Best carbs for Nortons

I have Jim's PWK carbs on my hot Norton Jim jetted them for the cam they have been on now for 7 years and once tuned I haven't touch the settings, the only problem I had with them every so often one float would stick and leave its mark if I left the fuel tap on but it was a easy fix, but I do miss the ticklers, but the PWKs have worked well with the JH Maggie and my hot motor.

Ashley

Craig said:

Just took a look in shed, found the manual mentioned above ... it is the ”Clymer Norton -Service-Repair Handbook” .... it states 80hp plus at rearwheel possible without the use of exotic parts ..... 750cc Nortons “built and campaigned by Rob Wood and Alex Jorgenson in AMA National Circuit racing , they used no special factory pieces that cannot be purchased” ..... going to have to read this last chapter .... from open end of velocity stacks to gasket face on cylinder head should be 9.5” or 240 mm , however they may need to be shortened to clear frame .....

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I've not seen that performance supplement before, sounds interesting. Can't find reference on the web either. Any chance of a scan?

Cheers

Sure,once my wife returns , maybe tomorrow , it is lengthy will send it via PM .... or other method if you like

Craig said:

My dyno is the seat of pants , .

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Well... the butt dyno is notorious for its erroneous conclusions. Not saying yours is wrong, of course!

My work with performance (car) engines and dyno/track testing revealed that very often, engine changes that were 'felt" to increase power frequently did the opposite. One of my favorite examples is the newly installed larger carburator that, per the driver, "really increased the power; you can feel it!" The car then proceeded to turn 1/2 second slower in the 1/4 mile. What he "felt" as a big power surge was the increase in power after the flat spot that the new carb created. The original, smaller CFM carb pulled immediately from low RPM and had a constant power increase to red line so there was no surge in the power curve - just smooth acceleration that produced a quicker car.

Craig said:

Just took a look in shed, found the manual mentioned above ... it is the ”Clymer Norton -Service-Repair Handbook” .... it states 80hp plus at rearwheel possible without the use of exotic parts ..... 750cc Nortons “built and campaigned by Rob Wood and Alex Jorgenson in AMA National Circuit racing , they used no special factory pieces that cannot be purchased” ..... going to have to read this last chapter .... from open end of velocity stacks to gasket face on cylinder head should be 9.5” or 240 mm , however they may need to be shortened to clear frame .....

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Maybe a little misleading. The only 750 Norton of Ron Wood's that made over 80 hp was a short stroke with billet crank, welded cases, Carrillo steel rods, forged pistons (Arias, I think, but not sure of that memory), trick Axtell cam, Axtell modified head with bigger valves, Dellorto carbs, and Lucas racing mag. Axtell wouldn't sell his Allegro cam to anyone he didn't already trust to build the engine properly, and he wouldn't do the serious head work for you unless he trusted you. The one piece Moldex crankshafts were not a stocked item, so you had to have them made on special order. Same for the pistons and rods. So, the statement of "no special factory parts that can't be purchased" is not exactly correct. Yes, they were not special factory parts, but that doesn't mean that you could purchase them. 80+ hp at the rear wheel from a Commando 750 isn't that easy! I'm pretty confident that the team of Axtell, Mike Libby, and Ron Wood were the first ones to do so without using methanol and nitro.

I've got a couple of Clymer Commando manuals, but they don't mention the supplement. I've heard about it for a while now, but never seen it. If you do manage to scan it, would you mind sending me a copy also? I'd love to see what it says. PM would be fine. Thanks.

Ken

Yes I will ! my Wife left earlier with her sister and 92yr old Mom , they have the old girl at hospital ... definitely get it done and sent .... think it 15 pages , came with my bike many years ago , photo of cover , look at upper right hand corner

Page one chapter 11

MexicoMike said:

Well... the butt dyno is notorious for its erroneous conclusions. Not saying yours is wrong, of course!

My work with performance (car) engines and dyno/track testing revealed that very often, engine changes that were 'felt" to increase power frequently did the opposite. One of my favorite examples is the newly installed larger carburator that, per the driver, "really increased the power; you can feel it!" The car then proceeded to turn 1/2 second slower in the 1/4 mile. What he "felt" as a big power surge was the increase in power after the flat spot that the new carb created. The original, smaller CFM carb pulled immediately from low RPM and had a constant power increase to red line so there was no surge in the power curve - just smooth acceleration that produced a quicker car.

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The performance increase with flatslides such as the PWK Ashman and I use is mainly in the midrange because thats what a flatslide has to offer. The efficiency of the flatslide seems to give the motor more pull in the midrange than you get with a round slide.

ashman said:

I have Jim's PWK carbs on my hot Norton Jim jetted them for the cam they have been on now for 7 years and once tuned I haven't touch the settings, the only problem I had with them every so often one float would stick and leave its mark if I left the fuel tap on but it was a easy fix, but I do miss the ticklers, but the PWKs have worked well with the JH Maggie and my hot motor.

Ashley

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Ashman - the hang up in the bowl is because of the 4 ribs on the sides of the float needle jet. The corners near the tip are too square and when one of the ribs lines up with the hole in the float needle jet it can hang up and cause flooding. Use a tiny jewelers file and carefully rub off those corners at a 45 deg angle and that will fix it. I missed this on the early carbs but fixed em all when I figured it out.

Craig said:

Sure,once my wife returns , maybe tomorrow , it is lengthy will send it via PM .... or other method if you like

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Thanks Craig, PM is fine. My manual definitely doesn't have that supplement. I love reading 'hop-up' articles from when the bikes were new.

jseng1 said:

Ashman - the hang up in the bowl is because of the 4 ribs on the sides of the float needle jet. The corners near the tip are too square and when one of the ribs lines up with the hole in the float needle jet it can hang up and cause flooding. Use a tiny jewelers file and carefully rub off those corners at a 45 deg angle and that will fix it. I missed this on the early carbs but fixed em all when I figured it out.

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Hi Jim when it first done it you made contact to me and told me how to fix the problem and so far hasn't done it again after adjusting the floats with a bit of side adjustment but you might not have known about the 45deg problem at the time so if it does it again I know what to do, as you say these carbs work well with the JH Maggie and my cam and best performance mid range.

Ashley

Craig said:

View attachment 13886 Page one chapter 11

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Yep that's the same as my manual I think I brought it new in 78/79 or around that time from my local British bike shop at the time I have picked up a few other manuals over the years but none have chapter 11 in it, it was very helpful when building my hot motor for the Featherbed frame.

Ashley

My wife has scanner hooked to printer only for her music .... plan to photo each page and send them in batches , hope that works

jseng1 said:

The performance increase with flatslides such as the PWK Ashman and I use is mainly in the midrange because thats what a flatslide has to offer. The efficiency of the flatslide seems to give the motor more pull in the midrange than you get with a round slide.

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Top end power gives bragging rights, however 'torque wins races'. When you feel a power increase, what you feel is probably mid-range improvement. However, often you don't know you have an improvement until you raise the overall gearing ad the bike accelerates faster as you race-change up through the gears. The heavy Commando crank is always reluctant to spin up on the throttle, so you need to keep it spinning well up in the usable rev range. If I race, I usually don't go below 5,500 RPM or above 7000 RPM. The gearbox is probably more important than the dyno figure for ultimate horsepower.

If you are using the standard gearbox in your Commando, you would probably be more likely to notice any improvement in midrange power. But the standard box is hopeless, if you want performance. Once you lose revs with the heavy crank, it takes ages to get the revs back to where the motor really pulls hard.

Al ,I very rarely reach past 4500 rpm , for fast rides as mentioned previously the Ducati suits me just fine .... the Commando runs with single 34VM mikuni and 21T countershaft sprocket , built for nice Sunday rides , does an excellent job of it too

[QUOTE="acotrel, post: If I race, I usually don't go below 5,500 RPM or above 7000 RPM. The gearbox is probably more important than the dyno figure for ultimate horsepower.[/QUOTE]
You do realise that a water cooled Yamaha TZ 350 E /F/G will have a wider power and than this?

Bernhard said:

[QUOTE="acotrel, post: If I race, I usually don't go below 5,500 RPM or above 7000 RPM. The gearbox is probably more important than the dyno figure for ultimate horsepower.

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You do realise that a water cooled Yamaha TZ 350 E /F/G will have a wider power and than this?[/QUOTE]

My motor has a power band from almost zero to 7000 RPM. I only use the top 1500 RPM. If I lose over 2000 RPM on a gear change, the bike is too slow due to the heavy crank. The problem is, you have to wait while the revs rise again from the lower point in the rev range. When I race-change I simply back-off slightly and stand on the lever. I lose as few revs as possible. I only ever use the bike on a race circuit and I never ride it slowly, so my situation is very different to that which occurs with a road bike. With close gears, a road bike would be much better when passing trucks. With a race bike, you play it like a piano.

The 750/850 Norton and TZ 350EFG Yamaha are as different as chalk and cheese, ones a road bike then attempted to convert it to a race bike the other is or was a GP winning machine. The 350 only produces about 60ish bhp but has a 4000 rpm power band as much as 4500 with the latter powerjet carbs and a finely worked out close ratio gearbox to suit the engine's characteristics. True it has no bottom end power- you don't need a pilot jet system on a GP bike it never has provision for lights or carrying your girlfriend/wife / mother/ grandmother- do you really want excess weight on the back if you are racing in open races? As much as I admire you on your Seeley Norton, give me a bike that was built to do a job i.e. win GP races over an adapted road bike for the race tracks any day- I know which will make the chequed flag first.

acotrel said:

The heavy Commando crank is always reluctant to spin up on the throttle, so you need to keep it spinning well up in the usable rev range.

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Bullocks. Maybe a stock motor, but a good hot street/race motor build can spin up very quickly. I have to watch mine constantly as I can hit redline very quickly, and I could never really do that before it went though its rebuild.