Motorized Bike Running too Lean

L

LastFreedom

New Member
Hi all,

In the last week, I finished my first build, however, I've run into some issues in adjusting the carb. The carb runs perpetually lean, and I can't get it to run rich as to better lubricate the engine during the break in period. I've moved the c-clip to the very bottom of the needle, and it only runs with the choke all the way on, otherwise it will shut off. I've done spark plug checks, and it appears "normal", as in a little bit of carbon at the base, and chocolate colored at the tip of the spark plug. At this setting the engine doesn't get super hot, and provides decent power, but burns an incredible amount of gas. However, at any other setting, the spark plug will turn white, and the engine will run extremely hot. Hot to the point that it actually melted the rubber gasket at the base of the CDI cable to the spark plug. Specs are: 80/66cc chinese kit off ebay, stock carb, 26 inch wheels, 44 tooth rear sprocket, 20mph cruising speed.
 
crassius said:
sounds like your carb is not seated properly
Click to expand...
I took apart the carb yesterday, o-ringed the junction between the intake manifold and the carb, so a vacuum leak there is unlikely. I also discovered that my cheap chinese kit's choke is actually opposite to what was indicated, so down was run, and up was choke. It still only gives decent power at the richest setting on the needle, and it's still burning an unusual amount of gas.
 
I don't like using an o-ring on a carb not slotted to take one, and if you have a steel intake, an o-ring won't solve the common problem of a bad chrome finish that needs just a touch of filing right at the tip to make a good seal - loosen carb a bit and twist side to side then take it off and look in carb to see if there are digs and scores in the aluminum, if so, file at 45 degree angle around intake.

Don't worry about excess fuel usage, as some of the older motors sold on ebay won't get good mileage until motor has run in for maybe 30 to 60 miles (less than 20 miles on first tank is common with these).
 
I've sanded down the manifold to try to get a better seal, and while it did provide a marginally more snug fit, it didn't seem to do much. The spark plug is still coming out dry with little to no carbon build up on the electrode after 15 minutes of riding at varied rpm's, even at the very bottom notch on the needle. Just noticed that there is a small amount of black liquid oil dripping from the bottom of the exhaust. Still doesn't explain why spark plug is dry as a bone.
 
a 2 stroke uses the oil in the gas as lubracation for the intire motor,oil driping out the exaust is normal.exes oil is expeled out the end of exaust
 
also, im sorry to say,break in the engine in first.it will not run good at first.the rings have got to seal.it takes a few hours on the engine to even begin to break in ,try to tune as little as possable to start,lets call it a learning curve,more and more as needed.fine tuning is an art .we all need to learn it.... any thing over 40 is in the tuneing
 
Last edited:
LastFreedom said:
Hi all,

In the last week, I finished my first build, however, I've run into some issues in adjusting the carb. The carb runs perpetually lean, and I can't get it to run rich as to better lubricate the engine during the break in period. I've moved the c-clip to the very bottom of the needle, and it only runs with the choke all the way on, otherwise it will shut off. I've done spark plug checks, and it appears "normal", as in a little bit of carbon at the base, and chocolate colored at the tip of the spark plug. At this setting the engine doesn't get super hot, and provides decent power, but burns an incredible amount of gas. However, at any other setting, the spark plug will turn white, and the engine will run extremely hot. Hot to the point that it actually melted the rubber gasket at the base of the CDI cable to the spark plug. Specs are: 80/66cc chinese kit off ebay, stock carb, 26 inch wheels, 44 tooth rear sprocket, 20mph cruising speed.
Click to expand...

Im having an identical problem..!! Literally identical!!.kick2:-||laff

Once you figure it out please tell me what you did...ill be keeping an eye on this post..
 
OP hasn't posted in a while - he saw some change after sanding intake, so I'm assuming he reread posts and decided to file intake to fix it
 
Update: Engine is running rich at long last after I started using synthetic oil at a mixture of 22-24:1. I filed down the edge of the intake manifold, and that got me another 1/8 inch of fit, so it seems to have helped a little bit. I tried moving the c-clip one notch up yesterday and attempted to see if it would hold up, but once again, it seems to have run lean, and the engine heated up like no other. I'm curious as to whether or not it's an issue with blowback, and I almost want to get a new carb and reed valves to see if it makes any significant improvement, because it looks like I have some gas and oil dripping from the air filter in the back of the carb
 
I took my carb off and noticed the throttle slide was up way way up...to fix it i adjusted the throttle cable from where is comes off the throttle grip (that piece of metal bent 45°)cleaned EVERYTHING with carb cleaner..i then slightly bent the 2 brass prongs above the floater out a little. I put everything back on (without adjusting the little clip on the needle) and also put rtv sealant on the intake where you put the carb on to stop any vaccum leaks. My bike is running like a champ now and the problem is fixed..

I dont know which specific thing i did to fix it, mabye everything combined, but that fixed the problem.

Yesterday I took it for the maiden voyage to work and back (7 1\2 miles each way with hills) and it performed awesome!

It has about 16 miles on it now...check it out...fucker moves too, solid 30mph!

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now, keep an eye on it as these motors tend to go leaner as the rings seat themselves in better - after a while, you may need to drop the needle a bit
 
crassius said:
now, keep an eye on it as these motors tend to go leaner as the rings seat themselves in better - after a while, you may need to drop the needle a bit
Click to expand...

Now does than mean rasing the clip on the neddle? There are 4 notches on my needle and right now its on the second groove down just as it came..
 
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