Cure for leaness

htown16 · Jul 21, 2015

I've got one plug that looks just slightly too lean. I would try raising the needle but the clip is already in the bottom notch. It's currently a .106, would going to a .107 be a possible solution? Just ordinary street driving, very little if any 3/4 throttle and above riding, so not much main jet input.

1up3down · Jul 21, 2015

one plug slightly richer or leaner looking than the other is no cause for concern or effort to make them the same, imo

even perfect jetting with a new motor can show slight plug differences

htown16 · Jul 21, 2015

Not so concerned that the plugs match. Just that the one really is too lean.

Anonymous · Jul 21, 2015

htown16 said:
I've got one plug that looks just slightly too lean. I would try raising the needle but the clip is already in the bottom notch. It's currently a .106, would going to a .107 be a possible solution? Just ordinary street driving, very little if any 3/4 throttle and above riding, so not much main jet input.

Check that the two pinholes are clear as they augment the fuel flow at early throttle opening before needle jets come into full draw then trial a smaller cutaway if available. I was surprised just how much running around town is done at these early throttle openings i.e. less than 4000rpm range.
Ta.

lrutt · Jul 22, 2015

You could likely correct that and have both carbys the same by adjusting float height. Make sure you are running same fuel level in each. that is important. A slightly higher level will run a little richer.

htown16 · Jul 22, 2015

Will have a look at the float levels.

Hobot · Jul 22, 2015

I like my float on the hi side so less than one air screw turn out for bit better start and low rpm but ideal is diddle floats till each pilot is 1.5 out which is Amal baseline feeding the rest. Just saying can get sense of float level effect by pilot screw position. If both pilots the same regardless of best position tends compensate equalize carb and chamber variations to help balancing r/l. Jay Leno shows his Norton twins not bluing pipes yet doing everything well, the big braggart.

vintner · Jul 22, 2015

Also have a check for air leaks at manifold etc.

htown16 · Jul 22, 2015

Here's some picts. Right side one looks about right to me, ring of carbon on the flat. Left just a bit lean, only about quarter ring of carbon on the flat. Pipes are also showing this, right is a straw gold with touch of blue and left has a lot of deep blue. Don't know how Jay Leno or should we say his mechanics do it. Maybe very rich photo's better. Maybe they change the pipes after each ride. Will get out to the garage and look at the float levels one of these days, about 105 degrees in there right now.

dave M · Jul 22, 2015

These plugs both look too lean to me in the photos.

Hobot · Jul 22, 2015

Talk about a big braggart Htown dammit dont ya know ya aint supposed to tell people yo-a from Texas, Magnolia no less, just let em guess, so as not to embrasures them cause they aint.

How many miles on those sweet looking plugs? I run 87 octane often enough I like to see more soot and no matter what I promise self I always get a bit carried away on a Combat 2S cam zone.

Jay makes specific mention of the nice intact chrome as buider signature tune, plus cheating with Ceramic coating, I forget between breaks what to do so paying attention here just in case...
http://www.nbc.com/jay-lenos-garage/vid ... ss/2783179

plain jane thats just as nice.
https://www.youtube.com/watch?v=1P1hMDrEHso

o0norton0o · Jul 22, 2015

dave M said:
These plugs both look too lean to me in the photos.

Exactly. They are pretty close to each other in color and both very lean. Both of my plugs have a light brown dusty color on the insulators. They are close in color to each other, but not exactly the same and I don't worry about it...

You should check your needle position in the carb body. Maybe move the clip down a notch to raise the needle to make both richer, especially if the clip is on the top notch of the needle presently....

htown16 · Jul 22, 2015

Probably less than 100 miles. Can't raise the needles, the clip is in the bottom notch on both.

dave M · Jul 22, 2015

I suggest you try a larger main jet and set the needles in the middle position.

o0norton0o · Jul 22, 2015

well....... from the looks of your signature, you have 6 british bikes, so I doubt I am going to tell you anything you haven't already heard, or aren't currently considering. There are a couple of different needle types, maybe you have the wrong needles in your carbs... How many notches on your carb needles and what carb's are they? 930's??

I've heard people say that if your gas cap's breather gets blocked that it could restrict gas flow... I've always been dubious of how much that would effect gas flow, but I supose it could...

If you only run your bike up to 6000 rpms and the plugs look that lean, I would think it's the needle and needle jet issue of some sort. (obviously you are thinking that too..)

daveM, I think you mean change the needle jet to a larger one, not the main jet.... Right???

Hobot · Jul 23, 2015

Actually with less than a tank of lean burn modern fuel its hard to tell much except ya do not have much oil leak into chambers so far. Shoot I could get similar on new plugs going to mail box and back. A few tanks will give more on general tune and seal while classic plug chops takes some expense and planning and still hard to interpet in todays world. It may or may not matter but reverse polarity spark gap in wasted spark ignitions is said to be up to 15 % weaker so might change HT leads for a few tanks and plugs to see if that matters or not. I like to open gap till some misfire then close some. Do not know if plug indexing gap is worth while in Nortons. Engines are a bit like rifles some bullets that work in one are not as accurate or hang up in another - only one way to find out, spend time and money but sometimes its worth it but only one way too ,,,

dave M · Jul 23, 2015

Actually I meant change the main jet, this should richen it up more or less across the board. I have found The standard specs for needles, needle jets and slide cutaways are pretty spot on for a standard engine. I always start a little bit rich on the mains when tuning an engine and work my way leaner.

Anonymous · Jul 23, 2015

dave M said:
Actually I meant change the main jet, this should richen it up more or less across the board. I have found The standard specs for needles, needle jets and slide cutaways are pretty spot on for a standard engine. I always start a little bit rich on the mains when tuning an engine and work my way leaner.

Hmmm. No. Drop the mains out completely and it has zero effect until near full open throttle.
Example: 106 needle jets on parallel needle can flow 106ml/min of fuel maximum (bottleneck). The needle taper then makes the transition from 106ml/min flow until main jet full flow of say 220ml/min is achieved.
Ta.

Hobot · Jul 23, 2015

Yes doing full tune of all circuits w/o main jet installed is a known traditional was for some. Btw if ya poke around the older wiser vendors and racers ya may stumble on what are call Amal race needles that have steeper tapper for more fuel faster till runing only through jet. That plus hi floats plus notched spray tube and .5 smaller cut out pleases me on my factory Combat better response before getting up on 2S cam 3rd piston.

Be restless til ya try a trip lip or serrated turbulizer across lower port entry and consider a plate about 1/3 the way up so helps small slide opening flow through faster and does not block more throttle.

htown16 · Jul 30, 2015

Okay, finished fooling around with the float levels. Initially, the left or slightly leaner side was at .25 below top of bowl. The right or slightly richer side was .32. I set them on the bench to as close to .17 as I could get them, depends on where you read the minicus in the tube. Checked them when on the bike and the right started flooding immediately, so had to lower it a touch. They still look close to .17 in the middle of the carb.
It appears in the front that there is little air gap and of course the back is lower. Bike started up on the second kick and seemed to run okay. Will need to do a test ride.

Cure for leaness

htown16

1up3down

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Anonymous

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lrutt

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Hobot

vintner

htown16

dave M

Hobot

o0norton0o

htown16

dave M

o0norton0o

Hobot

dave M

Anonymous

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Hobot

htown16

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