Carby Need recommendations for jet starting point

[Spare_Parts]

Hey everyone, I need some help with where to start with jet sizes.
Elevation is about 100 feet above sea level.
32:1 mix
Engine is a 66cc with port clean up, notched the skirt on the intake side and about 1mm ramp on the exhaust.
Stock speed carb. For now stock exhaust with the baffles drilled out but I will soon have the Zeda expansion chamber.

Right now it loses power on the top end and feels like it's not getting enough fuel. Also the exhaust has blued so I know it's lean. Haven't done any plug chops since I don't have jets to fix the problem.

Anyway, just looking for a range to start with jet sizes. Let me know if you need any more info.

Thank you, Eric.

 

[FurryOnTheInside]

Yeah I think read that the Speed carb is lean, stock. But I have the little NT so I can't answer your question.
I just came to say "change that air filter!" It's crying out for it. You'll need to rejet even bigger then.

You can get a super cheap plastic adapter that is bolted to the carb, just like the stock filter box does, and fits any of the 42mm foam or K&N style filters (although I have heard the K&N looking ones are not good)
Search on eBay for Carburetor air filter stack mini motor pit trail dirt bike , "song_top" is about the cheapest.

 

[gary55]

Hard to say much on proper jetting till you have the pipe you intend to use. The bluing on the pipe is of major concern. If it's at all possible to not ride it till you get the new pipe that would be smart. If not I would jet larger. Heat is the destroyer of these little engines, and it does it quickly.

 

[Spare_Parts]

Just ordered some jets, 71-75, and the pipe. If the 75 isn't big enough my neighbor has a micro drill set so I'll look into that.

I knew the bluing was a problem so I have only been riding at part throttle. The piston and jug are still in good shape so must have noticed it soon enough.

 

[6blueoval9]

Was the blueing coming from WOT or from cruising?....the biggest cause of a motor being burned up is from incorrect needle setting.

If the motor was lean at WOT it would most likely just bog out or sound like it wants to die.

If the motor was sputtering or just sounding like it had a mis in it like it would having the choke on, that's most likely from being too rich.

Your stock carb comes with a #70 jet which in most cases ends up being too rich even with a real pipe and some basic porting.

Definitely change out the filter as the speed filter is extremely restrictive and I would've figured would certainly cause an over rich condition because it pulls in very little air.

Sort of confusing on this one for me as it doesn't all make sense but I hope you get it figured out.

 

[butre]

check for air leaks and part throttle needle positioning. I have trouble believing a nearly stock engine is running lean with a speed carb

 

[6blueoval9]

Being it's slightly bigger by 1mm or so the speed carb would run a tad bit leaner in general with the 70 jet if the motor is requiring the added air flow but man that filter is just a joke it comes with....The stock NT filter is way way better in terms of air flow and even that filter sucks. Lol

 

[gary55]

If it was a filter prob. it would be rich not lean. I agree with Butre as the possible air leak. At 100 ft. the speed should run good. Have you tried any needle adjustments?

 

[6blueoval9]

If it was a filter prob. it would be rich not lean. I agree with Butre as the possible air leak. At 100 ft. the speed should run good. Have you tried any needle adjustments?

Yea, I was saying above how the filter would most likely cause an over rich condition being that very little air can be drawn from it, especially on the speed filter box.

Just a good filter alone would lean out the mixture some but I'm not thinking that lean with a 70 jet..lol

 

[Wags]

It would be helpfull to have a picture of your plug. It can tell you everything you need to know.