I have a early 90 blaster, I keep havin a lean problem, the motor when i got it needed to be built. I bored it 40, bought a stock carb. installed 310 jet, dg exhaust, put it together and the new reeds broke causin it to melt down the piston scarin the cylnder. Went and bored it 80 ran it for 2 months with no problem. 2 weeks ago the reeds broke again, caught it in time so no piston problem, went on a trail ride this last weekend and it leaned out melted piston and scared the wall again. Tore it down found nothing wrong with reeds or carb. Motor never got hot. I keep good check on plug and it stays maroon to black in color. Any help?

 

I also have milled head 40 and done some port work.

 

Sounds like there's no oil getting to the cylinder to me.

Still oil injected? Bypassed?

I've heard of oil pumps quitting and oil ports in carb clogging. Never hear of reeds breaking though. Are you using some cheap reeds? I'd at least recommend the factory Yamaha ones if not a "name brand".

Good luck figuring it out. and let us know how it goes.....

 

the reeds are vitos carbon fiber, have oil injection removed, and mix it 32 to 1

 

You're breakin' Carbon Fiber reeds? Really???

Seriously, There's got to be more to this situation. Reed Spacer? Pipe? Carb? Intake mods to airbox?

Are running it hot and letting it cool down real fast in fairly quick cycles or something? Running long runs at "all out"?

Drag Racing?

What is your riding style? And what kind of Fuel are you using?

Clues,..........Gimme clues........ (sorry I just can't see a problem with anything you've mentioned so far 'cept maybe the porting work is not done well or correctly......Porting is an art form as far as I can tell. Not something that should be done at home unless you are a pro already)

Breaking reeds can only (from an engeneering stand point) be caused by sonic issues(tip speed or ignition sound wave <backfire&gt[img]i/expressions/face-icon-small-wink.gif[/img] or from improper installation. Are the reed limiters installed?

 

yea ive broke 2 on mine and my bro has brike 1 on his, factory reed spacer, dg exhaust, stok carb with 310 jet, factory intake and air box without lid with no mods. I do sum drag racin, this last weekend I was on a trail ride when it went down, the reeds are fine this round. I ride trails mostly. Using pump gas. My cuz owns a machine shop(1st time he port as much as he done on mine), he also has a blaster that he ported just didnt go as far with his. have no reed limiters as my cuz or bro dont either.

 

and running a K&N

 

Pretty Puzzling other than the possible over-porting. I'm surprised on the reeds though. You do know what I'm talking about "reed limiters" right?....the stopper pieces that inhibit outward motion. Look pretty useless really, but they do serve a really big purpose. I'd bet the broken reeds could be eliminated of those are installed as they should be.

Now about that "lean" situation.... What makes you use the word lean?

The engineers who built these heads built some pretty good performance into them from the git-go. Porting is truly for competition type riding and is a huge inhibitor of durability. Most folks who do the porting and more (stroker cranks, and such) are big pocket people or have sponsors to foot the bill. I'd bet you're gonna go back a step or two before you get an engine that is more durable and a "daily driver" as such.

How many hours do you have on the last build?

Also, if the mix is lean (as described) then put the breather cover back on it. There's too much air for the fuel being introduced. If it's not really lean, but has a huge scavenging problem, then the heat may be building up due to exhaust restricions.............Not big enough exhaust.

Exhaust problems are odd as there can be a couple of things that are difficult (at best) to control. The toughest is the sound wave front may, in fact, be restricting the exhaust flow by "clogging" the exhaust gases. A bit too scientific to go much further than that, but that might be one direction to look. Slowing the flow may cause the excessive heat that's melting the piston. This kind of mimics running lean when you look at the results. But it is different. Although I suspect your Spark plug is REALLY BLACK instead of white/grey/ashy as it would be if too lean.

How's the timing set up? Advance key? Adjustable Stator plate? Correct plug? (not sure what that would be with the mods mentioned, but the factory one sounds good so far....

I have never burned a hole in a piston in a 2 stroke, so this is not normal to me. But I have done so in a four stroke and that indicated timing way too far advanced. (Volkswagen Aircooled).

Hope some of this helps.....

 

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Im thinkin its due to the over portin also. Gettin new sleve so we can cure that. Yea i know wat reed limiters are, i had taken mine off when i put it together, i think i still have them. As far as how many hours id say 15, ive taken on 4 all day trips, and do alot of ridin at home. My plug stays brown to slightly black. I have all stock timing components.