How lean can you go?

[bimotabob]

Hi

When I brought my FZR powered Bimota it run rich - sooty pipe, black plugs
the odd smoke under heavy throttle etc.
Now I have brought the gear to easily change the EFI fueling.
I have leaned out the whole map and then gone back and richened the idle
6% as it would stall etc.

It now has stronger acceration and gives more milage and gone is the sooty pipe but I don't own a gas sampler yet so the mixture ratio is unknown

How much can the mixture be out before problems start on a four stroke?
I have heard the saying "lean is mean - but not for long"
(though I have never heard of anyone ruining there engine over it)

Any advise is appreciated thanks.

[Sully60]

Hi Bimotabob
It might be a little inconvenient to do but reading sparkplugs is a reliable way of seeing if your fuelling is too far out. Without a gas analyser or the old skool colour tuning plugs (which are probably about as useful as a sunroof in a submarine in your motor) its the only way to see whats happening inside the combustion chambers.

I hope I'm not being to patronising here you may have done this before.

You need to take the sexy beast for a decent run and ride the way you normally do then check em' Unless your running leaded petrol (avgas) you don't want to see any white deposits as this indicates that things are getting a bit hot from being lean. A nice caramel colour around the centre electrode and insulator means your probably in the ball park and pretty safe.

You could also try tuniung by the seat of your pants if changing the fuelling is easy, you'll soon figure out what works best.

Good luck!

[hospitalfood]

dont know alot, but if you thrash it lean you risk burning holes in pistons and other damage as well, hence the mean but not for long, had my bike dynoed at Henderson Motorcycles last week due to mods I had done, only way to really know if your getting the most out of your engine. I was happy with the result.

[pete376403]

Even when the mixture s correct the pipe will still be black - thats unleaded gas. It was the lead in the old gas that would give the white colour to exhaust deposits. So as said, plug chop or gas analyser is the only sure way. If you're going to try for extreme lean, check up on the availability of replacement pistons first:shit:

[bimotabob]

dont know alot, but if you thrash it lean you risk burning holes in pistons and other damage as well, hence the mean but not for long, had my bike dynoed at Henderson Motorcycles last week due to mods I had done, only way to really know if your getting the most out of your engine. I was happy with the result.

Yeh burning holes is what I don't want! I don't know if the one place here in town with a dyno can check my mixture.


Even when the mixture s correct the pipe will still be black - thats unleaded gas. It was the lead in the old gas that would give the white colour to exhaust deposits. So as said, plug chop or gas analyser is the only sure way. If you're going to try for extreme lean, check up on the availability of replacement pistons first:shit:

Fair point about the colour these days but mine was black compared with my mates bikes with dynojet kits. Now it's kind of very dark brown.



Hi Bimotabob
It might be a little inconvenient to do but reading sparkplugs is a reliable way of seeing if your fuelling is too far out. Without a gas analyser or the old skool colour tuning plugs (which are probably about as useful as a sunroof in a submarine in your motor) its the only way to see whats happening inside the combustion chambers.

I hope I'm not being to patronising here you may have done this before.

You need to take the sexy beast for a decent run and ride the way you normally do then check em' Unless your running leaded petrol (avgas) you don't want to see any white deposits as this indicates that things are getting a bit hot from being lean. A nice caramel colour around the centre electrode and insulator means your probably in the ball park and pretty safe.

You could also try tuniung by the seat of your pants if changing the fuelling is easy, you'll soon figure out what works best.




Good luck!

Yeh taking the plugs out is a hassel but it sounds like I have little choice.
When I got dyna coils for a 2 stroke with weakish factory spark the much stronger ignition caused the centre of an electrode to vanish including some ceramic.
All the plugs went from brown to grey - now I'm very timid when it comes to combustion heat.

I'm hoping there is more leway with 4 strokes but I have little knowledge of this.

Cheers :yes:

[slowpoke]

Mate, you've got a luvverly boik there so do it justice: stick it on a dyno and have it set up by the pro's. They'll do a far better job in a much shorter time. It's short term pain but well worth it in the long run. Anything else is just guessing.