And then it hit me...

[Jethro Airhead]

I've been having heartache with my TX650A running rich - very rich. The plugs were heavy with carbon. I went through adjusting the needle position (aren't those teeny circlips loads of fun?) and looked at re-jetting mains: got some excellent advice from the forum, for which I'm eternally grateful.

I was flicking through the manual, to re-check the plug reading guide, where it says colder plugs will make a bike run rich. The same manual says the TX should have NGK B7ES - and lo and behold, when I pulled my plugs, they were B8ES; which I understand is colder.

I'm going to town tomorrow; I'll get some sevens and cross my fingers.

Still, at least I've accumulated a neat little collection of leaner mains - just in case.

Has anyone else had a similar experience?

Thanks for reading and cheers from down under.

 

[Grinder]

I was using the iriduim plugs that came with the Pamco kit and my plugs were always dark. I changed to Autolite 63's without doing anything else and the color tuned to a normal color. Bonus, the Autolites are much cheaper than the NGK's.

 

[pamcopete]

Colder plugs do not actually make the engine run richer, they just show the "color" of whatever the mixture is more obviously because they are a colder plug and do not burn off the evidence. The opposite is also true. You could have a rich mixture but if you run a hotter plug you may not see it because the hotter plug burns off the evidence.

If all heat ranges you try show a rich mixture, then it is too rich. Ideally, both a B7ES and a B8ES should show a little color with the B8ES showing more than the B7ES.

Of course, it gets a little more complicated than that. For example, if you have a lean slow jet and a rich main jet, then the spark plugs will burn off the evidence of a rich main jet just in the time it takes for you to slow down and park the bike while the engine is running on the slow jet. The reverse is also true. If you have a rich slow jet and a lean main jet, then the plugs will show the color of the rich slow jet also just in the time it takes to slow down and park the bike, so that is why there is the technique of chopping the power while running on the mains so you can see the true color of the mixture from the mains. The slow jets are easy. That's the color you see when you slow down and park the bike.

Note: Exception to the above. If you have really, really rich mains, then just the tip of the porcelain will be cleaned off by the slow jets. There will still be evidence of the rich mains deeper into the porcelain.

 

[irristeve]

Colder plugs do not actually make the engine run richer, they just show the "color" of whatever the mixture is more obviously because they are a colder plug and do not burn off the evidence. The opposite is also true. You could have a rich mixture but if you run a hotter plug you may not see it because the hotter plug burns off the evidence.

If all heat ranges you try show a rich mixture, then it is too rich. Ideally, both a B7ES and a B8ES should show a little color with the B8ES showing more than the B7ES.

Of course, it gets a little more complicated than that. For example, if you have a lean slow jet and a rich main jet, then the spark plugs will burn off the evidence of a rich main jet just in the time it takes for you to slow down and park the bike while the engine is running on the slow jet. The reverse is also true. If you have a rich slow jet and a lean main jet, then the plugs will show the color of the rich slow jet also just in the time it takes to slow down and park the bike, so that is why there is the technique of chopping the power while running on the mains so you can see the true color of the mixture from the mains. The slow jets are easy. That's the color you see when you slow down and park the bike.

Note: Exception to the above. If you have really, really rich mains, then just the tip of the porcelain will be cleaned off by the slow jets. There will still be evidence of the rich mains deeper into the porcelain.

Hi ya Pete been trying get hold of you re Pamco I sent back for repair hope to here from you soon take care Steve B

 

[Jethro Airhead]

Thanks, Pamcopete: yea, I understand the plugs didn't cause the richness, but simply exposed it. The root cause worries me because all jets are as the book (s) say they should be. I'll try sevens and even see if I can get Autolite's locally,as Grinder suggests, and do a read after a reasonable run. As they are now, they don't show any colour at all: they get any sootier, and it'll be a job for a chimney sweep. Thanks for your help, cheers