What does it feel like when a spot is rich or lean??

[Guest]

Hi Guys... Hope everyone is having a great 4th of July weekend.

I'm still chasing down what I believe is a jetting issue with my 850... I'm to the point where I'm pretty sure it's carb related.

Same story... Bike runs great at idle... cruises nicely, etc... Full throttle works great, right up to around 5500 RPM, then it stumbles and never really clears up. If I I ease up to that RPM and don't open the throttle up that far, then it'll pull pretty well until around 8000, then it'll start stumbling...

Sounds like needles or main jet (or combo of both) to me, but I need to understand which direction to go. I'm having a hard time finding a place to do a chop, but will here shortly.

In the meantime, I would like to know... WHAT does the bike feel like when it's rich, vs. what would it do if it were lean?

I've very close to having this solved, but just need to know which direction to go.

Thanks,

[BassCliff]

Hi,

Are there any modifications to the intake or exhaust? It sounds like you need a bigger main jet, but that's just a seat-of-the-pants guess. Plug chops will tell you more.

Have a look at this article:

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Thank you for your indulgence,

BassCliff

[mike_of_bbg]

Are your airbox and exhaust stock and leak-free?

[niclpnut]

Kinda hard to describe a feel/sound but if overly rich its kinda wet and rythmic, while lean is dry and flat.

If you are at high rpm/high gear, snap the closed and open hard. If it bogs and rpms drop then raise its probably rich.

The factory pro guide explains things really well.

Nic

[Darin Jordan]

Are your airbox and exhaust stock and leak-free?

Running K&N Pods, 4-1 Mac exhaust, Dynojet III jet kit installed as recommended (165 mains, Needles 3rd slot from top, 4.5 turns on Pilots)...

Just completed a valve adjust and carb balance, both of which made a nice difference, but this issue still remains as it was before I completed those. Checked all the plug wires and they are satisfactory. Exhaust header temps are all even after a ride.

I'd think maybe ignition, but it's very throttle position sensitive... it only happens at 1/2 throttle and up... Which is why I thought it might be needle setting.

So, am I correct in hearing that if it's lean, it'll just kind of lay over, but if it's rich, it'll "flutter" and stumble...???

[koolaid_kid]

It sounds like your needle, but you must select the proper main jet first, which requires either a wideband such as an LM-1 or LM-2, or plug chops. Once you get the proper main jet, then you can tune the needle. If you do it the other way around you will be in there again once the main jet is correct to readjust the needle.
AFA lean vs. rich, it's more of a feeling while you are riding the bike, difficult for me to describe.

[TheCafeKid]

Move your needle down another notch (toward the point). The DJ instructions are close but the needle is never right. Really you need to move it down a notch and then stack one more thin washer on top making it effectively a half notch down) but a full notch will be ok. Won't be perfect but a little rich is better than a little lean at WOT

[chef1366]

If it is jetted with a DJ kit correctly I'd check out the ignition.

[49er]

You asked about the difference in feel between too lean and too rich.

When an engine is moderately too lean, there is a hesitation/stumble on the throttle. When it is excessively lean the bike will have a severe bucking hesitation, which is the precursor of holed pistons.

When moderately too rich, there is a flat throttle response to acceleration (commonly called running fat). When excessively rich you get a pungent smell, black sooty smoke from the exhaust and often fouled spark plugs.

[Darin Jordan]

You asked about the difference in feel between too lean and too rich.

When an engine is moderately too lean, there is a hesitation/stumble on the throttle. When it is excessively lean the bike will have a severe bucking hesitation, which is the precursor of holed pistons.

When moderately too rich, there is a flat throttle response to acceleration (commonly called running fat). When excessively rich you get a pungent smell, black sooty smoke from the exhaust and often fouled spark plugs.

Thanks... that's what I was really looking for...

From your description, combined with the chop I did tonight, I'd say it's too lean. I had moved the needle UP one notch to the 2nd notch, and it made the problem worse.

The plugs were pretty white with almost no color in the center and on the electrode... there was some dark color around the outside, but I think that was from some of the idling and partial throttle stuff. I also couldn't get it to rev up to the 8500 like I could before.

I have a set of 170 mains ready for it that I was thinking about trying, since it really seems like it's lean in the mains at WOT. I'll get that right first, and then figure out the needle from there.

[MisterCinders]

You asked about the difference in feel between too lean and too rich.

When an engine is moderately too lean, there is a hesitation/stumble on the throttle. When it is excessively lean the bike will have a severe bucking hesitation, which is the precursor of holed pistons.

When moderately too rich, there is a flat throttle response to acceleration (commonly called running fat). When excessively rich you get a pungent smell, black sooty smoke from the exhaust and often fouled spark plugs.

One of the most helpful posts I have seen in ages. Thanks for this.

[Darin Jordan]

Well, guys... I put the needles back to the 3rd slot, and installed 170 mains... very little effect! The stumble is still there, and I'm a little frustrated...

HOWEVER, I shall persevere!

I've had every main in there from 155 up to 175, and had needle settings from 2 down from middle, to 2 up from middle, and NONE of this seems to have an overall effect on the severe WOT stumbling I'm getting.

SO, I'm going to go through the entire wiring harness, or at least those parts affecting the ignition, including cleaning up the fuse box, as BassCliff recommends. I'm also going to pick up a relay tonight and do the relay mod for the ignition. I'll test the voltage to the coils, and make sure the plug boots are sufficiently low resistance.

Going to make sure that the ignition system is delivering full spark throughout the RPM range and see if perhaps THAT is the issue.

What I discovered yesterday is that at full WOT, the bike pulls to 5000, and then starts stumbling/cutting out. It actually seems to do this at anything over about 1/2-2/3rds throttle, but is quite obvious at WOT. I DOES rev right up to around 8500 or so in the gears where that is possible to do without opening the throttle up that far, but even then, at some point you have to open it up further and then the stumble starts...

I may end up right back at jetting, but since it seems to happen at exactly the same RPM, regardless of gear or load, I suppose it could be a weak ignition. Time to eliminate that possiblity, anyhow...

[esj001]

Good thread--good descriptions--let us know if its ignition related when you figure it out----is there a way to save or bookmark threads?--ive just been commenting on the ones i want to find again--thought there might be an easier way

[mike_of_bbg]

is there a way to save or bookmark threads?

I have a "subsribe to this thread" link in a "thread tools" pull down in the upper right (under the main menu bar). Then there's a "subscribed threads" link under Quick Links.

[esj001]

thanks mike i will be using that from now on---been wondering for a while--sorry for the hijack darin