ILLYamaRider
New member
I have had this ViperER for over 10 years, and when I first got it I used to get around 15mpg. The last few years I have struggled to get to 10mpg riding trails up north. This years trips to the Northwoods I only got 9mpg (if that) riding on the trails. I am looking for suggestions on why my fuel economy has changed over the years without me changing anything on the sled. The sled still rides well and seems to have plenty of power, just awful fuel economy. I would consider myself a relatively aggressive rider. I also always put the 91 octane fuel without ethanol in since I think it stores and runs better. I seem to get this poor economy no matter the ambient temperature (rode in the mid 20s and below zero and still got only 9mpg). I do struggle with idle hang, but not sure if that would be enough to make it this bad. I can't seem to get the idle hang to go away. My specs are below for everything I could check so far:
Main Jets: 156.3 (Stock)
Pilot Jets: 45 (Stock)
Needle Clip Postion: 3.5 (4th postion with spacers on top) Per Mr. Viper (changed to this just this season, but I was getting poor mpg before this, previously stock 3 setting)
Fuel Screws: 2 turns out (per Mr. Viper) (changed to this just this season, but I was getting poor mpg before this, previously stock 1 7/8 setting)
Spark Plugs: NGK BR9EIX Iridium Plugs
Compression Test from 02/26/2017: Clutch end first (110psi, 125psi, 130psi) Tested with cold engine about 65F
Clutching: Heelclicker kit on the primary, with stock secondary
Track: Factory 1 inch Camoplast Track, no studs
Miles: 7300miles on the sled
Factory Airbox Intake
I weight about 220lbs with all my snow gear on.
Carbides: Woody's Doolies
Other Notes: Clean my power valves every year. Adjust the power valves gap with allen wrenches per instructions on here. Recently rebuilt all of the rear skid and replaced all of the wheel bearings. Replaced the sealed bearings on the jack shaft next the secondary, and the bearing next to the speedo gear.
I guess I am wondering if it is just time to refresh the old girl and do the top end with some new rings in hopes that would improve the fuel economy? Maybe a new set of factory reeds? I am not expecting to get back to 15mpg, but 13 or maybe 14 would be nice. Maybe I need to get find a leak down testor instead of just compression to really get it all checked out? I guess I just don't understand why it would have gone down and need some smaller jetting without changing anything on the sled. Any suggestions would be great. Thanks.
Main Jets: 156.3 (Stock)
Pilot Jets: 45 (Stock)
Needle Clip Postion: 3.5 (4th postion with spacers on top) Per Mr. Viper (changed to this just this season, but I was getting poor mpg before this, previously stock 3 setting)
Fuel Screws: 2 turns out (per Mr. Viper) (changed to this just this season, but I was getting poor mpg before this, previously stock 1 7/8 setting)
Spark Plugs: NGK BR9EIX Iridium Plugs
Compression Test from 02/26/2017: Clutch end first (110psi, 125psi, 130psi) Tested with cold engine about 65F
Clutching: Heelclicker kit on the primary, with stock secondary
Track: Factory 1 inch Camoplast Track, no studs
Miles: 7300miles on the sled
Factory Airbox Intake
I weight about 220lbs with all my snow gear on.
Carbides: Woody's Doolies
Other Notes: Clean my power valves every year. Adjust the power valves gap with allen wrenches per instructions on here. Recently rebuilt all of the rear skid and replaced all of the wheel bearings. Replaced the sealed bearings on the jack shaft next the secondary, and the bearing next to the speedo gear.
I guess I am wondering if it is just time to refresh the old girl and do the top end with some new rings in hopes that would improve the fuel economy? Maybe a new set of factory reeds? I am not expecting to get back to 15mpg, but 13 or maybe 14 would be nice. Maybe I need to get find a leak down testor instead of just compression to really get it all checked out? I guess I just don't understand why it would have gone down and need some smaller jetting without changing anything on the sled. Any suggestions would be great. Thanks.
Last edited:
Aggresive clutching will lower mpg, check reeds.
ILLYamaRider
New member
I used to get 14 or 15 with the heel clicker clutch kit that is still on the sled. Any chance something with that changed over time? I check it for flat spots, etc. But never re built it.
Sent from my SM-G930V using Tapatalk
Sent from my SM-G930V using Tapatalk
Some possible culprits include carb float needles not closing, starter circuits not closing, bad reed valves, dirty exhaust valves, plugged exhaust and the efficiency of the clutches.
Overstating the obvious, but either you are not making the power you used to, or something is robbing it. It can be one or more of a number of things.
Just start at the top and go all the way through it. Don't assume anything is good but verify again instead. You should find it. From intake and exhaust all the way through the engine, clutches, shafts, gears and chain, track, several bearings along the way, and the sliders.
Overstating the obvious, but either you are not making the power you used to, or something is robbing it. It can be one or more of a number of things.
Just start at the top and go all the way through it. Don't assume anything is good but verify again instead. You should find it. From intake and exhaust all the way through the engine, clutches, shafts, gears and chain, track, several bearings along the way, and the sliders.
R/t Performance
New member
I bought a 2002 viper with 6000 miles this spring and am struggling to get 100 miles out of a tank.
My buddy who owned a few of these sleds want me to move the clips back down but the sled runs and pull great. stock jets, clutch aftermarket can. Cleaned carbs/power valves and clips are 3.5 or 4
I do have a 1 1/4 rip saw track. I am thinking maybe it is reed issue. I
have smelt gas a few times after riding and was going to take a look for a fuel leak. But it the reeds leak it would blow gas into the air box. I also seen another post about reeds cracking around 7k mark
My buddy who owned a few of these sleds want me to move the clips back down but the sled runs and pull great. stock jets, clutch aftermarket can. Cleaned carbs/power valves and clips are 3.5 or 4
I do have a 1 1/4 rip saw track. I am thinking maybe it is reed issue. I
have smelt gas a few times after riding and was going to take a look for a fuel leak. But it the reeds leak it would blow gas into the air box. I also seen another post about reeds cracking around 7k mark
ILLYamaRider
New member
Next year I am going to throw a set of reeds on it, new needles, and double check my floats. Hopefully there will be some improvement.
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Sent from my SM-G930V using Tapatalk
R/t Performance
New member
Decide to go with Boysen power reeds.. apparently they bought carbon tech I emailed there tech and took days to get a response from boysen. planning to go to D U.P this weekend hopefully it will still have good power and better mpg.
Reeds where plastic and looked perfectly fine to me.( I am a auto mechanic but have limited two stroke experience)
Reeds where plastic and looked perfectly fine to me.( I am a auto mechanic but have limited two stroke experience)
hereismylife
Active member
Also check to make sure your manifold is not cracked. Make sure you check the underside with a mirror. They start as hairline cracks.