I read on advrider.com that a guy cut the slide spring in the carb - he cut it down by about an inch.
The theory is that the slide moves up with less restriction and therefore you feel a better throttle response.
I'm in the middle of doing all my mods right now, and I'm not sure if I should do this one or not?
I think I'm gonna go for it unless someone has a good reason otherwise. I'll only cut about 3/4 inch off.

 

Found out if this guy drilled the slide vent hole and cut the spring. What other mods has he done that may be different? Theories are cool, but do you want to be the guinea pig. Doing both might bugger up the fine control of the slide and give you weird engine oscilations inbetween quick throttle position movements.

 

You can get the carb to move as fast as you want but the revs won't increase unless you have enough air/fuel getting in there to do anything. With my mods listed below the bike performs well, however with the airbox lid off it has incredible acceleration compared to where it sits now and if the tire breaks loose it screams through the rpms.

 

I read the same kind of posts over on the KLX300 forum at Thumper Talk. After giving it some thought, I did cut about 3/4" off the carb spring. I can tell an improvement, but it's nothing radical. You get a slightly better throttle response. This mod definitely doesn't screw up the "fine tuning" of our bikes. Actually, if I was going to do it again I'd take off 1" instead. (Maybe next time I have the carb off I'll do that.) In the end though, it's still just a CVK carb. All the gurus over at Thumper Talk say the ultimate is an FCR.

 

A simple yet REVERSIBLE method to find out would be to TIE a couple of coils of the spring off. Then you could give it a try and if it doesn't do what you want, simply remove the tie off and you don't need to buy a new spring. That's what I would do.

The way the Keihin carb works is that it senses the vacuum from the engine and opens the slide in an appropriate amount. If you go too far, you can get into a BOG situation which only makes you think it's going faster.

Remember, if you feel a big hit when you open the throttle, kind of like when you made the secondaries manual on a four barrel carb, you could feel it, you are actually slowing the vehicle down.

Just a thought.

 

That was probably my post on ADV that you read. I cut my spring the same time that I re-jetted. So, I'm not able to give an accurate opinion of how much difference the spring mod made. Although, prior to re-jetting and cutting the spring I wasn't able to get the front wheel in the air.

Marty's right, you can zip tie the spring and try it out. You don't need to remove the carb to get to the spring, just remove the top diaphram cover. I haven't had any problems with bogging or oscillating. I have also drilled the slide vent and performed all the other free mods. I've put about 1200 miles on her since then without any problems.

 

I did all the mods including cutting the spring just shy of 3/4 inch. 128 main, 40 pilot, about 2 turns out.

One thing I wasn't too sure about was the needle position and the number of spacers to use. I got the dynojet kit. It had two washers, and the instructions said to use em. However, I've read a lot of other posts that said to use only one washer. So I went with one washer and e-clip on the 3rd slot from the top.

I'm very happy with the results. Power is much improved, no sputtering on decel... But I'm not sure that I've got it optimally tuned just yet. No complaints with how it runs though.

Oh yeah, and when we say cut the spring 3/4 inches we mean "sprung length" right? Not the actual length of wire right?
Because 3/4 inch sprung length equates to about 2.5 inches of wire when pulled straight. Yeah, dumb question.