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Discussion Starter #1
Hi, I'm posting on behalf of my brother-in-law whose Viper is broke down in my garage.
I haven't got any experience with Yamaha's but hope someone out there can shed some light on our problem.
When he brought it over, it would run, rev up and pull not too bad but it had a serious hesitation or miss. It would miss or stutter at idle as well as when you were on it. It would almost redline but as you approach the redline, it would come on and off very quickly, enough that you would see the tach drop off then come back.
I know it is difficult to describe through a keyboard. The guy he bought it from thought it was a carb problem, so they were cleaned twice actually. Now that it is back together, it doesn't want to start and backfired so bad it blew the gasket out between the manifold and the pipe.
In my humble opinion, it sounds more like he has an electrical problem rather than a fuel delivery problem.
If anyone has any input or ideas on what could be the problem, no matter how simple or how complicated, I would like to appreciate your comments.
Thanks in advance,
Brett.

P.S. According to him, the machine ran great two weeks ago up north and also on Saturday when he left his house, however, he said after getting into some real deep powder (over the hood) it began to act up as mentioned above.
 

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backfire....? that cant be good. sounds to me like a fuel problem. does it have spark? whats the compression? is the fuel pump bad? is there a crack in the lines? what kind of shape were the plugs in when you took them out, were they black, white, or tanish?
 

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Discussion Starter #3
backfire....? that cant be good. sounds to me like a fuel problem. does it have spark? whats the compression? is the fuel pump bad? is there a crack in the lines? what kind of shape were the plugs in when you took them out, were they black, white, or tanish?[/b]
1. It has spark when plugs are out and its pulled over-new plugs were installed as well.
2. Compression is roughly 95 lbs across-sounds low to me but it was reringed last year, the sled does however have 16,000 northern kms on it.
3. A formal test was not done on the fuel pump. With the carbs off and the plugs removed, we could pull it over and get fuel flowing from the lines.
4. The fuel lines did not leak and appeared to be in good shape, however we didn't replace them or thoroughly inspect the fuel lines, only what was apparent.
5. PTO and CEN plugs were light brown and dry, mag side was light grey and dry.

I hope this information might help you help me...!
Thanks again,
Brett.
 

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usually you get a grey color when water mixes with oil... im not familiar with the new types of wireing and onboard computers they have on sleds now a days.... sorry but thats the best i can offer help wise
 

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95 psi is low, did they hone when it was reringed, I'm not familiar with the viper but my Indy 5 has 120-125 in both, so im thinking that viper should be pushing 130. Maybe its time for a whole new top end. Grey isnt good. If he injested snow into the motor that can sometimes be fatal. Was that 95 across the board or was the greyish plug lower?
 

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I would pull the power valves out and maybe remove the exhaust manifold to look at the pistons. You should also be able to see the top of the pistons through the spark plug holes.There are no gaskets that need to be replaced by removing these parts and you will be able to get a bit of a look at possible damage. Also the compression should be way higher. I would say at least 120. My 97 700sx had 130 with abut 15000 kms on it. With new rings the Viper should be at least that.
 

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what compression gauge are you using?? I tested my comp with a cheap compression gauge I got at harbor freight, and i got 70lbs...barrowed a freinds snap on, and got 120+ across the board..
them cheap gauges, especially the ones with the long hoses, seam to read VERY low..
if nothin else, use your gauge whatever the brand, on another known to run good sled motor, and see if it seams to read correct?
 

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Discussion Starter #8
95 psi is low, did they hone when it was reringed, I'm not familiar with the viper but my Indy 5 has 120-125 in both, so im thinking that viper should be pushing 130. Maybe its time for a whole new top end. Grey isnt good. If he injested snow into the motor that can sometimes be fatal. Was that 95 across the board or was the greyish plug lower?[/b]
Dave, I don't know if it was honed when they reringed it.
The compression was within roughly 5lbs across.
I'm starting to get concerned...
As I had said, when he brought it over, it was stuttering a bit at idle. When I took it for a ride, it would 'miss' then start to fall off and pick up again. Very quick hesitations, almost like a tiny bit of water was passing through the carbs every 2-5 seconds or so, sometimes longer between hesitations. He assured me he had enough isopropyl in the tank to take care of any water issues. Could this be electrical?
What are the symptoms of a 'brain' or CDI box breaking down? Coils?
 

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Hey man, dont mean to hammer on the compression thing...but..my vmax4, read 70lbs across the board on all four cylinders with that cheap gauge I was using..
thing is, if you really are only getting 95lbs comp...thats bad...dont see the sled running very good, or consitant with that low of comp..usually 100lbs, is the absolute lowest for just about anything that runs on gas..not saying it flat would`nt run that low, but would probley be real hard to start, and lacking alota performance?

so..are you positive that comp testor your using is good? cant be reading low at all?
 

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Dave, I don't know if it was honed when they reringed it.
The compression was within roughly 5lbs across.
I'm starting to get concerned...
As I had said, when he brought it over, it was stuttering a bit at idle. When I took it for a ride, it would 'miss' then start to fall off and pick up again. Very quick hesitations, almost like a tiny bit of water was passing through the carbs every 2-5 seconds or so, sometimes longer between hesitations. He assured me he had enough isopropyl in the tank to take care of any water issues. Could this be electrical?
What are the symptoms of a 'brain' or CDI box breaking down? Coils?[/b]

What you are describing sounds a lot like water in the gas. I would drain the carbs and the tank. But keep the gas. Run some fresh gas that you know is good. And see if it fixes it. You could also check the spark individually for a thick blue arc and make sure all plugs are gapped correctly.
 

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95psi is low.... i have 125 in my 340 enticer and it was rebuilt 5 years ago. like homer said, you can inspect your pistons. i would look for any kind of abnormal wear. your rings would be stuck to the piston causing the low compresion issue
 

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Discussion Starter #12
AL-I hear what you are saying and agree, I have no way of objectively telling you that the gauge is correct in the readings it gives. It is possible that the gauge is reading lower compression than the actual, I believe it is a relatively cheap unit.
As for the way the machine runs/ran, it ran real well, not like a machine suffering from a serious need to be rebuilt due to low compression.
Dave- I did remove the carbs and clean the main jets and pilots, in doing this, I emptied the float bowls. Everything seemed good in the carbs. While they were off, I had my brother-in-law (from herein 'Todd') pull the engine over to see what the fuel looked like coming out of the fuel lines directly from the fuel pump. The fuel seemed to come out slowly and not out of all three lines immediately but did begin to flow. I caught it in a small container and examined to see if water was present but it didn't appear to be.

After I replaced the carbs is when we were unable to fire the sled again. It would try to run for a second or two but that was it. Pervious to removing the carbs, even though we had the problem of it running rough, no matter how many times we shut it off, we could always start it again with one pull.

I appreciate everyones input, I know I'm getting compulsive about this situation but I can't stand to see someone have to sit out due to a broke down sled.

Thanks again everyone and I look forward to anymore input.
Brett.
 

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On the viper , there is a wire harness that runs under the motor that wears though it will cause a major problem. i had it on my buddy's 02 . On his if I came into a corner hot it would die . you could drive all day but if you got some G's it stall.
 
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