Topic: How to increase top end and lower RPM's on 1977 CB750?

[Hicks750]

 When I am going 65-70 mph My RPM's are at 5.5 - 6,000 and it sounds like its working to hard. How can I increase top end and lower RPMs. One guy told me to change out the sprocket but Honda doesn't carry the size I need anymore. Any help would be appreciated.  ( 1977 CB750)


Thank you.

[TwoTired]

What sprockets do you have now?
Is your muffler loud?
Do you use the stock air box?

You will not increase top speed by lowering engine RPM.  Some bikes actually have a higher top end when down shifting and getting the RPMs back up into the power band.  Peak power band on the 750 is closer to red line, than mid band.

Doing what you suggest, would likely need a supercharger.

These engine like to rev and are balanced for it, just the opposite of Harleys.

Cheers,

[BobbyR]

I have a 78 and your RPMs are a bit high but that assumes you tach is on the money. TT is correct that for speed you need to be in the power band. It may seem to you that the engine is working hard but we have become accustomed to cars with overdrive. These engines were intended to rev and will actually run far better when run 5K and above for any distance. People try to lower the RPMs to increase gas mileage, which rarely works since you need to open the throttle more to get up to speed and climbing hills.

[754]

You should count your sprocket teeth, should be 17 or 18 on front and 48 on rear..

 You are running the equivalent of about a 15 or 16 front with a 48 rear..

  I bet it passes really well..

[mick750F]

   If the OP has an "F" then he might have a 14/43 set-up...

[Skunk Stripe]

That sounds about right for my 78. I know I am am right around 5500 at 70 mph or so. I think we need to remember that the speedo is usually reading fast and the tach could probably be anywhere or 500 rpm or more off.

[BobbyR]

+1

I get the same RPM to Speed 5500@70. I remember I have a 41 sprocket on the rear on my 78K which i read somewhere is the stock gearing. Gives you good jump around town and plenty of reserve on the Highway. Keep you motor tuned and change the Oil regularly and bike will be fine.