Reasons for middle cylinder burndown....

triple

triple

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Joined
Dec 3, 2005
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120
Age
44
Location
Madison, NH
I'm gonna be digging into my 99 srx this week. Last winter, I bought the sled, rode only a half mile, then the middle cylinder burnt. Got it fixed, got 400 miles on it, then it happened again. I didn't beat the hell out of this sled, I rarely held it wide open for more than 5 seconds.

The reason I bought an Srx was performance and reliabilty. What it lacks is reliability. I really want to make it through a season without any mishaps.

I'm looking for a list of things to look for when tearing it down, and some steps to follow so I'm not overlooking anything.

Thanks in advance!!!!!!!
 

mmmm sounds like a carb problem... take a carefully look at it and jet size in it
 
When you burned it down the 2ND time were you doing alot of wide open throttle runs OR was it nice steady pace at part throttle for most of the riding.
Let us know. Also what was the temperature and what size mains do you have in the sled.

ALl this information will help us solve your problem.
 
tomseal6 said:
When you burned it down the 2ND time were you doing alot of wide open throttle runs OR was it nice steady pace at part throttle for most of the riding.
Let us know. Also what was the temperature and what size mains do you have in the sled.

ALl this information will help us solve your problem.
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The 2nd time was WOT for 5 seconds, temp around 2*F. This happened after a 10 mile ride to the area it happened, and no wide open runs where made until the burndown.

I was told by the previous owner that the jets where stock.(I'll check and update in a day or two..) The sled has reeds and a clutch kit. I never could get it to rev above 8k all season, even after getting a stiffer spring and maxxing it out. (Secondary)

After everything happened, I realized the sled ran better after sitting for a minute or two. Must have been the center cylinder getting hot.

Thanks!
 
I am betting that you just have a jetting problem but check to see if the carb boot is secured properly to the carb,intake with no holes or tears.

I dont see how it could be a seal if you burn down the center.. not likely

I really curious to see what main jets you have in it and the needle clip position. The top cap of your carbs is how you get to the needles which controls your midrange. People do most of their riding at mid range and is where most melt downs occur. The lower the clip position on the needle, enrichens the mid range, the higher the clip position leans the mid range.
 
BTW

2 DEG F. is FREEKIN COLD!!!! Alot more oxygen laying around for your motor to breath and run hotter than normal. YOu just have to give it more fuel by rejetting. I am willing to bet more now that you were not jetted properly.
 
maxdlx said:
Have the carbs ever been cleaned really well. Maxdlx
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Just before I bought it. Then bang! Then fixed, then 400 miles, and BANG!!!

This sled definetly was no slouch, It was either ahead or beside a 2002 ZR800 in a few short runs. Nothing over 600 ft...

I appreciate the quick responses, TY always helps out without all the crap like you get with other sites.

Oh yes, the 400 miles I put on the sled, was with a new crank. Apparentely the crank was bad when it was rebuilt after my first burdown, which the seller tells me afterwards that the crank that was bad was a new crank in the first place. ( I didn't find this out until after purchasing the sled!) So I'm hoping this isn't a crank related issue.

The night it went down, the 2 outer cylinders had good color on the plugs, and the middle was chalk white. This is what I know and I assume it's just a topend until further notice.

This rebuild was done for free, as the mechanic that serviced it before I bought it felt it was his duty to do me right. Just thought I'd throw that out there, that is the only positive thing that has happened with this sled.
 
You may also have an air leak in your intake path after the carb.

Post good pics, and maybe we can point out a few things.

Be sure to find conclusive evidence of the root cause and address it, or it will likely happen again.
 
Where you located?

Better get to work and find out the cause of this. Snow will be here soon. Hope to see some good pictures and find out why its burning down.
 
tomseal6 said:
Where you located?

Better get to work and find out the cause of this. Snow will be here soon. Hope to see some good pictures and find out why its burning down.
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New Hampshire. ya it's comin!!!!!!!
 
2ooosrx said:
The RPM are to low and the motor does not have enough fuel going to it at top speed. Get your RPM's up to 8300 and check your plugs. my 2 cents

Bruce
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From a dead stop, this thing wouldn't rev past 8k. Usually you get the extra 200rpms past your ideal rpm, then they drop to what you want. Not this thing. 8k is it...

I'll get it jetted right, then test it somewhere. Maybe a field? Or will this not give me an accurate reading of what my clutching would be on snow?
 
Along with everything that has been mentioned, you might want to explore the crank issue to make sure it is okay - that was a major problem with all of the early tripples of all brands - not sure if Yamaha had a problem after 98, but it is just one more thing you should make sure is okay!!
 
yammiman said:
Along with everything that has been mentioned, you might want to explore the crank issue to make sure it is okay - that was a major problem with all of the early tripples of all brands - not sure if Yamaha had a problem after 98, but it is just one more thing you should make sure is okay!!
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The crank that was put in before the 400 miles was not the worrysome 98 crank. The mechanic who put it in assured me before I even asked. I guess 98 was the recall year, but some 99's had a problem, but not enough to present a recall. No TSB in 99 for the Srx 700. (So says my local dealership.)

I'll definetly keep an eye on the crank, and if it needs a crank and a cylinder+piston, TY will be the first to see my part out of this very clean Srx with Ohlins. No way can I justify even riding another mile on this if it's eating cranks.

I will be posting pics as soon as I get them. I should be getting into the engine by the end of the work week.
 
Just so you understand the crank issue, the cranks are not one piece - hence they would get out of phase on the stroke which results in burndowns - you might want to pull the motor completly apart and have the crank checked out just as an assurance thing - you'll be chasing your tail for a long time if that is what the problem is - it would also explain your peak RPM problem - I wouldn't think you would have an under rev with lean jetting or an air leak - it would want to scream just before it went "POP!!!"
 
yammiman said:
Just so you understand the crank issue, the cranks are not one piece - hence they would get out of phase on the stroke which results in burndowns - you might want to pull the motor completly apart and have the crank checked out just as an assurance thing - you'll be chasing your tail for a long time if that is what the problem is - it would also explain your peak RPM problem - I wouldn't think you would have an under rev with lean jetting or an air leak - it would want to scream just before it went "POP!!!"
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I HOPE YOU'RE WRONG!!!!!! LOL....

EDIT....It has a clutch kit, I'm not sure what is in it. It engages at 4500rpms, and "Hauck" stickers are in place. The previous owner didn't seem to know much about the kit and what it entailed. Even after the new crank was put in, it still wouldn't pull more than 8k. It didn't gradually drop then not go over 8k, it just never pulled it from the get go.
 
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