HEllo I just put bender pipes on my sled and I have been reading about venting the carbs to the atmosphere. I just have a few questions about it. IS It a good thing to do? Does is make it more reliable? DOes it get me better fuel mileage? ANy power loss? ANd what would I need my jetting to be right now I have it set at 165 mains across the board, 55 pilots 1 7/8 fuel screw and stock needles. THat is with the lines vented to the airbox. I have bender pipes peak performance head with 22cc domes.
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Venting to armosphere richens it up.
Agpetro
Member
Are you talking about the air box mod?
I am talking about the vent lines from the carbs .
snopax said:
I understand that it richens it up. BUt what I wanna know is what are the pros and cons in venting to the atmosphere vs venting to the airbox.
ANyone have any answers?
Macheater
New member
Venting to the atmosphere results in LESS consistent jetting. The reason being as the sled speed increases the underhood air is pressurised resulting in richer jetting. The faster you go the more pressure, hence the richer mixture. Couple things to think about. How much underhood pressure are you building and how MUCH is the mixture being enrichened. While it is possible to measure these things, it usually isn't practical, especially for a trail rider. So, again the big question remains how much richer is it going. On a two-stroke which may be on the edge jetting wise, this isn't necessarily a bad thing. Especially on a long run, the extra fuel can help cool those very hot pistons. Where it generally comes into play is the guy who's looking for that last little bit of performance. Either for the competitive rider/racer or the guy who just wants to outrun his buddy. So the drawback is potentially less power at high-speed do to a richer than ideal mixture.
On a setup that is vented to the airbox, the vent lines "see" the same pressure as the carb intake and there is not the enrichening effect at high-speed. The mixture is more consistent since it is NOT pressurized (enrichened)as the sled speed increases. Again, the tradeoff here is that if your on the edge jetting wise you do not have the extra margin of safety. Conversely, if you are jetted perfect, then in theory you should not lose any power due to mixture variations. The manufacturers would rather play it safe and have there machines run a little on the rich side as opposed to a meltdown and warranty claims. This is the main reason that most sleds have atmosphere venting from the factory.
For the average trail rider the difference may not be enough to alter the setup and take a chance on 'rolling the dice'. For the guy who wants that last few horsepower it may be worth doing some testing to find out if there is additional performance still on the table.
On a setup that is vented to the airbox, the vent lines "see" the same pressure as the carb intake and there is not the enrichening effect at high-speed. The mixture is more consistent since it is NOT pressurized (enrichened)as the sled speed increases. Again, the tradeoff here is that if your on the edge jetting wise you do not have the extra margin of safety. Conversely, if you are jetted perfect, then in theory you should not lose any power due to mixture variations. The manufacturers would rather play it safe and have there machines run a little on the rich side as opposed to a meltdown and warranty claims. This is the main reason that most sleds have atmosphere venting from the factory.
For the average trail rider the difference may not be enough to alter the setup and take a chance on 'rolling the dice'. For the guy who wants that last few horsepower it may be worth doing some testing to find out if there is additional performance still on the table.
Mac
Member
Jet to atmosphere. Control the jetting yourself.
http://www.totallyamaha.net/forums/showthread.php?t=56193&page=1&pp=10
http://www.totallyamaha.net/forums/showthread.php?t=56193&page=1&pp=10
I can not believe after 10 years, this is still a topic. It doesn't matter as long as your jetting is correct. If you increase your under hood air pressure, you are also increasing under hood air intake pressure. Where it becomes an issue is when your venting to a place that is not seeing similar pressures, like, cold air intakes. They are safer when vented to the box. As for fuel mileage, there is going to be no mileage change if both versions are jetted correctly. You will use smaller mains for out of the box venting but you will have less turbulent(higher pressure) air pushing fuel through them. Those sleds get crappy mileage because of the advanced timing compared to an srx. This causes excessive heat on the top of the piston, not in the pipe like the srx. This makes great power but creates heat issues no amount of good cooling head or extra heat exchanger can get rid of. Remember, the head only removes heat from the motor, not the piston, the piston is the other side of the combustion chamber. No, on a motor with viper timing, your removing that heat with 4$ a gallon liquid, washing the piston with fuel and/or, depending on pipe, running the motor at an rpm where the timing retards a few degrees, that creates two other problems.
First, your still washing the piston in unburned fuel but now your running your crank and clutch at higher rpms so it will not last as long as if you ran it normal, simple mechanics. Second, if your jetted for 9000rpms and you hold it there for a long run, get those pistons good and hot, everything working perfect, never going to blow up, 120mph down the lake, perfect, even got a little wood, now you let out of it a bit and it burns down because as the motor falls down through the mid 8000rpms, the timing is advancing when it should have been retarding causing even more heat on the pistons. Over the last 10 years of dealing with vipers and watching this board, this seems to be the prevailing story of what caused the burn down, that and two others. Trying to squeeze more fuel mileage out of it or clutching is off and run the sleds at too low an rpm, as in where the timing is fully advanced. There is one other way you burn down several pistons in a year, don't pay attention to what cdi box you left in your sled. Now that guy was a dummy.
First, your still washing the piston in unburned fuel but now your running your crank and clutch at higher rpms so it will not last as long as if you ran it normal, simple mechanics. Second, if your jetted for 9000rpms and you hold it there for a long run, get those pistons good and hot, everything working perfect, never going to blow up, 120mph down the lake, perfect, even got a little wood, now you let out of it a bit and it burns down because as the motor falls down through the mid 8000rpms, the timing is advancing when it should have been retarding causing even more heat on the pistons. Over the last 10 years of dealing with vipers and watching this board, this seems to be the prevailing story of what caused the burn down, that and two others. Trying to squeeze more fuel mileage out of it or clutching is off and run the sleds at too low an rpm, as in where the timing is fully advanced. There is one other way you burn down several pistons in a year, don't pay attention to what cdi box you left in your sled. Now that guy was a dummy.