Bucking, 4-stroking, Snatch, Kicking, Surging, Stuttering

[Ray Lovestead]

I have more trouble trying to jet my carb based upon these vague manufacturer described sounds.

Can anyone spend a moment "clearly" describing what lean sounds like/acts like versus rich?

I've looked in lots of sources and they all use these single words to describe it, but it's not enough to tell a n00b. Anyone have video of them?

Blubbering? Really? Blubbering? (straight out of the Honda manual)

Ray
_________________
"Karting Expert Since 2014"

[Steve O'Hara]

Ray,

I was 12 when I got my first McCulloch kart engine in 1967 and "blubbering" was the term commonly used back then for a rich misfire. 4 cycling, fat, rich... all the same thing.
Here is one simple rule of thumb... if you have a misfire condition where the two cycle engine doesn't sound clean it is almost always a rich condition but once in a while it can be lean and sound similar... to be sure you simply need to observe the exhaust outlet while running at wide open throttle.... if the motor is too rich there will be a visible haze of whitish smoke.
If the engine is lean there will be no smoke from the exhaust.
Caution, do not make that determination with your kart running on the stand or going out of the pits.... they all smoke even if the carb is set lean when running under light load or just after they have been at idle. The smoke test only tells you something if you have been running hard for at least a couple laps.
Good luck.
Steve O'Hara

[John Matthews]

Even if I could point you to a You Tube video I wouldn't do it. Go out to the track with someone that runs the same class and spend some time with them, tuning is a hands on process. The modern recording temp gauge makes it easier but ultimately your ear on your motor is the best tool.

Most racers will help you out with just the promise of a cold beverage, they've all been where you are too

Cheers,
_________________
John Matthews
Heartbeat Power, LLC.

[Jim McMahon]

Take out your main jet and run it on the nozzle. You'll hear it soon enough LOL
_________________
GPI Racing | WildKart | Maxter | Hoosier
Karting Festival @ Blackhawk Farms June 1st-2nd.

[Ray Lovestead]

Like what Steve said:

"if you have a misfire condition where the two cycle engine doesn't sound clean it is almost always a rich condition but once in a while it can be lean and sound similar... "

Also, not judging it by the white smoke in the pits is good info.

But I also cannot for the life of me hear pinging. And I can't tell you what 4-stroking sounds like.

My problem is in the mid range (1/4 to 3/4) and as I move the needle up and down it just moves the problem around the range. So I think I need a new needle diameter. But I can't tell if it is surging or bucking, 4-cycling or blubbering.

Can anyone give me a good multiword (not just "stutter") definition of the sound it makes when rich vs lean?

Here is my description of what I'm experiencing. I think it is 'bucking'. On the stand or on the track, when the throttle is around 1/4 to 1/2(ish), it seems to fail a little in power and then kick really really hard. So on the track I actually have to pin the throttle to get past this condition or I just end up jumping and 'bucking'. Is that rich?

And what do I need to do to adjust my needle?

Thanks!

Ray
_________________
"Karting Expert Since 2014"

[Ted Hamilton]

I learned from the safe side.... I'd rather run a tick rich than get that last .001 sec. from mixture....

What I did was turn both needles out past the recoomended starting position another half turn or so... and when I went out on track I first turned the low side in in small incremements until the kart accellerated cleanly to midrange with no bog or hesitation.

Once I achieved that, I'd then turn the high in until I got that same clean steady pull up through redline. Four-cycling sounds like the engine just kinda' stumbles, never cleans out, never pulls hard.... and when the low is rich but the high is about right it will hesistate like you described, and then once you reach midrange it'll kick you hard in the pants and take off.

That kick in the pants is basically what it always feels like when it comes "on the pipe", so what you're looking for is a clean acceleration from start all the way up, but with a kick in there from the pipe early on...

At least that's what it's like in DD land. I assume with the low-stall clutch, the 125 TaGs feel similar when the jetting's about right.

Another tip was to look at the exhaust coming off a slow speed turn -- if there's a little puff of white smoke but you're still getting clean accelleration, the jetting's about right.

As far as hearing ig, I have very sensitive high-pitch hearing, and when the engine is perfect there's a certain crispness to the exhaust sound, not quite a crack, but something like that. Hard to describe, and some people can never hear it... But it's a different quality of sound than the "close" settings.

Hope that helps.

~ted
_________________
Owner, www.hamiltonhelmets.com // UAS Racer #76 // Karting for karting's sake...keep it fun!

[Benn Herr]

When I look for rich or lean in the mid-range, the first thing I go by is how it sounds/responds to sudden throttle opening.

If things are correct, the response will be immediate, and the kart will gain speed.

If you are lean or rich there will be a hesitation. Sometimes slight, sometimes substantial. You can tell rich by when the engine is hesitating, you can hear it running until it finally cleans out and goes.

When it's lean you can't hear it running. To me it feels like when you step off a curb and the landing is just a couple of inches lower than you expect. The engine often runs better when you let off the throttle a little too.

Lean can also get you into bucking. A combination of rich/lean and your foot bouncing on the throttle can be really irritating!
_________________
Benn Herr
Come see our Superkart Build Off @
http://www.lostenduros.com/?page_id=1534
beherr3@cox.net
http://www.southwestkarters.com/
http://www.lostenduros.com/
Kart Design
Chandler, Az.

[John Matthews]

Hi Ray,

I can appreciate your frustration but there's very little to work with here, if you won't or can't find someone who can coach you on this at the track you're only real option is to lean it out until it sticks. Then you'll know what too lean is

When I build engines people sometimes ask me to "dyno tune" them for the best carb settings. I tell them I'd be happy to do that if they can send me about 2500 cubic meters of the air they plan on running

Seriously though you might be fighting a problem not related to your carb settings at all for what we know. Here are a few standard troubleshooting tips.

1. Rebuild your carb so you know everything's right. This isn't hard but most folks have to do it a few times before they are confident in their results.

2. Set your pop-off pressure. If you don't know how to set-up your pop-off pressure (assuming you're using a diaphragm carb) then get a pop-off gauge and learn. Remember you're at a different altitude than most of the country, things might be different.

3. Go to the track and start out with a baseline setting. Record head temp, egt, density altitude, ambient temperature, track temperature, lap times, trap speed, have an observer watch for exhaust smoke, etc.

4. Make notes on everything.

5. Make changes and record results.

6. Repeat

The best carb settings will be the ones that give the best lap times without sticking the motor. They will be different on different days. With experience you will be able to tell certain things by the sound of your motor but until then just make sure to run a little rich, it'll save you money

Cheers,
_________________
John Matthews
Heartbeat Power, LLC.

[Michael Taksa]

on the stand or in neutral for shifters, from idle or low RPM smash the gas pedal all the way down as fast as you can:
vroooooom! = you are jetted perfectly.
ba-ba-ba-ba-ba-ba-vrooooom! = rich.
baaaaaaaaaaaaaah - vrooooom = lean. on the lean you laso get a vroooom from doing it half throtle, but nothing at full throttle.
The best is to actually hear it once:) You can do it when kart is running good, mash the throttle on the stand and listen, then go rich and listen, then go lean and listen:) and remember warmed up motor runs differently then cold motor

[John Matthews]

Elevation[3] 5,335 ft (1,626 m)
_________________
John Matthews
Heartbeat Power, LLC.

[Ray Lovestead]

BTW - CR125, pumparound (so no need to check pop off pressure?).

I believe I have never had it right because I have always had a hesitation mid-throttle. But not always a Bah-bah-bah. bucking.

So by the Keihin chart, needle height should be the obvious thing to change first (and easiest).

When do I decide that I need another needle? I'm running DGH. Do you guys have a few sizes that you like to use? Or do you just stick with one standard and tune around it?

Ray
_________________
"Karting Expert Since 2014"

[Ray Lovestead]

BTW - this is great info from you guys. I'm going to take tomorrow off to get this done right at the track. I'm not leaving that place without it perfect!

Ray
_________________
"Karting Expert Since 2014"

[Michael Taksa]

What carb PWK or PWM? Go all the way up and then all the way down on the needle and see what difference it makes. If it does not make a difference try a different coil, and make sure the coil ground wires are ok, sometimes they become loose and give you all sorts of problems.

[Jim McMahon]

Here's some docs that I have collected over the years that might help you understand carb tuning. They are all based around slide carbs used on motorcycles and essentially the same principles apply.

https://www.dropbox.com/s/c9sewpznmbe0z21/DuncanRacingKeihinCarbJetting.pdf?m
https://www.dropbox.com/s/jbk7ai175hpkvph/Slide%20Carb%20Tuning%20Kartweb.pdf?m
https://www.dropbox.com/s/vh5b7a0917z408b/slide_valve.pdf?m
https://www.dropbox.com/s/9dz4kjwlvi1cwif/Mikuni%20Theory%20-%20Ian%20Williams%20Tuning.pdf?m
https://www.dropbox.com/s/tz2d0r5y86r11hb/Dellorto%20VHSH30_Manual%20Vortex%20ROK.pdf?m
https://www.dropbox.com/s/wv38984d1o1x8o8/VHSH30%20Throttle%20Opening%20and%20Stages.png?m
_________________
GPI Racing | WildKart | Maxter | Hoosier
Karting Festival @ Blackhawk Farms June 1st-2nd.

[Rodney Ebersole]

Good luck at the track today Ray.
I just wanted to post so I can refer back to Jims links some other time.
_________________
Rodney Ebersole