m600 mid range flat spot

[popelli]

Bike has a ,id range flat spot, bottom end pulls well, top end revs out fine but mid range is lack lustre

apart from dropping in a 900 motor is there a cure for this

motor is basically standard with dyno jetted carbs, top removed from airbox, sils hi level pipes

any suggestions?

[slob]

Check needle position in carbs?

[popelli]

carbs were set up by local shop who know what they are doing

very unlikely that needles are in wrong position

[Wildfire]

Dyno Jet needles are adjustable.

[pte1643]

Book in for a Dyno session.

That'll sort it.

[DrD]

Or try raising the dyno needles one notch

[Flip]

.....along with Wildfire & DrD!!

Very unlikely a properly set up Dyno-Jet kit will give those symptoms in my experience.

The thing you have to remember with carburettor jetting is that in most cases it is governed by throttle position NOT engine speed and the fuelling circuits kind of over lap a bit like this:

If the engine is having troubles at low rpm (idle to 1/4 throttle), the pilot system or slide valve is the likely problem. If the engine has problems between 1/4 and 3/4 throttle, the jet needle and needle jet (most likely the jet needle) is likely the problem. If the engine is running poorly at 3/4 to full throttle, the main jet is the likely problem.

Don't forget to raise the needle you lower the clip which makes it richer (you could try opening the choke a little while at the throttle opening giving problems and see how it reacts for an indication).

Now I quite like this sort of thing..... (we could get into the dark art of Plug Chops here)
But to begin with and to make any tests repeatable and accurate put some masking tape round the twist grip and another piece round the housing then mark the twist grip when closed with a line, then opposite that another line on the twist grip housing (this will give you your closed position) then (with the engine off) open the throttle fully and mark a line opposite again. Continue equally at 1/2, 1/4 and 3/4. You will then be able to see which circuit is your problem.

Of course there are a few other things to consider such as float level and carb balance but also worth a check before moving any needle heights is that the Diaphragms don't have any holes in as this may give you similar symptoms (although that's doubtful if it really is running okay at a wide open throttle position not just revving out on a steady throttle- BIG difference in carburation there).

It really depends how interested/bothered you are to do it yourself or pay someone to sort it I guess- or you could just buy a fuel injected bike and be done with it! :D

Flip's Tip for trying this is: Find a bit of a hill to go up, that way you can have the engine under some load to get the throttle wide open.

[pte1643]

you could just buy a fuel injected bike and be done with it! :D

That's one way to sort it. :D

To be fair, Carbs do sound nicer... All that lovely induction noise you just don't seem to get with FI.