CNS adjusting help needed- weird idling

[mattrgray]

So I've recently purchased my third cns carb, ( I love them but the clamps seem to like to break) but I cant get it to idle right. Has a number 72 jet. When I let off the throttle the idle is way up high around 3500 rpm but if I let it sit over 10 seconds it will drop down and very nicely idle at 1900-2300. If I try to tune it down while its at 3500 rpm it just dies. If I'm riding when I stop (I usually pull the clutch and ease to a stop) I have to let the clutch out and pull it back in while I'm almost stopped to slow down the engine. could you guys help me with this?

 

[crassius]

certainly sounds like an air leak, but could be slide sticking

 

[xseler]

I ran a CNS V3 carb for 3 years. Fought it weekly for most of that time. The easiest and best 'adjustment' I found was replacing it with a NT carb..............Easier to tune, stays tuned, and lost no top end speed.

Best of luck with your tuning!

 

[mattrgray]

certainly sounds like an air leak, but could be slide sticking

I've had air leaks in the past but I have gasket maker on the intake sealing the carburetor, and the slide feels free, it doesn't bind or anything

 

[mattrgray]

I ran a CNS V3 carb for 3 years. Fought it weekly for most of that time. The easiest and best 'adjustment' I found was replacing it with a NT carb..............Easier to tune, stays tuned, and lost no top end speed.

Best of luck with your tuning!

Yes I've found that with the NT my bike runs pretty good, but the cns gives me more low end torque and that is really helpful because I live in a hilly area.

 

[crassius]

could be leak at intake gasket, or if bike has been sitting a while, could be leak at base gasket - try spraying water around there to see

 

[mattrgray]

could be leak at intake gasket, or if bike has been sitting a while, could be leak at base gasket - try spraying water around there to see

I will try, but i just put my NT back on and it runs pretty good just a little less power in the low end but it idles great, comes right down to 2000 and holds steady. I've noticed that the throttle response is also alot better with the NT. I might be looking into the Mikuni VM18

 

[xseler]

Think this will be the next one I try.........a mixture adjustment screw sounds so much better than swapping jets!

http://www.bicycle-engines.com/2-Stroke-Dellorto-Copy-Carburetor.html

Good luck!

 

[mattrgray]

Think this will be the next one I try.........a mixture adjustment screw sounds so much better than swapping jets!

View attachment 95380

http://www.bicycle-engines.com/2-Stroke-Dellorto-Copy-Carburetor.html

Good luck!

Nice! and good luck to you. Not having to buy and change jets does sound nice, I might look into it myself.

 

[crassius]

wonder how easy to make an adjuster on bottom of float bowl as carbs had in 20s and 30s with lever for rich/lean to handle loads and hills

seems outboards had them too for speed for travel or power to pull skiers

guess just a tapered needle to stick up into jet would do it

 

[xseler]

My issue is that I take my bike from Oklahoma to New Mexico or the Colorado mountains and it's always a crapshoot on how it's gonna run. This carb would eliminate the guess work. 1200ft to 8500ft is a big variable.......and for some reason, it never seems to like the jet that worked last time.

 

[mattrgray]

wonder how easy to make an adjuster on bottom of float bowl as carbs had in 20s and 30s with lever for rich/lean to handle loads and hills

seems outboards had them too for speed for travel or power to pull skiers

guess just a tapered needle to stick up into jet would do it

I have an old outboard and the carburetor on it has a little thumb wheel under the bowl which moves a needle up and down below the jet, that sure would be nice on these bikes for on the fly tuning.

 

[crassius]

yeah, bowl on NT is thin - have to find a way to bond something thicker to it to make threads in

 

[Chaz]

Think this will be the next one I try.........a mixture adjustment screw sounds so much better than swapping jets!

http://www.bicycle-engines.com/2-Stroke-Dellorto-Copy-Carburetor.html

This is going on my list. Thanks for posting. Let us know your review when you get one.