I am having trouble with the bike running rich not one to be very understanding of how the carb works. I am struggling to work out what to do for best. My understanding as poor as it is, It has the standard jet and needle. It still runs rich even thought reading advice that when the timing is correct (I have set it three times and it is as good as I think I can get it.) I have moved the needle down to it's last notch. Still rich. I wonder if , after advice to drop down to a lower needle and jet if that would help.

Any suggestions would be good.
It seems to start with a reasonable idle but when I try to run it, it creates black soot on the rear stand.

Paul C

email (option): pcrisp@pipistrelle18.Karoo.co.uk

Hi Paul
Assuming you have the correct jet block, needle, jets etc check the condition of the slide/barb bore

Try to check with the slide partially raised, if it is worn it will move about

Mine did the same, so when I checked, it was worn, ran rich & sooted the stand like yours

Hopefully you will find the cause - but I'd rather a rich running m20 than a lean running one !!

Best regards

Jo'b

email (option): Jonnyob1@googlemail.com

Check you have the correct cutaway on the throttle slide..it should be a 6/4. This is marked on the top of the slide...Ian

email (option): ian@wright52.plus.com

It does have the 6/4 on it. It was a reconditioned one about a year ago. Has the standard jet and needle too. just cant get it to be a bit less rich, just keeps carboning up.
Just cant get my head around how to make it leaner.
Would be happy with slightly rich. But my last run it didnt get far and stalled, couldnt restart it. In the end got a friend to pick it up in his van.
Now trying to work out best route, drop down a jet size maybe and try again.

Hi Paul,

I have a pretty cool Amal publication about tuning the carb. It's period and from the makers.

Send me your address (physical) and I'll send you a copy.

Cheers

email (option): britool51@hotmail.com

Thanks for that.
I like to get hands on with my bike. Like the majority of people had to when out in the field. But feel at a disadvantage, not having the training they would have had and the backup and support from service depots.
It is good to have the people on this forum to act like backup service depots for info and guidance.

Paul C

email (option): pcrisp@pipistrelle18.Karoo.co.uk

Hi Paul

does your carb have a choke mechanism

is it free moving or stuck partially down etc

Do you run with an air filter

You also say re-conditioned, what exactly was done, a body rebore & new slide or just new jets etc ?

JO'B

email (option): jonnyob1@googlemail.com

Hi Paul..Assuming you don't have an air filter and your choke mechanism is functioning correctly the bike will run ok on the standard settings and it shouldn't be necessary to change jets. Main jet should be a 170. You said you had trouble starting the bike so the problem may be with the pilot end of the range... The adjustment screw in the side of the carb conrols the mixture at the bottom end but meters air, not petrol. There are some small drillings through the jet block and carb body that pass the air, and if these have become blocked with dirt it will richen the mixture.. Usually there will be some uneven running or a misfire as well as richness of the mixture.
The carb needs to be completely stripped to clean out these drillings...including removing the brass jet block from the carb body.
It seems a silly question but do you have a good strong spark and the correct grade of spark plug?...An NGK B6HS or a Champion L86C...Ian

email (option): ian@wright52.plus.com

Has anyone mentioned checking that the float needle is seating correctly and that the float height is correct ?

You could try lowering the float level with a long type mixing chamber nut.

To be honest, I've been struggling with slightly similar syptoms, but perhaps less extreme. The problem is that mine runs well and I have had it leaned off to the extent where it was unpleasant but the symptoms of richness remain when it's set up to run smoothly.

Ian will laugh with me but I'm convinced the recycled paint thinners that they now sell as fuel isn't helping. It's just so unstable and no two fill-ups are the same.

When I sent the carb away it was made up to the specs of 'as originally fitted'.
I have looked at the hole you mentioned through the bottom of the carb, even had the sleeve out it looks clear and aligns ok when sleeve back in. The mag on the bike is also a reconditioned mag, good spark. I do struggle to start a little but get a reasonable idle. The choke does come off completely, clears the slide. When I went for the run it did cough a little if I tried to throttle to much. If I then slowly throttled it give a reasonable response, throttle hard and it began to miss.
I will look at the float again see how it is. Then I will try the mixture screw see if it makes any difference.
Still feel as though I am stabbing in the dark though.



Paul C

email (option): pcrisp@pipistrelle18.Karoo.co.uk