Black Spark Plugs??

[BadGenetixx]

Hey guys, I'm fully aware that black tips on your spark plugs are evidence of an engine being run with a very rich fuel mixture and that this can be tuned when you're running an engine with high-performance parts.

However, I just tore down a Honda 5.5 hp that i had laying around and it had black spark plug tips. With a stock engine like this, how do you tune the mixture?? Thanks

 

[copenhagen59]

Every small engine I've ever takin the spark plug out of has been black.

 

[hal_armour]

needs more air !

Remember optimum tuning is 14.7 parts air to 1 part fuel. So if a plug is black it needs more air or less fuel. If you are sure no one previously drilled out or changed the jet then assume it has been starved for air. It is pretty common if the air filter is not kept super clean. Air can also be restricted if the exhaust is too small or clogged. Do what you can to get more air flowing through. Lots of aftermarket options like K & N air and headers, but some homemade solutions work pretty good too !

 

[texasfabguy]

What about rings?

 

[BadGenetixx]

Remember optimum tuning is 14.7 parts air to 1 part fuel. So if a plug is black it needs more air or less fuel. If you are sure no one previously drilled out or changed the jet then assume it has been starved for air. It is pretty common if the air filter is not kept super clean. Air can also be restricted if the exhaust is too small or clogged. Do what you can to get more air flowing through. Lots of aftermarket options like K & N air and headers, but some homemade solutions work pretty good too !

Thanks a lot for this advice. Does this mean I should drill out the main jet?? How would that alter the situation? BUt yes I'm beginning my modifications now, and i have an UNI air filter on the way. Thanks

 

[copenhagen59]

Hey guys, I'm fully aware that black tips on your spark plugs are evidence of an engine being run with a very rich fuel mixture and that this can be tuned when you're running an engine with high-performance parts.

However, I just tore down a Honda 5.5 hp that i had laying around and it had black spark plug tips. With a stock engine like this, how do you tune the mixture?? Thanks

After the very first time I ran my 6.5hp clone outta the box, I checked the plug and it was black.

My brand new 400ex , I rode it like 2 times and pulled the plug, it was black. Seen it too many times. The machines run and start good and don't blow any black smoke.

I believe it's just the nature of the beast, especially with a stock engine, as they have very restrictive intake/exhaust setups.

I've found that if you have one size bigger jet they start and idle alot easier.

Remember,

Lean is mean, but burns holes in pistons

 

[texasfabguy]

mine are all tan.

 

[hal_armour]

Black is too rich, drilling jet even richer !!

Thanks a lot for this advice. Does this mean I should drill out the main jet?? How would that alter the situation? BUt yes I'm beginning my modifications now, and i have an UNI air filter on the way. Thanks

Don't drill yet ! You already have too much fuel ! I would open up the air flow first. Run it and see the change in the plug, if it goes light brown you have what you wanted. If it goes white then it is too lean and now you can open up the jet. Start small, be patient and "tune it" by watching the plug. Once it is a nice light brown, stop drilling otherwise you will go back to black.

I know some guys just jump straight to the # 90 or the # 92, that is okay but it is a "shot gun" approach. You have the time, get your engine to " talk" to you, you will understand it and be able to trouble shoot it better in future.

As for the comment about "rings", I 100 % agree if they are passing; the oil from the case can make the "black". If you can check the cylinder walls for "oil streaks", go ahead. Otherwise assume that it is lack of air and carry on with opening up the air flow.

Not trying to take away from guys who design "Stage 2 kits" etc. They have done a lot of work to figure out what will work for the "majority of engines". They are upgrades though ! not repair parts, if you have a problem "upgrading might not fix it, you might just have the same problem with an upgraded engine.

If you take a "troubleshooting" approach you will know much more about small engines and how they work, rather just throwing money at them because it's better than doing nothing.

Your approach is good, ask, read, do and learn! Keep us posted too so that we all learn too !

 

[mr.modified]

Here's a plug chart. plug chart

Or if you'd prefer a better one, search google for sparkplug reading chart.

 

[Newoldstock]

For reasons I don;t fully understand a lot of clones run great and have dirty looking black plugs.
Lean them up and they don't run so great.

Could be issues with the heat range on the plugs and quality.

To that end I would sugest you buy a Real NGK plug and be sure its running black first.

I have a chum here with a shop and he has a case of fake Chinese NGK plugs. Oh ya and he knows they are fake and has them discounted to rid himself of a bad purchase.

 

[BadGenetixx]

Thanks again for all the advice guys - that spark plug chart is pretty helpful too. But yeah, I guess thats just how these engines work. I'll keep you guys updated on other mods and findings :thumbsup: