Cns mid range bogg solved!

Greg58 · May 13, 2011

While reading some old threads someone said to remove the vent tube from the bowl to the air intake, I removed the hose and replaced it with a longer piece off gas line and hung it over the carb. not hooked to anthing then silicone the hole in the intake base. no more booging I can just crank it open no spiting back. If anyone wants to try this just pull the hose off, cover the hole with tape and go for a ride. Turns out the engine was sucking gas from the vent tube!

Greg58 · May 17, 2011

Here is another way to fix the vent problem on the cns-b carb, use a 1/8" fuel filter that goes in the tank of a weed blower etc. and a small piece of fuel line. The vent remains open and the filter keeps debris out off the carb. Then use one of the plastic door panel ribbed 1/4" studs to seal the hole in the back of the air filter base.

DaveM · May 17, 2011

Good work, I hope this solves the problem for a lot of people using this carby. I have had some whipper snippers with this fuel tank filter I wish I had kept them now. I hope someone gives you some feed back to see if this solves their problems with this style of carby.

Again good work!

Greg58 · May 18, 2011

So far changing the vent tube has worked on every bike, if anyone trys it let us know what it does for you.

jerrydellg · May 18, 2011

I combined two of your suggestions. I took the whole fuel line/fuel fitlter assembly out of an old weedeater tank and attached it to the air intake nozzle. I'll see how that works. I'm fixin to go ride in a little while.

skiball83 · May 19, 2011

I belive that was me...my original post...
"I was riding my dax titan today and I wondered why it had two hoses coming out like the cns carb for our china girls. Then I realized the hoses are ment for a non venting gas cap. On the china girls, we have a venting gas cap. Maybe our cns problems are due to too much air getting in. I dont run the cns anymore and Im not going to switch back due to not wanting to bother with it. Although with the people using the cns carb I was thinking to cap off both of the hoses and see how it runs. The NT carb has no hoses and runs great. If anyone caps off the hoses on your cns, tests it, and gives us a review it would be appreciated. Lets see if my theory works. Just a thought."
Glad it worked for someone.
If it wasnt my idea opps, sorry, at least someone got the stupid carb to run right.

Greg58 · May 19, 2011

In my testing I tried closing the hose off it will not let fuel into the carb. I have a leaf blower gas filter on the end of a hose so it can let air out and keep everything else out too.

skiball83 · May 19, 2011

Ok cool. At least you tried it. I was just wondering if it would work. Congratulations on figuring it out. This post will probably help a lot of people that are still running that carb. I gave up on the pos CNS and put on a NT carb. Not one complaint with the NT so Im sticking with it. (I should have read your post better. Now rereading it there is no way that you got that idea from me, sorry.)

Greg58 · May 19, 2011

I keep tuning on this carb and it keeps running better and better, I have the e-clip on the 2nd notch, port matched intake and exhaust and removed all of the tube on the inside of the end cap on the muffler to get smooth exhaust flow. Just got 33.9 out of my little 48cc, I'm happy for now.

DaveM · May 19, 2011

Greg58,

You are right, I believe the hose that you have the leaf blower filter on is to vent the bowl and cannot be blocked off. So if enough vacuum is generated in the hose at the air filter it can suck fuel from the bowl. I believe this hose is not vented to the atmosphere/air to pass E.P.A requirements. On the NT carb the tickle button which I don't use is also the bowl vent. When the fuel comes in, the displaced air has to be vented. I do not have a Cns carb that is why I am following your post with interest. In Australia our kits are still coming with NT carbs and Speed carbs but that may change in the future. I may be wrong but am happy for someone else to prove me wrong.

Keep up the good work!

Regards,
DaveM.

porch lizard · Dec 12, 2011

I took my vent tube off my CNS carb and it worked alot better as far as steady throttle through all speeds. In the past, I've switched out 8 different jet sizes in the carb, and had the C clip in every different setting, adjusted the float level several times, and nothing took away the need to feather the choke to get it to run WOT. The removal of the vent tube cured that finally. I could run 30 mph, but needed to use the choke to get there. Thanks for the post, I hope more people can find this thread. Now I'll go through the different jet sizes again until I find the proper one. and the right C clip setting. Thanks again.

Greg58 · Dec 13, 2011

Glad it worked for you, these engines do not respond the same. Some members say it didn't change anything on theirs but some like you and I see a great improvement.

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