Carb help please!

C

Chickenegg787

New Member
I am new at this. . . obviously :) . . . and am having the worst time ever. I just want to get on this thing and ride.

Here's the back story:

I bought a Grubbee Skyhawk 80cc engine (the one on here, or king motor bikes that has the most reviews) last spring and assembled it through the course of the summer. I had everything working, except the chain was never tensioned right and i periodically had throttle cable trouble. . . Let's just say it 'kinda' worked, but never really 100% . . or even 90%. Anyways, I made one 5 mile round trip and then for the 124th time, the chain busted. It was late fall so I decided to wait until now to solve the chain problem.

I did that, had to get new CDI, and put a break on the cruiser it is mounted on. Through the testing process, i realized i wasn't sparking, so Using an Ohms meter and such, It came down to a new spark plug and CDI.

However, this is where I need help.

The engine did not start right away like it did in the summer. And it didn't start until I had the choke cable fully pulled on the choke lever. At this point, the engine kicked on, but continued to accelerate at a constant rate. The throttle was completely unresponsive so naturally I went for the kill switch. Before i could even due that, the choke lever arm vibrated a few clicks down and then the engine disengaged and shut off. Through a series of 'start and stops' i allowed the engine to warm up. Now the engine engaged on less choke, but it still continued to accelerate AND once i pulled the choke lever down past the pitch at which the engine started, the engine would turn off. Meanwile throttle is completely unresponsive.

I know it will require some carb work, but what???

Other things include: Same gas/oil as summer, throttle cable has some slack but successfully pulled barrel when twist throttle was tested, gas flow is 100% because it smells and some places visible, it is 35-40 degrees F here when i tested it. it has the carb with the red air filter cover.
 
I would pull the carb off the intake and leave it connected to the cable and check to see if the slide is closing.
 
Instead of pulling the carburetor, remove the air filter and with a mirror look into the carburetor throat while operating the choke lever.
 
Chickenegg787 said:
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Other things include: Same gas/oil as summer, throttle cable has some slack but successfully pulled barrel when twist throttle was tested, gas flow is 100% because it smells and some places visible, it is 35-40 degrees F here when i tested it. it has the carb with the red air filter cover.
Click to expand...


ok so this gas is over 6 months old?
Did you add stabil to the gas?
Is the gas a ethonol mix?
ethonol based gas sucks up water like a straw also gums up carbs if allowed to sit in the fuel bowl
 
Ron he has a cns, no choke plate to see from the back that's why i though about the slide.
 
Clean out your carb jets, specially the tiny idle jet. The idle jet on the CNS is extremely small and clogs easily, one of mine wouldn't come clean with carb spray, I had to ream it through with a very thin wire and pushed some crap out that was lodged in there. If you don't have anything small enough to push through the jets to clean them out get a twist tie from a garbage bag and strip the plastic off and use the wire....
Keep in mind, the CNS carb has 3 jets, the larger main jet, the "choke" enrichment jet, and the idle jet. If your idle jet is clogged you would need to run the choke jet more to compensate.....
On the unresponsive throttle, sure seems to me like the slide/barrel isn't moving when you pull the throttle, are you sure you have the slots lined up and the barrel is moving properly? If your barrel is moving properly it should draw the fuel from the main jet, but if the main jet is clogged....
 
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N/C is right about the jets, it's not hard to work on if you take your time. You can take pics as you remove one part at a time then reassemble in reverse order. What I do is remove the two screws from the top of the carb and pull the barrel out leaving it connected to the cables, just let the barrel hang to the side till you need to put it back in.
 
Thanks all, I'm going to clean out the carb right now and reassemble it. I am also going to replace the gas just because it wouldn't hurt to do so. I'll re post my results when I'm finished. Keep the ideas comming! I have learned so much already just from people like your selves commenting their knowledge on my specific situations. I'm so anxious to get this thing runnin' strong.
 
IT WORKS! YAY! I got it running and idling well, but now my next questions is that when i go to twist the throttle to full, it bogs down. at about 1/4 to 1/3 throttle is is fine and accelerates, but as soon as i twist past that point, it cuts out and bogs down. It seems if I pedal on top of the 1/4 throttle it allows for more accel. . . Idk. . . and also, I'm trying to get all the bad gas out so I let it idle for qite a while. I found a good postition of the idle screw so that it stayed on but also wasn't trying to run away. For what ever reason though, after about 5 minutes (sometimes a little more, sometimes less), it would jsut shut off for no reason. It sounds like it is idleing strong and then just cuts out. I start it up again and it idles perfectly fine for another 5 minutes or so...I feel like these problems are due to temperature and poor gas, but if there is any other info, PLZ help!!
 
I had the same problem, try engaging the choke when you have it at full throttle, if it runs better you will need to rejet it with a larger main jet. You can drill out the main jet, I think a # 71 drill is stock so go one size at a time, the lower the # drill the larger. Good luck.wee.
 
Congrats on getting her going...
On the idle and dying after running a while, I wouldn't worry. Could be temperature issues, air cooled 2-strokes are not well suited to idling, they need air flow over them to keep them cool. Or your clutch could be gripping a bit and draggin it down.
On the bogging, you need to determine what the condition is that is causing the bogging (rich or lean)? You could do a plug chop to determine that, or with the CNS carb another way to figure that out it by using the choke. Since the choke on the CNS is NOT a choke at all, rather an extra "enrichment jet" that adds more fuel to richen the mix rather than restricting the air flow.
Do this little test, take a ride, when the motor is warmed up ride into the throttle range where she starts to bogg, when she starts to bogg pull the choke lever out and see if that improves or worsens the condition. If the condition improves that means your running lean, since the extra fuel from the enrichment jet improved the condition. If it boggs worse then you are already too rich and the extra fuel is making things worse.
Once you determine what the condition is that is causing the bogg you need to tune the carb to eliminate that condition.
If you are not familiar with carbs the first thing you need to know is different parts of the carb effect different throttle ranges. The CNS is a bit different from the NT or Speed carbs because it has so many jets (3), where the NT only has one, so the tuning is a bit different.
On the CNS carb, the idle jet has the most effect on the low RPM condition, the needle setting has the most effect on mid throttle region, and the main jet size has the most effect at WOT (wide open throttle). Keep in mind it is a balance, adjusting one thing might effect another...
For instance, if you are running lean at WOT you might need to open up the main jet a bit, or install a larger main jet to allow more fuel to flow (I had to drill out my main jet to stop bogging at WOT). Once the main jet is opened more it will allow a more fuel flow at WOT, but also a bit more in the mid throttle range as well, so its a balance.
In the mid throttle range the needle has the most effect. The needle sits down inside the main jet when the throttle is released blocking off the fuel flow from it. As you pull the throttle the needle comes out of the main jet, and the taper of the needle allows more fuel to flow (because the needle is not plugging the jet as effectively). There is an "e" clip on the needle that sets its position, there are usually 5 slots to set the "e" clip on to adjust its position (and mid throttle mix). If you need to richen the mid throttle mix then move the "e" clip toward the tip of the needle (which pulls the needle out of the main jet a bit and lets more fuel flow). If you need to lean up the mid throttle mix then you need to move the "e" clip away from the pointed end of the needle to let it seat further into the main jet and further restrict the fuel flow.
When you reach WOT the needle is out of the main jet so the actual size of the jet is what determines the fuel flow. If you are bogging at WOT and it clears up when you open the choke jet then you might need to open the main jet a bit....
I posted a thread about tuning the CNS carb when I first did mine, it's kinda long but I think you will find it informative...
http://motorbicycling.com/showthread.php?t=32736&highlight=cns+carb+working+great
 
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