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It is not all that unusual with lower compressions (pump gas), aggresive exhaust port timing and bigger carbs (33mm +)) to have a dead spot. Sometimes they get real sensitive to changing RAD conditions and carb tuning can be a real PITA... Keep it at a constant throttle setting for 60 seconds or more and nail it. If it "hesitates" like you describe when you grab a handfull it's lean. If it "blubbers" your rich... Sounds like maybe you need bigger pilot jets and/or to raise the needles a notch. Slightley rich jetting produces a little bit better botton end anyway. If jetting doesn't correct it... All you have left is lower gearing and/or higher compression, but your carbs need to be metering fuel correctly regardless. Kinda sounds like your already fairly close since you don't mention a problem in 1st or 2nd. Doesn't sound like a fuel octane issue to me, wouldn't hurt to try some 100 octane before going through all the carb drama though, see what happens??? Good luck On edit: Make sure your carbs are synced too...

Wise choice... Not familiar with the t-6 pipes, but if they mount similar to t-5's around the stinger area get the K&N's with angled mounting flange. Not the straight flanges.

I do a little different variation of the heat cycle thing already mentioned... Quick warm up then ride 5 minutes constantly varying rpm below 1/2 throttle, cool down. Second 10 minutes varying rpm below 3/4 throttle w/very, short full throttle bursts, cool down. Third 20 minutes below 3/4 throttle with more frequent and longer full throttle bursts and a couple max rpm bursts, cool down. Break in complete. Need a couple minutes of varying low rpm operation to lap the the fresh hone, piston and rings, especially with tighter piston clearances and/or higher compressions (first cycle). Also need to bring it up to max rpm a few times during the initial break in (third cycle) if you ever expect to see those rpm's again in the future. IMHO anyway.

LOL! Guess I forgot about that part... :biggrin: :biggrin: Where exactly is Bonny Lake WA. BTW? Couldn't find it on the crummy map I have...

I figured you would get it Mopar :ermm: Not that I think I am some kind of "rocket surgeon" or anything, quite the opposite actually. After reading it again this morning though... If it sounds like I am trying to be a know it all or a smartass or something... I am not! Some of the stuff is just hard to explain in general terms I guess. I have read several post on here lately about MSV's and/or sqush clearances and fuel octanes and ignition timing, etc. where apparently the poster was trying to make some sense of it... Just thought I would take a stab at it is all. I have actually retained a couple things (usually learned the hard way...) over the past couple decades...

Squish clearance is just one factor in determining a Maximum Squish Velocity or "MSV". MSV is a measurement of the speed at which end gases are traveling toward the center of the combustion chamber as the piston nears top dead center. The speed these gases are traveling determines how much turbulance is taking place within the combustion chamber at a given degree of crankshaft rotation, which in turn indicates how well the gasoline and air are mixed or "atomized" within that fuel charge. The amount of atomization determines how fast the flame front initiated by the spark plug will travel, which in turn, along with ignition timing, fuel octane, etc. determines at what degree of crankshaft rotation maximum combustion chamber pressures occur. Ideally, maximum chamber pressures are reached very near top dead center of piston travel, too early and and the piston will be wasting inertia, as well as creating excessive heat, to overcome the chamber pressures as it passes TDC. To late and the gases from the expanding fuel charge are exerting less force on the piston since it is already traveling away from them as the piston moves back down the bore. The excessive heat generated by too early of a maximum chamber pressure is what causes uncontrolled "detonation" as the fresh fuel charge begins to spontaneously ignite from the excessive heat before the spark plug initiates the burn. These uncontrolled flame fronts then collide against each other pushing the piston around lateraly as well as generating even more heat and so on... Until the piston and rings eventually scrape away the film of oil between the piston and cylinder and it is metal to metal. Anyway, is that about as clear as as mud so far?

Do yourself a favor... Use Yamabond or 1211 to mate the case halfs...

Anybody mind if I add my .02 cents?

I was assuming that since there is no mention of pipes or cylinder porting we are talking about an otherwise stock motor. My "guesstimate" is based upon an otherwise stock motor w/a 65mm bore, making peak HP at apx. 7800 rpm, a premium pump gas compatable compression ratio, 12mm squish band width and .047" squish thickness. I am figuring an MSV in the mid 20's with this data. Like you say though, insert the 9,500 to 10,000 rpm data to the above and it is a whole different story... .055" clearance is bare minimum IMHO.

O.K. never mind then...

Yepper... That's what I was going to say, beat me to it...

Glad you guys like it. Lot of good reading/info IMHO... The Jennings file is kind of marginal (scanned sideways w/personal notes)... Price is right though...

If the rad fluid is not leaking externally and is nearly gone as you say... And it has not contaminated your trans fluid... Way better than average chance you have a blown head gasket or bad head/cylinder O-ring. Drain it and pressurize the cooling system or at least remove the head take a look. What you don't want to do is let it sit there with coolant in the combustion chamber and/or cases.

Stumbled onto these links in another forum... Free download in pdf. http://www.kreidler.nl/artikelen/performan...graham-bell.pdf http://edj.net/2stroke/jennings/2stroketunershandbook.pdf

I believe it is about 1.25mm at the inside of pickup. Kinda splittin hairs but .25mm adds up fast...

MSV = Maximum Squish Velocity. It is an indicator of combustion chamber turbulance, usually measured in meters per second. Or how fast end gases in the combustion chamber are traveling toward the center. In general, too much turbulance tends to promote a faster flame front in the combustion chamber. Thus, maximum chamber pressures would tend to occur too early, promoting detonation. Not enough turbulance would do the opposite and part of the unburned fresh fuel charge would leave through the exhaust port with the rest of the exhaust gases. You would have to purchase tens of thousands of dollars worth of computer assisted machining equipement and tooling to cut a head like that. Or you could do it the old fashioned way on manaul equipement, but it would take forever and cost a lot more than $140! Did you happen to notice the O-ring grooves... At any rate, my point was that the "swirly thingys" are probably not doing much, if anything, other than looking shiney. On the other hand that particular head is only about $15 - $25 more than a comparable non "swirly thingy" head...

Yeah that should do it. Slight overkill IMO with all the swirling pattern cut into it but that is pretty much it. The swirling pattern in the squish band area seems to become fairly popular every few years and is supposed to increase turbulance and atomization as well as direct the fuel charge toward the center of the combustion chamber for a more efficient burn. It is arguable wether or not the swirling does anything at all however... Besides the same thing is accomplished with an appropriate MSV for the application. Regardless, assuming all the numbers add up that head in the pic a very, very nice peice and whoever cut it does excellent work IMHO.

I wouldn't call it "naive". It kind of caught me by surprise the first one I did and I have done a lot of heads for a lot of different applications over the years... Banshee heads look just like all the rest and have plenty of material, except in those two areas??? Take a look at my other post in this thread about cutting the squish band. Once the head is indicated on the fixture it is not much more time to just go ahead and make the squish cut. Interesting avatar BTW. Kind of mesmerizing...

I have only done a couple 100 octane Banshee heads where (for whatever reason) the individual just had to have the OEM casting. So based on that limited experience, I wouldn't feel comfortable taking much more than .060" without the welding. Even then there is only going to be about 1/16" of material left, pretty thin IMO! If things are done correctly, an OEM casting cut for 92 octane fuel should be a noticable improvement on the old "Butt-O-Meter"... Not sure why your "meter" didn't register??? I am assuming when you mention "re chambered" you are referring to cutting the squish band? Assuming this, it is MHO again that removing more than .020" requires cutting the squish to keep all the numbers where they should be. And, since they are not a machined area from the factory, OEM casting squish areas should probably be cleaned up as part of the machining process anyway... They are kind of a mess!

For a 19cc flat plate volume: Face .120" off the head and re-cut the squish at 15.5 deg. finishing w/a .036" undercut and a blending radius appropriate for a 10mm squish band width. This should yeild an installed trapped volume of 13.40cc, a squish thickness of .050" and an MSV of 25 +/- which in IMHO would be a relatively safe 100 octane set-up. This is assuming a head gasket thickness of .010", base gasket thickness of .020" and 2GUY-2 head casting to start with. Do yourself a favor, check the chamber volume w/a buret before you install the head on the motor since the OEM castings appear to have a manufacturing tolerance of .3cc. Now the fun part... As you cut the head you will notice that whatever tooling your using to make the cuts (mill or Lathe) start "ticking" as you are approaching .110" on the facing operation. This is because the material is now paper thin at both the waterjacket inlet and outlet areas, so these areas will have to be cleaned up and aluminum plugs need to be tig welded in those areas. Obviously, the head now needs to be re-indicated onto whatever fixture you were using to hold it and finished. Those aftermarket heads should be sounding pretty good right about now maybe???

Lucky guess... Glad it worked out for you.

It is doable mathemaically, not sure how though since I flunked rocket surgery 101 in school. Thus I have to let a computer program crunch the numbers... I do know it involves the rod length (on centers) and stroke and that it is not a constant due to the lower end rod pin being off center of the crank axis so each degree (or fraction) would need to be calculated individually. Easiest way without computer help would probably be the old fashioned way with a degree wheel mounted to the end of the crank. If you have something specific you want to do e-mail me private and I'll do a sweep on the computer.

Sounds like either the fuel that is getting into the left combustion chamber is either not being completely burnt or there is just too much fuel getting in there and washing the color off the plug. Check your compression to see if fuel is blowing by the rings from the bottom end, both cylinders should be within 5psi of each other. Then take another look at the left reeds and carb, especially the float, float level and needle/seat assembly. Last start looking for ignition problems. Your sure the "smoke" is blue and not white. Nothing goofy going on with the coolant level...

I have not noticed any difference on a temp gauge either. Not saying there isn't one, just hard to tell on a 2" analog gauge... The big advantage to o-ring type heads is ease of r&r and the cost of additional domes. Plus OEM heads can't be faced much more than .070" without tig welding, so that pretty well eliminates them from the 100 octane plus compressions.

Blown head gasket maybe. Coolant tends to overflow when your pushing hot exhaust gases into the water jacket...