Idles varys from low to high?

B

Black_Moons

New Member
Hi, I have an intresting problem, my 2 stroke once I finaly got it running, idles low AND high, Altering beween low and high again slowly over 5~10 seconds, and back to low again over the same period of time.

Build info: Brand new 66cc engine, CNS racing carb, Eclip on 2nd to bottom of needle, Slightly advanced porting for the intake (Just so the intake is fully uncovered at TDC) By triming the piston skirt. Using a baffle/cat removed exhaust.


Checked for intake leaks by spraying some carb cleaner at my intake manifold setup, No apparent change in RPM.

Right now the idle mixture screw is all the way in for it to idle decently, Otherwise it only runs with the choke cracked open a little.

Also the cylinder started smoking heavily.. I think the paint was never cured, Seems the cylinder got hot pertty quick, within 5 mins or so...

Running 16:1 or so fuel for break in..
 
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Also, your oil mix is too low. You should use something around 32:1 for break-in. I will have to do some thinking on your idle. You could be running lean. That would explain the smoking head and the idle screw/choke issue. Good Luck!
 
Its the trimmed skirt on piston. That uncovers the ports earlier than normal. As it does that more of the exhaust can escape making the RPM's higher. But also at the same time the combustion are not all the same so it can make the RPM's higher and lower making it surge like that. Also as Vistaman73 said. Make sure any air bubbles are out of the gas line and the mixture is 32:1 Ratio. Good Luck!
 
Jnickum313 said:
Its the trimmed skirt on piston. That uncovers the ports earlier than normal. As it does that more of the exhaust can escape making the RPM's higher. But also at the same time the combustion are not all the same so it can make the RPM's higher and lower making it surge like that. Also as Vistaman73 said. Make sure any air bubbles are out of the gas line and the mixture is 32:1 Ratio. Good Luck!
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A windowed intake port on the piston skirt is not going to do that.
 
I think I may of found the problem.. the gasket used to seal the intake manifold to the carb was rubbish. I replaced it with a standard O ring and took me 5 mins to jam the intake back into the carb, Nice tight fit.

Also, found a fuel problem, The gas cap was a near perfect seal to the gas tank -_-; Drilled a vent hole into it. Now the fuel comes pouring into the carb just right.

I'll see how it drives in the morning. too late to annoy the neighbors :)
 
Goat Herder said:
A windowed intake port on the piston skirt is not going to do that.
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Correct...trimming the piston skirt will not cause his problem. Sounds as if he's found the trouble. I hope he returns to let us know.
I would suggest he shoot for a 24:1 fuel mix for break in then go down on oil to 32:1 afterwards.
Tom
 
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2door, good suggestion with the ratio. I always used 32:1 but 24:1 is really the best for break in.

I just thought he was running lean, but last night i was laying sleepless and though, fuel starvation! I was too late. i was thinking is there was a vacuum that would explain the weird idle. I'm glad you think it's solved. :)
 
Yeah, Vista, you are right. If his fuel cap wasn't venting then he had fuel starvation. Also the leak in his intake will cause him problems with erratic idle and surging. I had an older aluminum intake manifold that had a crack in it. When it was cold the crack would allow air in and fast idel but after the engine warmed up the crack would close up enough to let it run good. I had replaced the intake gasket but didn't find the crack until I went back to check things again because the gasket didn't fix the problem. I like the welded steel intakes better than the aluminum ones anyway.
Tom
 
yeah i have both, the chrome welded steel intake which is really thin and not good for the threads of the barb for a boost bottle i found, they strip easily. and the dull think aluminum intake, which has a smaller inner diameter, so i dont use it.
 
Yep, Got it idling real nice now that I replaced that WORTHLESS stock cns gasket (If you can even call it a gasket, doesnt even fit worth a damn), And with the tank cap drilled through, seems to idle well... Seems to have piss poor power, And noisy as **** because of my lame modifyed muffler (Needs expansion exhaust), But thats not a big deal. Needs to be tuned. Needs new exhaust, Needs braking in.

Fixed the big need so far: Idle. Shift kit + no idle = stalls every time you let off the throttle because of the freewheel.
 
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