Calling Fuel Carb Experts... - Snowmobile World : Your #1 Snowmobile Forum

Plamb · 01-07-2007, 10:03 PM

Since there is no snow... I have too much time to sit around and think about my sled. One problem I haven't been able to lick yet is a couple strange issues with my carbs. There is a little bit of a rich bog in the low to mid rpms... especially when the sled isn't fully warm or when the air temps are high. I changed from 420 mains to 410s, and that has helped but not eliminated the problem. Others on this site have been running 400s or even 390s with good luck, so I can always go a little further, but I don't want to overdo it because we do get some awfully cold temps here now and again and I don't want to be too lean for thos conditions. Another idea is to go down an e-clip position, or to mess with the air screws. I'm not sure I want to go there just yet, but I will if that is the right step. Also, my sled doesn't like to start when cold unless I choke it and feather the throttle a bit, which suggests that i'm lean at idle, right? If this is the case and I am lean at idle but rich in the middle, going down to 400 mains is probably the right step?

Also - could this be an oiling issue? How do i test to see if it is? Is there any benefit to bypassing the oil system and going to premix, besides losing a couple pounds? Are there any risks?

nhsledfreak · 01-08-2007, 12:38 AM

Quote:

Since there is no snow... I have too much time to sit around and think about my sled. One problem I haven't been able to lick yet is a couple strange issues with my carbs. There is a little bit of a rich bog in the low to mid rpms... especially when the sled isn't fully warm or when the air temps are high. I changed from 420 mains to 410s, and that has helped but not eliminated the problem. Others on this site have been running 400s or even 390s with good luck, so I can always go a little further, but I don't want to overdo it because we do get some awfully cold temps here now and again and I don't want to be too lean for thos conditions. Another idea is to go down an e-clip position, or to mess with the air screws. I'm not sure I want to go there just yet, but I will if that is the right step. Also, my sled doesn't like to start when cold unless I choke it and feather the throttle a bit, which suggests that i'm lean at idle, right? If this is the case and I am lean at idle but rich in the middle, going down to 400 mains is probably the right step?

Also - could this be an oiling issue? How do i test to see if it is? Is there any benefit to bypassing the oil system and going to premix, besides losing a couple pounds? Are there any risks?[/b]

Well first in my opinion stay with the oil injection bud. premix is a pain especially at the pumps. Now one thing to remember is the main jets are doing the work from 1/4 throttle up through to full. so I suggest you raise the e-clip 1 notch, this will smooth out your mid range over fueling. And 400's should be fine just run it fairly hard for a little ways then shut it right down and read the plug color. Paper bag brown is where you would like to be. Having to feather the throttle to start may very well mean over fuel not lean at all. Also be ready for idle changes on these adjustments. lean settings higher idle, I always set park break. Evey new Polaris sled I have owned has always been set up rich from factory for break in and warranty concerns.
A rich running engine will foul plugs not melt pistons '-) I set my buddies HO up and it pulls hard all the way through and we have 390's in her. They are a rocket once dialed in. And fly awesome.(in the air) Lol :hallo1:

tifa_5_2000 · 01-08-2007, 08:26 AM

theres no point in tuning your sled on the stand. wait till snow and see what it does.

nhsledfreak · 01-08-2007, 09:54 AM

Quote:

theres no point in tuning your sled on the stand. wait till snow and see what it does.[/b]

Not to totally disagree but tuning your sled on the stand is where you really should start. Final tuning comes with snow agreed then you get the load requirements. Honestly if we didn't tune on the stand we would never even place at the races we enter.

If you already have an issue and no where the iisue lies and what may be causing it then stand tuning is a proper approach to getting a start on it. SWRules

Plamb · 01-08-2007, 10:46 AM

NH did the HO you set up have the same bog as mine does? Did you change the clips on that one or just go down on the mains?

SnoFast · 01-08-2007, 10:52 AM

OK, a couple more points to consider, probasbly ones you already know, but just a reminder. All carbed sleds run rich in warm temps, ever ride in 40 degrees or warmer, burble city, or course you could jet to that temp, but why. It should run Ok with 410's, but not at 40 degrees. Would 400's work better, maybe, wait till the snow flys. A hard starting sled is ususally be a victim of clogged pilot jets, Most of the time I can get 2 years out of a new sled, before the carbs come off for a jet inspection, maybe your not so lucky and only got 1 year. Next, moving the main needle up or down is 1, easy to do, and 2, it's definitely fine tuning, so I might play around there first. One more point , and one that I will stress strongly, make only one adjustment at a time, ride it, read the plugs, determine if the change was for the good or bad, if good, then think about the 2nd change. If you change the mains, lower the needle, and adjust your air screws all at once, and now it runs worse, what caused the problem? By the way, I have never had a carbed sled or 2 stroke dirt bike that didn't burp and snort till it warmed up a little, well maybe a couple mildly tuned ones didn't, like my kids 340 Sport , of course that is a problem EFI sleds should not have. Maybe next year I'll have one.

Plamb · 01-08-2007, 11:03 AM

Thanks SnoFast

If the pilots are plugged, do you try to clean them or just replace? Where are the pilots on Mikuni carbs? I haven't worked on Mikunis much. Are they under the top cover?

nhsledfreak · 01-08-2007, 11:09 AM

Quote:

NH did the HO you set up have the same bog as mine does? Did you change the clips on that one or just go down on the mains?[/b]

We did both dropped the main jets and raised the e-clips. Sled had a terrible mid range bog unless it was -40 which we do get here but only for a week or so. And I totally agree with Snofast. Carburated machines will always have these issues. mechanical metering is far from flawless. EFI is nice but I like to dial my machines in.

Needle e-clips have alot to do with mid range that is what they are there for. I also suggest the same one adjustment at a time. then you know what made it better or worse and can go back if needed.

trx450r · 01-08-2007, 11:19 AM

It sounds like you could play with your fuel/airscrews a little to get better response.

The factories have been sending out the carbed sleds pretty lean on the pilot jet for the last 8 years or so.

Keep in mind that it takes awhile to build heat in your pipe. My ZR is a dog for around 5 miles or so until the pipe gets good and hot. Snofast also brought this up.

All the jets (except the needle) are located in the float bowl.

Plamb · 01-08-2007, 12:27 PM

Yes I'm only going to do it one thing at a time. First thing I did was go from 420s to 410s and that made it somewhat better - I rode it a hundred miles this way. I'm trying to decide what the next step is - change clips, change jets, or play with air screws. I think I'm going to change clips next and see how that goes.