Fuel mixture problem?

[zx-stewie]

What setting could affect the 0 - 3000 RPM range on a carburetor?

After I installed a full exhaust on the 9R last year the bike is a total dog in that RPM range. Their is already a jet kit on the bike. I know that some loss of bottom end power is to be expected when a race exhaust is installed, but the "lack of sack" seems to be excessive.

Once I'm above the low RPM range the bike is a rocket - no complaints.

Any ideas?

[Honclfibr]

how's your carb sync?

[TLRMan]

Low speed jets (pilot), can be adjusted with screw driver.
May be a slight transition to the needle also. move clip down one position. Will put a little more fuel in at midrange.

[zx-stewie]

how's your carb sync?

n'sync, thank you very much

Just checked that out a couple weeks ago and they were all suckin air in unison.


I'll tweak the mixute screws this weekend. Hopefully that will help.

If I remember correctly, I belive that the clips are already on the lowest position of the needles. yeesh.

[stoinkythepig]

I got a neat tool that will allow you to pop the pilot screw caps out without pulling the carbs. Lemme know if you want to use it.

[zx-stewie]

Originally posted by stoinkythepig
I got a neat tool that will allow you to pop the pilot screw caps out without pulling the carbs. Lemme know if you want to use it.

Thanks for the offer but I already pulled those covers off when I installed the jet kit a few years back.

With the kit they have you drill a small hole in the covers, thread in a screw, and then just pull out the screw with the cover attached.

[jimb12]

Sure sounds like the pilot fuel needs to be increased. If you could put it on a dyno with the a/f meter you could dial it in pretty well, though dyno time isn't cheap.

[zx-stewie]

Originally posted by jimb12
Sure sounds like the pilot fuel needs to be increased. If you could put it on a dyno with the a/f meter you could dial it in pretty well, though dyno time isn't cheap.

Yup, I agree. I backed the fuel mixture screw out as much as I dared and it didn't really make a difference. I ordered the next larger size pilot jets so hopefully that will do the trick.

I should have also mentioned that the motor is running hotter than it did before the exhaust replacement so I'm pretty sure that I do have a lean condition.

[stoinkythepig]

I'm pretty sure that I do have a lean condition.

Just put a block of wood under the kick stand

[Degsy]

Originally posted by stoinkythepig
Just put a block of wood under the kick stand

Degs

[zx-stewie]

Originally posted by stoinkythepig
Just put a block of wood under the kick stand

It must be time for lunch - I actually had to think about that one for a second.

[TLRMan]

you should prolly check yer main jets too...If you are sayin it runs hot...But wanna know something....The engine actually runs cooler when it is lean, and hotter when rich...
Don't you guys ever read Camerons stuff? geeez...

[stoinkythepig]

The engine actually runs cooler when it is lean, and hotter when rich...

Don't you guys ever read Camerons stuff? geeez...

I do but don't remember that one. Hmmmm...

[TLRMan]

Just being a goof....
and when I say cooler when lean, it's to a point of course....Like I'm not that stooopid.. But to really understand it you gotta study how flame fronts propagate, and also what you got for squish velocity/area, and how efficient the fuel vaporizes....

[zx-stewie]

Originally posted by TLRMan
Just being a goof....
and when I say cooler when lean, it's to a point of course....Like I'm not that stooopid.. But to really understand it you gotta study how flame fronts propagate, and also what you got for squish velocity/area, and how efficient the fuel vaporizes....

I'm not sure if this question was asked somewhere else because it kind of sounds familiar, but why is is that a lean fuel mixture causes excess heat as opposed to a rich mixture which has more fuel?

[stoinkythepig]

Originally posted by zx-stewie
I'm not sure if this question was asked somewhere else because it kind of sounds familiar, but why is is that a lean fuel mixture causes excess heat as opposed to a rich mixture which has more fuel?

In the simplest terms, a lean mixture burns hotter (and maybe faster) and a rich mixture burns cooler and not as completely. If you've ever used a cutting torch you know the flame is hottest with lots of oxygen. Well, the oxygen does not burn (it's not even flammable) but it leans out the mixture and allows the acetylene to burn much hotter. You also know that when the mixture is very rich you get a yellow flame (cooler) and lots of soot (incomplete combustion). I can't think of a better explanation so if you've never used a cutting torch you'll have to take my word for it...

[zx-stewie]

Originally posted by stoinkythepig
In the simplest terms, a lean mixture burns hotter (and maybe faster) and a rich mixture burns cooler and not as completely. If you've ever used a cutting torch you know the flame is hottest with lots of oxygen. Well, the oxygen does not burn (it's not even flammable) but it leans out the mixture and allows the acetylene to burn much hotter. You also know that when the mixture is very rich you get a yellow flame (cooler) and lots of soot (incomplete combustion). I can't think of a better explanation so if you've never used a cutting torch you'll have to take my word for it...

Hmmm...so is an engine making more power as the fuel mixture gets leaner? Or does the quicker combustion process (from a lean mixture) cause an incomplete power stroke which results in less power?

[TLRMan]

But if you go too lean the mixture doesn't burn at all...and gets cooler!

Make sure you cover detonation too Stoinky...


:

[stoinkythepig]

Originally posted by TLRMan
But if you go too lean the mixture doesn't burn at all...and gets cooler!

Make sure you cover detonation too Stoinky...


:

I covered that a little in my next post but ti didn't take.

[zx-stewie]

I put the new pilot jets in the bike today (#40's as opposed to the stock #38's) and the problem is no more. The bike doesn't run as hot as it used to either so everything is back to normal.

Thanks for everybody's help yo!!