Carbs are off, I don't want to miss anything!

[Darren69]

Actually is the choke coming off both carbs fully? It was a common issues with Dell Orto the plungers would not all go up and down equally/fully.

[Mr Gazza]

This could be a float height/operation issue, or perforated diaphragm.

Another thing to check would be the triangular grey plastic boxes that sit in the frame either side. It is important that these are present and that the relevant pipes are correctly placed in them and are in good condition, free of splits and leaks.
The boxes provide a place to draw still air from for the pipes, but I'm damned if I can remember what those pipes do and why they need still air except that if they don't it will run rough, though probably more at higher speeds than slow and definitely worse in windy weather.

[Darren69]

Originally Posted by Mr Gazza

This could be a float height/operation issue, or perforated diaphragm.

Another thing to check would be the triangular grey plastic boxes that sit in the frame either side. It is important that these are present and that the relevant pipes are correctly placed in them and are in good condition, free of splits and leaks.
The boxes provide a place to draw still air from for the pipes, but I'm damned if I can remember what those pipes do and why they need still air except that if they don't it will run rough, though probably more at higher speeds than slow and definitely worse in windy weather.

Sounds like an Italian bike, it depends on the weather

[Brian.]

Originally Posted by Mr Gazza

This could be a float height/operation issue, or perforated diaphragm.

The float height/operation is something I did wonder about Mr Gazza, even though there's no signs of overflowing. And I was going to check the diaphragms as a mattter of course, but I don't know what symptoms faulty ones would give.

Originally Posted by Mr Gazza

Another thing to check would be the triangular grey plastic boxes that sit in the frame either side. It is important that these are present and that the relevant pipes are correctly placed in them and are in good condition, free of splits and leaks.
The boxes provide a place to draw still air from for the pipes, but I'm damned if I can remember what those pipes do and why they need still air except that if they don't it will run rough, though probably more at higher speeds than slow and definitely worse in windy weather.

Now this is interesting, because the triandular box on the left has no pipes leading to it at all, the one on the right has one - a breather pipe which I put in there because it looked like that was where it should go, based on photos of other bikes. And the similar breather pipe from the other carb is incomplete.

So this could be at least part of the problem, although the worst problems in my bike's running are at low speed....

But that is definitely something that I must correct when I put it all back together.

But thanks for the reply

[tridentperu]

I had a similar issue with my M600 - very poor running at small throttle openings, running rich, sooting plugs, jerky running, only happy on big throttle openings, exactly what you describe.

I got very very good at taking the carbs off/ and back on again. I cleaned everything (several times), set everything according to the book, fitted new float kits, diaphragms were good - did it improve? No.

I won't bore you with the whole saga but in the end I bought a used set of carbs to try them, but they weren't in any fit state to use, so I kept them for spares.

What was immediately apparent when comparing parts from both were the needles - the needles from the spare carbs were much thicker (visibly) than the ones from my carbs, totally different in fact. I did a load of research and it turned out the the numpty who owned it before me (I bought it cheap it as a non runner) had fitted dynojet needles but left the original Mikuni needle jets in....Doh. Fuel was pouring through it as soon as you touched the throttle!

I fitted the std needles from the spare carbs and, hey presto, smooth running was achieved. That was a couple of years ago now and the bike has run great since, all I have done recently is weaken the mixture a bit on the pilots as it was running a bit rich on the smallest throttle openings, you could tell by minor fluffing and snatching low down - now, all sorted again.

And yes, the grey boxes are important as they allow the vacuum part of the carb, that control the diaphrams, to draw still air when the bike is going. If the pipes are left open to the elements, the diaphragms can go all over the place and upset it even more!

Iridium plugs have helped prevent plug fouling too.

Hope this helps,

Jim

[Brian.]

Originally Posted by Darren69

Actually is the choke coming off both carbs fully? It was a common issues with Dell Orto the plungers would not all go up and down equally/fully.

That's one of the first things I checked Darren, it would have been a nice easy fix too. But no such luck, they were both shutting fully with a bit of slack in the cable.

Thanks for the suggestion though.
Brian.