TOPIC:

I'm using BS34s. I'll start with a chronological list of things that I've tweaked.

-Changed main jets from 115 to 117.5; seemed to pull for longer (pulled until about 7.3k instead of 6.5)
-Went to open headers with 6" slash cut tips I made. I know this complicates things, but I like the sound. Didn't help, obviously, and ran very lean.
-Changed pilot from 37.5 to 40, main from 117.5 to 122.5, 2 shims added below stock needle clip, sync'd and timed. Pulls nicely until 8,000, then not much.


Before spending another $20 on 125 mains, I'm wondering if this could be an issue of restriction (stock headers, stock airbox, stock filter). It's great to ride in the first 8,000 RPM, but I paid for the whole tachometer, so...I'd like more. I'm fairly certain that fuel flow isn't a problem, as I can do several 0-50 pulls in first in rapid succession without starvation. I'm curious about pod filters or velocity stacks, but I'd love to sort this before going that route.

Your input is, as always, appreciated, and please enjoy this pic of my handiwork for your time. I truly have mastered the art of exhaust fabrication.

It sounds like you're bike is pretty well set up. The torque of a 750 peaks at around 7500, and power at around 9000.



If you want to increase your power and torque above those levels, you'll really need to start looking at cams. Fueling, porting, exhaust etc are all great mods to increase power across the range, but your power will just start dropping off after 9000rpm.

Oh yeah, the OTHER thing that it could have been. Okay, thank you, I'll try to just enjoy it as-is for a while

Irish Yobbo wrote: It sounds like you're bike is pretty well set up. The torque of a 750 peaks at around 7500, and power at around 9000.

If you want to increase your power and torque above those levels, you'll really need to start looking at cams. Fueling, porting, exhaust etc are all great mods to increase power across the range, but your power will just start dropping off after 9000rpm.

Wrong chart for that bike. The bike is a Spectre. Look at the squared off corners on the cooling fins.
The KZ750H/Es have rounded fins and 9/1 compression ratio. The Spectre and '82 GPz have squared
off corners and 9.5/1.


.

Nebr_Rex wrote: Wrong chart for that bike. The bike is a Spectre. Look at the squared off corners on the cooling fins.
The KZ750H/Es have rounded fins and 9/1 compression ratio. The Spectre and '82 GPz have squared
off corners and 9.5/1.
.

You're right. I can't find any power/torque curves for a Spectre but max torque seems to be at 7000rpm and max power at 9500.

So very similar to the KZ750H/E that I'm used to, but yes peak power should be a little higher up the range. I would expect it to keep pulling a little longer after 8000rpm. Power should still be increasing, but you simply won't have that pull-your-arms-off feeling as the torque drops down after 7000rpm.

I think you need to look at the big picture here, You are asking an almost 40 year old motorcycle to do something it could do when it was brand new. Besides messing around with the carburation has anything been done to the engine to freshen it up i.e. pistons, rings, head work etc.? Or are you just flogging away on an old tired motor?
Just because a chart from 4 decades ago says it has "X" amount of power doesn't mean an engine can still make that power. And I have rarely seen a bike or a car do well with open exhaust without other modifications to enhance the open exhaust.

Rick H.