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Old 02-03-2004, 05:24 PM   #1
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Default xxx-nt back pressure line

Hey guys I have a question. I have noticed that some top drivers do not run a back pressure line from the tank to pipe. They say it gives them more of a electric truck feel when getting on the gas. If anybody has done this or know what it does let me know. I have been racing electric on-road for a while now decided to get back in off-road with gas truck.
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Old 02-03-2004, 09:38 PM   #2
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I have tried it out and the fatory drivers I see at races alll use a pressure line but they might have tried running w/o one before, so I wouldn't go as far to say that they don't use them. It does make the engine smoother, you need to richen the main needle at least 1/4 turn but more like 1/2 or little more and bottom like 1/4 turn. I only ran it long enough to get it tuned good but would asume that it would get better fuel milage since it's just drawing in the fuel it needs and not being forced any excess fuel. One bad thing is that if the motor stalls you can't put finger on pipe to prime or force cool fuel into the engine to get it started again.
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Old 02-04-2004, 08:57 AM   #3
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Not a good idea, even if you richen your motor. You may not lose all your fuel draw, but it keeps it consistent with the backpressure in the tank. Thus, when the line is not hooked up, it leans out the motor badly. I was in a race once and had my pressure line come out of my pipe, and my truck down the straightaway was sick fast, and after inspection after the race, there was fuel everywhere and the line had come out. I temp. it, and it was near 300. It was scrary for me since i had just bumped up from that main and had to run again.
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Old 02-04-2004, 01:28 PM   #4
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Your motor leaned out and ran 300* b/c it was tuned for the use of a pressure line, not tuned w/o a pressure line functioning. You can tune the engine w/o a line on it and have it run good, with the line attached the engine loaded up more when in certain turns or sections of the track where w/o the line the engine held closer to it's tune and didn't bog when getting back on the power. So don't say not using a line is a bad idea when yours fell off. That's like saying don't try a different clutch setup b/c mine started to slip or something from spilt fuel. If oyu are going to try w/o a line just be sure to richen the needled up good to start and tune by ear more than temp b/c the at first the temp was the same as with a line but the engine sounded lean by ear until it was richened up enough.
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Old 02-04-2004, 03:38 PM   #5
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Thanks for the comments. Will try it tomorrow, All I need to do is tune the motor withoutthe line right?. And would it help to not let it run out of gas. Thanks
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Old 02-04-2004, 04:10 PM   #6
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I still do not recomend it. Even if you are an experienced motor tuner, what are the benefits of it? The motor is designed to be used with the back pressure line to feed fuel to the carb. If you can please tell me any good advantages of it i would like to hear.
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Old 02-04-2004, 05:45 PM   #7
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I only ran a few tanks through it w/o the line, it felt smoother more like an electric vehicle does compared to a gas car. Other than that I am not really sure if there is any mileage benefits as I didn't time each run wth and w/o the line, will have to wait until it's warm enough to run outside around here agin to try it again. You need to run a short piece of tubing from pressure fitting on pipe, like 1 inch long or so and stick a screw in it or use some sort of cap to plug it up. Then run another line from pressure fitting onto tank and the end of that line should be equal to the bottom of the tank or lower so that when you flip upside down fuel will not leak out, also keep the end of that in an area where dirt does not collect up. The motors are not designed to run with pressure lines forcing fuel into the engines, just like they are not all designed to run on the same brand fuel, plugs, weather conditions etc.., that's why there are needled on the carbs for you to adjust. Running w/o a pressure line is just something different that might work great for some people while others might not like it one bit, it's just part of an overall setup that some people might choose to keep the same as everyone else or they might want to be different from the rest of the herd and run w/o a line.

The person was asking what it did from people that have tried it and other things about it, I am just telling him some things I noticed when I tried it out and nothing more since I don't feel that it's a bad thing to run w/o the line as long that you richen the motor up plenty. Where when you "tried" running w/o the line it was b/c it fel off of your car during one of your runs, then you assume that there is nothing good about running w/o a line b/c your motor got super lean b/c it was tuned for the use of a pressure line.
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Old 02-05-2004, 11:02 AM   #8
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Ok i do know that it leaned out because the engine was tuned with the pressure line in place, and when that line is not pressurizing the tank, the motor isnt getting as much fuel with those settings. So to get the same effect without the pressure line you must richen up the motor. So in fact you are using more fuel when not using a pressure line it seems... but when the line is hooked back up it is pulling more fuel, and when you take the line off it pulls less fuel and you have to richen it... so it is pretty much the same infact. And you say it smooths out the power band much like an electric... ill have to try that, much easier to drive an electric truck than a nitro. Thanks for the reply, ill look into it, i just could not see a reason at the start of why you would want to do this, but if it smooths out the power delivery it may be worth it, just have to keep an eye on the motor and run time.
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Old 02-05-2004, 02:02 PM   #9
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I'm pretty sure that the engine also ran more consistent throughout the tank also where with a line it richens up a little when you fill it off then leans out some towards the bottom of the tank. Think of this, if you have a firehose with the pointy nozzle on it that has the water under pressure and then another hose with an opening equal to the diameter of the hose but the water only comes out under it's own pressure which would more water come out of over the other? With the pressure line the engine is running and there is always pressure from the pipe being exerted into the tank which forces fuel into the engine whether it needs it or will burn it or not. Without the line the engine only draws in how much fuel it needs due to the physics of how our rotray induction 2-stroke engines are.
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Old 02-05-2004, 03:41 PM   #10
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Thanks a bunch guys. Didn't mean to start a argument but it seems to have calmed down. I see the diff in the water hose deal being i am a pipefitter I see alot of thing under pressure and no pressure. So I beleive it will be ok. Also I ask this question because all I have raced is electric so now with gas it's taken a while to get used to it. And again thanks for the comments.
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Old 02-05-2004, 10:19 PM   #11
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If you're new to gas then I wouldn't mess with this, especially if you're not racing as for just bashing around the house then as long as it runs good is all that you need. if you still want to try it out at least now you know some of it's effects or things about it.
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Old 02-06-2004, 11:02 PM   #12
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Dont know who said it but running w/o the pressure you have to fatten it up if you do that you will be losing fuel milage.Just my .02 Losi and the motor manufactuer designed it that way,that means it works best that way.If you want a smoother feel try tuning the motor to the way you want it to feel.You can move the pipe fowards and backwards to change the powerband.You can fatten the bottom for a smoother feel on bottom,or lean it a little for more crisp throttle.I could go on forever,its all about time and experience w/a nitro motor...
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Old 02-07-2004, 01:53 PM   #13
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Ohhh man, I already explained the reasons why your mileage will stay the same or be better w/o the line even though you have to tune your needles richer.
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