Post rebuild tuning an MkIII

ag12680 · Feb 8, 2016

First experience tuning a Norton and need input to get it dialed in before running further.

'75 850 Electric Start with new rings and valve job. Have run it two warm up sessions to set the Boyer timing and retorque the head.

Running the original header pipes with crossover, Emgo peashooters and K&N filter.

Has new Amal Premiers with needle clips set on middle position, and mixture set 1.5 turns out.

Bike starts and idles fine. Runs up to RPM smoothly with popping in the midrange. New NGK plugs after chop show what I believe to be a lean condition.

Petcocks are new UK sourced with the AN tandem fuel line.

Don't want to put a hole in the piston. Move needle up a notch? Turn pilot mixture in and/or different main jets? I believe the Amals are 260 or 280.

First time I have ever worked on, heard or ridden a Norton and now I get it. The other funny thing is that it seems to vibrate much more on the second running session than the initial post rebuild start up?

Thanks much,

Andy --

Rohan · Feb 8, 2016

1st thing to do on hearing any popping in the exhausts is to check for exhaust leaks.
Only when you are certain there are none do you look further afield.
The smallest gap ANYWHERE to allow air in is all it takes.....

worntorn · Feb 8, 2016

To my eyes those look pretty good for modern fuel. You have a black ring on the plug base, this indicates things are a bit rich, maybe best to leave it that way for now.
The greyish colour on the tang is normal for today's fuel.
Twenty years ago it was a light tan that was ideal, not anymore.

Glen

JCD · Feb 9, 2016

Andy,
I've just completed a MK3 restoration. I had the same issue with midrange popping. I agree with Rohan to check for leaks anywhere around the exhaust, and cylinder head. Any air being pushed or pulled in will not be good.
That said, when I had checked and rechecked every critical area, including timing, etc., I was still having issues with mid range popping while rapping the throttle in neutral or under a load riding the bike. I then turned my focus on to the carbs, which were just a bit out of synch. I'm running JS flats slides, but the same principles would apply to your Premiers...if one slide is opening before the other, you will experience the popping in the mid range. I grabbed a feeler gauge and referenced the tuning guide to set correct slide gaps. There are plenty of threads here that describe the same process for your carbs. Best of luck...and post a pic of your Mk3. We'd all like to see it.

Best
JCD

ag12680 · Feb 9, 2016

Thanks guys for the quick replies...

Used new collets and tapered sealing washers while thoroughly cleaning the crossover but may have tweaked one of the short tubes getting it apart. What a pain...

Did the drill bit method on the slide sync but will check again. So what I'm hearing is that while a nuisance, I should be able to run it in further without any terminal damage?

Here it is sans brakes.

dennisgb · Feb 9, 2016

worntorn said:
To my eyes those look pretty good for modern fuel. You have a black ring on the plug base, this indicates things are a bit rich, maybe best to leave it that way for now.
The greyish colour on the tang is normal for today's fuel.
Twenty years ago it was a light tan that was ideal, not anymore.

Glen

+1 Those plugs look fine. If your really concerned find someone with an O2 sensor "sniffer" they can stick in the pipe(s) to get a reading, but those plugs look good.

Biscuit · Feb 9, 2016

I also agree that the plugs look fine. As to the popping,,, do you feel it's a slight miss-fire when you bring it up in neutral - no load? And is there a slight herky-jerky ness at low load, light throttle around 3000RPM? If these are the symptoms, you may try richening the pilot screws . The idle may deteriorate a bit. So you may want increase it back to where you like. This worked for me with the above symptoms.

Torontonian · Feb 9, 2016

My MK111 notes show needle notch is top position ,weakest. 3 1/2 slide.

Madnorton · Feb 9, 2016

Early days, get it running and put a couple of hundred miles on then you will be able to get the carbs spot on. Other than test equipment the only other real way to test is to ride it, when you are doing 70-80 mph and wack the throttle open (not gently) it should leap forward, if it does not then slightly close the throttle a little, if tends to run better then you maybe running lean. I get a bit of popping on shutting the throttle around town and after passing through villages, but at speed I get none, it has been like this for 6 years since I last set the carbs and fitted Iridiums.

Remember, always start from from standard settings and write down all your changes, even if you are a member of MENSA, you will still forget which way, turns etc.

I do admire those who like to tune their Nortons, must be like Krypton tuning a tractor!!

ag12680 · Feb 13, 2016

Thanks Biscuit and Madnorton -

It's doing exactly what you're saying.

According to the Amal tuning guide that came with the carbs. I need to settle the behavior of the mains and work down through the needle position and finally the pilot/airscrew mixture.

Once I get the brakes sorted I can actually put miles on it.

Many thanks...

Andy

ag12680 · Feb 21, 2016

Well, I've taken it for a 20 mile ride after turning in the pilot air screw to 1.25 turns and observed:

1. Pulls through RPM range in a linear fashion with no midrange popping as before. After letting off, there is no surge or popping.
2. Idles higher when up to operating temp - around 1200 vs. 900 post startup
3. Pipes have blued much further down than in the previous stock configuration (Black Caps)

Has 260 mains and 106 needle jet with the needle pulled all the way up.

Don't have a method of measuring EGT, but it seems to be running lean/hot.

Anybody have pipes that look like this?

Next I'm going to step the pilot mixture down, use the choke to test the main/midrange mix. Then go to a #19 pilot per JerryDoe

Inside of the open peashooters is a light tan.

Thanks as always...

Andy

Biscuit · Feb 21, 2016

Pipes look great, remember they are not double wall as Honda's were back in the day, they will get blue and gold. I think a 20 mi ride is sufficient to color the pipes to their end finish. Will maybe change a bit more on a good hot summer day ride, but if you were way lean You would have a much darker, angrier looking blue pipe. Mine, crossover equipped like yours, look the same as far as color and pattern is concerned though not nearly as pretty because they are the originals and 40 years old. The inside of my peas are also light brown and that's what I look for. Turning in the pilot screws richened it a bit at light load/small throttle openings, that alone is what probably stopped the slight popping/misfire you reported earlier. 260's may be a bit large here but will not have too much effect on day to day running unless you are tuning for ultimate speed. I 'm not familiar with Premier's replaceable pilot jets but personally I think you're in a good spot with what you have.

ag12680 · Feb 21, 2016

Thanks for sharing your experience...

These are actually the original pipes that the PO kept after installing a 2 into 1 system. They were blued for about 5" away from the head running 220 main jets in the original Amal carbs with black cap pipes.

So, when the bluing went much further down the length of the header running open peashooters - that raised my curiosity. Not concerned about the look.

Timed the Boyer at 5K which ended up requiring a few runs that involved pulling and repositioning the trigger. So it got hot.

Danno · May 1, 2016

Just starting to shake mine down after a long layup and a few changes. 850 Mk III motor, .020 overbore with slightly increased compression (no base gasket, Loctite Plastic Gasket) individual air filters, SS pipes with shorty Peashooters. Carbs have been re-sleeved, Stay-up floats, new gaskets etc. The needles, needle jets and mains are original spec.

I am getting some burbling at part throttle, although it seems to accelerate cleanly. Here are the plugs after about 20 miles of moderate running:

Code:

These are BP6ES plugs, one range hotter than normal because I was getting some fouling with 7s. The one plug looks to have a little oil fouling on the insulator. I have ordered new needles and needle jets since those are the only wear parts I didn't reeplace in the carbs.

htown16 · May 1, 2016

Danno,
IMHO going a plug range hotter is not a good idea. You need to identify the type of fouling. Oil could have a number of sources. First one I would look at would leaking down the valve guides and possible damaged valve stem seals. Carbon fouling a couple of likely suspects might be a worn needle jet or too rich a pilot air screw setting.
The plug on the right looks really concerning as the ground strap shows the same color almost all the way to the base. When timing and carbs are close you usually see a color change right at the bend of the strap. Close to the base means the plug is running hot. If it was my bike, I'd go back to the 7's and start finding what's causing the fouling.
Htown

Danno · May 1, 2016

I put a 7 back in the left side. The exhaust pipe on that side is dry carbon, but the one on the right (timing) side is a bit oily. It is an RH4 head, so I might have the dreaded intake port crack. Absolutely no bluing of the chrome so far.

htown16 · May 1, 2016

Jim C (comnoz) just commented in another thread title "Crackling Noise" that a 6 is way too hot and to get it out before it does damage. If there is anyones advice I trust on this forum, it's his.

Danno · May 2, 2016

Yeah it's just temporary until I figure out why it want's to oil-foul the right cylinder. As many as I observed on Youtube last night smoking from one or both sides, you'd think that one that doesn't smoke would keep running. Once I get the new needles and needle jets, hopefully the over-rich condition will be gone. Maybe excess fuel is washing the cylinder oil, but why wouldn't it do it on both? I'm just hoping it isn't a cracked intake port.

Post rebuild tuning an MkIII

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