Engine Trouble need advice on 66cc bog at high rpms

[Waxxumus]

Wellll, Im jetted with a rt dax carb at a #70. i should be theoretically at a 68. so its running a tad rich. but when i put 32:1 in it, my already fowled plug comes out with a white tinge on it, as if it is running too lean. Still need to try and put that third hole in for better fuel atomization. i d k. its been hard to tune perfectly. and right after I had the nt carb running perfectly choco brown XD

 

[KCvale]

I'm not familiar with that carb but you'll figure it out ;-}

 

[jonathan62019]

well i stripped my threads out lol i dont know how i was barely! twisting it with a tiny little wrench. going to tap it out today. i did run it with no air filter on and at high rpms i could feel gas coming out the back of the carb.. Do not know if that is usual or not. after i tap the hole and get it back on. ill mess with the float and see if that fixes. it.

 

[KCvale]

I did run it with no air filter on and at high rpms i could feel gas coming out the back of the carb..
Do not know if that is usual or not.

It can be normal if you have an expansion chamber exhaust as it is forcing unburnt fuel against the incoming fuel mix.
Otherwise you have carb float problem would be my guess.

An intake reed between the carb and cylinder can help with that but they have their disadvantages too, a restriction of the incoming fuel/air flow.

In short no, you should never have fuel spitting out anywhere on any engine build bud.

 

[crassius]

on an unmodified standard motor, when the piston comes down to compress the charge in bottom end, you may get a bit of back pressure out the carb just before piston closes intake port, also, when piston starts back up, there may be a bit of back pressure when the intake port first opens - if your air filter is on the carb, this shouldn't even be enough to see a drip there

 

[Waxxumus]

So do intake leaks, and throttle control and sparkplug gap.

Recently I put my gap from .024 to .028 and the engine responded better.

Said what the hell and gapped it to .031

Now she purrs down the street without any sign of 4 stroking, aside from the normal "Im at my max rpm im not going to do this forever" 4 stroking.

 

[Waxxumus]

on an unmodified standard motor, when the piston comes down to compress the charge in bottom end, you may get a bit of back pressure out the carb just before piston closes intake port, also, when piston starts back up, there may be a bit of back pressure when the intake port first opens - if your air filter is on the carb, this shouldn't even be enough to see a drip there

Spray some carb cleaner or starter fluid on the intake port while the engine is running. You have a leak? Carb cleaner instantly choked mine to death. So I fastened the bolts down tighter, and the engine started running richer. I thought i couldnt go any leaner on these jets. But we might be going down to a .67~.68 soon

 

[KCvale]

...Now she purrs down the street without any sign of 4 stroking, aside from the normal
"Im at my max rpm im not going to do this forever" 4 stroking.

Hehehe ;-}
Kind of like a long tailed cat in room full of rocking chairs ;-}