Idle screw all the way in and still wants more

Stormsorter

Member
Jun 10, 2010
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Jasper County Illinois
Engine sat for years after being run very little. Finally got around to working on my 62 Corvette shifter and would not idle down when hot. Tore it down replaced case gasket, base gasket was bad, mag side seal had blown out so replaced both with TCM double lip seals. 5mm just barely clears magnet and fit kinda tight, the stock one could be taken in and out with one finger. Now I have the opposite problem once it warms up the idle screw aint enough gotta raise the slide a bit more with the cable adjusters. Its also now topping out at 26mph when I was in low 30's with the air leak and slipping clutch. Bigger jet and raising the needle doesn't help just makes it 4 stroke like normal. No filter no difference, choke kills it and slow closing it doesn't change the idle either. It just acts like the NT aint big enough and the only mod is my old SBP expansion chamber and good wire and boot. Might have to try swapping the NT with the RT I have on the predator. When I had it on the 2stroke couldn't really tune the mid range it was rich even with the air leak and the smallest jet I have a 60. I dread trying to deal with the old CNS, I got no jets for it anyway though it didn't do to bad on the old pre Bikeberry real FlyingHorse 49cc once I put an NT needle in it. I'm stumped. Oh and before someone asks I don't have the CNS needle in the NT, took that needle from my first NT that wouldn't stay on an intake without tightening it so much that the slide would stick.
 
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Greg58

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May 1, 2011
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If I’m reading you post correctly with a air leak you had a leaner mixture, now that you have repaired the leaks you need to reduce the jet size to get the air to fuel ratio right. The larger jet only made matters worse, I have to jet every bike I build so I solder and drill till I get the tune right.
 

Stormsorter

Member
Jun 10, 2010
123
1
16
Jasper County Illinois
Hmm will give it a shot tomorrow but pretty sure its already lean. I'm use to setting it rich and bumping jet down one size at a time tell it stops 4 stroking but that was on the old CNS carb years ago.
 

Stormsorter

Member
Jun 10, 2010
123
1
16
Jasper County Illinois
Yep guess I've never seen one that rich before since I had previously used an old 16mm v1 CNS carb. Sadly the 14mm NT is just to small for the engine with a SBP pipe. A 71 was black, 69 was a medium grey, 68 was light grey and a little to lean with temps a little over 300 when I parked it. I still had to have the screw almost all the way in and no power at 26mph.

I put the 15mm RT back on but the idle and low throttle is way to rich with no way to adjust other than some stuff I read about notching the slide just right. I had to have the screw all the way in and use the cable adjuster to get it to idle but got it up to 30mph with a 61 in it but not going to bother tuning because the idle and low end issues. So looks like I'm waiting on jets for the CNS and flux so I can put my special manifold adapter for it back together since its the biggest bore carb I have and ran 33mph on a 49cc with a 40 or 41 tooth sprocket. And if its still weak I'll get a crank and jug for the old 49cc since I can find the info on how to tell what rod/crank I needed that I couldn't long ago when the rod bearing started to go.