Love my Mark III - but how about a little more power?

tricatcent said:

I have an 850 MKIII with a single MIkuni 34mm. I has a stock engine 8.5 compression

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What aircleaner setup do you have ?

This seems to be the problem in this thread ?
Unless there is a real problem somewhere...

My 850 has a single K&N conical filter, it may be a bit less restrictive than the flat type. Even mine looks a bit small and I may put a bigger one on. I have straight through 1 1/2" peashooter mufflers on 1 1/2" pipes. I am sure my exhaust is very unrestrictive. Also my bike is probably similar to the 750s in weight since it has no electric starter, or big battery, it has the earlier primary cover, and right hand shift. The wheels, tank and seat may be a bit lighter than a MK III also.

Crusadersports -

You asked about the rear sets on my Mark III.

I bought them in 2009 from Mick Hemmings.
72/74 Overstone Road, Northampton, England NN1 3JS
http://www.mickhemmings.com

They were not originally on my wish list, but after putting on the Corbin seat, I realized my riding position had dropped a couple of inches. Although I am only 5'10", my legs felt really cramped between the Corbin seat and the position of the stock foot pegs. Thought I would give the rear sets a try.

I am really impressed with their quality - lots of adjustability. And they were not that expensive - less than 150 pounds at the time, I think.

I see that clubmanracing.com has the same model for sale, though they are currently sold out. He was sold out when I was shopping, but right after I got mine from Mick Hemmings, the Clubman folks emailed me to say they had some in stock again. Guess they sold out once more....



Good luck.

Keith

Rohan said:

If removing the airfilter "made no difference to the mixture" but "the bike ran hotter" what does that tell you....

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Where did I say removing the air filter made it run hotter, MY previous statement STILL stands and getting stronger

So where does this sentence fit into it then ?

.It seemed to me the bike ran hotter and was a concern, could smell hot oil,

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.

Anyone seen an engine where removing the airfilter made no difference to the jetting ?
That statement just doesn't make any sense.

My experience with a restrictive air filter is that it can have a dramatic effect. Years ago I had a Red Hunter Ariel which flat out would run almost 90mph on the speedo. I wanted a lot more so I fitted a 10 to 1 piston, a hot cam, ported head , and a 32mm amal concentric with a Wassell paper element filter. I ran the bike in slowly as it ran very hot. After running in I took the bike out for some speed trials. I expected a quick bike but what I got was 80mph flat out and it ran so hot that when I attempted to stop the engine it would diesel on. I increased main jet size until the spark plug showed just soot, but it still dieseled on and had less power than before. An old timer looked at the bike and said, throw the air filter away. I took the bike out for another run, the power was up considerably, and it went straight up to 110mph speedo reading. The bike also ran cooler and the engine stopped without dieseling on. By reading the plug the correct main jet was a 250 with paper elemant air filter and a 310 without filter.
I could only conclude that if you don’t let your engine breathe properly it will have less power and run hotter. My 810 Commando only has thin foam filters in front of 32mm amals jetted correctly with 300 main jets. Because my air filtering is minimal I change the oil more often.
Ando

Several folks have said that the JS Motorsports flat side carbs would be a big performance improvement over what I have now on my Mark III - a single Mikuni 34M.

Does anyone have any actual data to quantify the difference? HP gain?

I see that the carb kit sold by JS Motorsports are a pair of Keihin PWK 32M carbs, plus filter, cable, etc. Cost = $445.

The Sudco web site (sudco.com) shows a couple of other options for twin carb kits for the Commando, namely the Keihin FCR (sold as a kit by CNW), and Mikuni 32's and 34's.





So there seem to be plenty of twin carb alternatives to the dreaded (in my personal experience since 1975) Amals.

Anybody have access to any data which compares the performance results of these:

• Mikuni twin 32 M
  JS (Keihin) PWK 32 M
  Keihin 35M

Or are they all pretty comparable?

Thanks again

Keith

Before spending lot's of hard earned...have you considered adjusting the way you over take?
Me, well if the car/truck is going 60 , its just a matter of a shift into third and full throttle, normally enough to see them off.
80 mph plus...well thats ..drop back and get a cup of tea :lol: personally as these old girls run out of steam around 100.. so i dont bother trying.
What i do know is there wasn't many cars back in the seventie's that could'nt be blown away..but some diesel's today have almost 200 bhp ,,they need another tool to blow them away. Save your dosh.. if you spent 2000 bucks its only another 15 brake ...

Hi, your problem is more a question of budget .....but to keep things simple: ditch the single carb and fit Jim Schmidt carbies, or if you are patient enough , go back to dual Amal, forget the other solutions unless, money is not a problem!
as you are in UK , the best advise someone told you is to phone and see pete Lovell, he is very nice bloke , and very competent into Commando , sure he could make your MK3 fly, but check with him first what you need /want, cause it's easy to make mistake , it's not always great fun to ride a tuned commando on the normal roads; you will miss the easy going caracteristics of your soft twin, you cannot win at both ends.......I had tried , several engines from tuned 920 to std 850 and 750 , and the most usefull is my faithfull 850; with twin carbs , RH10 head ( a bit milled), and 2i teeth.........IMHO!

john robert bould said:

Before spending lot's of hard earned...have you considered adjusting the way you over take?
Me, well if the car/truck is going 60 , its just a matter of a shift into third and full throttle, normally enough to see them off.
80 mph plus...well thats ..drop back and get a cup of tea :lol: personally as these old girls run out of steam around 100.. so i dont bother trying.
What i do know is there wasn't many cars back in the seventie's that could'nt be blown away..but some diesel's today have almost 200 bhp ,,they need another tool to blow them away. Save your dosh.. if you spent 2000 bucks its only another 15 brake ...

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No No - lets not do this - this makes sense - he must spend $$$ on a dual carb setup to get a bit more humph :mrgreen:

Mike, Mayby the nitro kit then,,,its worth many extra bhp...press the "O" shit button and hang on :lol:

pkeithkelly said:

Crusadersports -

You asked about the rear sets on my Mark III.

I bought them in 2009 from Mick Hemmings.
72/74 Overstone Road, Northampton, England NN1 3JS
http://www.mickhemmings.com

They were not originally on my wish list, but after putting on the Corbin seat, I realized my riding position had dropped a couple of inches. Although I am only 5'10", my legs felt really cramped between the Corbin seat and the position of the stock foot pegs. Thought I would give the rear sets a try.

I am really impressed with their quality - lots of adjustability. And they were not that expensive - less than 150 pounds at the time, I think.

I see that clubmanracing.com has the same model for sale, though they are currently sold out. He was sold out when I was shopping, but right after I got mine from Mick Hemmings, the Clubman folks emailed me to say they had some in stock again. Guess they sold out once more....

Good luck.

Keith

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Keith- many thanks mate and apologies for calling you Jeff!

Do you find there's sufficient leverage on the rear brake with these rear sets? I've always found rear sets a great improvement to nearly any bike but often there's trouble actually setting up the brake light so it works and getting that leverage so the brake is actaully worthy of the name! Not for nothing do many Brit bikes have a a great long rear brake lever with the pivot well behind the footrest! I wonder if this is even worse or ok with the hydraulic rear brake?

I too have a Corbin fitted but the bike has been off the road since before i got it. I'm only 5ft 4 so I expect I'll have the same fun! :mrgreen:

I run a MK1 850 which is basically standard, ie. standard cam, standard compression, with a VM34 Mikuni (no air cleaner), Tri-Spark ignition and, of course, a Fullauto Technologies head. The bike with this setup goes fairly hard from idle up and certainly doesn't hit a brick wall at 5000 rpm like it used to. Having said that, it is somewhat lighter than a stock Norton to the tune of some 12 to 15 kg or 26 to 32 pounds approximately. This is due to a Hayward belt drive, alloy rims and Maney alloy barrels. Having ridden several MK3s, I attribute most of the lack of performance to the excess weight as most owners by now have removed the annular discharge silencers and the plastic air boxes. I do a lot of miles each year with much of it on medium distance trips (Geraldton to Perth is 420 km or about 260 miles). I sit on 65 to 75 or even 80 mph depending on the mood and at these speeds overtaking in top gear is quite adequate. Just twist the throttle and you are past. It will run, like most posters bikes here, up to 100mph readily, and then it will slowly run to nearly 110 mph with a bit of a crouch and in a flappy touring jacket. I think top speed in these circumstances is dependant on your clothing and how close you can get to the paintwork. Oh, nearly forgot, I run a 22 tooth sprocket.

You may want to look at your gearing as well. The gearbox sprocket will make a big difference to your top gear acceleration. I ran a 23 tooth for some time with a standard head and my own and while a bit breathless in standard trim, the head made it a useable proposition. Even with a standard head and a 23 tooth sprocket it was a very relaxed ride at highway speeds, only running 3500 rpm at 70 mph. Overtaking in top was still useful and I felt no need to drop to third which, gearing wise, equates to about top gear on a 750 with a standard 19 tooth sprocket. I have found, that for me, the 22 tooth is the best compromise.

Now, I'm not saying to go out and buy a Fullauto Technologies head , which is more than your budget will allow, but I am saying for me, the performance of a standard 850, or 750 for that matter is perfectly adequate in most circumstances. The fact that you ride more modern bikes with much more power probably spoils things for you in that department to some extent. You just have to modify your riding style and frame of mind to suit. I run a Buell X1 as well and while the Buell is a real animal on the road, the Norton is a nicer ride overall.

I spent much time in my first few years of ownership just setting the bike up and addressing certain issues that I came across as I became familiar with the bike. It would hit a brick wall at 5000 rpm and was reluctant to rev past it. After buying the Sudco Mikuni tuning book (worth every cent) I found that my bike had the wrong rubber manifold adapter which had a restriction in it. Basically, it went down to a 31 mm restrictor. I bought the correct one and bang, power in the top end restored. Not that I go there much. I just love the low end and mid range that a standard Norton provides.

Regarding performance enhancements, back in the 70s I had a MK2 850 which the previous owner had fitted a 2S (Combat) cam, a 2 into 1 exhaust, and removed the aircleaners of the Anals and rejetted. This thing got to 4500 rpm and went like a scalded cat. Very impressive.

Regarding name calling, I come on this site and find that it is a very respectful place and a nice place to be. Please keep it that way.

Fullauto said:

I attribute most of the lack of performance to the excess weight (OF THE) owners

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slightly modified, may not be applicable in all instances :shock:

Crusadersports -

RE: question about rear sets and rear brake.

Non issue in my experience.

Keith

I do not have much experience with Nortons as I am a fairly new owner, but when I purchased my MKIII, it had the single 34mm Mikuni on it along with a Boyer ignition. I decided to go with the PWK flatslides from Jim Schmidt, and could not be happier. Jim's customer service was awesome and they were a straight swap.

During this time, I also swapped the Boyer for the Power-Arc ignition and the bike is transformed into a beast. Before, it would lug along, and now the bike is so much more responsive and revs much quicker. For the price, and ease of installation, JS flatslides are the best bang for the buck hands down. Hope this helps a little bit, and your bike is absolutely gorgeous!

Keith, I ran single Mikuni 34 on my 850 for 15 years and about a year and a half ago I switched to JSmotorsport's flat slides.

Just do it, don't agonize over the decision any more. Lots of people here can attest to buying the flat slides.

Honestly, you will be amazed and wish you had made this changeover earlier.

Again, they start first or second kick, idle like a rock, and just flat flow, flow, flow, all the way up.

The conventional wisdom is that a single carb is "better", presumably strong, off idle up to around 4500rpm when they run out of poof.

Remember, conventional wisdom only has to be right 51% of the time to be the prevailing contention!

When I installed my flat slides, my 850 came alive, and I honestly feel that it is stronger than the single Mikuni not only above 4500 (hugely so), but it is also stronger right off idle and through the midrange.

Nope, I have never dyne tested my single versus my new flatslides, just going by seat of pants feel.
And if it feels good, do it, as Flip Wilson used to say!

once again, I'm late in putting my 2 cents in, as I don't have the time to check the forum everyday. That being said, I hope you are still checking this topic. Not being a master mechanic or nearly as knowledgeable as most of the contributers to this forum, I probably shouldn"t say anything, but sometimes a different point of view can be educational. I took your query to mean that you were looking for a little more get up an go rather than a motor rebuild. Is this true? If so, here's what I think. I agree with the point that something is not quite right with your overall set up. Don't have any idea what it could be, but you should have plenty of juice to be able to pass like you want. A single mikuni, set up properly, with timing correct, will still give you plenty of rpms, unless you are into racing. The set up on my mk111, with a Sonny Angel manifold,allows me to run very strong up to about 6800 rpms, and at 100 mph it is still pulling. I also have a K&N filter custom made to accomodate the angled manifold. 750 headers and straight thru Interstate mufflers. Boyer ignition. Dual carbs were removed many years ago as I was tired of fiddling with them. The mk111 is a heavy bike (by Norton standards), so by nature it's not going to be as fast as the earlier ones. I ride regularly with a guy has a Bonneville, MAP pistons and rods, hot cam, belt primary, dual amals, Boyer, much lighter motorcycle, and we weigh about the same. He has trouble keeping front wheel on the ground when we race, but the Norton is right there with him, and starts to pull away in 3rd. He catches me in 4th at about 105, and then we ease off. He has a lot of cash invested in the motor, and it is quick, but is it worth it? Only the owner of each bike can answer that question. I did notice Jim Comstock was pretty silent on your post. I find that intersesting. Get a better air filter.

Once Jim chimes in the guy will need a" fist full of dollars" :lol:

Rohan said:

We think you should just try it with a decent big air cleaner to begin with.
Commandos have a fair bit of go as stock.

A lot of these missile cars around have 'hi-flow' air cleaner elements available, and gain quite a fair number of ponies just from that. Not that this has much to do with Commandos, but that air cleaner you have seems to be the reverse idea, bottling it up as it were...

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Agreed. I found that air cleaner thats sold with the mikuni kits to be way to restrictive. The bike was running way too rich, no matter how the carb was tuned. So I pitched the little cleaner and replaced it with a big foam UNI filter ($20). Now I'm running the needle one notch below the middle, and the biggest main jet (240?) that came with the kit. I'm sure highway performance could still be improved, but passing cars that are going 60 isn't a problem.... with a downshift, 19T sprocket here.

cheers,

Don