Getting jetting closer and having fun with friends

[jasonp]

We all went out and pulled snowmoble signs as part of being in the club. Pretty fun day all went mud bogging and ****. Everybody was telling me to skip my fourwheeler over the pond.. Yeah have another beer. Great time seeing all those fourwheelers/friends out on the trail.. to bad we can't have something like that around just for fourwheeling.

I got to try more jetting stuff and found that I'm at a 120 was at a 125 main now and it's still a little rich as the engine is still breaking up on the very top end. I set the needle in the middle position just to see if what would happen. Sure enough way to rich.. stutters bad when in the upper rpms running half throttle or so. I tried with the needle all the way lean and it seem to have to much effect. The engine felt soft and didn't want to respond. 2 position didn't help either still a little rich, better though. So I'm thinking a leaner needle jet, which is the part that the jet needle slides into. Also I'm having a problem with tuning the accel pump. (If any of you have the stock carb appart measure the distance with a feeler gauge between the white plastic dealy and the accel pump rod.) I'm starting to hate this carb.. I'll tell you that much. haha
Anyway the ******* thing is a monster in the mid range. This cam delivers the goods about 3000 rpm to 7500 rpm. It's not a screamer like a bigger cam, though it feels better then stock. It's got the meat right at lower mids. I like that. Going down dirt roads and kicking it down looking back you could see the tires where just burning a throwing rocks like mad. Getting the jetting closer really helped power. I'll keep working at it and see if I can get it even closer.
Thanks for reading.

 

[griff]

The part the needle slides into is the emulsion tube (at the bottom of that, in the bowl, is the main), no need to mess with it.

If it still seems too fat everywhere, drop the pilot jet down 1 size.

 

[jasonp]

pilot jet?? Really? I thought this jet only effected idle?? Man, griff this is hard!
I was going to change needle jets because I have the richest one for this carb... and with the clip in the middle of the jet needle and running super rich. I thought this might help me tune the carb better with a leaner needle jet as I thought it effected 1/4 throttle to 3/4?

 

[jasonp]

The whole carb is running rich except the idle circuit.. That from the best of my knowledge. I'm starting to question that though. haha

 

[griff]

The pilot jet circuit is always dumping fuel, regardless of the throttle position or rpm. Its primary area of effect is idle and off-idle, but its still providing fuel even if if youre on the needle or all the way to the main.

It doesnt magically "turn off" just because more fuel is being pulled from needle or main circuits.

If you believe your good on the main, and the needle in on the leanest position, (this all assumes you have your float-height set properly) and its still too rich, drop the pilot down 1 size.

Hope that makes sense.

 

[vestige019]

i have the same exact problem with my carb

so i just turned my gas off a little because im too scared to take my carb apart.

and guess what it works great. lol

 

[jasonp]

The pilot jet circuit is always dumping fuel, regardless of the throttle position or rpm. Its primary area of effect is idle and off-idle, but its still providing fuel even if if youre on the needle or all the way to the main.

It doesnt magically "turn off" just because more fuel is being pulled from needle or main circuits.

If you believe your good on the main, and the needle in on the leanest position, (this all assumes you have your float-height set properly) and its still too rich, drop the pilot down 1 size.

Hope that makes sense.

Thank you griff, that makes perfect sense.

 

[jasonp]

I didn't know this but griff I'm sure you do... I called sudco and talked to jason about jetting. He said go get your main jet right first because that effects the needle jet and flow through the jet needle... get it right and then tune the other parts.. I thought that was interesting.
Also Griff I'm going down a couple sizes on the pilot and up on the air screw so I will hopefully get less fuel flow through that circuit under full throttle..?

 

[griff]

The way I approach tuning when dealing with unknown configs is similar.

1. Get the idle set, adjust the screw, et all. This so I can get it started and idling on its own. May fine tune later depending on what I need for transition to the needle.

2. Set the needle to some mid position, just for the moment. Doesnt matter if it runs like crap in the mid-range right now, as long as it runs.

3. (this is where the tuning really starts) Start with my best guess as to what main should be rich. Basically I keep dropping mains from there 1 size until I reach a lean sputtering threshold (takes some practice to feel this) at full throttle at high rpm, then go back up 1 size and use that as my baseline.

Note: its easier to detect going lean, than it is to detect going rich. This is why you start intentionally rich, and work your way down.

4. Then start dropping the needle until it reaches a lean sputtering threshold, then raise 1 shim and/or clip position. Use that as baseline

5. Tweak the a/f screw as needed to match transition to needle, and have good off-idle response.

From there, you can adjust float height and pilot jet size if whatever your doing seems to rich (or too lean) no matter what you do. This assumes you know the needle is at least intended for your application.

Always make ONE change at a time, test it, then go from there. A lot of guys make multiple changes at one time, and usually make things worse.

At least, thats the basics I use.

 

[jasonp]

10-4... What I've found what works for me.. I don't know if this is right or not.??
I work from rich to lean.. basically I set the bike up so it will sputter at high rpm. Then come down a size at a time on the main until it rev's free. I've found on my bike if I go any leaner then that then I loose a little power. Same goes for the needle... Start rich and work down until the sputter goes away...