Viper test run.. F...!!!

Robbe144

Robbe144

New member
Joined
Dec 13, 2011
Messages
39
Location
Sweden
Finally got it all together and took the sled out for a test ride.
Perfect low speed 1,5 turns out.
Perfect needle jetting, picture with 3 spark plugs. (pto-cen-mag)
So far I was very satisfied.
Ok let's do some wot runs. Hm wait here, didn't it stop by itself just before I pushed the stopper.....? Picture of mag spark plug.

My compression tester have gone missing so I have to wait with that.
I put my finger in the spark plug holes and there is a big difference in pressure and vacuum between the mag and the others. I also gave it 10 approx pulls with ignition off. Mag is dry, the others are wet.
I have sprayed the carb and it seems to be without restrictions.
Can the fuel line have closed in that sharp bend that goes to mag carb? Just bought new clear fuel lines from a snowmobile shop and they felt every soft.
 

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eww that single plug pic looks like you toasted the mag piston.

When I look at the spark plugs where theres 3 of them I see it was right on the spot especially the center one, its burned clear past the curve of the ground strap, the center electrode appears to be silver across the tip, the brown coloring is good but the information of all 3 of those things means its spot on at that temp and you have no margin for temp drop. Keep in mind your carb circuits overlap and that's the reading of the pilot jet, and the needle circuit together, when you get into wide open you will omit those circuits if its a long enough stretch. The pilot jet does flow approx. 2-3% even at wide open but if the main is too small it wont save it.

On a viper the center and mag run the higher compression and make more heat then the pto does.
 
Yes that piston is gone, my guess also. I have set it up according to the good info I got here.
I have pilot screw 1,5, 50 lows, needles 3,5-4-4, 160-160-162,5 mains, vented to airbox. CPR pipes. Temperature -14C sea level. This is the coldest riding temp here.
I think this jetting should be ok and maybe the fuel line caused it. (or should I go up to 165 on the mag side?) The other two plugs looked just as good as the other picture after that wot run.

I will take it apart and see how it looks.
I will start looking for a used cylinder&piston set, new rings and gaskets as per http://www.totallyamaha.net/forums/...-piston-wisdom?p=637729&viewfull=1#post637729
The mag piston look different, pto-cen has a small circle on top in the middle, mag doesn't.
 
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Disassembled it tonight. I'm no expert but to me it looks like I was lucky...
The piston melted but I don't think it was that much damage on cylinder or head.? I cannot feel any scratches with my fingers.
Taking the cylinder and head to the shop tomorrow and see if they can do anything about the melted aluminium.
 

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Ok.
Do the other two also look like lean oil ratio?
I set it leaner last year because I thought the oil ratio was too rich. (I don't remember how rich but maybe one tank of oil for two tanks of fuel) Distance on the cable still within spec though. Of course I can reset it.
 
Also in my experience if there's an oil problem it will score on the intake side did you say it died on decel or??? My piped vipe likes a 165 main on the mag side. 50 pilot needle at 4. you've got four corner scoring there. It's possible your touch lean and you also have an oil problem.

Sent from my E6560C using Tapatalk
 
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When checking jetting, use a glass benda light and watch piston wash. You will see things far quicker than checking a plug.
 
I would richen it up a bit and maybe jet it up a notch. Right now you running right on the edge right now with no room for temp changes.
Lean is mean when racing but bad when everyday riding.
 
The fuel line pinched on my SRX causing a complete burndown of the mag cyl, all from a pinched fuel line and it was pinched because someone didn't route it right but mine snapped the rod and more, I have bad pics if you must see it. This was in 2014 I think.
 

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the jetting specs would be fine for pretty cold temps , they are specs I have used in a lot of cpr piped vipers with zero issues, those specs are designed to be used with premium fuel. meaning 93-94 octane gas, so if your using a lower octane fuel youll need to go richer then the previous specs on jetting. I don't think you have a oil issue, the piston got hot, very hot and when they do the heat is transfer goes to the cylinder and scuffs it, as well as melting the exhaust crown back,exposing the ring. you are right and you are lucky as just a little bit more time and the ring would of turned orange gone soft and then bend and come out of the ring groove and gouged the cylinder.

sounds like your fuel lines are a place to look if you say they are soft wall tubing and especially the mag one with the tight bend in it. I also would ask about the fuel octane. I don't see any detonation on the the other 2 piston tops and they are not all dry and dull grey so I would say you need to check the lines and the fuel being used.
 
Thanks a lot for all the good input!

It didn't stop during deceleration. It felt like it just died a millisecond before I hit the killer button.
I will reroute the fuel lines so I don't have to take them off every time I turn the carbs around, the "curves" will be nice and soft. Will use better quality and more expensive ones.

Will also replace the filter in the tank if there is one. The fuel is not squirting out of the loose fuel lines, more like slooowly flowing... I will try and get one of those small snake lights then.

The fuel I used is the best retail type you can get in Sweden and brand new. I don't know if it's good enough for this jetting though. Pds attached it's in Swedish but maybe it's readable anyway? :)

I bought a oem piston thanks to a member here, should be on the way soon :) Will put some time on the cylinder and head to get the aluminum out and a liiittle hone.
 

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That fuel is 92.75 as rated here in the US, it's Ron+mon/2. Now does it contain ethanol? Ethanol Which is an oxygenator, it states max 2.7% that's not much I don't think. Slp setup states increase jetting %10 if ethanol is at %10.
 
Yes ^^^ 2 sizes up if running ethanol. We have no choice sometimes up here in Canada eh!

Sent from my E6560C using Tapatalk
 
Same as you Viktory2k1 ...
Found this softy lying and looking pretty guilty :mad:

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Not sure what others are thinking but maybe octane booster or slightly richer but Im not sure about which circuit. mrviper state 93-94 octane, you are very close to that, with at most 5% ethanol.
 
Robbe144 said:
Same as you Viktory2k1 ...
Found this softy lying and looking pretty guilty :mad:

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Again with the ethanol. It turns fuel lines soft. Something I've learned to check alot. We have up to 10% ethanol here. We can readily get petrocan 94 but its full of ethanol and sled no likey! Up here I run shell v-power 91 because after lots of research its the only one I can be sure has zero ethanol in it and I swear I can feel a real difference running this gas. Anyway, glad you found the culprit.

Sent from my E6560C using Tapatalk
 
go to the Yamaha dealer and buy a chunk of the oem fuel line, that looks like it was kinked to me.
 
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