Plug pics

Bernoullis equation is common sense.

http://www.princeton.edu/~asmits/Bicycl ... oulli.html

It's not rocket science unless you are building a liquid fuel motor. It is all explained rationally and simply here :

http://www.livescience.com/47446-fluid-dynamics.html

Hi,

considering that the picture was taken after normal riding I would see the darker as normal. Normally you ride the last mile to your garage in the city, where the pilot system has an big impact. I would check the left one side for air leaks and try to set it more rich at the pilot screw.

Ralf

Don't you guys usually set the pilot screws by winding each of them out three turns from fully closed, start the bike idling and if the screws control the petrol, wind them in until you get the miss then back off slightly ? I wouldn't expect that difference in plug colour from poor idle screw adjustment, the bike would run like a bucket of bolts when idling.

acotrel said:

Don't you guys usually set the pilot screws by winding each of them out three turns from fully closed, start the bike idling and if the screws control the petrol, wind them in until you get the miss then back off slightly ? I wouldn't expect that difference in plug colour from poor idle screw adjustment, the bike would run like a bucket of bolts when idling.

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You're right, normally 3 half turns is ok, but the correct setting can differ about 1/2 turn. It is often tricky to hit the best spot. I experienced that a half turn can change the plug color.

Edit: I would check for air leaks anyway.

Amals are designed for base level fuel level that gives best idle and response off idle with 1.5 pilot air screw turns open but as long as feul level adequate the engine responds to stumble at too many or too few turns then its quite adequate to get best idle and response to move on to other issues causeing stumbles etc. Idle is supposed to be set with engine fully warmed and should need a tickle or choke for initail start of the day or if totally cooled for many hours. If not then base line tune is too rich and may wear bores faster.

Wow, guy asks a question about spark plugs and we end up with engineering fact/fiction/theory/ideas/myth/better ideas and etc. Comical that a lot of posts go this route no matter what the original thread was. If all of you gentlemen had been on the Norton engineering staff back in the day, we would for sure have had an awesome bulletproof machine,,,, or none at all. :mrgreen: I do so enjoy it though. :wink:

Biscuit said:

Wow, guy asks a question about spark plugs and we end up with engineering fact/fiction/theory/ideas/myth/better ideas and etc. Comical that a lot of posts go this route no matter what the original thread was.

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Getting to be the rule rather than the exception...

Biscuit said:

Wow, guy asks a question about spark plugs and we end up with engineering fact/fiction/theory/ideas/myth/better ideas and etc. Comical that a lot of posts go this route no matter what the original thread was. If all of you gentlemen had been on the Norton engineering staff back in the day, we would for sure have had an awesome bulletproof machine,,,, or none at all. :mrgreen: I do so enjoy it though. :wink:

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I don't believe this thread was hi-jacked. A question was asked and answered. If you have not got the smarts to understand what is involved, that is your problem. There is not much on an early commando which could have been done better for which the customer would have accepted and paid the price. A decent management system would have been good, however the basic bike design is limited in potential. That is the beauty of it.

Bugger - somehow I have deleted the text from here when I intended to quote the text.
Sorry about that.
Ta.

Thread originator here. Yes, my original question, which was do these plugs indicate any need for significant changes in jetting or ignition setting, was well answered and I do appreciate that. I guess I started the tangent when I posted that the left hand carb, the one with the leaner plug, was flooding at times especially after the tickler was pressed, perhaps indicating the float level was too high. It also massively flooded when I accidently left the fuel tap on the other day. I took the carb apart, an Amal Premiere with a stay up float and aluminum needle, and found that the top of the float when the tang was pushed down was proud of the bowl by a small amount. My guess is that the top of the float was fouling on the base of the carb body and not letting the valve seat. Anyway, I very slightly bent the tang on the float so that the top of the float was level with the top of the bowl. When I reassembled the carb the flooding problem seemed to be cured. I also checked the fuel levels in both carbs with a u-tube. Both measured right at .24" which is the bottom of the Amal recommended range. It also depends where you measure at the front of the bowl or center because of the tilt of the carbs.
I'm aware that the setting the fuel/float level is the first step in carb tuning and am trying to keep within Amal specs. There has been a ton of discussion on setting the stayup floats on the Triumph Bonneville forums and this seems to be a common complaint. Set them near the top of the Amal range and they tend to foul on the base of the carb body. Some people attribute it to the way the tang on the float interacts with the float needle. I have them on my 74 Bonneville and found it ran best when set right at the bottom of the Amal range at .24.
Plan is to put some new plugs in, see how it runs and then do another plug check to see if there was any effect from slightly adjusting the fuel level.

htown16 said:

Plan is to put some new plugs in, see how it runs and then do another plug check to see if there was any effect from slightly adjusting the fuel level.

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You could change over the plugs to the others side at first.

Towner said:

htown16 said:

Plan is to put some new plugs in, see how it runs and then do another plug check to see if there was any effect from slightly adjusting the fuel level.

Click to expand...

You could change over the plugs to the others side at first.

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At this point what would swapping plugs prove? Would just muddy the waters I think. To observe any changes accurately new plugs are called for. Just as htown16 plans on doing. If plug colors equal out, and you're satisfied, fine. If not, consider what I mentioned earlier about swapping needle jets along with needles, or complete carbs. Granted, would be a pain in the ass to tickle the carbs as a permanent installation but temporarily would not be much trouble. This would tell you for sure if the different plug shades were carburetor caused or engine condition.

And by the way acotrel I never thought of this thread getting hi-jacked, only straying a bit with extraneous sparring...And I do have the "smarts" to understand what is involved with tuning Amal carbs. 50 years with the same Commando with it's original (though sleaved) carbs gives one a fair idea of how they work. Did you not notice these guys :mrgreen: :lol: ? I was just having fun.

:lol: :lol: :lol: Oh no Biscuit.
By your own admission, the fun police are building their case!
Prepare for swift and violent retribution until the status quo is re-established. :lol: :lol: :lol:
Ta.

Back to you OP. Thanks.

When people start controlling the discussion to the simplistic level, I am outta here. The issues with the commando design are not always simple. These days at least in Australia, we are obsessed with 'dumbing down' - perish the thought that anybody might actually develop some engineering skills. I suggest we should all think long and hard about where the real value lies in forums such as this one. Why would anyone bother to read Jim Comstock's or Fast Eddie's posts - you could buy yourself a very nice Japanese four cylinder bike and never go there ?

Hi all,
I asked a question of Burlen Limited - The SU and AMAL Carburettor Companies via email:
" I have a question about the following product: - MK 1 AMAL Concentric.
I can understand how a high fuel in bowl level may result in a rich air:fuel mixture as it creates a condition similar to flooding with ticklers.
Since fuel is drawn from the bottom of the float bowl for idle circuit and main jet surely setting the fuel level at say 10+mm from bowl lip will still ensure fuel is drawn through jets.
I can appreciate that setting a lower fuel level means could create a lag in throttle response time as the fuel must be lifted the additional few mm. Only uncovering the jet or idle intake could result in an ongoing lean fuel condition perhaps caused by the float needle/seat assembly restricting fuel flow. Please provide the rationale for stating in your literature that a lower fuel level in the float bowl results in a lean condition.
Thank you."

Their response was:
"The basic principal is a stronger force of air is required to lift the fuel though the jet from the bowl, put simply more air equals a weaker mixture.
We hope this is of help."

As they are the manufacturers of AMAL carburettors, it appears I am wrong and I therefore apologise and stand corrected.
Ta.

Biscuit said:

Towner said:

htown16 said:

Plan is to put some new plugs in, see how it runs and then do another plug check to see if there was any effect from slightly adjusting the fuel level.

Click to expand...

You could change over the plugs to the others side at first.

Click to expand...

At this point what would swapping plugs prove? Would just muddy the waters I think. To observe any changes accurately new plugs are called for.

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OK - may be better to check whether the fuel level job was successfull at first. But I suppose this didn't cause it. He said that the leaner side was higher anyway. And I experienced that a minor change of the float height does not change much. You just have to ensure that the height of both floats are equal. The plug colors have to be equal then or you have another problem.

Ralf

I have been all over the place with float levels in a few Cdos, one that would not even start till float reset high enough that the pilot screw became effective in both directions. I can feel the difference off idle response with a bit higher float level so pilot screws set just a tad less than 1 turn out ~ .7 & ~ .9 in my factory Combat - set by just bumping valve seat by guessing then seeing if it started and was tunableable, so left em that way for a few years now and no intension to shoot for the ideal 1.5 turns. Point being as long as pilot screw turns will bog engine turning out or back in then float level is quite good enough. Higher feul level &or lower spray tubes, especially with notch gives feul a shorter-faster path to climb & spill out into air flow. I can not remember how long ago was last time I measured float level to gasket surface if that gives idea how uninformed hobot is on this. On the 850 that would not start I held bowls with feul hose on off to side to see where float actually closed valve [had owner help to work taps] with bowl slight cannted like mounted.

acotrel said:

---- you could buy yourself a very nice Japanese four cylinder bike and never go there ?

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Why limit yourself to a 4 cyl. You could get a very nice twin too, the FZ07 comes to mind, RC51, TL1000 etc... but now I'm guilty of helping to de-rail this interesting thread. Sorry htown16

Do keep in mind the R plug looks as much oil wet as fuel sooty though both within expected variations. So once fuel dialed in if still shows darker and lighter on same sides, implies opening top to check sealing.

Got everything back in and went for a test ride today. Left hand carb tickles normally now and does't continue to leak gas. Started on one kick, pulls good, idles good. Now to enjoy some spring riding weather.