Viper bog unless WOT - help

MtnMax600

MtnMax600

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Feb 14, 2005
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Sacramento
My 03 viper mtn has developed a nasty habit that i cant seem to shake. At WOT it rips...but from ~6000 until i get to over 8000 RPM it feels like it is running on 2 cylinders. SO if i am cruising under 6000 it feels fine, but around 7-7500 it really is running ragged, then when I pin it...hold on cuz she takes off like a rocket.

At the start of the season it ran fine for like 6 days of riding. Then as i was riding in the powder it got the normal pow bog, but it never went away.

Things Ive tried:
1. I thought it was the plugs so I changed them. No help
2. thought the carbs were plugged so cleaned them, after opening them up they looked fine, nothing was clogged. No help
3. I cleaned the powervalves, werent too dirty but are clean now. No help
4. Bypassed TORS, thought maybe it was acting up. No help
5. Cleaned the clutches.

What else can I try??
 

you got anything hanging in the clutches, all rollers weight's moving freely
nothing is wore out binding??
 
My first guess would be something in the clutches too, since it seems to be fine below 6k and above 7.5k. I have seen a worn out belt cause a mid-range bog before.

To verify that it isn't dropping a cylinder, try holding it at the rpm that is a problem for a little bit and then do a plug check. If one is dropping, you should be able to see a black/wet plug on the cylinder that is the problem.
 
When I cleaned the clutches I checked the rollers and they spun freely...but thats pretty much all I checked with them. Tomorrow when I have it out I will try what you said mod-it. If one cylinder is wet/black what could be causing it?
 
I had a similar problem last weekend and found the problem. I had the air box out before the trip and forgot to hook up the two lines between the carb. rack and the air box. I hope its something that simple for you.
 
You should always check your carbs BEFORE you ride every year.Dirty carbs and improper storage are the 2 quickest ways to screw an engine on the first couple of trips out.
I would at least check the plug cap resistance value or just replace them.They are cheap and can be an easy cure for int. misses and fouling plugs.
 
So i had the sled out over the weekend...what a terrible weekend for it to crap out. 6+ feet of new snow.

Anyhow I ran it for a bit while it was bogging then did a plug check. The PTO clyinder looked wet like it wasnt firing. But if I run it wide open the plug looks fine. So what would be causing it to drop the cylinder in the certain RPM range?
 
I would pull the carbs and tear 'em right apart, clean/blow evreything out, then go from there..
 
Not ingesting snow, I ran it on hardpack last week after cleaning the carbs and powervalves and it does the same thing. Doesnt seem to matter what conditions I am riding in.
 
Bad caps will do what you are talking about.If you want to verify it switch the cap with wet plug with the cap on one of the dry plugs.If the wet plug changes holes you have your answer.
 
I have not tried new spark plug caps. Next time I am out I will try swapping them.

In order to check the resistance what points do I need to put the meter on?
 
So I replaced the cap on the cyl that wasnt firing and it had no change. What else might be causing a mid range drop out of the cylinder. I have a video I recorded where you can hear what it is doing. I will post it later.

I also blew a belt out the last time I rode, maybe 5 miles into the ride. I cant remember ever blowing a belt on the viper, maybe once. Belt was not old. This has me thinking something in the clutch, but would the clutch have anything to do with a cyl dropout?
 
Hate to say it but you may have lost the crank seal when the belt blew, Did you remove any belt material from behind the clutch that was wrapped around the crank?
 
No, nothing was wrapped around the crank behind the clutch. BTW, the bog problem developed way before the belt blew
 
If you broke a fairly new belt, you need to check all your clutch specs., center to center, etc.

Also check your motor mounts to make sure you don't have one broke.

*EDIT*
After thinking more about this, I'm really leaning towards you having a broken motor mount. The motor would twist, throwing your center to center out and cause a bad bog, also would explain the broken belt. When your sled bogs, it can't burn all the gas being thrown at it and could explain the wet plug(s). I'm not near the expert that many on here are, but this makes sense to me.

I have also seen a bog and breaking belts caused from a sled being stuffed into a ditch and twisting the frame, which also threw the center to center out of whack.
 
Last edited:
Engine mounts are fine. I checked the stator thinking it might be going but it tests fine. I also checked the compression and it is low.
mag=105
center=103
pto=97

Could the problem be the engine is just getting tired/going out and needs rebuild? Would the low compression cause the problem described?
 
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