Idle screw bottomed out - and still running rich!

This is a problem I've been troubleshooting and still haven't been able to solve.

While colourtuning, the only way to lean out the cylinder is to bottom out the idle adjusting screw cutting off all fuel from the carb - so where is the fuel still coming from? I'm running rich 1/2 a turn from bottomed out!

I've cleaned and cleaned again the carbs. I've adjusted the floats from 14mm to 18mm in 1mm increments (currently at 18) and now I'm out of ideas.

Any suggestions?

 

I had the same problem i switched to a hotter plug BP6ES then reset the mixture screws. they are fine now. whats your airfilter look like?

 

If it was just one i would think float needle valve was leaking but if its all 4 then i would be looking at the enrichment side, is the choke stuck partially on.

 

Mixed-up Main and Pilot Fuel Jet?
Stuck Diaphragm Pistons not seating.
Idle Adjustment Rod opening the Throttles too far to Idle letting-in Main Jet Fuel?

Wrong size Pilot Jet.
Mixed-up Air Jets?

That's about the whole list, I imagine.

 

ok what are you adjusting?? the idle screw doesn't have anything to do with the mixture. There is a misture (air jet) that adjusts the mixture for the pilot circuit is this what you mean?

 

What Rick is saying is if the idle circuit is not correct you may have the butterflies open too far which allows it to draw fuel off the mid range circuit (needle jets). If you're butterflies are open any more than a very tiny crack the mixture screws have little discernible effect.

You also might check your float heights. Fuel too high in the bowl will make it rich also.

Of course a stuck or mis adjusted enrichment system is the easiest thing to fix and should be checked first.

 

Overly rich mixtures due to the Enrichment Valves being slightly open is a possibility, particularly if the Bike was not well maintained and the Carbs were in need of a cleaning.

In frustration, trying to get the Bike to start, PO's are known to have quickly forced the Enrichment Valves open. Sometimes, in anger over a Bike that will not start, the Enrichment Valves were forced open with such an angry motion that the narrow shaft ... where the lifting forks fit ... becomes "Bent-out-of-shape" and no longer operates with a smoothness as the forks engage the "Top Hat".

With the narrow shaft tilted, the Enrichment Valve gets "Hung-up" in its lifting forks and fails to seat.
It does not take very much of a deformity to the shaft to render it unable to seat ... thereby causing an additional amount of Fuel to be sent to the Combustion Chamber throwing-off the Air-Fuel Ratio, and in extreme cases, causing Plugs to be fouled in short order.

Look at the Enrichment Valves closely.
If the top of the Valve is deformed and not straight, it will have to be straightened to allow the Valve full closure.

Remove the Enrichment Valve from the Carb Body.
Heat the upper-end of the shaft.
Carefully and slowly adjust the end to remove the bend in the shaft.
Use needle nosed pliers and apply slow and steady force.
Or ...
Heat the end and roll it on the surface of a flat and straight surface.

Don't try to bend it back into shape without heating it; the risk of it snapping right off is very high!