Experienced tech cannot figure out FI issues.

[Krandall]

The timing marks stock don't line up perfectly from the factory. Mine were off I can't remember how much. But you try to move it one tooth the other way, and it'lll be off the other direction as well.

Even if it smokes a bit. (which I'd say is due to poor ring condition).. It shouldn't be enough to foul out plugs like that.

I'd say get a leak down test done. That'll at least tell ya one part.

I've seen bad TPS issues. And I never fouled a plug.

Maybe I missed it in one of the posts.. But is the bike stock? As in.. Stock intake, exhaust, and fuel controller. If you have an AM fuel controller like a dobech or PCIII have you tried a new fuel map?

[fastline]

Engine is worn out.  Failed a leakdown test miserably.  Found wear through the plating in the cylinder.  One right had over .100" ring end gap.  We are hopeful that the bad engine was causing all the plug fouling issues.  Might as well throw some higher compression at it too....

[Peelz]

yeah thatll do it.

bore that sucka out! 

wearing out a stock motor like that...somebody must have been beating the crap out of that thing!

[fastline]

Well, the owner did tell me to "do what I would do with it".  I warned him that is a bad idea.  Port the head, cam, big bore, 13:1 piston.  He is doing nothing but riding the kids around so hard to justify I guess.  What sucks for him is he just bought this bike and has 2 hrs on it.  I can tell now having been in the engine that the previous owner knew good and well that the engine was toast when he sold it.  The bore otherwise is perfectly in spec!  If he would have just thrown a piston in it on schedule, it would still be a strong engine.  I had .003" piston clearance and maximum value is .005". 

I have been warning people about these engines.  They have very little piston skirt to stabilize the piston.  Once the piston starts slapping a bit, they will cock in the bore and destroy it and typically right where this one is,,,right at TDC. 

I will admit that this is the first teardown for me on  a 700.  I LOVE this engine!!!!  Yamaha got it right!!!  It comes apart NICE, very well designed, and tons of room for go fast parts.  What a HUGE upgrade from the 660s. 

[Peelz]

I will admit that this is the first teardown for me on  a 700.  I LOVE this engine!!!!  Yamaha got it right!!!  It comes apart NICE, very well designed, and tons of room for go fast parts.  What a HUGE upgrade from the 660s.

yeah I was surprised at how simple it is to tear into vs. my old 660... id like to see this engine in a dual purpose bike in the states...   

[Hefe]

someone should mount one in a 450r

[Peelz]

someone should mount one in a 450r

and make it street legal