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How to minimize tune changes as tank empties?

How to minimize tune changes as tank empties?

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Old 07-28-2011, 02:11 PM
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No worries... If there is a problem then it would be nice to find out what it is and fix it. I know I have been having strange flameouts. But, my engine doesn't lean out. It richins the idle mixture. In my case, I feel it is my carb.
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Old 07-28-2011, 02:15 PM
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Originally Posted by Ben Burtle View Post
No worries... If there is a problem then it would be nice to find out what it is and fix it. I know I have been having strange flameouts. But, my engine doesn't lean out. It richins the idle mixture. In my case, I feel it is my carb.
your mixture richens towards the end of the tank? hmmm

lean your lsn a little more and richen the top a touch
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Old 07-28-2011, 02:31 PM
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Originally Posted by houston View Post
your mixture richens towards the end of the tank? hmmm

lean your lsn a little more and richen the top a touch
I'm switching out the metering needle to a different style. I don't think my new carbs are liking me. LOL
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Old 07-28-2011, 02:33 PM
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Originally Posted by Ben Burtle View Post
I'm switching out the metering needle to a different style. I don't think my new carbs are liking me. LOL
you refering to the "new" OS carb ?

i have heard that from more than you
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Old 07-28-2011, 02:38 PM
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Yes, I plan to go back to the 21J carb setup. The engine is remarkable though.
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Old 07-28-2011, 06:57 PM
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Originally Posted by Lonestar View Post
Howdy Y'all

What is the best way to mitigate that nasty effect we all know of and that creates material changes in our .21's tunes as the tank empties? You know the syndrom... to feel "right" for the last third of the tank, the mill has to be tuned a bit rich the first two thirds... tank after tank... perfectly repeatable (and not talking letting the mill cool between tanks, just refueling tank on tank on tank).

I was told it was a matter of pressure line volume as this is the only thing one can really think of that varies when the tank empties (more volume to fill => less pressure in there => pushing less juice in carb) but then again with a diameter of 1/10" it'd take meters of fuel line to "dilute" the tank emptying effect.

Are there any cool tricks you guys can share?

Thanks!
Paul
massimo fantini back pressure mod, had a mod he did onroad with a pressure line needle tune, i tried it a while ago but not long enough to try to race it or test tuning changes. i think that was his best option at the time and he swore by it.

found it, wow 2008:

http://www.rctech.net/forum/nitro-of...ssure-mod.html
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Old 07-28-2011, 07:05 PM
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Originally Posted by j_blaze14 View Post
massimo fantini back pressure mod, had a mod he did onroad with a pressure line needle tune, i tried it a while ago but not long enough to try to race it or test tuning changes. i think that was his best option at the time and he swore by it.

found it, wow 2008:

http://www.rctech.net/forum/nitro-of...ssure-mod.html
i saw that a while ago

http://www.jonehrc.com/2008/07/23/ba...the-euro-2008/
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Old 07-28-2011, 07:07 PM
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you beat me with the link^^^
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Old 07-28-2011, 08:14 PM
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I haven't heard the results, but some people have been using the Cline or Ironworks fuel regulators. Muffler pressure is used instead of crankcase pressure.

http://www.ironbaymodelcompany.com/i...es/Page438.htm
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Old 07-29-2011, 03:06 AM
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Originally Posted by Ambros303 View Post
The effect is caused by this:
Full tank = little volume to pressurize (just the pressure tube and the small space in the lid. As the tank empties the volume to pressurize gets bigger and bigger (pressure tube and a growing part of the tank) This causes a lower overall pressure (same pressure being applied from pipe but a bigger volume) = less fuel being pushed into the carb = leaner setting. Some tanks are better then others but even Kyosho has it to some extend when you pay attention. You can also see it by the temperature: when the tank is almost empty your engine temps will be higher. Fill it up again and temps go down a bit again.

Best way is to tune with a half full tank: a compromise between the 2 extremes (full/empty).
Thanks for describing it much better than me


Originally Posted by Ambros303 View Post
Best way is to tune with a half full tank: a compromise between the 2 extremes (full/empty).
Which is what I'm doing now... but for the sake of engine lifetime I'm tuning on to the empty tank

Paul
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Old 07-29-2011, 03:06 AM
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Originally Posted by houston View Post
I am thinking that the underside of the lid that allows the pressure into the tank is insufficient, possible remedy drill out orifice
Ooooh interesting. Will have a look. Thank you Sir for the valuable input, as usual.

Paul
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Old 07-29-2011, 04:01 AM
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Originally Posted by Ambros303 View Post
+1
That's also how a lot of people get fuel in their pressure line.
Overfill the tank, the lid has very little room inside which forces fuel into the fuel line when shutting the lid
If you do mod your fuel tank lid to take more volume, your tank will be bigger as to volume and you will be over 125ml and you get a penalty according to rules... So, this might cure your problem, but will get you out of the race :-(

Team Orion used to make a pressure regulator for the backpressure. You could adjust the pressure from the pipe, when the enigine wen`t to idle, you still had the high pressure in your tank. I liked the idea, bought one but never got aroaund to test it.

I have had experience with your problem before, but on the two times i have seen this, it is soemthing inside the high end needle blocking and opening the hole on the needleseat. This hacve happend at big races were my fueltank have been messured for volume. You can clearly see it when you take the high end needle out. It has a small silverline aroaund the needle, a scratch. flushed out with fuel and fixed the problem.
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Old 07-29-2011, 11:27 AM
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Originally Posted by am View Post
If you do mod your fuel tank lid to take more volume, your tank will be bigger as to volume and you will be over 125ml and you get a penalty according to rules... So, this might cure your problem, but will get you out of the race :-(

Team Orion used to make a pressure regulator for the backpressure. You could adjust the pressure from the pipe, when the enigine wen`t to idle, you still had the high pressure in your tank. I liked the idea, bought one but never got aroaund to test it.

I have had experience with your problem before, but on the two times i have seen this, it is soemthing inside the high end needle blocking and opening the hole on the needleseat. This hacve happend at big races were my fueltank have been messured for volume. You can clearly see it when you take the high end needle out. It has a small silverline aroaund the needle, a scratch. flushed out with fuel and fixed the problem.
I wasn't talking about modding the lid. More pointing out that overfilling your tank will force fuel up your fuel line, specially with tanks that have little space in the lid
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