cns carb v.3 tuning

[nightcruiser]

Thanks Nightcruiser!

I'm pretty good with the speed screw.
It's the mix screw that makes me a touch nervous. So it kinda works like the needle in the main jet. The more I back out the screw, the richer the mix. or is it an air bleed...

Am I correct in assuming that more fuel in the bowl makes the mixture richer across the board? Does it have other effects? Does it compensate for a slightly tilted carb?

sorry for all the questions. Thank you for all the answers.

The mix screw is an air bleed, its not fussy, just find the point where the motor idles at the highest speed and leave it there.

More fuel in the bowl does richen things up... A float adjustment can compensate for an angled carb (within reason) and at least keep the carb from overflowing. The effect of the float setting and a tilted carb can be more pronounced when going up/down hills, I tend to judge my float setting by how she performs riding hills. If she does good going up and down then it's probably set pretty close to right.

 

[PAracer]

Good stuff! Thanks again. I'll see what I can do with it this weekend.

 

[PAracer]

I just did some tweaking on the carb. I tried monkeying with the idle mix screw and the float.

I did like you said with the mix screw. I started with the screw one turn out from seated. I ended up backing it out another couple turns. End of story there.

The float adjustment. that was the ticket! The bike idles smooth as buttered silk, and it revs like no other engine I have ever worked on. So, what part did I actually bend? I bent the part that actually pushes on the plunger that actuates the inlet valve. Bend the tab up to lower the fuel level (leans out the mixture) Pushing the tab down to raise the fuel level.

The way I adjusted it was with trial and error. I set it so that the float would just barely open the valve. The valve has plenty of flow, so I think it's safe from running low. Small adjustments are the key

My adjust prosess:
Fill the fuel bowl by opening the petcock.
Close the petcock.
remove the bowl and bend the tab up a bit (dump the fuel into bucket. Empty the bowl after each adjustment).
put bowl back in place (you don't need to use the screws, but the gasket should be in there)
Open petcock to see if the bowl fills.
If the bowl filled, bend the tab up a little more.
Replace bowl and open petcock again.
keep adjusting upward until the bowl no longer fills.
Now, bend the tab down a bit this time.
put the bowl back on and open petcock.
if the bowl filled, you're done.
Bowl didn't fill? Bend tab down again.

You want the adjustment to be just over the point where the bowl doesn't fill. If it fills too much, you will have flooding and poor performance. if it doesn't fill, the bike won't run. but when you find the sweet spot, you'll be happy.

 

[nightcruiser]

The float adjustment. that was the ticket! The bike idles smooth as buttered silk, and it revs like no other engine I have ever worked on.

Contrats on getting her tuned up man! I've been really happy with the way my CNS runs, I'm assuming you're happy with your CNS now? That's a bit of a hot topic here on the forum, there's a group of people that always seem to advise people to just throw their CNS carb away and get an NT...

I'm assuming you have the high flow cone style air filter which I think comes with all CNS V3 carbs? If you have the plastic one instead you might need to keep an eye on the foam insert, it gets oily kinda quick and makes the motor run like crap, so you gotta clean that thing all the time. Also, if you notice your idle or low speed riding starts getting rough, clean the carb and pay special attention to the IDLE jet, it's really small and clogs very easily, when its clogged you will probably have hard start, rough idle and jerky low end. I actually had to poke a small twist tie wire through mine to clean it out once, carb spray just wasn't getting it....

 

[PAracer]

Affirmative. I'm pretty happy right now. I do have the blue hi flow filter. I will keep an eye on the idle characteristics.

I still have a bit of 4 stroking at the top end. i'm thinking that might calm down as the motor breaks in. I'm still under 50 miles on this bike.

 

[nightcruiser]

Affirmative. I'm pretty happy right now. I do have the blue hi flow filter. I will keep an eye on the idle characteristics.

I still have a bit of 4 stroking at the top end. I'm thinking that might calm down as the motor breaks in. I'm still under 50 miles on this bike.

Well, you might have to give the carb another tune if your already rich and still running a break-in mix of fuel (with extra oil in it). When you change over to standard fuel mix (with less oil in it) your mix will richen up just a tad more on you. I usually wait until the motor is broke-in and running standard fuel mix before I do too much tuning on the carb so I don't have to do it twice.

My motor doesn't do much 4 stroking at all unless I put the choke (enrichment jet) on. If your 4 stroking at WOT after break-in then you're probably too rich, if you already have the float set on the low side you might need to reduce the size of the main jet a bit to lean out the mix. You can use the enrichment jet to test if you have rich/lean mix, while riding in the range where your bike bogs or 4 strokes pull the enrichment jet on, if it smooths out your too lean it, if it gets worse your too rich already. Another easy test to check your float setting, turn off the fuel valve while riding, if the motor pepps up a few seconds later she would probably run better with a lower fuel level in the bowl. Just some general hints on tuning a CNS carb for others that may read this...