How fast will she go?

Ok, So now that I have over 1000 miles on her, I can open her up and maybe join th "Ton up" club. but before I do….

How fast will a stock 1974 850 go? And how fast should a 75 850 with JS motorsports flat side carbs and CNW engine/tranny go?

It depends on who you ask.

My '75 Interstate 850 will do close to 110; doesn't have a problem getting up to the ton, but that last 10% takes the most effort.

I'll bet your will do 110+ indicated. The ton should be fairly easy.

Skyguyz said:

Ok, So now that I have over 1000 miles on her, I can open her up and maybe join th "Ton up" club. but before I do….

How fast will a stock 1974 850 go? And how fast should a 75 850 with JS motorsports flat side carbs and CNW engine/tranny go?

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My '74 with your old single Mikuni hit about 105 or so and had some more to give. The bike looks great.

Be safe when you Ton up.

All Commandos should top the ton by 15-20 mph if holding on long enough, especially 850's, for the waiting long enough part, which is more never wracking to pilot than engine and drive train. Definitely nip up fasteners from cradle to head before and *after* such an attempt as good test for adequate case venting breathing system oil sealing. A Commando pilot should be able to sit bolt up right past the ton on any Cdo and a few more mph if tucking down. W/o special features inside its too nerve wracking to me on engine innards to go above 90 mph much but still feels good to know ya can now and then.

Skyguyz said:

...how fast should a 75 850 with JS motorsports flat side carbs and CNW engine/tranny go?

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Heck, call Matt and ask him. He should have a pretty good idea, based on the gearing you have installed, and based on his records of the build...

Just do it, find out, and let us know!

Personally, I don't bother going over the ton much (unless on a track). For me, the fun factor is in trying to minimise the time taken to go 0-100-0 MPH...

Post your results and we'll try and get a competition going (bugger, there I go again, the Doctor warned me about this...)

Get you chin on the tank,tuck in your knee's ,elbow's and you should get a 12 month ban and a big fine :lol:

john robert bould said:

Get you chin on the tank,tuck in your knee's ,elbow's and you should get a 12 month ban and a big fine :lol:

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Or even prison!

Hence my propensity for sub-ton-fun.

Thats one of the cleanest, most immaculate Norts I have seen. How does it run with the JS flatside carbs and did you change any jets or needle position? How far open are the idle air mix screws.

Jim

Yes . Things have changed over the years...40 years ago..i raced on the road with the local Triumph saint mounted Cop! Saw him a few weeks ago in the supermarket..we laughed about the antics we got up to...he's 68 now. im 64 ,,,great times allas :cry:

Fast Eddie: I plan on doing only once to see where I can note the limits on this machine. If I need to go any faster then I'll leave it up to my fast bike; A 2013 MV Agusta F4 capable of 186 MPH putting out 195 HP. (*At the track only!) Insane speed are not meant for the street.

Jim, (of JS Motorsports Thanks for the nice words. I have not done any fiddling with the jets at all and the air screw is about 1 1/2 to 1 3/4 turns out. It runs super smooth and just purrs. (*It runs even better than it looks.) And thanks again for the new improved rubber carb mounts. They work fantastic!

Great balance..Commando, MV and Kwak triple...I love the Jap strokers..nothing sounds like them...My Yam RZV 500 V4 is heaven at 8000 rpm...hit 10000 and grin is ear to ear.

I have a book with all of the Commando road tests by different motorcycle magazines from 1968-1976

there is a difference between actual road tested top speeds and "calculated" per hp, redline, gearing

there has never been a "stock" Commando that had a road tested top speed of over 112 in any of the magazine road tests, the Calculated ones show about 120mph, but those are decidedly not actual

most of the tests show a 109 top speed rider "prone" and 106 sitting up

and with five Commandos that I have owned, this rings true

If you are a big guy, that is big wide tall body, do not expect extreme speeds. Weight is not much of a factor at this speed, so fat, heavy smallish body types do well, NBA Superstars not so much.
Adding a GPS to the mix can really subdue the fun.

One of the fellows along on a trip last year was bragging a bit, claimed he was doing the ton on his Vincent while going up an eight percent grade. While there are some good runners that will do this, his is original low compression plus worn out and smoking, so it seemed like BS.
It was just speedo error of an undisclosed amount. We did a speed check using my GPS at 70 MPH and learned that his Smiths was off a lot to the + side, he did not say how much.
Most of the speedos are at least somewhat optimistic, perhaps that is a good way to have them.

A Commando should manage a bit more than 112 with a small rider though. Bruce Main Smith got a high of 119 and a two way average of right around 112 in 1962 with a new 650SS. This was electronically times at MIRA in the rain. Bruce was not a small man either. It is not stated but I imagine he did the full tuck in for that speed.

Glen

worntorn said:

If you are a big guy, that is big wide tall body, do not expect extreme speeds. Weight is not much of a factor at this speed, so fat, heavy smallish body types do well, NBA Superstars not so much.
Adding a GPS to the mix can really subdue the fun.

One of the fellows along on a trip last year was bragging a bit, claimed he was doing the ton on his Vincent while going up an eight percent grade. While there are some good runners that will do this, his is original low compression plus worn out and smoking, so it seemed like BS.
It was just speedo error of an undisclosed amount. We did a speed check using my GPS at 70 MPH and learned that his Smiths was off a lot to the + side, he did not say how much.
Most of the speedos are at least somewhat optimistic, perhaps that is a good way to have them.

A Commando should manage a bit more than 112 with a small rider though. Bruce Main Smith got a high of 119 and a two way average of right around 112 in 1962 with a new 650SS. This was electronically times at MIRA in the rain. Bruce was not a small man either. It is not stated but I imagine he did the full tuck in for that speed.

Glen

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Ha! There's a name Glen, BMS owned my Vincent. By '61 it'd done 132,000 miles due to him! I got in touch with him recently and he sent some pics from back in the day. Very cool!
Oh, and sorry for the hijack here guys!

Bruce wrote a very good repair booklet for Vincents. I have one of these and use it a lot. He was also a very big fan of the Norton Dominators, particularly the 600 ss and 650 ss.
Good to hear he is alive and kicking.


Glen

the cycle magazines showed a measured top speed of 109 for a Norton 650ss

the "Manxman" was of different configuration and had a reported top speed approaching 120

Commandos are not Manxmen or 650ss's, which Heinz Kegler considered the very best Norton twin

I have never been able to discern anything of consequence on the Manxman that was different from the 650 SS. The rating of 52 HP was given to it, but that was questioned by the one US road test I read from 1961. The tester did not believe the bike was producing that much power. Perhaps Norton got called out and decided to use a more conservative figure for the 650ss when it appeared the next year.
I actually have a copy of Bruce Mainsmiths road test for the 650ss from "Motorcycling" magazine. The two way average is 111.9 mph, electronically timed at Mira.
Performance wise, the Commando has the same engine design, but more of it. So it really should have the power to reach a bit higher speed.
It is interesting that relatively low gearing and very high RPM was used to achieve those speeds. Overall ratio on the 650SS was 4.53 to one.
I rode a 99 geared this way last week. It felt like a trail bike and was definitely too low geared for modern roads. On a short stretch of freeway I considered riding it a about fifty MPH on the shoulder, so low geared it was. The owner has since fitted a two tooth larger CS sprocket and this has transformed the bike. It purrs along at 65 MPH very comfortably now. And the 4.53 , as low as it was, is not the stock ratio for the 99. Stock is around 4.7 to one!

Will have to look in the white book to see what CS sprocket on the Commando would give a similar overall ratio to the 4.53, I suspect maybe an 18 or 19 tooth would do it.

Glen

Glen

My stock 74 850 use to get 116 mph and no more with stock gearing and only got to 6,500 rpm, but only had my stock motor for 4 years before I built it to the Featherbed frame and a hot motor, after I built this bike up with the balanced motor, S2 cam and other work it would run freely and have been over 125 mph on a straight run, how do I know this, radar speed trap,(coppers) :roll: and it was still pulling.

Ashley

I've only held on to Peel till top out once and never could wait long enough to top out on any thing else. Really do have to tuck close to help near end of top out, which makes looking ahead or at guages troublesome. How many of ya have tried that. It can be a teeth gritter not for fear of losing control but running out of road or engine containment. Look deeper into Smith speedo accuracy when working right they are accurate to the mph. Not my opinion but published tests you might be able to find too. If ya really get to dicing with potent moderns - WOT throttle on real Commandos ain't gonna keep up after a few seconds in opens and no way to catch up. Same with my SV650 though, handles as good as any corner cripple but is a power dog against 120+ hp hot shots. Would be interesting to know how much an upper fairing is worth on road power Commando.