I haven't used my GPS to check it but I ride by one of those radar signs that tells your speed near a school zone. The funny thing is at lower speeds it says I'm going faster than the bike says, but over 45 the bike indicates a higher speed than the radar. at 70mph on the bike it said 66mph. Even with the 13 tooth C/S I've seen indicated speeds in excess of 80mph and have not had it quite at redline. As the weather improves I'll use the GPS and see just how fast it really is.

 

Do these carb'ed bikes have rev limiters? If so I've never hit it, I used to alot on my Harley.

 

Checked against GPS my speedo is quite consistent 10% over.
I think the rev limiter is at 10,500 rpm. But I've never hit it (yet).

 

Rev limiter? Used to hit it all the time.

Not at first. Once I opened up the carb and exhaust I hit the rev limiter a lot, now that its a 351 the power is down lower.

Thinking of a 15 tooth front sprocket for fuel mileage. 85 on my 250SF is WAY faster than 85 on my BMW 1100.

David

 

I'm running 13 Front / 49 Rear and got up to 69 mph (GPS & Vapor) yesterday at about 8,200 rpm. It wanted to start dancing a little on the new Pirelli MT17 front and pretty new MT21 rear (both DOT knobbies), so that was fast enough.

Also hit the rev limiter a couple times on yesterday's ride. Vapor computer says max RPM was 10,190.

 

An update...I've upped my top number since my first post. About a month ago I was heading to meet up with some other guys for a dual sport ride. It was really windy. On the freeway, in a tight tuck with that strong tail wind (maybe 30mph), I saw indicated 101 mph...so really more like 90. I've still never had any stability issues ('09 stock suspension other than reducing sag, stock D605 tires).

Later that same day on the way home headed into the wind, I had to do the same tight tuck just to maintain 70 mph indicated. Aero plays a huge role with the limited horsepower of these bikes.

On a calm windless day, flat ground I can see about 82 untucked, or up to the low 90s tucked - again indicated by the speedo, so about 10% higher than actual.

 

Since this is still alive, I went to 15/39. Got the engine running 6,000 at indicated 61 mph. Nice and smooth. Saw 89 mph one day, not tucked in. Figuring in the 7% error of the speedo, that is 83 in real life. One time one way. Probably a tail wind.

This has nothing to do with the gearing, it just runs out of *****. Doesn't matter what gear its in. Usually indicated 83/84 mph is all I will see.

David

 

David,

how do you like the 15 tooth sprocket? I'm thinking about getting one of them now that I have the 351. I'm always looking for another 6th gear on the SF now....

 

It did it! Bike is comfortable at indicated 62 mph. No more vibration in the bars. I put about 40 to 50 miles on this bike per day, so comfort is a good thing. I also have the TM36-68 carb. With the big jug, carb and 15/39 gearing everything is working together. Bike is right in its torque curve at 6,000 rpm so its ready and raring to go when I twist the throttle. Getting 57 to 62 mpg, average 60 mpg every day.

Rear tire is wearing fast. A small cost.

I also have an occasional misfire starting at 6500 rpm and up. The bigger front sprocket got me just below that at cruising speed, so the misfire is less of a concern. Stock chain and the little guard still fits.

I too was looking for 7th gear. I don't think it made any difference in top end. Second gear throttle wheelies are a thing of the past . I can deal with that. I can flip it backwards in first. That is enough for me. Cover your rear brake.

David

 

Good God! I start to bite my nails at 65mph. May just be 'cause I only have a little over 800 miles riding experience overall, but some of those speeds posted seem unreal.

Now I've done started wondering what me and my bike could do. Hmmm....