72' 750 vs 75' 850. Normal?

Many years ago I rode a 1972 750 Interstate. Recently I got a 1975 MKIII. The difference in performance between the two seems overly big. The MKIII just does not have the acceleration or high speed pulling power. I have new Amals and Trispark ignition. The valves are set, timing dead on, carbs set better than was ever the case with the 72'. Is this power difference to be just the way it is or should I be digging for a cause?

When I had my 1969 750 "S", I weighed 165 pounds, now with an 850, I'm asking it to pull 25 more pounds so I know it will not accelerate as fast as my old 750 even with a few more cubes. If you are in the same club, that could be part of the answer :mrgreen: Then there is failing memory, I remember I was faster too :lol:

Jean

Well, I had not thought about the issue of dragging around more weight but now that you mention it I am 40 pounds heavier. Would my thinning hair compensate by creating less drag?

:lol: You have to remember you are born with a set number of hair folicules and as time goes by, they mirate from the top of your head to places like your ears. The gain made with reduced drag on the head is ofset by the drag caused by your furry ears (sadly, I'm in the same boat ) Don't forget, I am wider than I was too or in PC terms, more aerodynamicaly challenged, you could be too :mrgreen:

Time to punch that motor out to 1000cc or put on a supercharger :lol:

Jean

I'm pretty bald and I don't think it makes up for the 40 pounds. In those days I didn't ride 85 hp bikes every day and then go to the 55 hp on my Norton either. As Jean says both it and I were faster back then. This is not to say you couldn't have a worn cam or something.

Hi there, the gearing could be too the solution?? so check your gearbox sprocket ........but I agree with you after owning both, the 850 MK3 is definitly slower... take it as it comes , as I had tried , 2s cam and 10,2 pistons in that 850, and it was not still a good challenge versus my 750, but at that time ,i was young (25 years ago), and not so clever (for example , I can't tell you what head was in that 850!!), and those goodies , were just bolt on , without any patient timing or blue printing, bear in mind too that 850 were slightly heavier (as us ..........). My two cents.......Hello Jean, we had begun to modify the combat cases of my friends , according to your mods, did you see on the "other forum" the mods of Dave Comeau, regarding scavenging of those cases, he added 1 or 2 extra holes to improve scavenging.Will post you pictures as soon as the job will advance.Have a nice day old chaps.........

Hi Coop,

Maybe the 750 was a Combat with 19T drive sprocket? Those really did shift at warp speed. The Mk3 in good nick with twin Amals, not overgeared can still make respectable acceleration and sustain a comfortable all day 80MPH cruise. Sort of a "kick in the pants" compared to "pulls like a train".

Mick

Yes, a '72 Interstate would very likely have been a 65 BHP Combat engined model.

The 72 Interstate you rode was very likely a combat motor. I think all of them imported into the US were. Norton marketed the Commando as a "high speed motorcycle", and a Combat 750 is just that. In a roll-on from 60 mph my buddy's Combat Interstate easily walks away from my MKII 850, and we have the same gearing.

Oh yeah, besides the extra weight you may be carrying :wink: the MKIII is lots heavier with the electric start and steel compared to the fiberglass '72. And if you have the stock mufflers and intake the MKIII is a slug.

On the plus side, the 850 has a broader power band and gobs of low end torque. The Combat motor is rather unhappy below 4000 rpm whereas the 850 is perfectly content plodding along in 4th gear at 50 mph and still offering respectable throttle response. Overall the 850 is a more streetable machine.

Thanks for the replies. From your comments it appears that there are a number of reasons why my MK III feels slow.
1. I am fat
2. I have hairy ears.
3. MK III's are heavier.
4. My old Interstate morphed into a Combat version.

Conclusion: I want my MK III to be as fast as the old Interstate was, and I am going to look into an ear shave.

Coop said:

Conclusion: I want my MK III to be as fast as the old Interstate was, and I am going to look into an ear shave.

Click to expand...

No mention of losing weight? If I didn't ride a bicycle more than a motorcycle, it would be a lot more than 25 pounds I would have to haul around

Jean

The Combat revs quicker and is faster than a Mark III.
You don't say if your Mark III has the stock air box and bean cans.
If it does, install a K & N , Pea shooters, bump than main, it'll wake up.
(But it's still no Combat)

Coop said:

Conclusion: I want my MK III to be as fast as the old Interstate was...

Click to expand...

And so it starts... :lol: :lol:

I don't know about others experiences but in stock form my old Commando used to be quicker than 650 cc Brit bikes. It only seemed to make sense as it had an extra 100 cc. I heard there were some very hot Triumphs, but the only one I saw was a Bonnie fitted with a Morgo kit if I recall the name correctly. I always thought if we swapped bikes the Bonnie might have been faster than my Norton, but the rider carried over 100 lbs more than the 135 lbs I weighed.

Hey Cookie, seeing as how you're a local guy you may remember the hill climbs out on Redwood road back in the 60's? I remember the only bikes that could take the really steep hills were (modified) Bonnevilles. From seeing them I always had the impression the Bonnevilles were strong. Even after the 2 strokes like the Grieves and Huskys came the Triumphs seemed strongest on the long, steep climbs. I never saw a Norton out there.
I rode a 305 Superhawk back then (on the street) and always lusted for a larger Brit bike but sadly couldn't afford one. I am reliving my youth now and really enjoy the opportunity to ride and compare these old bikes.

At that time I was up in Maine. I remember seeing Triumphs as big race winners in the magazines, they always got the most press and even Marlon Brando apparently won that trophy with one. When you had Steve McQueen and Bud Ekins you had it all back then.
When you met one on the street they did not fare as well. Until the Commando got popular over here nobody ever heard of Nortons where I was. There were a few desert sleds but that was about it. After a while Commandos became accepted as a very quick bike in my area.
I see that you have a lot of bikes there. If you have a stock Commando and a stock Bonnie from about the same vintage try them both in a quarter mile. I'd be very surprised if the Commando did not win, especially if it was a Combat.
Norton had a wonderful reputation in England and with some of us who devoured English magazines when we could get them. It seemed like there were a hundred Triumphs to a Norton though.
When I look back I was very lucky to have run into a G15 CSR for about the price of your Honda. I bet your Honda required less tinkering and I'd be willing to guarantee it was easier to start wet. Probably more riding for the money in fact. The G15 did thrash everything it met though, until a Honda 750.
My Commando was pretty quick when I got it but it was a tough choice between it and the 750 Honda. I had to finance it anyway and a few more payments would have made little difference. I think the Honda was as quick but the ride and handling of the Commando sold me on the spot. Oddly enough I didn't even test ride the popular Triumphs and BSAs.
By the time I bought the Commando I was just beginning to understand that stoplight to stoplight was not everything. With the Commando I could compete with my college friends and still have fairly reliable transportation to cruise with my girlfriend.
When the Combat came out I was tempted to trade but its reputation as a grenade stopped me. I was tempted again by the Kawasaki 900 until I rode one. I suspect a bike with those handling faults would get a lawsuit today.
Years later we had a 750 Triumph around for a few years and it was just a bit weaker than my detuned Commando. I'll probably buy a 650 Bonnie someday just to see how they feel for more than a quick test ride.

I agree with the comment Commandos were faster when I was younger. At 20 years old I bought and rode my first - a '72 750 combat roadster. I weighed 165lbs then - now 180lbs. In 1973 at the Ontario Raceway (southern California) you could run the quarter mile and get a form showing quarter mile time and terminal speed. Wish I had not lost that form, but it did 12.1 sec at 103mph. The machine was completly as shipped from the factory with the exception the local Norton dealer replaced the auto advance with a '73 version (believe this was a recall item). In 1981 I bought my second Commando a '73 750 high compression roadster (RH6 head) and was dissapointed it didn't perform as well as the '72. Currently I'm back on a '72 combat. The performance is better than the '73, but still not as crazy as that first combat - 19T versus 21T counter sprocket likely the difference. Also when 20 years old I didn't mind or didn't know better. The engine really launches at 7,000 rpm redline, so naturally assumed this is where the engine just gets strong and continued to rev it. No, I never broke the engine...other things broke from the vibration.

Also have experience with a '68 Bonneville I restored several years ago iwith a very nice DeLong camshaft. Riding that on Norton club rides...could not keep up with the Commandos, so sold it.

I suspect your Combat was a bit quicker than my 70 or 71, I can't recall now what year that bike was. Seems like 12.5 was my best pass at Unity. I had a cam, modified exhaust, intake, and re jetted at that time, but obviously I wasn't as good as the factory boys. Still, on the street there wasn't a lot that was faster stoplight to stoplight. Does 0 to 60 in 4.2 sound right or am I senile again?

From september 1969, Cycle magazine, 0-60 for a 750 Commando "S" ... 5.6 seconds, ¼ mile 13.18 seconds. The very first "superbike" shootout by Cycle in march 1970 had a "stock" Commando "S" doing the ¼ mile in 12.69 seconds. The Commando was well prepared, but stock in every respect, the only evidence of the bike being worked on were shimmed rockers (instead of springs), still, it beat all the other bikes in the ¼, even the Honda 750 which ran with a 4" slick.

Jean

The best I did on my "S" was 13.996, best of three runs, the only time I raced it, then the gearbox broke again