Best cruising RPM

I'm getting used to riding my recently completed restoration of a 72 Combat.

Some of the work I did included a new standard cam , a spacer under the barrel to lower compression from the Combat 10/1, putting on a Mikuni VM 34mm carb and Pazon ignition. Starts first kick and runs well.

I'd like to know what a good rpm range would be at cruise that is easy on the engine and for good gas mileage, with downshifting when needed for strong excelleration. The bike has lots of torque but I'd rather not strain it at too low rpms if I can avoid it.

Thanks for replies
Bob

Well if you changed thee exhaust on your 7 to a three inch and put some nice Borla cat back on then you would find that the magic number changes right. Commandos vary a lot bike to bike and so do the sweet spots. There is very good torque down low but your not on the cam till you hit 4000 the engine is happy just getting on the cam. On my bike that's 4250 yours will be different. I found my sweet spot on a dyno it's the point were almost any throttle setting will be responded to without lugging. It's around 4000 on most stock bikes I have played with. It is a little hard to feel in the seat of the pants driving on the road at speed. A dyno run does help it shows the drop off in torque and the building of HP that happens between 3-4000. Above 4000 the HP out runs the torque up to about 6500 than the torque fully returns that you made at say back at 3000. Now I have met a number of riders that cruise on the low end peak torque about 3000 on most bikes it can get vibrations really pulsing. When you feel a smoothness take over the machine and the engine seems eager to bust out that's the best I can describe it.

mine is a stock combat and a 21 tooth sprocket. it likes about 4,000 4,200 . it will give 50 - 55 MPG and is cruising at 70 MPH


windy

Somewhere around 4000 rpm is the typical sweet spot for stock cam profiles, but it depends on a lot of variables. Gearing, carb tuning, exhaust flow etc will all affect your throttle response and gas mileage. Each bike is a bit different.

I have a stock `71 (non-combat) that I got in `72 from a guy who'd put on a larger rear whee/tire and what "appears at first count" to be a 21-tooth drive sprocket for California/interstate cruise purposes. With a normal wheel/tire over the last 35 years I cruise 70 mph at exactly 4,000 RPM. (It's happy w/ anything over 3,000, though.)

I've been advised that the "original" sprocketing was 20-ish, and that since I've got everything (engine/gear box) torn down for the Winter I should consider dropping back to the 20-tooth version.

What say y'all who've been here/done that?

bill said:

mine is a stock combat and a 21 tooth sprocket. it likes about 4,000 4,200 . it will give 50 - 55 MPG and is cruising at 70 MPH


windy

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I'm right with Windy here. After I had my 72 Combat restored Windy convinced me to change to a 21-tooth sprocket since my riding habits were leaning towards highway cruising up to the twisty country roads north of Tampa Bay. Instead of the "buzzy" 19-tooth sprocket originally on my Combat, the 21-tooth offers a relatively vibration free 70 mph @ 4000 rpm and a tad over 4500 rpm at 80 mph. Once I'm off the highway and getting it on in the curves, the bike delivers outstanding acceleration and generally keeps up with the Ducati and Thruxton guys I run with.

Thanks everyone for the replies.

Looks like the number getting the most thumbs up is 4,000 +/-

I did change out the 19 tooth sprocket for a 21 toother so 70 at 4,000 sounds about right.

Bob