Needing Air

Re: Needing Air quantified

needing said:

Hi WZ507.
I only have a standard Smiths tacho so the incemental RPM changes can only be a guess.
The AFR gauge also fluctuates as seen in the video but I may be able to trial another one.
Which of the recording sheets below best suits your needs?

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I like the first option, where the idle air screw is rotated from closed to 4 full turns open (if I understand the format option properly).

Hi WZ507.
Goodo. I'll give it a whirl and hopefully it eventually translates through to other bike's AMALs.
I'll summarise the mod stages of each phase of tuning to my carbys when trials are complete.
Ta.

Trial run into the hills and along the coast today with all phase 1 mods in place.
AFR looks to be between 11.5 to 14+ at various (inc. cruising) speeds with lean spikes under hard acceleration. Standard component set-up is 30° BTDC, 32mm bodies, 105 needle jets, 200 main jets, mid notched long needles, 850 notched spray nozzles, 32->30 tapered manifolds and 3.5 cutaway slides.
Dyno runs to optimise ignition timing and phase 1 carby tuning scheduled for midday tomorrow.

Hi WZ507.
Quick update: a quarter turn inward of the air screws dropped AFR from approx. 14 to 13. An eigth turn assessment may be more use given such a large change.
Ta.

if you really have a Combat spec 750 then something must be wrong with your TDC mark or spark timing as both my real Combats would back fire so bad at 29* to 32* it would either toss me to ground hard or injure my foot bone or knee joint. I thought I had gotten Trixie extra good tuned with Amals and points optimally for 29* best timed by light but when I put pressure in chambers and balanced crank not to turn saw Trixie TDC mark was off most of one degree so really only 28* total adv - which is limit I hit on Peel too before hurting me to start, so both exactly same 28* or Ouch. If you have base plate and copper gasket instead of just FlameRign like Peel or Trixie then might of lowered CR enough to tolerate one more degree adv. but takes some the zing out of 2S cam.

I do not know if extra high octane would help the backfire above initial timing to get away with 29+* full adv starts but I do not think it would help at the slow kick over rpm only at faster rpms under load. Maybe you have leaned out enough to slow combustion down enough to take more adv but that lean lowers heat PoWer so less thrill nailing it. There are forums on mileage misers so would be bragging rights to get over 60 mpg out of a spunky responsive Combat that invites you over the ton because it gets so eager to do so its hard to resist. HIghest mileage reported is a fella on Brit Iron list in UK that averages 70 mpg but geared tallish for freeway type commutes.

When bored might try an rough cut 1/16 inch intruding manifold gasket though I think only the lower half turbulizer is doing the trick either re suspending fuel or easing the port bend or both.

needing said:

lean spikes under hard acceleration.

Click to expand...

200 Main Jet? That seems way lean to me.

Ta has me me on his Foe/Troll list so he won't see this so somebody could pass that on to Mr. Wizard.

Fee fie foe fum PeteV 200 main jet is definitely on extra lean side for a real Combat spec engine, 10CR and 2S cam, so maybe what is allowing the milegage miser 30* adv w/o back fire injury. Aircraft pilots have learned they can go extra lean in steady flight on full spark adv efficiency d/t too lean to burn fast or hot enough to detonate. But aircraft pilot doing this are watching all CHT and EGT as well as detonation sensors to guide them. Still if needing has gotten extra good fuel atomization then could be doing something better than rest of us, if not seeking full power potential of real Combat spec engine. IIRC my Trixie Combat likes 240 jets but she has race needle with more tapper richness before WOT reached. Trixie 19T gets 50s mpg if run easy and speed limit legal. The HD groups I quiz at gas stops say they also get 50s mph if going easy at legal rates. Trixie drops to low 40 mpg if kicking up heels over 6000 for most an hour but Peel ~22T ratio with belt drive got like 33 mpg in sport bike spanking games that would last 30-60 min mostly above 6500 but upper 50s on 90 mph easy cruise.

Its all about Commando love to me not motorcycle jerks socializing so must be thick skinned to follow experimenters to accept or reject their findings.

pete.v said:

needing said:

lean spikes under hard acceleration.

Click to expand...

200 Main Jet? That seems way lean to me.

Ta has me me on his Foe/Troll list so he won't see this so somebody could pass that on to Mr. Wizard.

Click to expand...

Somebody had to do it!

Nater_Potater said:

pete.v said:

needing said:

lean spikes under hard acceleration.

Click to expand...

200 Main Jet? That seems way lean to me.

Ta has me me on his Foe/Troll list so he won't see this so somebody could pass that on to Mr. Wizard.

Click to expand...

Somebody had to do it!

Click to expand...

I tried putting someone on the Foe list once I think it was Aussie Phil Yates. It didn't matter cause I always had to look at he wrote.

You can add me to your foe list if you want to, but i bet you'll look too

Re: Needing Air and fuel to burn efficiently

Hi hobot.
I forgot to mention that the Exhaust Gas Temperature (EGT) gauge on my bike operated in the 700 to 740°C range during the high speed running of yesterday's test ride. Plug and piston crown inspection shows no hint of damage (beautifully clean in fact).
The timing is set at 30° BTDC having compensated for a large TDC error. Dyno run today will establish optimum setting I hope. No problem with kickback but the sealing ring under the skirt requires that I open the throttle slightly when kicking to actually allow the tickle flooded fuel into the engine (chokes were removed long ago).
Combat engine 0.5mm copper base gasket and original copper head gasket with 200psi compression. Cam designation unknown.
Ta.

needing said:

, 200 main jets, .

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That seems terribly lean - as noted here previously - if you ever got it up onto the main jet ?
Presumeably not, or would have seen egt much higher than that....

Rohan said:

needing said:

, 200 main jets, .

Click to expand...

That seems terribly lean - as noted here previously - if you ever got it up onto the main jet ?
Presumeably not, or would have seen egt much higher than that....

Click to expand...

I thought it was important to jet from rich to lean to avoid damage during testing.

forgot to mention that the Exhaust Gas Temperature (EGT) gauge on my bike operated in the 700 to 740°C range during the high speed running of yesterday's test ride. Plug and piston crown inspection shows no hint of damage (beautifully clean in fact).
The timing is set at 30° BTDC having compensated for a large TDC error. Dyno run today will establish optimum setting I hope. No problem with kickback but the sealing ring under the skirt requires that I open the throttle slightly when kicking to actually allow the tickle flooded fuel into the engine (chokes were removed long ago).
Combat engine 0.5mm copper base gasket and original copper head gasket with 200psi compression. Cam designation unknown

Click to expand...

Hm I set spark degree by feel too then look later to measure. 200 psi is full Combat effective CR, I guess its a success to need to crack slide to kick over and I notice some drag on number 3 vs 3.5 cut out. I believe this slightly richer slide helps my 1 step on cold starts on shut throttle and just a tickle, often just one side. Self contest to guess how much bowls empty to hold plunger just long enough not to drip.

I always like to hear about Commando power successes so keep at it till tranny crys out and all your fasteners so dry they rust.

Hi hobot.
Float bowl fuel level is set at 5mm below lip of bowl on both carbys.
Ta.

5mm means nothing just a number, its level should be set by gosh by golly until pilot screw has the best effect you seek which I will assume you did then later took float level measure, or did ya just set float by some rule or by trial error - because your pilots screws at least were effective to get good idle? Maybe be optimal now but how do ya know?

hobot said:

5mm means nothing just a number, its level should be set by gosh by golly until pilot screw has the best effect you seek which I will assume you did then later took float level measure, or did ya just set float by some rule or by trial error - because your pilots screws at least were effective to get good idle? Maybe be optimal now but how do ya know?

Click to expand...

Hi hobot.
The float bowl fuel level was set ages ago. The -5mm from lip (when bowl is level) ensures zero flooding risk when carbys are fitted at the angle for Norton Commando engines. The count of three to tickle flood validates this setting and the difference in fuel lift through the jets is indeterminable.
The same set of bowls, their internals and gaskets are used on each set of carbys to eliminate variation in tuning experiments.
Ta.

alrighty you know your baselines then so carry on refining the basic starter kit Norton once sold.

Re: Needing Air quickly going in one end and out the other

Dyno runs successful for my roadgoing Norton Commando Combat Roadster.
Last power run (in 3rd gear) shown in video (peak RPM at 7962). Top speed 170km/h.
Chart redacted to show only AMAL carbys throttle opening of interest.
Ta. to Tony at Race Bike Services.
Click to activate video.

Re: Needing Air inside the tyre

My current back tyre is a Roadrider 120/90x18. Unlike the 19" rim, the 18" does not have a rim lock to securely fix the tyre to the rim. The down side of developing the tuning of AMAL carbys is the separation of the valve stem from the tube rubber around it. 100km from home but a single bolt QD back wheel made swapping to a 19" easy-peasy (thank you Norton engineers!). Note to self: no lubricant to be used on tyre when refitting after tube replacement and maybe add a bead of cyanoacrylate (superglue) to the bead when reinstalled. Gotta love that Combat power! Do they make a 18" rim lock?
Ta.

Use tyre soap, forget glue, don't ride on a soft tyre.

Ta-ta, your post is too crytic to interpet. Did the dyno spin 120x18 on rim or you are just concerned that it might, on a fully inflated tube/tire? My P!! lowered frame and forks dragster had 3 rim locks but that was for flat drag slick. I do not think engine under 70 hp 70 trq can develop enough tractionon on street profile and compound tire to spin in rim even w/o locks just air pressure grip. 18 inch rim locks are common size to find online or bone yards with cycles made up to late 70s with spoke rims/hubs before solid cast wheel became cheaper. Another alternative with less mass to spin is the Tubeliss semi tubeless inner inner tube that off roader use to keep tire on with very low PSI. Its not DOT rated for hwy use fitted one to Peel 18 WM3 rim and spoke with the maker about hwy use and we both agreed likely just fine as the only worry would be heat developed at hi sustained speeds but there not nearly the heating flex of road inflated tire compared to the easy flexing of most flat tire off road. There is some concern maybe over 130 mph or so when centrifugal forces might lift the Tubliss locker out of rim valley enough to leak spoke air but its inflated to 110 PSI and rather tough material so I doubt that would bother it. Btw I could not view the whole image of the dyno curve.

http://nuetech.com/tubliss/#sthash.YdVBo8xo.dpbs