SLP piped Viper mileage trouble

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bigreis

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SLP piped Viper issues/complaints

I was finally able to get out and put some decent miles on with my newly piped Viper (SLP's) yesterday. I was honestly pretty disappointed with the performance. Other than being a little louder (which I don't consider an improvement), I really didn't notice any significant improvement in performance over the other stock Viper I was riding with. I am hoping that someone will be able to let me know what I need to do to get it dialed in to be able to experience the "arm stretching" acceleration I have read about in so many other threads. Here are my observations over the 230 mile ride yesterday:

1. Fuel economy was a nightmare. I expected to lose a few mpg with the pipes, but I didn't think that I would run out of gas on the trail 61.8 miles into the ride (and yes, it was full when we left). 5 mpg for moderately aggressive trail riding is nuts in my opinion. Fortunately I had a siphon and was able to steal a few gallons from my buddy's Viper to get me to the gas station. I spent a little over $150 in gas on ride... I hope the wife doesn't read this!

2. The plugs didn't indicate an excessively rich condition (slight tan color on electrodes), but I did notice a significant amount of raw fuel spray in the airbox. It was pretty wet under the airbox all day. I did verify that none of the carbs or fuel lines were leaking. I haven't noticed excessive fuel in the airbox prior to installing the pipes, so perhaps it was running richer than the plugs led me to believe.

3. Midrange throttle response was a little boggy, so I dropped the needles a half step (went from 4 to 3.5) about halfway into the ride. That cleaned up the midrange a little, but didn't change the fuel economy at all.

4. Top speed was about 8 mph faster than before I had the pipes. I have a 136" M-10 and before the pipes the best I could get was 98 on the speedo. I hit 106 in a long pull. It is overreving... 9100 rpm. Nonetheless, I would have expected having another 25 or so horsepower to give a higher top speed. I was only a sled length or two infront of the stock Viper over after about a 1/4 mile, then he started to pull away (he said his speedo was showing 117 when he declared victory).

So obviously something is not correct. I am currently jetted according to SLP's recommendations for -20F @ 0 - 3000 ft (165 main, 47.5 pilot, 4th needle position, fuel screws 1-3/4) Yesterday it was in the low 20's, so technically it should have been running a little rich. Could that have been enough to cause such awful mileage? I find it hard to believe that I was running crazy rich based on the way the plugs looked. I have an ATACC that I will be installing before I go for another ride.

So here are a few questions that I have:

1. Is the "excessive" amount of fuel in the airbox a sign of an overly rich condition, or is that normal for a piped sled?

2. What changes in mileage have you guys noticed with the addition of an ATACC?

3. Can not being clutched properly (overrev condition) be a large contributor to my poor mileage?

4. I currently have two 13.9 mm steel rivets in 8EK's with stock springs. To bring the RPM down from 9100 to 8900, should I put a 17.2 mm rivet in both holes, or just the inner or outer?

5. When properly setup, should the difference between my sled and a stock Viper honestly be "night and day?"

Thanks for taking the time to read all of this and I look forward to getting some help with this.
 
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Well Yes your mileage will go down, but not to the number you are experiencing. I have a 136" hartman kit, 1.25" ripsaw, w/ 162 1.340" roetins in my piped '02 Viper, and I am currently experiencing 8.5 mpg on average. Tonight I went 61miles and it took 7.0gallons. I am running 8tooth drivers and a corrected gear ratio of 1.78. I am running 167.5 mains, 47.5 pilots @ 1 7/8 turn on air screw and the needle is set at 4. I am running less than 3000' more like 800-1800'. I have 8DN20's weighing at apprx. 51gr(can't remember), w/ a Trail Port from Mr.Viper(Don Pizor). Peak Performance Head, SLP's triples. Couldn't be happier w/ the setup out of the '02. Definately quicker than stock Viper. Running around 87-8800rpms.
 
Got Bender pipes get about 5mpg sometimes less depends on how soft and deep the snow is. Have way more power and speed then other stock vipers i ride with. Don't have any trouble beating them.
 
It is your clutching, I had the same problem with my Viper after I modded it, start throwing some more weight on the clutch weights and it will make a big difference. i went from 'so-so' to 'holy cow!' with a bit more weight in my clutch, and it improved fuel mileage for me too (still dropped some from stock Viper mileage, but not down to 5mpg)
 
You gotta run those pipes at 87-8900 rpm. They will cut your mileage by 1/2 plus u gotta run premium to boot.
 
WNYViper said:
It is your clutching, I had the same problem with my Viper after I modded it, start throwing some more weight on the clutch weights and it will make a big difference. i went from 'so-so' to 'holy cow!' with a bit more weight in my clutch, and it improved fuel mileage for me too (still dropped some from stock Viper mileage, but not down to 5mpg)
Click to expand...

adding clutch weight loads the motor harder & will decrease fuel mileage!!!
bob
 
Really can't help you with your problems, but if you decide pipes are not something for you, I'd be interested.....I know they work great in the MTNs....
 
Thanks for the replies everyone. I am just having a really hard time wrapping my brain around why there is such a huge difference in mpg people are seeing with pipes. There must be a very small "sweet spot" to hit with clutching and jetting in order to get to the 8 mpg range.

I completely understand that overloading or lugging an engine will destroy its efficiency, but I would think that the same would be true by overrevving it by not loading it enough. In a car or motorcycle, if you take off in 3rd gear all of the time and then upshift too fast, you are going get really bad mileage and performance. To me, this is the extreme of loading the engine too much. On the opposite extreme, if you run down the highway in 3rd gear, your mileage is also going to be crap... not to mention being really hard on the engine. So if a snowmobile transmission works on the same principal, then in an overrev condition I would think that the engine is running fast but not doing the work it is capable of at that given amount of fuel.

So my question to the guys that know more about this than I do: does adding more weight to the primary ALWAYS, ALWAYS, ALWAYS decrease mileage, even if you are currently in an overreving setup?
 
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bufalobob said:
adding clutch weight loads the motor harder & will decrease fuel mileage!!!
bob
Click to expand...

Right, but I was over-revving so much and it was taking longer to get up to speed so I was burning more fuel to cover the same distance in similar time to what I am now. I was already jetted to have it loaded to its potential, so correct clutching helped get it into its power band to use the fuel efficiently. (But I might be completely wrong with my thinking, I am just a rider)
 
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That is exactly what I was getting at. MrViper, Turk or BeTheViper want to chime in on this? I am sure it is getting old talking about piped Vipers and the poor mileage, but it sounds like some are seeing "decent" performance and others may as well throw their pipes in the trash. It would sure be nice to figure out once and for all what causes some of us to get 4-5 mpg and others to get 8-9 mpg on a piped Viper. Seems like a really significant difference to me...
 
I agree with the others that you need to look into the clutching, you are going to find that your clutches are going to be HOT because of your over rev condition. You are making quite a bit more horse power (and torque specs are now different) and your efficiency of your clutch is now out of align with your current high power set up, you are going to need more grip on the belt. IF you did not change anything in your clutch since you installed the pipes you WILL need to add weight in the primary and change the spring to help you get back to the "sweet spot" as you call it to gain the back any slip and or inefficency in the clutch....

Bigreis as you if you take off in 3rd gear your milage will suck but you put alot of strain elsewhere in the system(clutch) and the same principle goes for if you run too tall of a gear - instead of trying to reach 90 mph and having the motor sing to get there, when you find the right combo your sled will effortlessly get to speed and your mileage will be there too. Plus you'll gain that arm stretching feeling that is talked about.
 
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Sxr700Bandit said:
I agree with the others that you need to look into the clutching, you are going to find that your clutches are going to be HOT because of your over rev condition. You are making quite a bit more horse power (and torque specs are now different) and your efficiency of your clutch is now out of align with your current high power set up, you are going to need more grip on the belt. IF you did not change anything in your clutch since you installed the pipes you WILL need to add weight in the primary and change the spring to help you get back to the "sweet spot" as you call it to gain the back any slip and or inefficency in the clutch.....
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I clutched the sled according to SLP specs... which surprisingly called for REMOVING weight from the stock clutch. They call for 13.9 mm steel rivets in both holes of the 8EK weights. Stock is a 17.2 mm steel rivet in the outer hole and a 13.9 mm steel rivet in the inner hole. It didn't make any sense to me why you would take weight off of the primary and not change anything else when you are adding more horse power to the system. I think I understand the principals of clutch tuning, but I have zero "real world" experience. Does anyone have a suggestion on where to start? I am thinking I will put 17.2 mm steel rivets back in the outer holes for sure. Should I put 17.2's in the inner holes while I have it apart too? Should I make a spring change too, or just start with more weight?
 
Just got off the phone with Dustin from SLP. He was great to deal with and gave me a bunch of suggestions to get this dialed in. He recommended that I start out by going to 17.2 mm rivets in both holes (which is up from the 13.9 in both that I currently have) and also dropping a tooth on the upper gear (going to a 21 tooth instead of the 22 I am running now.) I can't say that I am crazy about changing the gear right now, so maybe I will start with the weights and then take it from there. The reason he suggested dropping down a gear is to account for the 136" track. What do you guys think?
 
Add the weight, try it... change the gear and try that ... You will like both the changes I would say, just like to do one thing at a time, then you will know what each change makes.......
 
I changed the gear in my sxr and it woke my sled up and also helped with my clutching issues.

This is why I mentioned what I said the other day.
 
JonHolovach said:
Got Bender pipes get about 5mpg sometimes less depends on how soft and deep the snow is. Have way more power and speed then other stock vipers i ride with. Don't have any trouble beating them.
Click to expand...

When my viper was stock i got 12 to 14mpg. I am running bender triple pipes and i am getting 10mpg.
 
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