small quantities of fuel go bad faster than larger ones. Possibily this guy didn't ride for extended periods (like the hot Florida summer) and found the gas to be bad, and possibly the carb gummed up a little. just a guess...

  • mikeolichney

Posted October 02, 2001 - 11:10 AM


You don't need to run it dry. The carb has a very convenient drain tube. Just turn the allen head valve at the bottom of the carb and the gas will drain onto the ground.

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  • Boit

Posted October 02, 2001 - 03:05 PM


I was thinking about that arguement about draining the fuels causing the float level to change. The tang between the float buoys is what is adjusted to maintain the float level. I suppose the tang could get bent if you moto after you turn the petcock off, but who would do that? I see a benefit of draining the bowl in that the needle valve is not being pressed up into the seat which over time, makes for the formation of a little groove around the circumference of the rubber portion of the valve causing leak-by. Personally, I close the petcock and run the engine at a fast idle for about a minute and a half before loading up at the end of the day. I've noticed that if I leave the bowl full, some gas vents out on the ride home.

[This message has been edited by Boit (edited October 02, 2001).]

  • Chris_Slade

Posted October 03, 2001 - 07:54 PM


Let me ask one thing...with a comment....
I cannot believe running the bike out of gas is bad for it, I'm sorry. First, my manual says that's actually how to shut it off after a ride (obviously thinking of eduroing or something, then done for the day/week or whatever). Second....having that 'lean' condition at idle speeds CANNOT be as bad as closing the slide in the carb at 10000 rpm. (AKA, letting off the gas) I mean, come are starving the engine for fuel immensely, thats why it slows down so fast. So, how is having a few RPM's at no fuel any worse than a few HUNDRED with minimal fuel???

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  • mcarp

Posted October 04, 2001 - 04:41 AM


All I know if if I did not drain the carb (no not dumping gas on the ground, ever head of the "environment?"), I would incure flooding problems about 8/10 times.

Generally the road to the trailhead is full of potholes so the bike does get tossed around a bit. This is probably a HUGE factor.

Boit- do you mean jumping-moto or just riding at all? I normally turn it off 1/8 mile from the truck and just ride it until it starts to sputter. By the time this happens, I'm at the truck and ready to turn it off. Just curious, I suppose any kind of big bumps *could* toss the float out of alignment. Again, I have not found this to the be case.


  • Sanch

Posted October 04, 2001 - 10:37 AM


As a new rider, I want to thank everyone for their comments. It's good to know that a resource like this is available. I know I'll spending a lot of time here...thanks again.

  • Boit

Posted October 04, 2001 - 02:44 PM


Mcarp: I meant riding hard. What I was getting at is if you close the petcock and continue riding hard, especially doing any jumps, you run the risk of twisting the throttle and the engine balking. Can you say "instant endo"?

On further consideration of the float tang getting bent, it seems highly unlikely. The float rides on the level of the fuel and nothing prevents the float from being slammed to the top and hitting the needle valve during normal M/Xing. However, I'm not sure if the engine would continue to run if the bowl were emptied enough such that the float was not being support at all by fuel. The pilot jet is not nearly as deep into the fuel as the main jet. And even if it did continue to run, would the tang be at risk of being bent upwards? These are "what-if's" questions.

Chris Slade; I agree that shutting off the gas and running the engine at low RPM's not harming the engine at all. As far as chopping the throttle at 10,000 RPM hurting the engine because you starve it for fuel is only partially correct. Closing the throttle only returns the carb to it's idle circuit and maintains a normal fuel/air ratio. I.E., the slide is bottomed out and only the cut-away allows air past which pulls fuel thru the pilot jet and into the engine. This doesn't create a lean mixture. RPM's don't factor into this equation. If they did, internal combustion engine would not last very long. What you DO get is engine braking.

I have a Stroker built KLX that has much more dramatic engine braking than my 426 due mostly to cam profile differences.

[This message has been edited by Boit (edited October 04, 2001).]

[This message has been edited by Boit (edited October 04, 2001).]

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