OMG I have to tune a CNS!!! Help

[skrew37]

I notice after riding for about 10mins it starts to bog down. Is this a air issue, I've drilled the jet to #64 and have clip at the middle position. My spark plug is black but it's not gunking up, it's slightly wet but nothing serious. I've been running about a week now still breaking in.

Mine started to bog down too. At first it ran great, then would lose power and bog down when I gave it anything more than half-throttle. Then it would eventually gain power again. Could this be an air leak as well? I bought a new (extra) jet and drilled it to #68 to start and will then make adjustments from there. But first how would I check for an air leak?

 

[DuctTapedGoat]

Spray carb cleaner around the areas you think you're leaking at, primarily the intake and bottom of the carb at the bowl. It's like a buck an a half at wally world.

And to Droc089:

Black and wet is NOT good, break in or not. You need to lean out (not oil, but fuel).

If you bog after a certain amount of time, your fuel bowl isn't staying filled is what I would imagine. Check for pinches in your fuel line, clean your fuel filters and inlets. Adjust the tang on the floats.

If that all fails - there is a RES (reserve) marking on your gas tank petcock, use that in place of on and it will give you slightly more flow.

 

[jtgolden]

I'm glad I can finally join in this topic.


I am the proud owner of a CNSv2/GenB carb, and I'm even prouder that I got it working.

Everything I did is as follows.

Tightened BOTH jets.
Adjusted float tang.
Chopped choke cable.
Replaced cover with drilled out NT cover.
Replaced intake with MM intake (though I should have tested teflon tape first).

wait i thought there was only one jet under where the float is. where is the other and which should i drill?

 

[DuctTapedGoat]

To the side of the main jet is a recessed jet - that is the pilot/idle jet. It was loose as a goose when I took a look day one. That is what the two screws adjust. Don't drill that one, it's adjustable with the screws.

The one you CAN (not should) drill out is the larger one in the center. Don't drill until you've adjusted everything else and then decided you MUST due to no other option.

 

[biknut]

wait i thought there was only one jet under where the float is. where is the other and which should i drill?

The CNS carbs have a pilot jet and a main jet. You'll probably only have to drill the main.

 

[jtgolden]

The CNS carbs have a pilot jet and a main jet. You'll probably only have to drill the main.

Alright and the main jet is at the bottom where the float is correct?

and thnx u all r awesome help

 

[biknut]

I notice after riding for about 10mins it starts to bog down. Is this a air issue, I've drilled the jet to #64 and have clip at the middle position. My spark plug is black but it's not gunking up, it's slightly wet but nothing serious. I've been running about a week now still breaking in.

A possibilty could be the gas cap vent. I recently checked 4 stock tanks I have, and 2 had no vent at all and held a vacuum. 1 vented very slow. Only 1 of the 4 was vented well enough.

Try loosening the cap and see if it runs better.

 

[biknut]

Alright and the main jet is at the bottom where the float is correct?

and thnx u all r awesome help

Yeah that's right. Take the float bowl off to get to it. It's the bigger of the 2 jets.

 

[droc089]

Spray carb cleaner around the areas you think you're leaking at, primarily the intake and bottom of the carb at the bowl. It's like a buck an a half at wally world.

And to Droc089:

Black and wet is NOT good, break in or not. You need to lean out (not oil, but fuel).

If you bog after a certain amount of time, your fuel bowl isn't staying filled is what I would imagine. Check for pinches in your fuel line, clean your fuel filters and inlets. Adjust the tang on the floats.

If that all fails - there is a RES (reserve) marking on your gas tank petcock, use that in place of on and it will give you slightly more flow.

thanks duct, the reason why I'm not worried about it being black is because after my first ride it has been that way every since and I couldn't clean it off. The wetness on it is very small, I've seen some picture of some bad ones. I think my float could be the couplet. Saturday after I drilled the carb out and put the float bowl back together, turned the gas on and gas came shooting out of everywhere on my carb. after opening the float bowl again a little prymind needle thing (don't know how else to describe it) popped out. I stuck it back in it place and had no more leaks, but could that have been the problem before. I rode it yesterday to work and it kinda bogged going there but was fine coming home.

 

[droc089]

Here's a picture of my spark. Kinda hard to tell anything but it's got a brown color around the edge then the middle is black. The wetness is the brown.

 

[DuctTapedGoat]

That's way dark, I imagine it wouldn't have much left until it fouls.

StuntBase - Spark Plug Reading

Here's a good site to look at spark plug readings.

 

[skrew37]

That's what mine looked like too. I took it out and scrubbed the h out of it with a wire brush. I ran close to 20 miles last weekend and was able to open it up full throttle. I haven't looked at it again. Tonight, I plan on taking apart the carb, cleaning and re-tightening everything back together. I'm going to make a better attempt at cleaning the spark plug again and see how everything goes.

 

[droc089]

so it seems I jetted to far. Time to find some solder I suppose lol.

 

[DuctTapedGoat]

Jetting should really be a last resort until you're sure the air leaks are solved - you can add fuel to match how much air is coming in, but it's kind of a workaround to the actual problem - which isn't that it feels like it's not getting enough fuel, but that there is too much air for how much fuel is being delivered.

 

[droc089]

I actually thought about drilling holes in the red cover, maybe that could compensate for the fuel level. or just get a air filter soon

 

[biknut]

I actually thought about drilling holes in the red cover, maybe that could compensate for the fuel level. or just get a air filter soon

The stock air cleaner flows as much air as the motor can use.

 

[skrew37]

Good point, DTG. I'll save my new jet until I trouble every possiblity... droc089, I tried drilling holes, but I have a clearance issue. What I ended up doing is taking off the black plastic waffle screen/grate piece and the black sponge, flipping them around and screwing it back together. The plastic piece clamps the mesh sponge on. Then, I wrapped a piece of inner tube around the edge and hose-clamped it on, sealing the edge (in my mind). Then finally, I stretched a single layer of pantyhose over the whole homemade filter assembly and secured with a rubber band. I feel like this traps a little more dust than the sponge alone. It doesn't seem restrictive and I don't know how I could get a better airflow to filtering ratio. If anyone thinks this is a good idea, I'll try to post pics. If not, please tell me I'm silly and what the best thing for low to no clearance and the best airflow is...

 

[skrew37]

Also, is it a bad idea to use a semi-permanent gasket maker/sealant on the mating surfaces? I haven't taken a carb apart before. I'm confident that I can disassemble/ reassemble one and was wondering if it would eliminate any potential air leaks...

 

[biknut]

Also, is it a bad idea to use a semi-permanent gasket maker/sealant on the mating surfaces? I haven't taken a carb apart before. I'm confident that I can disassemble/ reassemble one and was wondering if it would eliminate any potential air leaks...

You can use gasket sealer on the intake manifold/head connection. Some people put a little silicone sealer on the manifold before sliding the carb onto it.

 

[skrew37]

I'll try that. I put an o-ring in there and it seems to work, but maybe it's leaking there. Couldn't hurt I guess. Also what I was wondering is if anyone tried sealer where the upper and lower halves of the carb come together. Is there a gasket in there already?