Finally it is running smoothly

[LoftCol]

I have been issues with a flat spot at around 3000 revs since I brought the bike is Sept 2024, the carbs were serviced and rebuilt about 500 miles ago, new coils, spark plugs, leads. Getting a bit fed up with it and limited mechanical skills, I was ready to change the exhaust. I decided to remove the baffles in the current exhaust, I found that they had been wrapped in a fine gauze and were completely sooted up , almost solid. I removed the DIY baffle, thinking that there was nothing to loose. It isn't much louder without the gauze, and runs really well, flat spot gone, pulls really well, accelerates nicely. I suspect that the gauze has been there since 2004 when it was officially inspected for a Department of Transport test.

Does 70mph at about 4000 revs seem about right?

Thanks

[DiverRay]

Yes, 70mph at 4,000 is about correct. These WERE designed to do a 1/4 mile in under 12 seconds, and gearing was part of that. If you can get an 850 final drive and do the conversion, you will drop to about 3,500rpm at 70mph. It also helps the fuel mileage a bit. I have the final drive for my special, that has the 16" rear tire. I just need the time to do it!

[LoftCol]

I thought about doing that as well, just waiting for the right one to come along

[LoftCol]

So it looks like mine is about right speed/revs wise. Thanks

[Bonz]

4000 RPM with stock gearing on a Special is 60 mph. 3750 rpm for a Standard at 60 mph. I'm getting this from road tests from Cycle World back in the day. Do the calculation for how many RPM per each mile per hour. 3750÷60 = 62.5 rpm/mph. Multiply that by 70 mph and you get 4375 rpm at 70 mph.

My experience with an 80SG was 4,000 RPM at 60 MPH stock, 3600 RPM with the FD mod at 60 mph.

A Standard with the FD mod at 70 mph would make sense to be at 4,000 rpm. But not with a stock final drive.

[DEEBS11]

I put an XS750 (almost identical to the XS850) on my rig. With the 165 15" car tire I turn about 4,000 RPM's @ 70MPH. Perfect.