T500 Running Rich on One Cylinder

[tricky1962]

My T500 has, I believe a genuine 15000 miles on the clock.

Over the last 1000 miles or so it has started to foul the plug on the right hand cylinder only.

I have used new plugs, gapped the points, checked the timing, checked the air filter and cleaned and adjusted the carb.

Admittedly, I ride gently, rarely over 4500 rpm, mostly trickling along in high gear. However, the right hand cylinder is running too rich but the left hand one is fine. I have lowered the needle a notch, screwed the idle mixture screw right in and am currently using a warmer plug on the right hand side to try and get the plug to last longer than a few hundred miles.

Just before this nonsense started, both cylinders were idling rich (as in mixture screws were right in) so I cleaned the pilot jets and checked the float heights. The points were out on both cylinders and the right hand cylinder float height was too low. Fixed those problems and now this one.

So in summary, float height spot on, ignition spot on why is it running rich?

Any thoughts gratefully appreciated

[jabcb]

Is your battery fully charged?
Check to see that its charging properly.

Some of the T-series bikes tend to have problems with the spark on one cylinder when the voltage is low.

[tricky1962]

Thanks for the reply.

I've just checked, the battery is showing 12.88V with ignition off, 13.0V at tickover with the lights on and over 14.5V at 3000rpm with the lights on so I don't think voltage is the cause.

I have just increased the float height from 27mm to 30mm and this has leaned out the mixture quite alot, arguably too lean now, so I've richened up the idle mixture, will see what that does then move the needle back up if necessary. One stage at a time

[Vintageman]

Is your Needle Jet pitted inside metering barrel (bright light and good eyes to see into Needle Jet a ways) or outlet egg shaped not round due to wear? Jet Needle good not worn?

Any little specs wedge in Needle Jet carb body air passage blocking or made it into Needle Jet outer rim area blocking air to mix/atomize fuel passing by needle?

[tricky1962]

Thanks for the comments

As far as I can see the needle jet is clear and not oval to the naked eye. I have cleaned the carb passages so there shouldn't be anything there to interfere with air/fuel flow.

Currently, the idle screw is back to 1 1/4 turns out, the needle is dropped one notch and the float down 3mm. The plug is tan around the metal rim and the insulator is off white/grey.

I'm going to give it 500 miles and then check again. I don't have the desire to fiddle and just want to ride the bloody thing without the plugs fouling, summer is here after all!

Thanks again for the help chaps