Viper Center Cylinder Burned Down

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hondaracer2oo4

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Dec 31, 2009
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Location
New Hampshire
I am working on a 2003 Viper 700 for a buddy. It has 5500 miles on it. He burned down the center cylinder last winter and it has been sitting since. I always do the pre season tune up for him on this machine. Every year on these yamaha vipers the pilot jets are always clogged with crud that I have to pick at and blow out with the compressor. Last year was no different, I pulled the carbs and found clogged pilot jets. I cleaned them and the other jets and reinstalled. Upon start up it didnt want to start, it was flooded for some reason. When it did start it backfired so badly on start up that it split the W pipe for the exhaust. I welded up the split and the machine seemed to run fine. Well he brought it up north to go on his annual ride. He said that he loaded it on the trailer with no issues and it seemed to run fine. When he got up north and went for the first ride, he knew immediately it was not running right. He said that they pulled the air box off and opened up the drains to the carbs, he says that the center carb had no fuel come out. He said that they then took the carbs off, played around with them a little, checked the pilot jet and other jets, everything looked good. Put it back togeather and it ran perfect. They then went out and road about 50 miles with no issues and perfect running. He states that he came out of a corner onto a straight away with WOT for about 15 seconds, he suddenly noticed that the machine was slowing down and he saw that the gauges were dead. He coasted to a stop and tried to start but the motor was stuck. He pulled plugs and found center plug has aluminum on it. They towed it back and it has been sitting ever since.

Now I am tearing into it to find out the damage and find the reason for the burn down. So far I have found that when I pulled the carbs, the left and center had ZERO fuel in them and the right one had a small dribble in the bottom of the bowl. I found that the pilot jet on the center cylinder was clogged with varnish(I could see light through the plug but it must have been a very thin film over the hole) I blew the jet out and found no other clogged jets in the carbs, Needle and seats worked appropriately.

Next I removed the fuel pump and disassembled, I found that one of the small diaphragms inside has a crack across it. So the fuel pump will need to be replaced, that was all I found wrong in the fuel pump.

So this is as far as I have gotten with tearing into it. I was hopefully looking for some advice on what else I should be on the look out for. I know that a clogged pilot could cause the burn down but I am baffled about the lack of any fuel in the carbs. I suppose it could have evaporated over the year it has been sitting.
 
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No, I did not. I wasn't aware that they had prefilters before the needle and seat. I will take the seats out tomorrow and take a look. Does the filter just fall out with the seat out or do I have to pick it out? Thanks!
 
hondaracer2oo4 said:
No, I did not. I wasn't aware that they had prefilters before the needle and seat. I will take the seats out tomorrow and take a look. Does the filter just fall out with the seat out or do I have to pick it out? Thanks!
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Try searching "top hat". Alot of guys chuck em rather than clean, up to you. When you pull the seat its a plastic ring with a screen covering it, the snap on/off. Often times when we tear into a fresh burn down its hard to pinpoint an exact cause....waiting a year it will be harder.
 
Yea, I know it can be difficult to pin point cause but unless I find the culprit it will likely have another burn down. Thanks for any help or pointers that everyone might have!
 
Ok today I removed the seats and checked the bonnets. They were clear as day, no problem there. Also checked the main jet sizes they are pto 156.3 and middle+mag 158.3.

Next I removed the W pipe, it was differently leaking around the exhaust seal to the expansion chamber pipe. Could this be any issue at all?( I can't think of any reason for it to affect it and I would think it would affect all three)

I pulled the head off and took these pics. As you can see center cylinder with mild burn down mostly around front but continuing around the piston. PTO and MAG pistons look pristine!

What is everyone thought on cleaning the head up with muriatic acid and reusing? Thanks!
 

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the pic with the other 2 cylinders shows lean to me as well.
 
Mrviper and staggs, thanks for the input! Why would just the center cylinder have the issue on not the mag side too?? I know you said the others are lean too but why is the center one so bad? I don't even see any pitting on the top of the MAG side like it was detonating at all?

Would the fix be to raise the needle to the fourth clip position and use 91 octane? The owner did admit that he runs 87 and occiasonally 89. What about the excessive heat?
 
hondaracer2oo4 said:
Mrviper and staggs, thanks for the input! Why would just the center cylinder have the issue on not the mag side too?? I know you said the others are lean too but why is the center one so bad? I don't even see any pitting on the top of the MAG side like it was detonating at all?

Would the fix be to raise the needle to the fourth clip position and use 91 octane? The owner did admit that he runs 87 and occiasonally 89. What about the excessive heat?
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I would guess that if you pull the rings off the mag cylinder and look at the tops and bottoms of them, they look like dried rain drops on your cars windshield and paint on a hot sunny day, thats the first signs of detonation. thats the rings bouncing in the piston groove from the detonation starting and shaking the piston.

of course the center and mag have the highest compression so thats why 90% of all viper burn those 2 cylinders down, now add in the fact this guy is running 87 cheap gas and he has been ultra lucky to not have done this before. If he rides fast thats likely what has saved him before. he was more on the main and less on the needle and thats where most every problem with these is compounded and comes to fruition.

I would suggest raising the needles after your repair the engine and convince him that gas (higher quality-higher octane0 is cheaper then pistons and cylinders. :o|
 
Alright, sounds like a plan!

Now my questions about what is usable and what is not.

Do I need to pull the motor and do a whole rebuild or if I pull the cylinders and the crank feels smooth and tight I can just do a top end rebuild?

If the head cleans up and I get the aluminum off that center cylinder head is it re usable?

Next I will try to clean up that center cylinder, if it has any grooves in it I will replace it with a new one?

Are the mag and pto pistons reusable? This sled has 5500 miles on it. Could I just replace the rings? If so should I throw in some new wrist pin bearings?

Next is if I need to do all three pistons should I go OEM on everything or would Wiesco be alright?

Any suggestions on a gasket kit?

Lastly anything else I should look at doing? Thanks alot everyone!!
 
hondaracer2oo4 said:
Alright, sounds like a plan!

Now my questions about what is usable and what is not.

Do I need to pull the motor and do a whole rebuild or if I pull the cylinders and the crank feels smooth and tight I can just do a top end rebuild?

(yes, if no debris is all down inside, or youll at minimum need to wash out the junk, and remove with a suction hose)

If the head cleans up and I get the aluminum off that center cylinder head is it re usable?

(yes,but muratic acid will eat aluminum so you use it to remove molten aluminum off the cylinder plating, you cant use it on the alum head as it will eat it. best to either stick in a lathe or carefully use a flapper wheel or dremel and remove rugh stuff)

Next I will try to clean up that center cylinder, if it has any grooves in it I will replace it with a new one? ( new, or have it replated, or good used one, looks pretty bad but thats just a pic)

Are the mag and pto pistons reusable? This sled has 5500 miles on it. Could I just replace the rings? If so should I throw in some new wrist pin bearings?

(yes pistons reuseable, rings would be a good idea at that mileage, and so would the wristpin bearings if they look blue or have discolored cages)

Next is if I need to do all three pistons should I go OEM on everything or would Wiesco be alright?

(oem yamaha only if you want reliability, stick with oem and it will run a long time with zero issues)

Any suggestions on a gasket kit?

( all you need is a new head gasket, the base gasket you can reuse , get oem yamaha, not that bad priced.)

Lastly anything else I should look at doing? Thanks alot everyone!!
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(look up the raising the needles on a viper info and set the carbs up for him)
answers to questions above inside the ( ).
 
Thanks mrviper,

What is the best way to wash out the lower end? What should I use for a fluid medium? Just pour it in and spin the crank around a whole bunch, then suck out with tube?

I didnt realize the head was aluminum. Ill have to carefully remove the aluminum from the piston.

Base gasket reuasble? Never heard of this, is it fiber or metal?

Looking up your right up on the raising the needle now!
 
hondaracer2oo4 said:
Thanks mrviper,

What is the best way to wash out the lower end? What should I use for a fluid medium? Just pour it in and spin the crank around a whole bunch, then suck out with tube?

I didnt realize the head was aluminum. Ill have to carefully remove the aluminum from the piston.

Base gasket reuasble? Never heard of this, is it fiber or metal?

Looking up your right up on the raising the needle now!
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kerosene or diesel fuel works good then reoil the crank bearings after you suck out any debris with shop vac connected to a small tube to get inside case. i have a air powered suction hose thing i use works great.

base gasket is steel , i usually reuse them just wipe off with wd40 and reinstall, never had one leak, they are pretty tough.
 
Cylinder problems

When my center cylinder burnt down it was much worse than yours.. It happend to me twice in the same season. Was the snow marginal on the day of burn down?

Not the best engine Yamaha built..
 
vibeguy,

The snow last year was marginal at best but they were riding in Pittsburg nh which should have been some of the best snow for the season. What was your conclusion on the burn down? Did you burn up the center cylinder twice?
 
My first thought right off the bat last year when it happened was that he hadn't got the boot from the airbox back onto the carb correctly since it can be such a pain to slip over. When I opened up the hood to check it out all of the boots where perfectly on the carbs and tight so I ruled out that as a possible issue. What made me wonder was that he said that when he turned the middle carb drain and it was empty he claims. After that they played around with the carbs a little and it ran fine for about 50 miles after that. Then burn down, which could have been caused by that carb not letting fuel in the bowl again but I found nothing clogging that fuel line or in the bonnet filter for that carb or anything that would have made the float stick closed.

As far as a bad seal? Which seal would you be referring to?
 
vibeguy said:
Not the best engine Yamaha built..
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Huh? May not be the best built ever, but they are a lot better than others period. I have 9100 miles on mine and have never had one problem. Like anything else with an engine, do your proper maintenance and use the correct fuel. Not the engines fault they guy ran sub par fuel. Like Mr Viper said, he was lucky to have made it this long.
 
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