So I get gifted three 44mm powerjet Lectrons from some snowmobile or other and I'm convinced without even looking at the numbers that I'd never make them work on the 750 . More like a toilet and less like a carburettor .
Then again I was recently gifted a Volvo gas turbo of unknown origin that mates up to the Lectron with little hassle , blow or suck through . I'm not a fan of hot air forced induction in any case and even taking into account the added latent heat of evaporation of alcohol (methanol or ethanol )I still don't like the suck through option despite the increase in efficiency due to the denser medium with the fuel present .Then again the blow through method again leaves me with 44mm carburettors as I can't see perverting the plumbing to use one of Joe Wiseguy's one into two manifolds for a single carb application . Also where to put the intercooler(s) and not totally ugly the bike ?So I get gifted three 44mm powerjet Lectrons from some snowmocile or other and I'm convinced without even looking at the numbers that I'd never make them work on the 750 . More like a toilet and less like a carburettor .
So barring something else coming along I'll fab the spigots for the 44's just to see how bad it really is . All the while looking for something 36 to 40mm that plays well with alcohol .
So the 18" I see there will be available UK/EURO and JP only
as they say , krap .
I suppose I could try for a hard rain tire in 18" but the issue is , well , a longish story.
Several years ago Harley Davidson America decided to pitch in and do what it could to help out waning interest in AMA sanctioned flattrack racing by supporting essentially a spec class based on it's 883 Sportster . Here is where the tire comes in . In a deal with its accessory arm Screaming Eagle and Dunlop , H-D offered an affordable race spares including the K-180 in 18" . The rest of American flattrack had long since moved to 19" front and rear so the 18" was a bit of an anachronism made possible only by the support of HD . Fairly good support it was however as the Screaming Eagle catalog listed the tire for all of $75 for several years .
Now onto the RED BIKE . Yes the infamous is it done yet , decades long rumored motorcycle project . i have over $600 tied up in the decision to lace up an 18" rim out back . At 18" I can fit a near 4" width , at 19" I can't . Only mildly ironic that the rim came off a mid '70's Sportster . I suppose that a alloy dirt bike swing arm and slightly longer wheelbase could accommodate a 19" rim but really by the time I was done I'd be scrapping the $600 already in plus the near $1000 needed to acquire the alloy swinger , modify for twin shock , new hub , spokes , rim , tire , brake ....
So I take apart a "256" crankshaft and find this ?! An '81 crankshaft is included for comparison . I've never seen this before . Anyone have an idea what Yamaha was up to here ? It could be something that was done after original assembly but I took the crank apart personally and it shows no evidence of having been apart before .
The combination of roller bearing main and rod as well as the bending loads on the crank won't let you inside of .037" piston to head unless it is a fresh set of bearings and you are inspecting every few hours of running time .
The combination of a three angle valve grind with out blending the angles , no back cut on the intake , no front cut on the intake , minor short turn radius work and filling in the far side of the bowl went a long way toward promoting effective combustion chamber turbulence and actually reduced the ignition lead necessary for peak power .
A cam profile that buries the intake valve head in the valve pocket of the piston for as long as possible also contributes to improved flow . I'll leave that as a rate of angular change extrapolated as a non linear output for your experimentation . Suffice to say that when you get the valve started is as important as how fast you accelerate it off the seat . There all sorts of arguments for and against long rods specifically in the XS that I don't care about . The major reason I installed the long rods and light valves is that I'm able to "dwell" the intake valve head in the piston relief for a considerably longer period of time without unobtainium valve components . The whole point is that after low lift flow , mean average initial flow into the cylinder , across the back of the valve needs to transition onto the surface of the piston and in our case piston dome , without encountering significant impediment . Only when the piston finally retreats from the valve and flow transitions into gross mean flow does the port itself really start to work and become the ultimate obstruction to flow. Jack's thread from '04 when coupled with pics saved elsewhere is a very good guide of what NOT to do more than what to do . Not that Jack did it wrong by any stretch but he does go into great detail what NOT to do .
Opening up the bore 5mm gives you a 2.5mm ring all the way around the outside of the combustion chamber that can be made larger if the head is decked a moderate amount . A constant wedge of between 5 and 7.5 degrees is what I've used for ages . It shouldn't surprise you that the 5 degree was mostly for heads like the Small block Chevrolet and the 7.5 degree was more effective in hemispherical chambers .
So if you are to weld on the heads the obvious would be the intake port floor and the short turn radius . What isn't so obvious is reducing the bowl volume to the point that the majority of the volume under the seat is venturi .
I've only approached 42 degrees total lead in the alcoholic because that's just the nature of the beast . More often maximum power would come well before detonation and generally prior to 38 degrees total lead . On pump gas maximum power should usually be found before 36 degrees and as little as 30 degrees if the above information is applied .
I'll only add a little food for thought here as an advanced exercise . The exhaust port can in some cases benefit from sinking the valve into the head slightly if it is done specifically to raise average flow velocity . That whole can of worms for another time .
I'm a little frustrated today because I didn't get nearly the time to work on the beast as I wanted and most of the issue was outside my control so I took it out on the keyboard instead .
By the way I've said before , I'm here to make your head hurt and your eyes bleed . How am I doing ?