Lean, Rich, what is going on

LunchMoney

New Member
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Apr 25, 2023
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Lithuania
Hello dear people,

I have a 66cc china doll, about 5-6 liters of gas were rand thru the engine and was using 25:1 ratio with a non synthetic oil. Ran great, although needed it to be more rich, the second notch from the bottom of the needle and it seemed the engine was quite hot and the spark plug had no obvious color so i'm guessing it was lean. Now I have switched over to a full synthetic oil, running about 40:1-ish (my measurements were off) and at first it lost lost power, the plug is still lean imo. I have tried to move the clip to the most rich position, but then at 80% throttle it starts 4-strocking. No air leaks were noticeable, the idle is great. What should I do guys? Help!
 
What should I do guys? Help!
Now put the needle in the second most rich position and try it again, If it is still not right, then go the next notch up from the bottom.

Also make sure to NEVER guess or have your measurements off as you put it...Even with synthetic 2 stroke oil, I wouldn't recommend any less oil than 32:1 mix...Oil is the only friction protection, heat protection, that you have for the air cooled motor...Why risk it?
 
2 things to keep in mind. 75% to 100% throttle is entirely the main jet size. Below 75% is the needle setting. If you change the main jet size, the needle may occasionally need adjusting.

Sounds to me like you may need to change the main jet first. Once you know that is good, adjust the needle accordingly.
 
2 things to keep in mind. 75% to 100% throttle is entirely the main jet size. Below 75% is the needle setting. If you change the main jet size, the needle may occasionally need adjusting.
If he has a stock China Girl setup over there in Lithuania with the stock carburetor, he is only going to have just the ONE and ONLY jet on an NT or JRL BoFeng carby that come with these...The #70 jet is what comes stock with those carby's.

The Highest elevation in the entire country is only 694 ft. so I do not think carb jets would be too much of a factor in this, but just adequate needle adjustment as well as making sure there are no air leaks.

(The only reason I know about Lithuania, its 30 islands in its lakes and rivers, and its elevations, is my late step father was Lithuanian...lol.)
 
If he has a stock China Girl setup over there in Lithuania with the stock carburetor, he is only going to have just the ONE and ONLY jet on an NT or JRL BoFeng carby that come with these...The #70 jet is what comes stock with those carby's.

The Highest elevation in the entire country is only 694 ft. so I do not think carb jets would be too much of a factor in this, but just adequate needle adjustment as well as making sure there are no air leaks.

(The only reason I know about Lithuania, its 30 islands in its lakes and rivers, and its elevations, is my late step father was Lithuanian...lol.)
I bring up the main jet because he said at 80% throttle or greater it starts 4 stroking. That screams main jet, not needle. 70 may be a touch too big and it needs a 68 or 65.

Not saying I am right, or that's what it is either. Could be the ignition not being able to keep up at high load, aka spark suppression.
 
I bring up the main jet because he said at 80% throttle or greater it starts 4 stroking. That screams main jet, not needle. 70 may be a touch too big and it needs a 68 or 65.

Not saying I am right, or that's what it is either. Could be the ignition not being able to keep up at high load, aka spark suppression.
You and I are also used to some 4 stroking when not under load, but just cruising along, because we both run Phantoms and thats just the way they run...lol...But when we want to really hit it, these suckers just zoom out with zero hesitation...lol.
 
You and I are also used to some 4 stroking when not under load but cruising along because we both run Phantoms and thats just the way they run...lol...But when we want to really hit it, these suckers just zoom out with zero hesitation...lol.
And that's my point. We don't 4 stroke during acceleration. He does.
 
Thank you all for your replies! It's nice that somebody knows Lithuania :D I don't think i can find any main jets in Lithuania, maybe aliexpress then
 
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