need help jetting

[pinit]

I have a 03 800 polaris motor put a slp single pipe on it., I went to kickass filters and it seems to be running pig rich with 350 main jets at 6500-8000 feet. I called slp they told me that when I removed the air box and removed the two hoses that run from the carbs to the air box is what caused it to go way rich. Slp told me that those two lines aply vacume to the float bowls and with out the vacume it goes rich. I'm clear down to 300 mail jets with the needle on the leanest possision and still not seeing anything over 1150 degrees at wot. So has anyone been down the same road any input would be great Rodger

 

[sled_guy]

Put the airbox back on it and throw those filters away.

The Polaris twin does not like drawing warm/hot air from under the hood. SLP's explaination isn't exactly right but the theory is there. You are pulling warm, likely very warm, air into the filters. That warm air causes the motor to run really rich... right up until it doesn't and then you squeak it.

Put the airbox back on and draw fresh cool air from outside the hood... and yes, plug the lines back into the air box. Then the 350s will be about right for 7k feet.

sled_guy

 

[NoSecondChances]

I have a 03 800 polaris motor put a slp single pipe on it., I went to kickass filters and it seems to be running pig rich with 350 main jets at 6500-8000 feet. I called slp they told me that when I removed the air box and removed the two hoses that run from the carbs to the air box is what caused it to go way rich. Slp told me that those two lines aply vacume to the float bowls and with out the vacume it goes rich. I'm clear down to 300 mail jets with the needle on the leanest possision and still not seeing anything over 1150 degrees at wot. So has anyone been down the same road any input would be great Rodger

Been there, done that. You're venting to atmosphere so you're vacuum from the airbox is gone, atmo pressure is pushing fuel up the tubes (blow lightly into one of your vent lines and watch the fuel puddle up in the throat of your carb - similar theory). Without the negative pressure on your vents, more pressure is facilitating the fuel to flow up easier. refer to this thread.
http://www.snowest.com/forum/showthread.php?t=56878&highlight=Carb+venting

A real easy test for this to see if you are sucking hot air or its the venting: Put the stock airbox back on, but leave the vent lines unhooked. If it runs fat like it is, its the venting. If it runs lean and you need to re-jet up, its the hot air. I did this on my sled and no change with the airbox on or off and the vent lines unhooked. It might be different on yours. I'd jet up to what you think is safe and then stick the box on, if its OK or really fat still, then drop back down. If you get back down to 300's and everything looks the same as it did without the box, then its the venting. This will tell you if its hot air or venting. Often people think that they can throw pods on and not do anything, but they do require some tuning. I added stacks to mine to speed up air velocity and get the filters up into the cold air stream. If necessary, I can drill a hole in the stack and plug my vent line into it to gain the low pressure back, but would then have to jet up again. Send me a PM if you need more info. Good luck.

P.S. don't only jet by EGT temps. Use plugs and wash, then correlate that temp to what you see in the motor. EGT is only really a reference point, its not indicative of where your motor is really at. I run at about 1150 average, 1220 max.

 

[pinit]

I would love to put the air box back on but it won't fit in my cmx chassie. I looked at the wash with 350 mains in about 1/2 -3/4 inch of wash and was even trying to wash the top of the piston off towards the exhaust. After looking at the wash that is when I decided to get serius with jetting down. Have not checked wash after going to 300 mains but plugs look great. Before jetting down I even took the hood and podsoff took a run and did no help any. I'm pretty confident that it is due to the vent tubes but have not ran in to this problem berfore so I thought I would ask thanks for that help

 

[Scott]

Where do you get that steel tubing?

 

[NoSecondChances]

Where do you get that steel tubing?

Not steel, aluminum (even better ). You can thank the Yamaha guys for that, its turbo intake tubing, super light and works good. I bought 2 - 90 degree elbows and cut the length to fit my chassis. The red stuff is the silicon connector (I used one and cut it in half).

http://vibrantperformance.com/catal..._1036&osCsid=b14e2afa504ff8cd7984d0339339b452

I ordered it through a local automotive performance dealer here in Calgary(Unlimited Performance) but you should be able to get it a bunch of places since it is pretty common.

 

[Snoman69]

Thanks for the link NoSecond..... I have been pondering on what to use for that... I have been in a debate whether to modify the airbox, or run socks.... That looks like a slick setup...