Various problems after rebuild 1973 commando 850

Hi all,

Last year i bought a commando roadster 850 that was rebuilt by someone with a good reputation in the dutch Classic Norton scene. I forgot the name, but i does not matter anyway. I rebuild bikes myself and can fix most problems. I have 2 classic brit bikes (also a bonneville) and no specific mechanical experience on Nortons.

When i bought the Norton, i found out pretty quickly that some of the things looked perfect, but were not done very good. The coils were clamped too hard, and one gave up after only one ride. The main fuel tap leaked. The carbs were not adjusted very well, etc.
I started last year to do some modifications. I want a reliable and low (relatively) maintenance bike. So i installed a Pazon ignition, replaced the coils and fitted a single Mikuni VM34. Never got to properly tuning it until now.

Last week i drained the oil and started the bike for the first time with the Mikuni. Started good, but was way too rich on idle. I had to screw the air screw out 4-5 turns for it to stay running. So replaced the idle jet (35) with a smaller 30. Now it idles as low as 400-500rpm with air screw 2-3/4 out. It seems to have a good gas response, but the idle stays fluctuating a bit, regardless of the air screw. If i set the idle to 800-900rpm, it still does. Do i need an even smaller pilot? I read that the basic setting is 35 pilot and air screw 1-1/2 turns out. Spark plug is light tan after idling for a few minutes.
I do have the feeling that the throttle slide is further closed on this carb than i am used to when adjusting idle on other bikes.

One detail... i have a whole bunch of old batteries that i removed from my daily drivers after suspecting lower performance. I took one that seems good for testing. It holds its power but it is definitely not new. I read somewhere about a bad battery causing bad idling on a Commando in combination with a boyer ignition. Is this possible with Pazon? The manual says they only need 10volts to operate. And since my headlight is bright and it starts good...

Then... i let the bike idle (when adjusting and re-checking ignition timing) for maybe 10-15 minutes. Until a point when suddenly a splash of oil leaked from between the primary casings when i gave it a twist on the throttle. I shut it off, went looking for the cause and noticed also the rocker oil feed lines melted at their connection on the banjo's. So... is this normal? No, off coarse not. I mean... do they get heated that hard and fast just from idling and revving a few times? And do the cases warp easily from the heat?
Is it possible that the inner case is not shimmed properly? If the outer case nut is fastened, i can feel the case moving slightly when i press on it towards the front. I guess it should be the other way around? That the surface first touches the far points, and gets fully closed in the center after fastening?

Yes it's a huge learning curve but best twisted out on the Commando. The Battery should hold a good charge say between 12 and 13 volts on a voltmeter check otherwise less will give those poor running symptoms easily confused with carb stuff. Melted up feed lines at head says the P.O. perhaps made his own lines ? And a primary with too much oilage says to me the crankseal has failed from age. Keep talkin'.

Thanks for the reply!

I measured the battery at 12,31 volts (at the auxiliary socket, engine not running). So i assume that is not the strange idle thing. I must say, the VM is not yet tuned. I am supposed to do the main jets first and work down, but i like a good idle for testing on a kickstart only bike .

The rocker feed lines can be homemade. I can't compare with original. But that's a good point. The lower line seems to have the original protector on it. Would it be a good idea to make my own stainless steel lines with the original banjo's and DASH 3 pfte hose? They should be oil and temperature resistant.

I did not check the crank seal yet. I don't know if there is to much oil in the primary. Checking as soon as possible. If broken, would further testing hurt something if i keep the oil levels topped up?

Hi,

I can't tell you much about Mikuni, because I prefer the standard Amal assembly. But if your alternator works fine, it could not be a matter of low power. Due to the oil issue, you have to check whether your bike has a wet sumping issue. Drain the sump after shutting the engine immediately. It shouldn't be much more than 150ml. The melted oil line can never be caused by hot oil or hot engine. I suppose someone got it heated by a torch or similiar. If you live in Holland you can contact Constant from HNW. He is an experienced expert.
http://www.hollandnortonworks.eu/?lang=EN&page=12

Ralf

Hi Towner,

I like the amals myself. They do a perfect job on my bonnie. But it took me a while to get there. And they need adjustments now and then. I am planning to build the norton more as a hassle free bike. The single carb setup is perfect for that. And i have some experience tuning the VM carbs on 4-cylinders. And i like the flexibility of them.

The oil line melted when i was standing next to it. It became liquid. So i guess it was not original material anymore.

As for wet sumping. I did had to drain the oil... but after a year, i assume that is just normal. I am planning to fit an anti wet sumping valve. But first things first.

I live in the North of Belgium. Holland is just one twist of the throttle ;-)

Check float level up/dn to compensate air screw closer to expected. Suspect throttle slide and bore wear letting air leak preventing decent low idle. Rocking primary case needs more or less shims behind the center post mount to allow fitting flush fixed flat to crank case. May have to shim clutch basket if it rubs on proper mounted inner case. Got though major fasteners every few heat cycles on increasing intervals till stable. Only need one 5000ish ohm resistor in plug HT leads so might check plug, cap and leads for that low rpm spark hindrance.

Hi Hobot... will do. I do check float levels as standard on old carbs. Did not think of it on a new one. The throttle slide has no wear as the carb body/slide are new. They also fit nice and tight.

I read about the shimming of the center post. I hope i can temporarily stop the leak and do that as soon as i have to do some bigger engine work. For what i understand, the inner primary cover needs to come off for it? Would be nicer to combine with a sprocket change or clutch work. But it's on the to do list.

I run Pazon ignition, new NGK B7ES (non resistor type) plugs, PVL coils (dual 6v) and original HT leads and caps. You mean i need a resistor cap to function properly? Or you mean to not combine a resistor cap and resistor plug?

Ugh yeah not many short cuts to access stuff on Commando but primary cover is just a cover to hold oil so no biggie if wiggles some it nothing rubbing. Basically eventually must go through stem to stern, by expedient peicemeals or taking it all at once or rather one longer continuous series of hang ups. A fully fettered Commando is the pie in the sky to shoot for best we can.

something doesn't make sense

a Mikuni 34 is a perfect carb for your 850

and the 35 pilot you had in originally also should be perfect with the air screw turned roughly one and a half turns out from seated

what does the number say on your slide?

it is possible you have the wrong cutaway

what does the needle say on it and what clip is it in, what size main jet is in there?

you should not be having any of these problems, Mikunis are great carbs

have your pulled the plugs, rotated the motor and checked your valve clearances?

Must check tomorrow for cutaway and needle.
Main jet is 260, but i did not check if that's good.

Spark plugs are new NGK B7ES's since yesterday (previous plugs fouled after the rich first startup) and the pazon is set to 31° full advance.
Checked valve clearances yesterday, they were perfect.
Bike starts now (with smaller pilot jet) from first kick, but the kickstarter wants to break my leg!
With the smaller pilot jet it reacts also good on the enrichener.

The problem is probably less of an issue as i make you guys believe. The bike will not stall if i set the idle to 450rpm. Even So it is not a very irregular. But it just does not run perfectly smooth. Less smooth then my Bonnie (with twin amals, that will idle at 500rpm also).
Going to check the needle and slide tomorrow. No wait.. i'll do it now!

needle= 6DH.3 c-clip on middle (3th groove)
slide= 2.5

first, the correct Commando NGK plug is a BP7ES and not the ones you are using

the "P" stands for Projected, and I have no idea if your present plugs,NGK B7ES, which are minus the P will still work just fine, hopefully plug expert can affirm or deny

and run a feeler gauge through the plug gaps to verify it is around 28th or so

when you give it a good healthy kick does it kick back at you?

if so your timing could be too advanced, did you check it with a strobe light?

I can't remember if 260 is correct or too rich for a 34 Mikuni on an 850, somebody???

lastly, I do not understand your thinking or wanting your bike to idle at 450rpm?

your idle should be right at 1000rpm, personally I have mine at 1100, that way the motor is a lot less unlikely to stall at a stop sign and with it idling there it keeps the oil pumping better

is it possible your only problem is trying to idle way too low?

dimitri said:

. The bike will not stall if i set the idle to 450rpm.

Click to expand...

450 is way too low. If your ignition has idle stabilisation it would be trying to "pick the revs up". Try 900 to 1000. According to experts, lack of cam oiling occurs at very low idle.

I must clarify some things. I don't want it to idle at 450rpm. But i set the idle mixture on my bikes that way. As an opposite to the 'highest rpm when adjusting the air screw (or mixture screw on some of my bikes)' i like to set the bike to allow idling very low without stalling. It is just a way to find the sweet spot. After it is set, i adjust the idle back to 1000rpm. In this particular case, i can hear the same small irregularity at 450rpm as at 1000rpm. Maybe someone else would not notice.

Good tip on the projected tip. I am aware of what they do. Must have checked at the wrong source prior to buying the plugs.
There could be a chance that i am leaning out the mixture to compensate for the non projected plug. A projected tip will be able to burn itself clean at a slightly richer mixture. Could explain the airscrew setting.
I always check plug gaps before installing them.

The ignition is set with a strobe, yes, and is set exactly on 31°, as pazon specifies. I do have a kickback, but not when starting it. Only when ignition is on and i am putting the kickstart against compression stroke before i actually kick it. Just going a bit to far.

For now, i must fix that rocker feed line first. So i guess i am set back a few days. But i heard a few good things to check!

So far many thanks!

1up3down said:

first, the correct Commando NGK plug is a BP7ES and not the ones you are using

the "P" stands for Projected, and I have no idea if your present plugs,NGK B7ES, which are minus the P will still work just fine, hopefully plug expert can affirm or deny

and run a feeler gauge through the plug gaps to verify it is around 28th or so

when you give it a good healthy kick does it kick back at you?

if so your timing could be too advanced, did you check it with a strobe light?

I can't remember if 260 is correct or too rich for a 34 Mikuni on an 850, somebody???

lastly, I do not understand your thinking or wanting your bike to idle at 450rpm?

your idle should be right at 1000rpm, personally I have mine at 1100, that way the motor is a lot less unlikely to stall at a stop sign and with it idling there it keeps the oil pumping better

is it possible your only problem is trying to idle way too low?

Click to expand...

Nortiboy said:

dimitri said:

. The bike will not stall if i set the idle to 450rpm.

Click to expand...

450 is way too low. If your ignition has idle stabilisation it would be trying to "pick the revs up". Try 900 to 1000. According to experts, lack of cam oiling occurs at very low idle.

Click to expand...

I can say (my clothes and my garage floor can confirm) that oil feed to the rockers is not a problem at low idle. :-D
but that 450 was just miscommunication. See my previous post. I am with you guys. I like the idle at a healthy 1000rpm

What i don't understand is what an ignition module (without any direct link to the carburation or injection) could do to pick the revs up. It might have less advance at 450rpm than it has at 1000. But i don't think any separate ignition module is programmed to vary the advance at low speeds to see if the revs rise. So i don't think it could cause a fluctuation. Or does it?

Since it hasn't been said yet, 10 to 15 minutes idling with no airflow is WAY too long for standing still.
The motor could well get hot enough to melt the oil lines, although that does seem a little strange.

Most aircooled engines can't be idled for more than about 5 minutes standing still,
and on a hot day probably considerably less.

Nope idling slow does not burn enough fuel to over heat engine or oil in 15 min so don't put that guilt trip on this fella. I've measured CHT, EGT and oil temp to know for sure. What is bad about long slow idle is extra ring blow by and not much oil flow onto cam/lifters but not that big a deal either unless a chronic habit over many years.

The Owners Manual for various bikes warns about idling them standing still for more than 5 minutes, max.
I certainly wouldn't idle my bikes for more than that.
And would believe it over anything you say any day.
You can feel them getting HOT, in the cylinder head dept.

Especially if the idle mix hasn't been dialled in yet.
Thats a quick way to blue the pipes...

dimitri said:

The ignition is set with a strobe, yes, and is set exactly on 31°, as pazon specifies.

Click to expand...

I experienced that the pazon should better be strobed at 4000rpm to set the ignition timing, not at 5000rpm as Boyer recommends.

Towner said:

dimitri said:

The ignition is set with a strobe, yes, and is set exactly on 31°, as pazon specifies.

Click to expand...

I experienced that the pazon should better be strobed at 4000rpm to set the ignition timing, not at 5000rpm as Boyer recommends.

Click to expand...

Yes, i strobed it at 4000rpm, as in the pazon manual. They say strobe at 3000rpm for 29°advance if you are breaking in. Or at 4000rpm for 31°. It does advance slightly when you rev higher, like the manual says. Should i try the original setting of 28° at 4000rpm?
Correct spark plugs are ordered (together with new HT wires and caps). I will do that firstly to see any change.

@Rohan: Thanks for the advice. I really appreciate any input. I would not let my bikes idle for extended periods if it was not for adjusting reasons. But in my experience, i follow Hobot on this one. I am not talking about Commando's in particular, but i had air-cooled engines idle for much longer with temperature sensors connected. They should not overheat that fast. In fact, when properly adjusted and under normal conditions, the temperature stabilizes at a certain point. If the Norton does overheat (and i don't say it can't just by idling, you guys know better than i do), it would be caused by a wrong setting or the particular design of the engine. And that's one of the things i'm trying to find out ;-).
Just for fun: many of the stuff manuals warn you for are disclaimers, legal stuff and product placement. My Commando 961 manual says i can only use fuchs oil. And funny enough, there is a wrong procedure to measure oil level, causing overfilling when owners don't have experience with dry sumps .

dimitri said:

Should i try the original setting of 28° at 4000rpm?

Click to expand...

No, I think that would not improve idling.

Ralf