The restoration gremlins

Good day all. I have been utilizing the vast knowledge of this forum for a little over a year now to help me in my norton restoration. Up until now, I have found answers for almost every question I have ever had but today I am stumped. I have been fiddling around to try and sort this out over the last couple days but I have decided to check with the pros.

So here's the details.

The bike is a 850 mkII. The engine was fully rebuilt. I have never ridden a norton before this one so I am not totally familiar with the way things should feel/sound but I have a fairly good understanding of motorcycles.

There are a couple concerns I am having when riding. First off, it sounds like i am getting backfiring from my carbs. It sounds like a little pop every now and again when I am at a steady throttle. The other is that the bike sort of pulses and lags until I get up to about 3000 rpm, especially bad when it isn't up to full heat yet. I discovered today that putting the choke on while riding totally fixed that issue, but I really don't feel like riding around with my choke on. It gets better when the bike is fully warmed up but at lower RPM's it still pulses a bit. I thought it might be a air/fuel mix issue (inspired by the choke discovery) but after setting up the carbs, they are at 1 turn out (the accepted starting point for tuning the carbs being 1 1/2 turns out) so I figured that the half turn richened it up enough, though I could be way off base. I have tried adjusting the mixture before, but have found that if I increase the richness any more the engine begins to falter noticeably. It currently idles happily at 1k with out any stuttering or pulsing.
I have set the timing at 31 degrees and have a boyer MKIII ignition. I sadly don't have a strobe but it is on my list of tools to procure in the near future. I have read that backfiring into the carbs is caused by the timing being too advanced to I thought I might adjust it one degree at a time up to 35 and see what happens. Timing is something I have very little experience with so any insight into that would be very helpful. I am also running 96 octane gas, as the burn rate is slower I thought it might be a factor as well.

Thank you for your help.

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I just realized I also have a bit off issue with kick back when starting. It happens probably every other time I start the bike, and always on the first kick. The bike generally starts on the second or third.

I also just realized that I think my idea of retarding the timing is backwards. I should work from my 31 degree point to 28 degree point. If you are wondering where I am getting my numbers from, I am going on the assumption that the people at Boyer knew what they were doing when they chose the 32 degree mark. I just want to see what happens when I move that mark, as every bike is different.

kicking back is a telling symptom of the timing being too far advanced

the 31 degree thing is when fully advanced, confirmed with a strobe light when the rpms are blipped up

until you get a strobe why not retard the timing a couple of degrees and see if the kick back stops and
maybe it will take care of the lower rpm pulsing

ioginy said:

I thought it might be a air/fuel mix issue (inspired by the choke discovery) but after setting up the carbs, they are at 1 turn out (the accepted starting point for tuning the carbs being 1 1/2 turns out) so I figured that the half turn richened it up enough, though I could be way off base. I have tried adjusting the mixture before, but have found that if I increase the richness any more the engine begins to falter noticeably. It currently idles happily at 1k with out any stuttering or pulsing. .

Click to expand...

Unlike every other carb on the planet (?), Amal carbs set the idle through adjusting the AIR SUPPLY.
When you turn the idle needles out 1 & 1/2 turns, that should be just right.
1k rpm idle sounds a shade high, BTW.

Turning the idle screws out another 1/2 turn would lean it off - so you are already too lean at idle.
If your idle screws are set only 1 turn out, then you are getting air into the system someplace else.
O-rings, cable entry points, worn slides.

That worn slides one is common, if they've done high miles. Or not even that high miles.
This is assuming your float levels are set correctly, and not swimming too low.
And the slides are adjusted down as far as they need to be.
The 'book' tells how to adjust amals, doing it any other way about never works...

Could be, too, that your idle jets are blocked or partly blocked.
Also a common problem - fuel drying out and blocking it off.
Poking out the little fuelways is quite an art...

Ain't Nortons fun !
Hopethishelps.

Timeing a Boyer statically is really a crap shoot and should be strobed as soon as possible. You could be well be advanced enough to cause that kick-back. You didn't mention what groove you're running your metering needles. Unless they are already at the top clip, you could try lowering them for a richer part throttle mixture.

All of the above plus check carb fasteners and balance tube and possible exhaust area leaks. Never forget Boyah wires can vibe apart inside and it kind of goes bonkers timing wise on less than 10.5 volts. Always keep in back of mind the ethanol gas tendancy to collect water in lowest spots of fuel system. Do have a look around after dark and jiggle stuff, which may not be anything to do with current problem but could well be after all the diddling around solving fuel side is done. If ya get bored you can fiddle float level so best idle with 1.5 pilot air screws out but my Combat has .7 and .9 turns out bowl levels now and so fine all around I ain't bothered to tune finer. If not yet indexed the crank degree's don't trust the factory dial very much.

you could try lowering them for a richer part throttle mixture.

Click to expand...

Right thought, but wrong way around.
Needs to lift them up a notch to richen the mix at part throttle settings.

Your pilot jets are blocked with crud.

Like you, I have just finished a total rebuild of my bike (1970 model). After sorting out a gearchange issue I thought I was home and hosed.
But last weekend when I tried to go for a final shakedown ride, it refused to start. I checked for sparks on my home-made ignition tester and there was little or nothing to see.
Plugs are new NGKs.
Ignition is Boyer MK3.
The last time I ran it was a couple of weeks ago when I strobed it to 31 degrees.
One of the reasons I did the rebuild (there were many reasons) was that it tended to cut out unexpectedly while cruising along.
I am now about to re-fit the old AAU, which never gave any trouble and never caused kickbacks like the Boyer has.

Cheers
Martin

Torontonian said:

Your pilot jets are blocked with crud.

Click to expand...

+1. Classic lean low end. Most likely clogged idle circuit. If not that, a vacuum leak.

Or bad battery ?

DIRTY PICTURE .



These Amals probably arnt as bad as Webers as regards ' once theyve got like that ' , but
if they have been corroded & pitted , then ' restored ' , passageways arnt likely to still be
parralel sided & cositant Dia. . Though thred be evidance of heavy pitting otherwise .

A new build is likely to pass a bit of ' forign matter ' through fuel , no matter how miticulous the build .
Periodic removal of floats ( or Drain Plugs ) dropping fuel into a can / jar for inspection . A bit of fine red
powders not unuseual . Particularly from Gas Stations with OLD tanks , woter Rusty . Low use Rural Gas Stations
the fuels likely older & could pick up a bit of moisture . So a Inline Filter is usefull in some areas . If not mandatory .,


Ran the lucas points with BSA Auto Advance & stiffer springs @ 31 degrees fully advaced .
Got the odd ' chuff ' pushing through or on a soft kick , ignition ' on ' . Hiccup perhaps . :lol:

The BSA Adv is 15 as opposed to 12 , so is 1 degree static. Theoretically .
Slight wear in stops etc can get varyation . If its all clean & oiled &
checked the pivot posts are square & true & points faces mate
they are accurate at the rpms we use .



Worth looking at cap screws / allen head fasteners .

If theyre worn theyre junk .

Setting static , I nudge the slop out ( fwd. ) to get true ' under load ' setting , running the 31 degrees .
as in I dont want MORE than the 31 whatsoever at all , but I want the 31 , thank you . but on Mk II Concentrics .
It can make it a bit intractable for city rideing . Hence the 28 degrees the throttles likely less toey .
and the machine more tractable / less demanding .

If youre not looking for Z1s to smoke , at the stoplights .

So rideing style & vicinity may dictate exact setting . After experiment .

Clear idle jet easy to check. Shoot cleaner into one of the 3 ports connected to idle jet and it should come out the other 2. Check all 3. I've been told to adjust float for best running at 1.5 turns out and then run maybe 1/8th turn rich. If you haven't read this do it. http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

When looking at the opening of the carb (air intake) there is a small plug that plugs one end of the pilot circuit. I found one of mine to be leaking and plugged it with some goo. It made a huge difference in balancing the carbs!

Russ

amal-carb-pilot-circuit-t8029.html?hilit=pilot

Raising the needle CLIPS = lowering the NEEDLES = LEANER

Lowering the CLIPS - raising the NEEDLES = RICHER

Easy to get confusion in the discussion...

With a Boyer you really have to use a strobe to time the engine at full advance.