Discussion in 'Norton Commando Motorcycles (Classic)' started by Fullauto, Oct 23, 2017.
Thanks Ken, that makes sense now.
I did this a couple of years ago with a innovate lm gauge and a long sniffer pipe, reached down into header pipe for a single mikuni some things I found
1/ cruising along the motor way on light load 60mph you are still using the slide
2/ with all the needles so called available the mid range is quite hard to set
3/ when I thought I had the lower end set right on the motorway it knocked mildly when off then back on the gas in the hills and twisties
4/ aimed for low 12's at top under load, gauge worked really well here, picked up a 1 number jet change told me it was going rich and I could hear the different engine note and the gauge told me what was happening
5/ when I got it to a happy point the cyl head temp seemed to rise enough to cause more porous oil leaks
When I do it again I will do it in conjunction with an exhaust gas temp gauge just in case running at a good air fuel ratio isn't quite as good as it seems
Good info, thanks!
How can one air fuel ratio be right for all the different types of petrol which are available around the world ? Chemistry is not like that. Getting the mid range jetting right is critical to achieving best performance. However once it is right, atmospheric conditions can affect it more. I think most guys run their mid-range jetting slightly too rich and if the bike is slightly sluggish, they probably don't even notice. The mid-range jetting which gives best performance in both two-strokes and four-strokes is just slightly on the rich side of destruction. If you are racing, there is a bit to be gained by going there.
That's what a dyno is for. An air fuel ratio meter is a guide and you use it with a dyno to get the best performance.
Ken said "Remember when we all thought that our Nortons made 60 BHP?Hohohohoho! Some still do!"
Im one of those who believe that the stock bikes do make about 60 bhp at crank, as rated. Start changing things and you might get less, especially if you choose a high lift cam then stifle it with a single carb.
These bikes, when new, ran the quarter mile in the 12s , you need about 60-65 bhp to do that ( and a quick , light rider)
My 63 BSA Super Rocket came from the factory with an official dyno sheet that certified the engine at 46 bhp on the crankshaft.
It's in as new, stock condition and tuned properly but the 850 Commando feels like it has double the output of the BSA. On a 70 mph hill for the BSA , the Commando can pull 95 mph, GPS.
It would be very interesting to get that Beeza on a dyno Glen and we could then clearly see the difference between crank and rear wheel hp.
My Commando, when it was recorded at 56rwhp, felt like a rocket ship when ridden side by side with my mates mk111 that has a never-been-stripped motor.
Unfortunately, I couldn’t persuade him to put his on the dyno!
I went to a motorcycle club sprint many years ago. The fastest bike there was a new Super Rocket BSA. It ran about 12.8 seconds for the quarter mile. 50 BHP with a light bike is plenty with which to do yourself a mischief. Sixties Triumph Bonneville 650s only had about 46 BHP and are still pretty quick. I would not be surprised if many commandos had a genuine 60 BHP. I don't know what my motor is turning out, but what I like about it is the grunt. Every time I have raised the overall gearing, it has accelerated faster. It seems to love methanol fuel more than any other motor I've ever had. - There is one thing to remember about tuning bikes - it is possible to tune them to a stand-still.
Wow! Not just go faster but actually accelerate faster! Have you considered a 57 tooth primary and 19 tooth secondary?
You might get enough acceleration to achieve escape velocity for your journey to Mars!
I have the new book out, Norton Commando, the Bible
From my understanding, just about the only "stock" Commandos getting in the 12s quarter mile time were prepared by factory expert Jim Baker teamed up with factory expert rider Dave Rowlins, while almost all of the road tests of stock bikes in that era were turning in !3.3 - 13.7
quarter mile times. Norton's claimed 60hp at the crank was undoubtably abnormal, under ideal track conditions with, in perfect tune and with experienced riders on board
Notable also is the claimed top speeds with many road tests stating anywhere from 114 to 124 for stock Commandos, I don't buy it
Back in the early 70s when I weighed 135 pounds and flat out on the tank on my stock 850 I was lucky to see 108 on the speedo
Nigel, did the stock Mk3 have the stock silencers in place?
I'll have to jump in and say same experience here with my 850 back in the 70's though you may have been referring to a 750. I may have reached 110 mph which is not far from 114 mph. What burned by butt was my friends 68 fast back with a 19 tooth primary would smoke me throughout the speed range.
What I know now is that a moderate bump in performance can be had with a good valve seat dressing and moderate increase in compression ratio. I recall the 850's were supposed to be at 8.5:1 compression ratio stock yet I have read on this forum apparent actual numbers as low as 7. something :1. My whole point is that I can see the 114-124 mph threshold as plausible with a "blueprinting" of the engine while using only factory stock components. Now you may have to do a "Rollie Free" to get those speeds but................
No Glen, peashooters.
+1 Dances on the trip to Mars!!!!
Hi didn't we do this a few years back?
Norman White 12.26
I'll go against the grain again in that
I think the factory CR number is right.
I just syringe measured two 850s, both with untouched heads and I get a CR of 8.53 to one with a thin 20 thou flame ring gasket or 8.23 to one with a 40 thou copper gasket.
One engine is assembled ( the MK3) the other is disassembled and on the bench.
Happy to provide the arithmetic if there is any interest.
Yes Chris, we have done this before many times re the 1/4 mile stuff. There were lots of disbelievers in the 70s so Norman decided to settle it.
Then there was Cook Neilson with the 12.69. It has been suggested that it was a specially tuned bike provided by the factory. Lousy tuning job I'd say, it had a plugged fuel tap and ran like a slug until Neilson and Co. found the problem!
Mine was 7.6:1.
I guess that if nothing else, it shows that things were variable...
turns out with further reading that the actual top speeds quoted by the Commando road tests in that era were only estimates based upon the assumption that the motor could really pull redline - a good example being the stock 850s with a 21 tooth front sprocket, they simply could not pull to even 6000rpm in 4th , but quarter mile times sold bikes in those days and sales exploded in America when the 750 Commando came out the quickest in the first superbike shootout comparison
I've had both my 750's on the dyno with Amals and mikuni, the results were very similar at between 41 and 42 with bog standard motors. Can't find the print outs but trust me that's the HP figures carburation was on the rich side, the last time it was lean but made no odds to HP . I'm taking them back up now I've swopped carbs and had my old ones resleeved but I recon the HP results will be no different.
Hi, It was John Baker and Dave Rawlins. I had a John Baker modified short stroke head way back when, and knew Rawlins, he often helped me on useful things, including pointing me at the guy I bought that head from. I made contact with Dave a few weeks ago on facebook, pleasant surprise to make contact. Less pleasing to discover his health situation has been a bit hard in recent years.
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