Help With Carburetor!

Greg58 said:
I think mine was a #70 drill size.
Click to expand...

Thanks a lot for that info. I just know my jet was a bit small at #72... I would be at #70 myself if I hadn't mixed that bit up with the #69....
Now I am curious to check the jet on the second kit I purchased at the same time. #70/#69 seems to be about the right place, I guess if you wanted to push it more you could go a couple sizes bigger, but I'm really happy at #69...
 
Greg58 said:
Greg here, I don't know which engine Perry is running but on all the 48cc grubee's we have built removing the vent tube made a world of differance. It turned out that at about 3/8 to 1/2 open the vacume from the engine was drawing fuel up the vent tube into the carb through the air cleaner, some say it did not help them but on all six 48cc we built this was the trick.
Click to expand...

Hey Greg, I just was poking aroung inside a CNS carb and got a chance to look at where the black vent tube connects on the inside of the carb. As I had suspected, the hole where that tube connects is up at the very top of the carb and does not extend down into the bowl. The fuel level in the carb should never be up that high, it is way above the float and the needle valve and everything, the opening is in the upper most part of the carb. So, if you are drawing fuel through that black vent tube into your carb through the air filter there is something wrong with the fuel level in your carb, it would seem you need to do a float adjustment. Perhaps if the vacume is strong enough it might be able to draw a tiny splash of fuel when you are on rough terrain and the fuel in the carb is splashing around, but when still or riding on smooth pavement there should be no way fuel is getting up to that vent tube. Take a look for yourself the next time you have a CNS carb open...
 
Last edited:
I did adjust the float level but it did not help, It would do it much more when climbing a grade because the carb would be tilted back or close to level. I have had my carb apart about ten times so far, the tube change was the fix. I don't see any reason for the bowl vent tube to vent to the air filter any way, considering the evaporation rate of fuel on hot day it should make a diff. in tuning.
 
Last edited:
Greg58 said:
I did adjust the float level but it did not help, It would do it much more when climbing a grade because the carb would be tilted back or close to level.
Click to expand...

I did my best to install my engine so the carb was level, but there are other factors involved, so mine ended up tilting a little bit forward (like pouring into the engine). This makes that vent on the inside be even higher and less likely to be an issue, which might explain a bit why some people get improvements from pulling that vent tube and others do not. It might have a lot to do with the carb angle...

Climbing a grade makes sense, that opening is at the back/top of the carb, so if you tilt the carb back fuel will rise in that area. Although I just climbed a steep @$$ hill at 20+ MPH without any signs of problems, engine ran just as good going up the steep grade as it does on flat land (with vent tube connected). Since my carb was tilted a little forward I adjusted my float to keep the fuel level a little lower in the carb (cause the engine side is artificially high due to the carb tilt). Perhaps since I have the fuel level set on the lower side in the carb the tilt going up the hill wasn't enough to cause this problem for me.

PS it just came to mind, before I adjusted my float to lower the fuel level in the carb I noticed that the engine would die if I went over bumps at low rpm (like when I was coasting in after a ride). Perhaps this was happening cause the higher fuel level in the carb let fuel splash up to that vent and get sucked in when the carb got bumped around. This problem is gone now too, she never stalls no matter how bumpy the terrain. I had thought this change might be due to fixing an air leak, but after chatting with you I am thinking perhaps it was fuel getting up through that vent causing her to die.
 
Last edited:
I just took my cns carb off and just got my nt carb so It's not my forte on adjusting carb but I could use some advice the throttle cable looks easy enough to swap but it's got a primer button and the idle screw that's where I lack knowledge should I just install it and push the primer a couple time or what would you people do,and what what about the manual choke
 
I have a nt as a back-up, I just installed it and tried to start the engine. Once it started I stoped and adjusted the idle, and let it idle for awhile then rode it as I allways do. I didn't use the primmer bulb but if it was cooler weather it may be needed.
 
What I do is start the engine and get it to idle at the rpm I want, then I adjust the air mixture screw (closest to the air filter) ccw till I get max. rpm then I lower the idle again to the rpm I want the engine to idle at.
 
Last edited:
You must log in or register to reply here.
Back
Top