Backfiring and No power...... - Snowmobile Forum

theword · #1 (**permalink**) 10-20-2007, 12:18 PM

I have a 1996 polaris ultra 680. I have cleaned out the carbs and all plugs and wires are new. I have adjusted the carbs to the way that I was told by someone that I really didnt trust. I was loading my snowmobile last night and the throtle responce was good from 1900 rpms to 4000 rps. Than anything over that it would back fire and then bogg down. I have a fealing that it is to rich. It runs really good at low idel and starts on a half of a pull or a flick of the starter. I was wondering if I should take it a little leaner. Now there is two screws on the carbs. One is a small one close to the front of the carbs. The second one that is on the carbs is the big one on the side. I think that the big one is the lean or rich one and I should turn it in about a 3/4 of a turn. If anyone can help me on this please help! I will be making sure that the spark plugs are good as well since the backfiring.

OCR · #2 (**permalink**) 10-22-2007, 09:49 AM

backfiring is an indication that the carbs are too lean.
The big screw on the side is the idle speed adjust (the one with the knurles on it).
The air screw is the smaller one and it should be 3/4 to 1 tul turn out from gently ottomed to start with.

theword · #3 (**permalink**) 10-22-2007, 02:23 PM

Thanks for the information on the carbs.

VOHK · #4 (**permalink**) 10-22-2007, 09:20 PM

Many of those were equipped with an idle mixture screw also, generally close to the spigot side, these are typically set at 1-1 1/2 turns out from lightly seated. The backfiring is most likely caused by a lean condition, often caused by an ubstruction due to long periods of non use. Make certain the carbs are clean and every orrifice allows flow. The pilot jets are the likely culprit, check the emulsification circuit the feeds them also.

theword · #5 (**permalink**) 10-22-2007, 10:26 PM

Thanks guys I have found the mix on the screw. No I have found that I have to rehone the juggs. I found that after it was running right there was alot of oil comming out of the exhaust. So now I am going to rebuild the motor.

Just my luck with snowmobiles! I just can't get away from them! Well thanks Guys again!

OCR · #6 (**permalink**) 10-24-2007, 12:11 PM

You should run it long enough to get the pipes up to operation temp, then the excess oil will stop.

theword · #7 (**permalink**) 10-24-2007, 03:04 PM

Thanks I will try it and see if it stops. I did look at the side and top of the pistons and they looked newer. I also called around and asked a local polaris dealer that I know the owner at and he said that he can rebiuld the motor and bore out the cyclinders 50 thousans over. All new Wiseco pistons and bearings for around $450. My dad had his rxl 650 done by him and his sled seemed to gain about 20 hp. I am thinking that the price and parts are a good deal. What do you think?

VOHK · #8 (**permalink**) 10-29-2007, 03:21 PM

You probably will quantify a power gain though I doubt 20hp. I am not a fan of forged pistons due to there thermal size differentials requiring greater clearances but each to there own.

theword · #9 (**permalink**) 10-30-2007, 01:00 PM

I found out that the cyclinder walls are coated with Nikasil. So I have my motor back together and now that I have done that the smoking has almost stopped. I told them at chopper city sports that the snowmobile was an older mans. They said that he may have fogged the motor really well and that the motor will smoke for about 25 miles or so. They told me to try that and see. Well good wast of time but now that I know that the motor is biult really well and that there are new seals I can hope that there will not be any thing wrong this season. Thanks for all of the help from everyone!