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Author Topic: Set-up for optimum highway performance-'78 cb750?  (Read 2194 times)

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Offline Kev Nemo

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Set-up for optimum highway performance-'78 cb750?
« on: May 22, 2008, 08:23:22 AM »
New to the board and old bikes. I wanted some info on a good performance setup for higher speeds/rpm ranges. I know from working with older cars, certain performance setups will rob power at the top end (especially drag setups). I'm wondering because I'm planning on using my bike as a weekly commuter, 60 miles a day, at speeds between 70-80 (or possibly higher) ;D
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Offline ger87410

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Re: Set-up for optimum highway performance-'78 cb750?
« Reply #1 on: May 22, 2008, 08:41:01 AM »
I've taken mine passed 80 without even trying.

They're top speed is around 120.

Methinks you'll become mostly concerned with mpg...

Here's a recent thread on THAT topic: http://forums.sohc4.net/index.php?topic=35004.0

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eldar

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Re: Set-up for optimum highway performance-'78 cb750?
« Reply #2 on: May 22, 2008, 10:47:33 AM »
If the bike is tuned well, you should get around 40+ mpg on the highway with stock gearing.
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Offline mystic_1

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Re: Set-up for optimum highway performance-'78 cb750?
« Reply #3 on: May 22, 2008, 11:00:29 AM »
My more-or-less stock K0 motor pulls 70-80 on the highway with little problem.  For a more comfortable ride at those speeds, switch the final drive sprockets to a taller ratio, but then you're sacrificing some off-the-line performance.

mystic_1
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jjwaller

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Re: Set-up for optimum highway performance-'78 cb750?
« Reply #4 on: May 22, 2008, 02:42:50 PM »
With 78 carbs, go up to 120 main jets, drill the airbox a bit,
and install K+N filter.
Had my original 78F set up this way and mileage went from
low 40's to an honest 50MPG.
The 78's are set up too lean from the factory for EPA.
Robs too much power.
Have fun.
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Offline ger87410

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Re: Set-up for optimum highway performance-'78 cb750?
« Reply #5 on: May 22, 2008, 02:47:17 PM »
Quote from: jjwaller on May 22, 2008, 02:42:50 PM
With 78 carbs, go up to 120 main jets, drill the airbox a bit,
At the risk of sounding stupid: what do you mean by 'drill the airbox a bit'? 

Do you mean make it so more unfiltered air can enter the airbox to get filtered (more openings in the airbox), or make it it so that more filtered air is able to pass to the carbs (large orifice), or both?
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78750

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Re: Set-up for optimum highway performance-'78 cb750?
« Reply #6 on: May 22, 2008, 04:08:50 PM »
since the carbs were properly set and new Dyna coils......49 on the hwy
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jjwaller

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Re: Set-up for optimum highway performance-'78 cb750?
« Reply #7 on: May 22, 2008, 06:22:59 PM »
Quote from: ger87410 on May 22, 2008, 02:47:17 PM
Quote from: jjwaller on May 22, 2008, 02:42:50 PM
With 78 carbs, go up to 120 main jets, drill the airbox a bit,
At the risk of sounding stupid: what do you mean by 'drill the airbox a bit'? 

Do you mean make it so more unfiltered air can enter the airbox to get filtered (more openings in the airbox), or make it it so that more filtered air is able to pass to the carbs (large orifice), or both?

Drill 3 or 4 3/8 holes in the back lower corner of the airbox.  Increases air flow and is still filtered.
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