ssanddemon

I'll be interested to see what you are putting out. Not many guys dyno'ing the lighly built motors; it would be nice to have a comparison since so many of us guys are right in the same build range as you. I race a buddy of mine all the time who has almost your exact setup, and since I have been kicking his ass lately, I will add a few hp and be right in the ballpark for my motor. Please post the sheet if you have a scanner, that would be the best!

My bad ! I was looking at mm not inch measurements. Actually the clearance is supposed to be .0024 to .0026 (factory), so we're both off, me by a lot! Anyway, the aftermarket pistons fit noticeably tighter thereby giving less blowby and making more power. And as I look at the specs, I see that the maximum size is 64.1, so Jason's cyls. at 64.5 are in need of an overbore.

Yeah, let us know how it worked!

Mixing in some race gas (like 1/2 and 1/2) will give a very noticeable gain. I case matched the cylinders when I had the crank out for welding, and it helped the top end power. Gearing down will help a lot, depending on your terrain. I went down a tooth in the front to 13, and it closed the gear spacing up across the board.

92 db, I beleive. I know the Toomeys are like 99 db, so it's somewhere in there.

I just swapped in some Wiseco's and didn't bore out to the next size (still @ factory bore). Reason being, I hated that .060 clearance the factory slugs have; they're rattly and make less power. My cylinders showed absolutely no wear, and didn't have a ridge at the top. I took some 400 grit sandpaper and scuffed in a new crosshatch to make the rings seat and did the normal break in. No problems yet after 20 hard 4+ hr. rides. Personally, I would say that if you don't have crosshatch all the way to the top, the cyls. should go the next size up. They wear more at the top of ring travel and end up being out of parrallel as time goes on. In addition, if there is any ridge at the top, your new rings may have just the slightest bit higher contact in the cylinder, and can hit this ridge, causing instant damage. If in doubt, bore it out!

Not a dumb question at all. I run 1/2 and 1/2 Toomey and factory. Just set it up as soft as possible with no slippage. Some guys run all stock springs on performance clutches; works real good with a lighly built engine.

Dunno what the factory ones cost, but Ricky Stator's 200 watt is like a third of that.

Joe knows his stuff. I'll retract my previous statement with apologies, Brian!

You're a good sport, KW!

And yes, it's easy. Two hrs. max for a rookie. Details in your shop manual. Maybe take this opportunity to upgrade to an aluminum water pump impeller. The OEM plastic one is a time bomb waiting to ruin your weekend- WHEN (not if) it comes apart.

Pull off the clutch side cover and replace the water pump shaft seal and then unplug the two case vents. When the trans heats up, the coolant in the oil will turn to steam and pressurize the case if the vents are plugged. I'm thinking there's no way a head gasket will give this symptom, gotta be the water pump seal.

Never heard of the "yamaha strip" but then again I don't use a cheater bar on 6mm bolts. Follow the torque values for the particular size bolt and you will never have problems unless the guy before you wrecked things first.

Pull the fuel petcock out of the tank and cut the strainer socks off the ends. They are plugged and only letting a dribble thru. Now you can simply run a clear fuel filter before the carbs and see when it's plugged. I almost guarantee this is the fix, based on your description of the problem.

Install a V-Force with other engine mods like pipes and porting. No mods = no gain with the V-Force; just my experience.

Is the pointer in the case lining up with the mark on the clutch lever at zero free play? That is the base adjustment for the clutch. The book will detail this for you; that is where I would start.

My shee and most others I have seen idle just beautifully. The YZ 250 and other bikes I have had do not but banshees generally do. A high, uneven idle is usually caused by a lean condition, so I would pull the carbs apart and look for a plugged jet, most notably the pilots, which have very small holes, easily plugged by a grain of sand.

One word: Throttlecable! Well, at least that was the problem with mine. Cable lubed the bejeezus out of it, no more sticking.

Man, you guys who are smacking the big nut on with an impact are just begging to strip the mainshaft! The age- old trick is to place a penny (or something else that is similar sized AND SOFT, LIKE BRASS) between the output shaft gear of the crank and the gear on the basket. When you attempt to turn the assembly, it wedges them together, but will not damage the gear teeth. Reverse the rotation to remove the (now bent) penny. Use on either side of the gears to loosen or tighten, allows you to use a torque wrench like you should for proper reassembly; works like a charm!

Wait a minute. You have a 310 on one side and a 330 on the other? I guess that could make it run kinda funky!

Sand in the tire? It would take a lot but... I would try it again with the wheels off. That should narrow it down some.

It leaked before? Needs carbs rebuilt/needles & seats. Probably the iffy needles dried out while the carbs were off and are leaking really bad now. The best time to have the carbs gone thru was when they were off the first time, but you have probably figured that out by now . They shouldn't leak at all unless the bike is on a STEEP slope.

Did you pull out the floats and put them back in upside-down? Gotta be something like that....

Pull out the fuel petcock and cut off the screens. Then run a cheap fuel filter before the carbs. What elev. did the bike come from? I'm asking because 5k where you are now is prety high. if the guy has it jetted for lower elev. it will be rich where you are at. May be running super rich for a second, then starving out from plugged filters.

Factory head on Ebay: $15 to $50. 'Nuff said.