Want more horse power

Metal

Metal

XS650 Custom shop
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Hello everyone
So you all mostly know my bike
1970 Xs1
Big bore 750
Xs1 cam
Vm34s
Ported Head
Pamco
PMA

So I want to make a few changes to it.
I want more power top end speed and I want less vibration.
I’m actually thinking my head is killing power so I was going to go for a polished port on a new head. Thoughts?
Because of the 750 bore I’m getting vibrations at hi speed. My hands are numb after an hour or so of riding. My crank was balanced with the pistons and rods by Falicon cranks in Florida when I built the engine a couple summers ago. Do you think there is a way to reduce the vibrations so more using a rephase or some kind of more detailed balance
I want to dyno the bike at this point to just get it perfect. Is there a bike dyno in the California Bay Area or Central Valley or California for that matter.
I was wondering if I raised the compression slightly if that would help. I’ve already got head weeping and leaking base gasket issues so I was going to machine them this winter to stop the issue.
So I’d like to hear your 2 cents

Cheers Dan
 
1. Re. vibration, go around the motor mount bolts with a torque wrench and make sure they're tightened to spec. The chop job you did on the top mount isn't helping at all. Rephasing will move the harshest vibration around in the rpm range; it won't reduce it. I don't know what Falicon did with your crank, but if you're going after vibration the best thing you can do for yourself at this point is to put the crank on V blocks and work the flywheels with a dead blow hammer until you get as close as you can to zero detectable runout at the journals, and have your piston assemblies beam balanced. BTW is your crank welded? If not, flywheels could separate.

2. Re. performance: motor needs to breathe, and those tiny little filters are choking it. Was your head ported by somebody who knows what he's doing, or by somebody who just hogged out ports that were bigger than optimal to start with? Re. compression, you can run up to around 10:1 on 91 or 92 octane premium pump gas, but you're better off keeping the CR at or below 9.5:1. Reasons: 1. The higher the compression ratio, the hotter the operating temperature. 2. The higher the compression ratio, the greater your risk of holing a piston if you wind up needing to fuel in a place where you can't get anything but 87 octane or wind up taking on some fuel that isn't what it should be. Finally, you need to make a choice between style and performance. Those short head pipes are tuned to develop peak power at engine speeds way higher than your motor will rev., and if they're 1-3/4" OD, they're tuned for peak torque at rpms you can't reach as well. Think about a hotter cam when you have the basics squared away--especially pipes, filters, and port work. It all has to work together, and you're using some components that are fighting you now and will fight you worse with a performance camshaft.
 
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Hi Dan:

Well, it’s an XS650 so that means that is essentially 1950s-60s German-Japanese technology that was designed to compete with 1940s British technology (and it did that very well). Sooo, if you want more power and less vibration.....I’d suggest you buy a modern bike and just enjoy what you’ve got.

The Suzuki SV650 is also a 650 twin, but it makes about 25 HP MORE than the XS650 and it weighs about 25 pound LESS plus it has EFI, ABS and produces very little vibration and it’s as solid and reliable a block of granite.

From your note, you’ve already increased displacement, but your bike is basically what it is - and if you try to push it much harder with a higher CR or other changes, I’d guess that you'll create something with less reliability and durability. You might gain a little with some exhaust or cam changes, but a powertrain is a system and it all has to work together. Simply changing one or two things seldom pays off.

Just my $0.02.
 
Aw, let's keep it real, Pete! That 25 horse difference only applies if you're looking at the manufacturer's published numbers and don't take account of where those numbers come from. Yamaha published gross horsepower read at the crank on a nekkid engine with no alternator, etc. to push. (All the makers did that back in the day, but we used to say that those Japanese horses ran pretty small.) The numbers published for the SV650, however, show net horsepower measured at the wheel. Bottom line: comparing stocker to stocker, the Zook puts over 30 more horsepower to the ground, and exceeds the reliability limit for a full race 750 big bore Yamaha XS650 motor.

But it's not a chopper! It has a real suspension. It has a real front brake. It won't put noise in everybody's face. And it will dance. If you want to look like a badass on an SV650, you have to actually ride like a badass, you can't use the excuse that "It isn't made for that."
 
Have you considered that leaving your hands over your head sitting on the couch at home for an hour would have them go numb? Loosing the stubby air filters and pipes would be my first changes for better torque at lower RPM. Then retard the timing a bit see what that does for vibration control.
 
Never could see why a bike of this form needs more power or speed. I've owned a couple of chops, and a stock 650 is more than enough. I remember a buddy sticking a 396 with a blower in a T-bucket. No point other than looks.
 
We really are trying to help....
That rear sprocket looks pretty small. what gearing are you running?
My 750 is currently 17- 33 i may go 32 but no smaller...
 
gggGary said:
We really are trying to help....
That rear sprocket looks pretty small. what gearing are you running?
My 750 is currently 17- 33 i may go 32 but no smaller...
Click to expand...
I’m running a 29 and a 18 but I still have more torque and not enough top end so I’m thinking of going to a 18/29.
 
Last edited:
grizld1 said:
1. Re. vibration, go around the motor mount bolts with a torque wrench and make sure they're tightened to spec. The chop job you did on the top mount isn't helping at all. Rephasing will move the harshest vibration around in the rpm range; it won't reduce it. I don't know what Falicon did with your crank, but if you're going after vibration the best thing you can do for yourself at this point is to put the crank on V blocks and work the flywheels with a dead blow hammer until you get as close as you can to zero detectable runout at the journals, and have your piston assemblies beam balanced. BTW is your crank welded? If not, flywheels could separate.

2. Re. performance: motor needs to breathe, and those tiny little filters are choking it. Was your head ported by somebody who knows what he's doing, or by somebody who just hogged out ports that were bigger than optimal to start with? Re. compression, you can run up to around 10:1 on 91 or 92 octane premium pump gas, but you're better off keeping the CR at or below 9.5:1. Reasons: 1. The higher the compression ratio, the hotter the operating temperature. 2. The higher the compression ratio, the greater your risk of holing a piston if you wind up needing to fuel in a place where you can't get anything but 87 octane or wind up taking on some fuel that isn't what it should be. Finally, you need to make a choice between style and performance. Those short head pipes are tuned to develop peak power at engine speeds way higher than your motor will rev., and if they're 1-3/4" OD, they're tuned for peak torque at rpms you can't reach as well. Think about a hotter cam when you have the basics squared away--especially pipes, filters, and port work. It all has to work together, and you're using some components that are fighting you now and will fight you worse with a performance camshaft.
Click to expand...

Some excellent suggestions. I’ll definitely change out the filters for some velocity stacks and make a longer set of pipes.
 
MaxPete said:
Hi Dan:

Well, it’s an XS650 so that means that is essentially 1950s-60s German-Japanese technology that was designed to compete with 1940s British technology (and it did that very well). Sooo, if you want more power and less vibration.....I’d suggest you buy a modern bike and just enjoy what you’ve got.

The Suzuki SV650 is also a 650 twin, but it makes about 25 HP MORE than the XS650 and it weighs about 25 pound LESS plus it has EFI, ABS and produces very little vibration and it’s as solid and reliable a block of granite.

From your note, you’ve already increased displacement, but your bike is basically what it is - and if you try to push it much harder with a higher CR or other changes, I’d guess that you'll create something with less reliability and durability. You might gain a little with some exhaust or cam changes, but a powertrain is a system and it all has to work together. Simply changing one or two things seldom pays off.

Just my $0.02.
Click to expand...
Thank Pete but not my cup of tea
 
If you want your motor to last very long, forget about velocity stacks and get a pair of air filters with some area to them on that bike, the bigger the better. To improve breathing over what you have you'd have to use stacks with nothing but gravel strainers on them. If you use stacks with any kind of decent filter medium, you'll strangle the motor worse than you're already doing. You're not getting good top end power partly because you've geared the bike too tall.
 
Metal said:
I’m running a 29 and a 18 but I still have more torque and not enough top end so I’m thinking of going to a 18/29.
Click to expand...

It should feel underpowered with that gearing. First change the front sprocket to 17, ride that, you'll notice the increase in torque. Then change the rear sprocket to 32 or 31. That will feel like a whole different engine.

Velocity stacks will just shorten the life of your engine.

I'm serious about the gel filled grips. Big grips are very uncomfortable for me, The gel grips are small enough and cut out LOTS of vibration.

Scott
 
If you know someone with a cnc lathe you can have stacks with good filters. I made the ones on my bike and have a set for the BS38s going on my next bike. If they make any difference, I don't know it. I'm guessing the difference would be small enough to need a dyno to see.
 

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I have built many and there just is not to many things to do to get rid of all the vibration. The bike was built as a fair priced bike to get around with not a racer. Build is nice but hardtail setup is going to give you the worst ride over 70 mph. I have put a turbo on one and just ate up clutches and no big power and even tried NOS for that quick hit but did nothing to be impressed with. Bike is very clean switch up some gears and go buy a mouth piece so your teeth don't rattle and just have fun on a cool looking bike. You did one good thing was to send your crank to FALICON they are great had many race cranks done buy them. I get guys asking all the time I want to go faster and I say write me a check for $10,000 and we will start from there. LOL
 
Horse Power = Balls
If you don't have any no matter what horse power you have your screwed.
I built the three stooges two years ago all big bore busa motors. All bikes had same setup all motors the same for a club in SC. Two bikes ran low 7 second quarters and the other barely made it into the 8 seconds. Guy called and complained his bike was not as fast as the other two. Wanted his money back not pleased with the motor. So me and a buddy of mine who still races took a ride to there track to see if something was wrong with there motor. Well there track was 8th mile and I wanted to test on 1/4 mile. We stayed overnight and a track off of RTE 40 was having a test session in NC not far so we went there. Now owner of bike maybe 140lbs and my rider 220 lbs. I let him make first pass and was in the mid 8 seconds. Cooled bike down and my rider went mid 7 seconds over 170 mph first pass on a bike he never rose. So you can ask for as much horse power as you want but could you ride it. I still don't think this guy got the bike into the 7's and other two bikes have dipped into the high 6's. That's HORSE POWER
 

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