Saw carb tuning help

Karl Snarl

Well-Known Member
Joined
Sep 20, 2019
Messages
5,691
When I'm riding it and give it throttle, it'll rev up like normal, then all of a sudden the engine will die, like it doesn't have enough fuel. Letting off the throttle restarts the engine. This doesn't happen with no load (clutch disengaged).
When it dies, pull the clutch in and pop the plug, it will tell you if it's to much or to little.
 

noah9988

Active Member
Joined
Jul 3, 2021
Messages
228
So, it was rich, but I discovered that the intake bolts backed out and it was flopping around. I found this after going back to my bofeng carb that was tuned good, it was actually behaving the same way the saw carb was. I'm rebuilding it with a new cylinder, rings, and gaskets I made with gasket material. I'm going to use the bofeng and make sure everything is correct before trying the saw carb again.
 

Karl Snarl

Well-Known Member
Joined
Sep 20, 2019
Messages
5,691
So, it was rich, but I discovered that the intake bolts backed out and it was flopping around. I found this after going back to my bofeng carb that was tuned good, it was actually behaving the same way the saw carb was. I'm rebuilding it with a new cylinder, rings, and gaskets I made with gasket material. I'm going to use the bofeng and make sure everything is correct before trying the saw carb again.
That's what I figured from the plug chop on the begining. Gladd you got it nailed down.
 

noah9988

Active Member
Joined
Jul 3, 2021
Messages
228
That's what I figured from the plug chop on the begining. Gladd you got it nailed down.
I don't know why it would cause it to make it run like it did though... I would imagine that it would create an air leak and run it super lean.
 

Karl Snarl

Well-Known Member
Joined
Sep 20, 2019
Messages
5,691
I don't know why it would cause it to make it run like it did though... I would imagine that it would create an air leak and run it super lean.
You turned the jets up to compensate for the extra air, but as it bounced and moved, it changed the requirements, an all that extra fuel brought extra oil. The high heat turned it into carbon as it burned. You not trying to burn the oil. Some will burn, yeah, but most of the oil, should carry away debris as it exits the chamber. The high heat left no oil to carry it out, leaving deposits on the plug.
 

noah9988

Active Member
Joined
Jul 3, 2021
Messages
228
You turned the jets up to compensate for the extra air, but as it bounced and moved, it changed the requirements, an all that extra fuel brought extra oil. The high heat turned it into carbon as it burned. You not trying to burn the oil. Some will burn, yeah, but most of the oil, should carry away debris as it exits the chamber. The high heat left no oil to carry it out, leaving deposits on the plug.
That's interesting. I was also surprised to find a layer of very stubborn carbon on my piston.
 

Karl Snarl

Well-Known Member
Joined
Sep 20, 2019
Messages
5,691
Hmm, yes they were pretty small though, there were a few around the edges.
Each wing should reach about half way across the piston. Maybe not all the way, your intake system and porting will determine how far. They should reach about 2/3 the piston in the forward to back position. Again has to do with intake and porting, plus squish distance. The squish area of the piston when set right is relatively cool, and clean. There will be a little junk, we are burning stuff in there after all. When in perfect tune, the residue on the piston crown, should wipe off easily. You were way to rich from the air leak, so your wings should have a carbon hunk around them. An running a bit extra oil, if the right amount of fuel, should still leave relatively easy to clean residue. The oil is what keeps the inside of the chamber clean. It carries away all the junk. So these guys that run 50:1 and higher, are losing the ability to carry junk from the fuel and air that makes it in, away. Idc if you use saber or whatever that says you can go 100:1. it doesn't carry the junk away, there is not enough oil to do so. So instead it hangs out and wears parts down till it finally gets spit out, or sticks to something in the chamber. If you don't get a little drip, drip from the pipe when you come to ride it after sitting over night, you are to low on oil. There shouldn't be a big puddle, but a few drips, maybe a quarter sized puddle or smaller under the exhaust tip if you run a stock muffler.
 
Top