please define these carb terms

[Jaydela180]

Having a hard time distinguishing between hesitation and flat spot. Also between stumble, stutter and bog. Are they interchangable or slightly diffrent?

I've been upping main jets to richen what I think is a flat spot near upper midrange. Pretty much engine just roars at a higher pitch with no real reponse on the road. Flat spot, right?

Hard to diagnose problem by searching old threads when i may be mixing up terms. Thanks in advance.

 

[blknoel]

Hesitation : won't rev up when you open up the throttle more (or has a lag)

Flat spot: will rev up but no perceived power rise during that period (on a dyno graph the power curve just plateaus)

Or at least that's what I've have been thinking.

 

[XSLeo]

Your main jet effects mostly the WOT response, that's from about 3/4 throttle up.
The mid range is more effected by the needle. Your upper mid range is effected by both to a small amount.
When you up the main jet it can richen the upper mid range a bit. Often you need to lower the needle to lean the upper mid range. You do this by raising the clip on the needle.
Leo

 

[5twins]

A stumble or stutter are pretty much the same thing and are when the engine breaks up or gurgles and sputters. It is usually caused by being overly rich but there is such a thing as a lean stutter as well. It takes an experienced ear to tell the difference many times. Also, the info on what you're doing and have done so far to the carbs. As an example, if you've done a bunch of mods to the bike but haven't re-jetted from stock, chances are good the symptoms you're experiencing are lean ones.

The sound of the stutter or stumble can also be an indication of whether it's rich or lean. Lean ones usually have a sharper pitch or crackle to them, rich ones are more muffled or sloppy sounding.

 

[Jaydela180]

Okay. So I do have a "flat spot". So I'm still a little lean not there. Thanks

 

[Jaydela180]

Here's a little back ground:

Signature shows starting point of jetting for mods. Have climbed to a 47.5 pilot at 2 turns out and a 147.5 main. This is the jetting as of today, and will most likely be different tomorrow.

I have been fighting this flat spot with bigger jets thinking they'll bleed over. It is just not the case though. i think it is time to shim some needles and bring jets back down a bit.

 

[Jaydela180]

One last thing... Have been upping jets talso to get some sort of color on plugs. I know they don't color like the used to, or everyone has a different way of reading them. But smoke ring is super faint after 100 miles and porcelain is damn near white. Maybe top thread has a little bit of color.

Even switched to a bp8es to see if anything would present itself, but not much of a change.

Any suggestions are appreciated. Thanks in advance.

PS carbs synced and checked for leaks.

 

[5twins]

You can shim the needles richer in the BS34s but not by too much or they bind. I think you can only go a MM or so. As an experiment to see if this will help, you can move the steel washer that's in there on top of the clip to under it. That will shim the needles about 1/2mm richer .....

 

[Jaydela180]

That is what I'll do. Thanks

 

[GreasyC]

Open pipes are known to cause flat spots in the torque curve. There's possibly some rpm at which they're boosting you up above average as well. Holes are the trade off. That and deafness.