Britbike forum Forums British Motorcycle specific Brands Norton bulletin board Norton Top End Job coming up ....

I was careful mounting the pipes so that I didn't put any kind of misalignment strain on the join between the pipes and the head. It took two of us to mount them up .... me at the head making sure that the pipes were aligned cleanly to the head so that the "crush washer" would crush evenly, and so that the pipe slid all the way to the crush washer by hand while Fay slid the silencers along the pipes as she went to align the mounting bolts through the hangers to the silencer. Using the proper tool (I actually have one now, thanks RF!), I tightened the finned "nut" tightly and it seems very secure. I expect to tighten it down regularly as it accumulates heat cycles and the "crush" washer crushes to its final thickness.

I'm glad to hear about "best all weather air cleaner", since the Norton is often very far from home with no control over the weather. The black-capped silencers are quiet and the bike seems to run well, but as I mentioned, one of them needs to be replaced and I want to replace them with whatever the "best" silencer is in this enlightened year of 2022 with 47 running years since the bike was built ...

Lannis

However, the silencer bracket is either inverted or is not the standard bracket and therefore lowering the exhaust system presumably because the LH 750 pipe won't fit under the primary with the bracket in its normal position and the pipe should be parallel with the primary case.


Compare the line of your exhaust...


...with the standard factory item...


...and standard LH black cap/bean can bracket configuration:

Lannis

I cruised my pipe rack and pulled 3 LH roadster pipes down. One is a conventional OEM flare MK3 balanced pipe, one is a spigot 850 balanced pipe and 3rd is appears to be an after market flared LH MK3 with no balance provision.

The MK3 vs aftermarket flared pipe shows the correct MK3 vertical drop.
The MK3 vs 850 vertical drop difference is definitely visibly shorter .

My current use for the AM pipes is as "dyno" pipes with the thermocouples inserted about 1-1/2" from the port.

Certainly would be nice to rediscover the source for the "no-balance", flare mount MK3 roadster pipes.

'I'm glad to hear about "best all weather air cleaner", since the Norton is often very far from home with no control over the weather. The black-capped silencers are quiet and the bike seems to run well, but as I mentioned, one of them needs to be replaced and I want to replace them with whatever the "best" silencer is in this enlightened year of 2022 with 47 running years since the bike was built ...'

I solved that problem, when caught in hellish rain in Tellico Plains with Gumby & a few others.... I pulled up in front of a brewpub, as I unbolted my soaked ham can air filter, stuffed it in my tail pack, they brought me an ice cold IPA to the curb, quaffed it down and away we went in 10 minutes....
No dust on a rainy day. However, the nylon cord I use for a key fob was sucked into the left carb, giving me half a hang throttle.

So I've been getting the Norton back on the road after its top end job.

1) Carb cables adjusted so that they start raising the slides at the same time.

2) Started it up and got it hot twice, then retorqued the cylinder heads and rechecked valve lash.

3) Took it out for a 60 mile ride.

Good news is that it's not smoking at all, so the oil rings must be doing their job. It starts easy and pulls good and hard, and runs without a lot of noise.

It seems to be "out of balance" ... surges and pops some when I back off the throttle and it's slowing down. I have a pair of carb vacuum gauges, and the vacuum ports are right there on top of the intake tracts. Is there a good way to "balance" the Norton engine with the vacuum gauges? Going from compression readings of 50 and 105 to 140+ and 140+, it's not surprising it might need a little tuning ....

Lannis

You checked/strobe timed the ignition timing. On both cylinders ?
All good ?
Retards back at idle, as it should. ?

Genuine popping in the exhausts is generally an exhaust leak.
Checked that the slip fittings betwixt mufflers and pipes are airtight.
And the pipes into the head are firm and leak free.

You can sometimes richen up the idle mixture to reduce this.
But by then its way rich ...

I never had much success with vacuum gauges.
Found it better to remove a plug lead and fit it to a spare plug on the fins.
That way, you can verify that each cylinder on its own can idle /'rev' OK
(it will be a tad rough on only one cylinder).
If you've got leccy ignition (don't recall) never leave a plug lead not sparking.
Also put a pencil etc under each carb slide in turn, and verify they are about the same revs.
Synch synch synch synch is the name of the game.
But you knew that ....
Hopethishelps.

Well, that's one vote against vacuum gauges, and none in support, so I'd better review the old "tune it like two singles" process and get to twisting pilot, carb top, and throttle stop screws..... Pazon on this one so no dwell, gap, and sync issues there.

Lannis

I’m surprised to see anyone voting against vacuum gauges.

You should adjust the throttle stop screws so the vacuum is the same on both sides.

Then jam the twist grip very slightly open, so the engine is running faster than idle speed. Adjust the individual throttle cables so the vacuum is the same on both sides.

You have to do the idling mixture screws by ear, or Colortune. If a mixture screw doesn’t seem to be making any difference to the idle, then the pilot jet is likely blocked.

Completely agree, synching the carbs using vacuum gauges is by far the best way to tune the engine.

A couple of quick checks which might help are as follows:-
- open the throttle and then snap it shut, you should be able to hear the slides clack against the throttle stops at exactly the same time, if they don't then adjust the cables and/or stops as required.
- with the throttle wide open, check both slides are equally at the top, if not adjust the cable
- make sure there is a bit of slack in the cables so that the slides arent being held open by the cable.

If you have a digital ignition fitted with an idle stabilisation curve then normal idle tuning rules do not apply. When tuning the idle mixture screw the idle stabilisation curve will cover up the drop in revs when the mixture goes off. So in this case the colortune is best and the use of the vacuum gauges also rather than by ear. Been there and got the T shirt.

In theory vacuum measurement helpful. However the actual implementation is difficult in practice.
My short story is (long):
I had several sets of 4 gang (mechanical) gauges and found them to not be indicating identical when all hooked up to the same source. In addition the dampening of the dynamic pulsations with either fixed orifices or adjustable dampers was challenging.

In the final result, I found them to be amazing at how well the flew across the room into the trash can.

Hooking them to NHT will disable the balance tube effect which affects the idle mixture of both cylinders.
Perfect valve adjustment, identical ignition timing will go a long way to improve balance potential. Idle pulses I typically do by ear and feel of the exhaust. pulsations to set ratio and volume. To finish the carb adjustment process at above idle, I use undamped mercury carb stix and run the bike on the load cell (brake dyno). High speed cable synchronization is @ 12-15hp in high gear at moderate highway speed on the load cell.
Unfortunately this was more of a training aid as virtually nobody goes to this extent. Once you are really good at tuning the need for gauges goes away.
Also who ever said it was "easy"?
Not me!

I used a water manometer, home made from aquarium hose and valves.

But as Dave says, you can usually balance the carbs on an old twin well enough without vacuum checks. My current setup has no adaptors for balance tube or vacuum gauges, so I have to muddle through.

Put a single Mikuni, that will fix everything....LOL
When I see posts of pix of very amatureish Commando wire&cable bundles under the tank, between the neck and iso mount, I wonder how one ever expects to get any kind of smooth and reliable engine (carb) control. Everything tie wrapped into contorted positions that get jerked about when the handlebars are turned or the twitching of the bowden clutch cable when put under pulled compression.
The tune up starts as the bike is being assembled with better than kindergarten level bike assembly.
How many inspect the idle needles to see if they have at least a matching pair? There are, after all, I discovered several variations over the years... I've got a bin full to select from to make matched pairs.This certainly helps while adjusting the mixture make similar response while tweeking. This is done while alternately detuning one side making one side pull and the other side coasting to adjust the pulling side. Alternating to the other side and achieving equal tune than after satisfactory responses setting both to an indistinguishable balanced pull...

I was asked to do tech sessions at the INOA rally in July. After many times at past rallies I was asked by some folks to bring the "dyno" load cell, I may finally break down and bring it this year. I've been offered both morning and afternoons every day of the rally. If I start now I can possibly accomplish that this year.
https://nortonrally.com/

http://atlanticgreen.com/images/dynotn.jpg

Did you refit the exhaust system correctly as mentioned (also 2nd. and 3rd. pictures) in my previous post?

Or, wouldn't the '750'(?) LH pipe fit under the Mk3 primary case with the 064150 exhaust bracket fitted correctly, not inverted as the visible LH bracket is in your picture?