[coxy_gg]

hi,
just wondering if anyone could help me out here, ive got a 2006 gasgas pro 250 and the plug always seems to be really black when i take it out after any riding done. the mixture is set at 3 1/2 turns out, the needle is on the second from bottom setting with standard jets in the carb, mixture we use is 65ml oil to 5 litres of fuel super unleaded and the bike has only recently had an engine rebuild(within last two months), the bike doesnt smoke what so ever when running, on tickover or even when at full revs. Anybody any ideas on what i can do to make the plug the brown colour its suppose to be?

cheers coxy

This post has been edited by coxy_gg: 16 June 2010 - 07:11 PM

[Stork955]

Gday, your bike is too rich. If the plug looks "dry" and black, this is caused by fuel. Check the aircleaner is OK first (clean and not over-oiled) and then you may need to drop the needle one notch. Ride for a while and pull the plug and see how it looks.


Cheers,


Stork

[coxy_gg]

if the bike was running too rich which i figured i would of thought that when idling or on low speeds it would like choke itself up am i right in thinking this?? becuase the bike runs sweet as a nut at any amount of revs. Air filter is fine, cleaned after every ride and the right amount of oil is on it so its not that. might try dropping the needle height but dont want to start messing about with the bike if its going to not run right.

cheers Coxy

[Stork955]

Gday, not necessarily. Over a long time if the bike is rich it may get to the point of misfiring when the carbon buildup on the plug becomes too much, if it is slightly rich this may take a few rides. Dropping the needle one notch will only sharpen it up a little, and should clean up your plug to a nice brown. The mixture screw will only affect idle mixture which may have some small effect but not a lot overall. It does sound like it is out too far -the usual rule of thumb is around 1 - 2 turns depending on where you are. Anyway, if you make any adjustments, do only one at a time and if you notice a poor result, just reset back to where you were in the first place.

Cheers,

Stork.

[coxy_gg]

ok thank you for your help. So by droppin the needle i need to put it onto the bottom setting right? As its on the second from bottom one now. Im riding at the weekend so will try that. The fuel mixture screw is set to what was standard when i got the bike and ive spoken to some other people who say that it is correct. Im sure its the keihin carb that should be set at 1-2 turns out. Cheers coxy!

[JSE]

coxy_gg, on Jun 17 2010, 05:05 PM, said:

ok thank you for your help. So by droppin the needle i need to put it onto the bottom setting right? As its on the second from bottom one now. Im riding at the weekend so will try that. The fuel mixture screw is set to what was standard when i got the bike and ive spoken to some other people who say that it is correct. Im sure its the keihin carb that should be set at 1-2 turns out. Cheers coxy!

When you raise the small circlip to one of the upper grooves, you are "leaning out" the needle, or dropping it as some say. So, you want to move the circlip up one groove to get a leaner mixture "raise the clip, lower the needle".

If you have the Keihin carb, you have an air screw adjustment, not a fuel screw adjustment, so adjusting it out will give a leaner mixture, whereas adjusting a fuel screw out (like on a Dellorto) will give a richer mixture, so you need to be sure what kind of carb you have.

Generally, there is no "standard" setting for a fuel/air screw (which is why it's adjustable and not set from the factory) but on the Keihin PWK28, for instance, if the pilot jet size, needle clip setting and needle jet/needle profile are correct for the ambient conditions, when the air screw is adjusted for best throttle response and low-speed running, it will be in the 1.5 turns out range.

Jon