Engine air leak???

[Darens]

I have an XT and walbro 990 carb with CPI pipe. engine ran fine for a couple of tanks after pipe was put on, then started to really bog until about 3/4 of full RPM then takes off like a banshee. I have tuned it every way possible and nothing will change it. Another guy I know is sending his straight to Redcat and they are going to look at it, cause they say it shouldn't run like that. My question is does anyone out there have any idea why??? Is it a seal leak? Please no tuning responses. I have done everything to it, changed head and piston and rings, different carb. Nothing changes it. HELP!

 

[Deluge]

Take a can of electric parts cleaner or carb cleaner and spray around the gasket areas. If the idle changes when you hit a particular spot, that's where your air leak is at.

You said no tuning responses, but once you add a pipe you HAVE to re-tune the engine. Have you done that?

Also, have you vented your fuel tank? That's a common problem with these vehicles. The gas cap vent gets clogged and causes running issues. Quick fix would be to take the cap off, take it apart and clean it thoroughly. See if that helps.

 

[Darens]

I have been running this car for over a year and have done all the above. I was thinking about spraying something on it to see. thanks.

 

[phreerider]

the middle throttle bog sounds TOO LEAN, if you run super low ratio gas to oil like below 20:1 its already lean , check mix, first thing .

temp and humidity, elevation ?

carbon build up on piston could cause similar but very late in the life of motor. what about compression? somewhere around 10 lbs. (not sure about the exact #)

normal runtimes ? super dusty environment?

and the plug? what heat dispersion

Alcohol free gas or it may corrode internals of carb.... so NO ethanol mixes.

2 stroke are sensitive to these pararmeters esp. hi-performance /higher revving.

definitely part of the process gotta love it!

interesting about your buddy sending it to redcat for a look, really ?

 

[Darens]

Warranty for him, his is only two weeks old when it started to act like that.

 

[phreerider]

i'm challenged with hobby-grade warranty stuff, some short term electronic stuff maybe , the rest draws in consumers that might not be hobbyist , just consumers.

his sounds like tank vent esp. if heats up then dies cools abit then starts right up, but won' t take throttle as it gains heat, esp. a top end of the throttle range...the telltale is gas cap blow back when opening a hot tank or the obvious swollen tank!

 

[Darens]

It bogs right from idle until about 3/4 RPM then it takes off. I have done everything possible when it comes to tuning. And I am not a NOOB with this stuff, have been running and selling this stuff for 10 years! This is just one thing I can't seem to figure out, and I can't seem to let a problem go until I figure it out. New carb, new coil, new spark plug. The weird thing is that I havve to richen out the low end by 2-3 turns in order for the motor to fire up, then lean it right back out to keep it running properly. Is it just wore out or what??

 

[phreerider]

compression? crack in case?, pulse on carb gasket aligned?

tip might be broken in carb needles?

2-3complete turns is considerable, seems like it would flood instantly. tough one boss