3rd burndown why?

SNOWRULES

SNOWRULES

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Joined
Dec 18, 2005
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361
Age
40
Location
Ottawa. Ontario, Canada
Pictures of my burndown on my 2000 sxr 700. it has burned down twice already once on the center and once on the mag both of those were lean bundowns as the piston was melted away from the exhaust port. found that those 2 burndowns were cause by a leaky carb boot. but this one is different. doesn't seem like a lean burndown seems more like a mechanical failure like it just hooked a ring or something anyways gimme your input and how my other 2 pistons look for wash. Motor is a 2000 sxr 700 case ported by mr.viper, psi tripple pipes, boost bottle, reed spacers, srx reeds and 2 layers of head gasket. compression on my gauge is 138 to 140 so i don't think i'm running too high a compression. jetting is 153.8 mains, needle at 4 clip with both washers underneath and 45 pilots at 1.75 turns out. i had just rebuilt the motor the weekend before with all new gaskets and carb boots so i've run it at least 500 kms since the last burndown. i'm at my wits end and this is getting expensive especially when it keeps taking out my cylinders too.
 

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A buddy of mine says he has a "zipper " on his motor because he has had it apart sooooo many times. He figures that he has narrowed it down to the local gas station. If he does not add iso when he fills up there he is pulling the "zipper" open again. He only goes on local rides because his doo can not stray from from gas stations. This may not be your problem but poor gas quality can really hurt finely tuned motors.
 
welcome to the club ... but your engine seem to be lean a little.. happend twice to me but lucky didnt hurt the cylinder only the top burn
 
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piston on the right looks lean, actually looks like it's running in detonation, why don't you put it back together this time with the 3 piece gasket in it and richen it up a little.
 
ya i was kinda thinking gas. but with my compression only at 138 140 i didn't think it was an issue. i ran that sled before the porting with compression of about 145 to 148 and never had a problem stopping at the same gas stations. but then i guess the porting adds extra heat and power. i dunno i'm about to give up lol
 
800 wich is that? on my computer they show up one under the other. adding the other layer is a good thought would probably rule out poor gas cause then i should have a big enough squish for it not to matter. in terms of jetting from my plug color anyways i was ok always a dark coffee color in my wot and midrange tests. i would think if it was jetting that it would have blown up in the 500kms before that cause i ran it in colder temps and even harder than the day it blew.
 
lol, I was always suspicious. Guess I'm going to have to come over more often in the summer and keep an eye on what you are doing.

Lets get it fixed up! ttt
 
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Which is what, what? I think you meant the head gasket, you said you used 2 pieces of the stock gasket, I would put the stock thickness gasket in it, 3 piece, and richen it up. Meaning take a little compreesion out of it, give it a little more fuel, go run it and see that it lives and then you can always go back the other way, I would also drain the fuek tank and start with new, just for good measure.
 
sorry 800 you said piston on the right looks lean to me there's no right all my pictures are one under the other on my screen didn't know wich piston you meant
 
oops, the piston on the right as you posted them in the thread, meaning the lower right or the right one that is still in one piece. Can't tell which cyl it is by the pic.
 
I'm seeing the pic's vertical....lol


anyway bottom piston look's lean,piston above that one look's spot on...

have some crud in that carb??
 
i did run the same compression like u last year on my srx 140. and this year i got some problem with same compression but cylinder ported so i guess something goes wrong with the compression and the heat
 
see I'm seeing them 4 pics in a square, how about this, the good piston with the dent in the top looks spot on the other non blown up piston is lean
 
1.)too lean yet on main jets, I think youd need to be up around 157.5-160's mains. lean is only mean in a short drag race, you simply cant make them live on long pulls without running cornsyrup thru them(112-116octane fuels) and then your losing power anyways from too high of octane in the fuel. The jetting may need to be staggered, meaning 1 cylinder may want more fuel then others, not uncommon with mod engines or with engine with pipes. You can run 3 differnt sized jets if thats what the motor wants.

2.)gas isnt good enough quality, you need to get better fuel for it. Somehow you need to add octane to the fuel, wether its using a mix of race gas,octane booster kept in the trunk. Octane booster wont make 87 into 93 but it can definitely help from this problem, about a half bottle to a tank. What octane rating gas are you using?

the pic of the one piston with the wash a good 1/4 inch around edge is where you want to be(pic 668), the other pic with no wash is headed lean,(669) its not awfull lean but that would be a short drag race jetting i would want not for lake running, it needs more fuel for long pulls like you guys do up there. Dont be afraid to give it fuel!!!
 
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so Don you think that damage is from being lean or detonating? i guess i'll up my jet sizes accross the board and see if i can keep her alive. i've been running 91 to 94 octane whatever is the highest at the station. never any less than 91 though. i guess that means i should go with the 3 layers of head gasket as well if you think that gas is one of my issues
 
the headgasket thickness is only .010" of an inch its not the differance between alive or dead, but jetting looks lean to me as far as size goes. I used 155 mains in a single pipe sxr, I know its alot colder up there where you are then down here in the south......lol

what I think would be a good idea is too add more main jet, leave the rest alone and buy a few bottles of octane booster and put themin the trunk, as you really dont know what your getting at fuel stops. if you get gas after someone else who gets base 87 octane fuel, your getting 87 fuel as well, its in the pump,line and nozzle still, as soon as you turn on the gaspump its the first thing headed in your tank. cheap insurance the octane booster is.
 
ok so i'll keep running 2 layers of head gasket or maybe 1 lol, and maybe start with 160 mains and needle at clip 5 with both washers on top. dunno if that's enough fuel in the mid. hope so. and i guess i'll see what happens from there. also maybe from now on i'll try to look for dedicated premium only pumps not ones that use the same nozzle for all 3 grades. never really thought of that but makes alot of sense. thanks Don
 
Or if your in a group and you pull up to a multi-grade pump try to be the
last sled fueling up using the premium,you'll know it'll be all flushed out
by then,thats what i do...hehehe
 
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