Carb Tuning the Frankensled

[440Longtrack]

Hello I was hoping to get a couple of recommendations for tuning a single carbed snowmobile.

The platform is an 88 polaris 440 longtrack that is bored .060 over. I have plenty experience tuning carbs to factory engine/specs but because this is bored oversize I would like to make sure I am not creating a lean mixture.

It was probably more than what its worth to buy pistons and get the jugs machined but its main use will be a nice light sled for the gf to screw around on and for an ice fishing sled. I haven't spent more than a couple of hours trying to adjust this after top end done because it was at the end of the season and nearing the -5 C mark.

While holding the throttle wide open it will start after a few pulls and doesn't need help to keep running but after finishing the work last winter and testing it around the property it seems to loose a bit of power on the top end and after warming up it will slowly die out and is very tough to get running again.

I haven't done crank seals because the brake clean spray on crank seal areas while running doesn't create any change and my plan is to order a fuel pump/rebuild kit because that has never been done yet. Carb has been cleaned out and there are no blockages, float sticks open sometimes so I am going to replace needle and seat since cleaning only improved that slightly, new plugs and new top end gaskets including intake flange, no rip in carb to intake manifold rubber. Unsure of current needle and jet numbers and I have tried different needle clip positions and it didn't seem to make much of a difference.

I did the to end because the compression was 50psi in each cyl and took about 20 min to start when I got it, now its starting very easy in comparison but could still use some fine tuning that I have only experience with stock engines. Cylinders were machined as per spec to each cylinder, Pistons both facing the proper directions (as per arrows on top) and they were the single ring type. It is currently running on 50:1 premixed gas as the last owner deleted injection system. I am used to 50:1 on everything I have so I can't say if this is too much.

Thanks for any opinions, It has been parked for summer but would like to start with a potential "base point" for when it gets colder

Thanks, that's about as much detail as I can include for any potential assistance

 

[racerdave]

Truthfully I would not worry about rejetting if it has the the original/correct jets it came with for the temp you ride in.. It was more than likely too rich to begin with. Make sure your fuel is fresh, fuel pump working correctly,clean tank lines etc. Fresh plugs. Correct belt, preferably new. Fresh clutch springs, etc. I would go to 40-1.