Monobloc Tunning

[Andy M]

I've been running in my A7SS over the last few months. Until recently I was mainly riding on quiet back lanes, mostly up to about half throttle. The engine seems to be pulling nicely once warmed up and the plugs have generally been a nice brown colour.

However recently I've had a couple of blasts with her wide open, after which the plugs are rather sooty. From that I assume that the bike is running a bit rich and that I should think about reducing the main jet size.

I've got an air filter fitted, but I'm using the standard size, 270, main jet.  What I don't know is just how sensitive the mixture is to the main jet size.
Do I try going down just one size to a 260, or should I jump a couple of sizes and try 240?

What's normal when working on the carb tuning?
Thanks for any advice,
Andy

[chaterlea25]

Hi Andy,
Some thoughts??
The needle position controls the mixture from app 1/4 to 3/4 throttle, so firstly I would drop the needle one notch
Reduce main jets one size at a time is the method, that way you lessen the risk of lean running problems
Is the main jet a genuine one? lots of shite pattern ones out there
Is your air filter clean and not restricting airflow?
it might pass enough at lower revs but be choking at higher
HTH
John O R

[Andy M]

Thanks John,

I've already moved the needle once to lean up the engine at lower  throttle.

I've no idea where the main jet came from, so may try a new genuine one. But get the point that if I'm going smaller I try one size at a time.
The air filter is quite new and relatively clean, so I don't think that's the a problem.

Andy

[beezermacc]

The Shooting Star was never intended to run with an air filter. Fitting an air filter will affect your mixture quite considerably. By way of example a Super Rocket with an air filter has a main jet of 290, without an air filter 400. You will probably need to go down quite a few sizes, probably in the 230/240 region to achieve cleaner running by which time you will be starting to notice a drop in power.

[Triton Thrasher]

Often, if the main jet is too big, you will motice a hesitation, then a recovery, when you close the throttle from fully open to about 7/8 open.

If the main jet is too small, the bike may seem to pull harder at 7/8 throttle than at full throttle.