Commander tunning

[foneill04]

Hi looking for help tunning/balancing the SU carbs on my commander
Starts ok and runs but not sure if it’s rich or weak
Iv tried taking one HT lead off start the bike and
Tinker with the mixture the tick over speed
Works with right hand cylinder
But the left cylinder doesn’t seem to set the revs
Very well ?
I am screw the adjuster many turns with very little change

[Anthony Duffield]

I found that trying to adjust the mixture (height of the main jet) on the bike is very difficult, just small adjustments can make a big difference.

The best thing to do is to remove the carbs and if not recently overhauled do so and set the main jet height in accordance with the instructions.

To set the idle speed follow the instructions in the book, if you find that when the thermistor cuts in the idle speed is difficult to set it is likely that you have a drop in compression on one rotor, if this is the case disconnect the thermistor and use the bike until you can arrange for an overhaul.

[foneill04]

Thank you for the reply

Where am I likely to find the thermistor?and how does it effect the running?

While the carbs were off I set the jets level

Once running tunned as stated running one cylinder at a time
What seemed to be best setting
Was ?
7and 1/2 turns out off side
4 and 3/4 near side

Seems big difference

But not to bad on a run

Little hiccups on tick over !

But it’s not quite right

The carbs where overhauled during resent rebuild
Engine went to Startright
He was pleased with it nothing major Graham said

Regards
Frank

[Anthony Duffield]

Frank,

The thermistor is near the thermostat housing RH side look for a device screwed into the engine with two wires it is close to the temperature gauge sender which has just one wire. On an engine with poor compression disconnecting the thermistor masks the problem and allows for a decent ick over, but as your engine is recently overhauled compression should not be an issue.

7and 1/2 turns out off side, 4 and 3/4 near side is not unusual note that the the nearside is connected to the scavenge drain so it is getting more air via this connection resulting in the idle screw being set differently to the off side.

As Graham has recently overhauled the engine I would suggest you have a chat with him, he is by far the best person to provide good advice.

[foneill04]

Thanks again for the reply

One final question I’m trying iridium spark plugs is it best to stick with the original type
Frank

[Anthony Duffield]

Frank,

I have never used iridium spark plugs so unable to provide any recommendations, I have used NGK C8E for many years but this year at the TT I had a few issues with oiling the plugs so am trying a hotter plug NGK C7E to see if that improves things, so far so good.

Tony

[foneill04]

Thanks Tony

If I struggle with these
Il give them a try
Frank

[foneill04]

Just done 15 miles
Stopping and tunning the carbs
Feels much more responsive
A couple of turns in

Was hunting on tick over that’s almost gone
So now

Off side about 4 an 1/4 turns out
And n/side 2 an 1/8 tours out

Is that round about right ?

So to recap
Was about 7 1/4 o/s
4 1/2 n/side big difference
Frank

[foneill04]

Only the near side carb has a choke set up and cable
Is that usual ?

Regards
Frank

[Assen]

Both carbs have an choke-system and cable.
Good advice is, to take both choke-systems apart and change the standard-o-ring for a harder Viton-type.
The original o-rings become to soon to sloppy, and don't seal good enough anymore wich can result in all kinds of running-problems.
If i'm correct Tony also mentioned this on this forum...

Jannes