I just spent alot more money on Carrillo rod and new bottom end to make my original 720 a 763 and i have another 720 [samcoeds built from Oklahahoma] and i went down to Abbots with both bikes to get a new chain, and decided to put them both to a hard test against each other on the pavement, its about 600 ft at least... now Abbot can ride hes notorious so we were matched up pretty good, he was on my DS763 and i was on my DS720, both bikes jetted properly and all, both have fresh motors and rings ect same fuel too., i beat him by 3-5 bike lengths on 720 easily everytime!!! i wasnt even hammering it that bad on top either with 720, im wondering why the 720 beat 763, please any suggestion is much appreciated...the 763 has combustion chamber work, great port job,109 grind cams , stage 3 valves 13:1 compression 45mm carb and has ran very strong in the past........ the 720 has 14:1 comression, 1 mm larger valves, i dont know who ported it, 450 cams, lightened fly wheel and timing key up 4 degrees and 48mm carb hogged out intake, WHY, WHY, WHY did the 720 easily mopp up the 763, could it be the 720 revs higher?, it almost feel just as torqy than bigger motor, it might be timing or what?? does anyone know what up with this?????? could Samcoe performance have actually made my 763 a weaker running bike?, i honestly think it was faster before, or could it be that the 762 only has 1 hr on its new parts and needs to loosen up?? the 720 has about 7 hrs on it... who knows WHY??????

 

do you both weigh the same?

did you swap bikes and repeat the race?

are they geared the same?

same rear tire and same rear tire diameter?

both have same clutch setup?

both running same spark plug? heat range? gap?

if coils are not grounded as good on one bike, it could have less spark. or if battery ground lead is not grounded as good. I tighten the bolts a lot tighter than from the factory. spark plug caps screwed in tight?

both running woods cdi box? FYI, someone posted dyno results from two woods cdi boxes - one box gained no HP and the other gained 5HP, makes you wonder whcich cdi you got.

the 48 carb, extra 4 degrees of timing, lightened flywheel, higher compression might be enough to offset the extra torque of the 760. But 3-5 lengths sounds like something is not right with the 760.

 

This does not surprise me...
I raced my old 760 against a Ron Woods stage 2 on the pavement (quite a few times)and only beat it by a few lengths
But at the hill (Sand Mountain,NV) I would just annihilate him,no pun intended hahahaha
I think the torque of the 763 isn't fully utilized untill it has a good load on it???
I am sure the 720 will out rev the long stroked 763cc...
Also the TM 45 could be choking down the 763,go to the twin 39mm kehins if you want to get the full potential out of it


Jeff

 

Scooby, we are both about 215-220-lbs, we did not swipe bikes but my buddie is a veteran pro i told him to short shift and he said it did better, the 763 is 1 tooth taller on counter sprocket with about the sane size tires, both have pami springs with barnett plates, 763 has hydrolic clutch, spark plug is a 9 on 720 and 8 on 763, spark plugs are tight, everything grounded, same CDIs one thing though, the intake on 763 is ceramic coated and smooth could that mean anything? should i roughen it up anyways or is that better for alky.. thanks and i agree that the 763 should be doing better, the 720 has +4 swingarm and 763 has +3 swingarm and front end comes up but he was up on gas tank and could control that, it did not seem to be an issue..thanks, Mario

 

I hate to say this but Sam at Samcoe performance isnt all that maticulous at all, could he have not got the valve clearenses correct, could that be it? knowing my 760 it should have clowned and annihilated the 720, but 720 does run good though.

 

I've seen a significant drop in power when running a spark plug too cold. Are both the plugs non-resistor plugs? I think the non-resistor plugs deliver more electrical power from the coils.

I would think the 1 tooth taller on the 760 would help acceleration and take advantage of the torque. If the 760 was spinning tires due to torque, that could be one factor slowing it down.

I assume they have the same pipe?

I dont think the smooth 1-into-2 intake makes any difference.

If one guy lets off the throttle, pulls the clutch in all the way, shifts gears, releases the clutch lever, and gets back on the throttle while the other guy shifts full throttle feathering the clutch lever, this easily makes a bike length or more of difference.

The 720 is running 4 + 4 = 8 degrees of advance over stock???

A hill race is also going to create a larger gap between bikes when the lower powered bike stops accelerating on the incline and the higher powered bike still continues to accelerate. On a flat short race both bikes will never stop accelerating.

1 hour is not enough break-in time.

 

I would swap the carbs. Are the needle tubes drilled out on either one?

 

when i was talking with gary the non stroked engines do rev great it is the hill where the stroke shines. i think that lighten crank has a lot to do with it i allows it to rev quicker. again gary is the one to call he is in the process of lightening cranks and there must be a reason[img]i/expressions/face-icon-small-smile.gif[/img] and seems like that 720 is setup for flat drags, may have been a perfect setup for it. let us know how it works on the hill. i don't know how fast my 720 went on the flats but quads that i had lost to in the past where nothing i could let them start and say ok i think i'll go now and pass in third. and i don't know after that it was just fast, and as jeff said the dual carbs is a better setup. looks like you have a lot of dailing in to do. sorry it wasn't smooth sailing.

 

I would check valve clearences. I had them set mine up for me and they were to tight.

 

Thanks for the help fellas, i dont think the needle tubes are drilled, the 763 carrillo rod was alot lighter than stock i felt it myself, and i dont know what else besides flywheel [ thats what stacy told me ]has been lightened on 720, any ways thanks again for imput i will check valve clearances and a few other things and see whats really going on...