Running rich & temp lack of gears?

Again, another follow up thread from this one as I continue to struggle to get her running well.

She was all over the shop. Seemed to pull well when under revs & climbing 2-3k RPMs and in 2nd-3rd gear but as soon as I came down to idle I had to blip the throttle else she'd cut out. If I increased the revs she'd revive herself. There was no popping & banging whilst riding but after she cut out at a junction and I gave her a few kicks with no success she'd let out an almighty bang.

I managed to get her home to check the plugs which were very black & sooty.

In the thread linked above I've detailed my carb & ignition set up.

I'm in the middle (3rd) needle clip & 1 1/2 turns out on the mixture screw. As it seems to be running rich, do I either move the clip up to 2nd (leaner) or back the screw out to 1 3/4? Or both? She idles at a tad over 1k RPM.

I've now replaced the Boyer power box which charges as it should. I've tested with a voltmeter whilst the engine is in various stats, off, off with ancillaries on, on at idle with ancillaries on/off, on at 3k RPM with ancillaries on/off and it all behaves at it should, voltage dropping, voltage increasing etc.. so that's fine.

I also noticed a loss of gears whilst coming down a slight but long hill.. I was really struggling to engage anything at all. Once I got her back I had her on her centre stand I could rotate the rear wheel & engage all gears. Was it just an anomaly? I haven't touched anything in that area & haven't had that problem before.

Sorry for the lengthy post.. out of my depth & in despair.

I see you are up in Warwick I wonder if there are any commando owners on this forum in your area that could lend a hand
It just sounds like the bike needs setting up right
How long have you had it? Did you ever run it with twin carbs ?

Hi Luke

Have you tried riding the bike with the air filter removed . The filter looks like a K&N when was the last time it was cleaned and oiled ? In case you didn't know you should use K&N filter cleaner solution not petrol or solvent to clean.

The lack of gears as you describe could simply be the hairpin spring in the outer gearbox cover

baz said:

I see you are up in Warwick I wonder if there are any commando owners on this forum in your area that could lend a hand
It just sounds like the bike needs setting up right
How long have you had it? Did you ever run it with twin carbs ?

Click to expand...

I've been in touch with a couple of local chaps but nobody confident enough to meddle with the Mikuni. I've got a chap coming over from a local classic car & motorbike club who helped me get her running before so he's fairly knowledgeable but doesn't live & breathe Commandos.

I inherited it from my old man & he had it for 5-6 years. He bought it with the Mikuni on it so I know it's been up & running before!

Esmerela said:

Hi Luke

Have you tried riding the bike with the air filter removed . The filter looks like a K&N when was the last time it was cleaned and oiled ? In case you didn't know you should use K&N filter cleaner solution not petrol or solvent to clean.

Click to expand...

Hmm, interesting! I'll definitely give that a try as I haven't cleaned the air filter since inheriting the bike & I can't recall my dad ever doing it since he bought it in 2013.

baz said:

The lack of gears as you describe could simply be the hairpin spring in the outer gearbox cover

Click to expand...

I'll take the outer cover off & have a little look tonight.

https://andover-norton.co.uk/en/shop-details/15139/gearchange-return-spring

Is it that part you're referring to?

A single mikuni is an easy carb to work on
They make a commando a nice bike to ride unless you want to go fast
You will need to go back through the tuning sequence, and as someone said in an earlier post maybe the enrichiner/choke circuit isn't working right
Or float too high etc

Luke Turner said:

I'll take the outer cover off & have a little look tonight.

https://andover-norton.co.uk/en/shop-details/15139/gearchange-return-spring

Is it that part you're referring to?

Click to expand...

No
It's the hairpin spring

baz said:

A single mikuni is an easy carb to work on
They make a commando a nice bike to ride unless you want to go fast
You will need to go back through the tuning sequence, and as someone said in an earlier post maybe the enrichiner/choke circuit isn't working right
Or float too high etc

Click to expand...

I've just ordered the Sudco tuning manual which will be arriving next week.

How could I test the choke? All I can see is the lever operates the plunger as it should. It needs the choke to start then I knock it off once she's warmed up.

The float should be 17-19mm and it's set at 18mm.

Undo the choke plunger sleeve nut and take out the plunger
Check the rubber seal on the bottom of the plunger for damage/ deterioration also check the bottom of the plunger hole for any dirt etc

baz said:

No
It's the hairpin spring

Click to expand...

I can't seem to locate that part then. Will take the cover off tonight to familiarise myself.

I don't want to go beyond the 1 1/2 turns on the mixture screw so I'll change the needle to the 2nd or even 1st position as an extreme to see what that does to the richness.

A lot of people tend to set bikes up too rich in my opinion
Trying the clip in the top of the needle isn't extreme
Having the pilot air adjusting screw 2 turns out isn't extreme
You need to mark your throttle in at least 4 positions and see what your bike does in those positions
Remember it's about throttle openings not revs

Generally mikuni kits are pretty good straight out of the box
It's so long since I've worked on them I can't remember the spec etc
I was hoping someone would chime in with an 850 like yours and give you some settings that they are using in the UK
Cheers

1. Confirm enrichener is ok. (sounds like it probably is)
2. Warm up bike, back out mixture screw till it misfires. If it keeps idling faster past two turns, pilot jet is too large.

If the pilot jet is correct , back the pilot air screw out until it's revs highest then adjust it back in maybe quarter of a turn until the idle screw back to a normal tickover

baz said:

If the pilot jet is correct , back the pilot air screw out until it's revs highest then adjust it back in maybe quarter of a turn until the idle screw back to a normal tickover

Click to expand...

Is this with moving the needle clip to the 1st or 2nd position?

Leave the needle alone til this gets correct.
Then move to the needle.
Then the main jet.

Mixture needs to be between 1 and 2 turns.
My combat ran a 25 pilot at 1 1/4 turns

You have to keep in mind the separate circuits of the carburettor
Although there is a fair bit of overlap