Jump to content
Sign in to follow this  

2 stroke jetting leaner with tuning?

Recommended Posts

Has anyone found that their 2 stroke has gotten a donor part, or head skim etc. That it appears to prefer leaner jetting? When I compare my bikes jetting to others on the forum at similar elevation, it seems to get upset at the same jetting.

Is this because the bike is running more efficiently, thus requires leaner jetting, or do you think there's something up with the carb? The float height it correct, the needle (float and jet) are new. But the bike prefers the needle at top clip, and between 5 - 10 jet sizes down.

Share this post


Link to post
Share on other sites

Also post :

 

-at what elevation you ride (higher humidity also requires leaner jetting)

-type of fuel used / octane rating

-if squish band height is stock or corrected

-if standard size or oversized / big bore

-using genuine OEM jets or aftermarket 'equivalents'

Edited by mlatour

Share this post


Link to post
Share on other sites

Bike - GasGas EC300 2006

Factory Inox Pipe 

Heavy Fly Wheel

Squish corrected to 1mm

Compression ratio 13:1

Standard bore

99 Octane

32:1 Fully Synth 2t

Riding at sea level in the UK so -10c / +30c

BR7EIS plug

K&N Air filter

New Reeds

 

Main jet = 172 (stock is 178, most ride between 168 - 180) and it sputters at high revs, it feels more electrical to me, but I've changed literally everything (stator, cdi, ht coil). The only wire I haven't changed is the ign coil from CDI wire. 

 

It seems to rev that high cleanly at full throttle when not under load (neutral) but when riding, if I get to the very peak revs, where a 2 stroke normally flattens out, this sputters and causes the bike to lurch, never clearing out.

Edited by moto_psycho

Share this post


Link to post
Share on other sites

There is the possibility that your Needle Jet is worn/ovaled from years of the needle rattling around in it.

This is a tricky one to find normally.

Symptoms are running rich at stock settings, especially at low rpm, which makes you try to lean it out... but it never finds the sweet spot because there is extra fuel sneaking in at every throttle opening.

The real key to this is, if you run stock pilot, do you have to drop the needle down and open air screw to clean it up? This says that too much fuel before main jet is activated, and can only be a couple of things.

Keep trying...you'll find it!

Share this post


Link to post
Share on other sites

Unfortunately that is exactly the case. The bike runs amazi gly well though, idles well and awesome power through the range. But surely that doesn't affect full throttle?

Do you know the inner diameter of the needle guide? I know they aren't replaceable, but I work in a machine shop so anything is possible!

I'd be surprised if this is the cause of my problems though.

Share this post


Link to post
Share on other sites

It "Shouldn't" affect full throttle. Theoretically the main jet should limit the fuel since the needle jet is way bigger than the main.

If you have the carb out, it's worth a look anyway. Pull slide out and shine a torch down from top and see if it is oval.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...