C40TLRY (40 hp 2 stroke) sneezing at idle

[tassingh]

I am new to the forum and thought I could get some help with my problem.
I have a 2000 40hp 2 stoke that I can't seem to get it to idle properly. It sneezes/ squawks and some times kills at idle. Top end it runs great.
I have going through the carburetors a few times, adjusted air screws with not much difference in performance. Took compression readings of 120 on all cylinders with one or two lbs. difference between cylinders. Changed plugs to eliminate any issues there, adjusted carburetor timing linkage.............. any thoughts?

[99yam40]

Lean sneeze.
Apparently you have not done a good enough job of cleaning yet, or something else is a problem

Did you clean the prime start system and make sure it works properly?
What position is the red lever in while you are running the motor?

[tassingh]

I cleaned it, but I'm not sure if it's working properly ( don't know how to test it). It's in the up position and when I put it down the motor runs rich, changes RPM's, so I'm assuming it's working?
Since I posted this thread, I checked the vacuum pull on all 3 carbs with my hand, and it seemed that the lower cylinder had less and didn't effect the RPM's as much as the other 2. I pulled the reed plate to inspect for damage or a leaking gasket. reeds looked OK, but it may have had a leak on the lower gasket ( a little discoloration) and could have been sucking air? My other thought was possibly the lower seals maybe leaking? The problem seems to be pointing to the lower cylinder. ....... any thoughts?

[99yam40]

there should be 3 postions of the red lever.
full counterclockwise would be the normal
next is the open, and then full clockwise should be off

[99yam40]

Fuel pump runs off of the bottom cylinder crankcase and the lower crank seal could leak also.

I did find some of the recirculation check valves bad on my C40TLRX when I went through it

[99yam40]

Oh yea, did you do the link and sync of the carbs when you reinstalled them?
needs to be done each time you put them back on.
Service manual will ahve all specs and procedures for your motor

[rodbolt17]

lean sneeze.
its a backfire.
in your car engine or lawn mower 4 stroke this would shoot fire from the intake.

your discussing a two stroke.

means the explosion from a lean intake mix is expanding underneath the piston not on top of it.
should be on top.

this makes a sealed cylinder in the crankcase, as the reeds seal off the intake.
this exploding lean mix in the crankcase actually tries to reverse engine rotation.
remember the explosion is now on the wrong side of the piston.

find and fix the cause of a lean condition in the crank case and your ****en.

[zenoahphobic]

lean sneeze.
its a backfire.
in your car engine or lawn mower 4 stroke this would shoot fire from the intake.

your discussing a two stroke.

means the explosion from a lean intake mix is expanding underneath the piston not on top of it.
should be on top.

this makes a sealed cylinder in the crankcase, as the reeds seal off the intake.
this exploding lean mix in the crankcase actually tries to reverse engine rotation.
remember the explosion is now on the wrong side of the piston.

There are of course two stroke (more correctly onestrokes) that are deliberately designed to do this. My father had a diesel generator in this configuration.

There were twostroke (correctly one stroke) engines that deliberately did this. My dad had a diesel generator that worked in this configuration.

d and fix the cause of a lean condition in the crank case and your ****en.

Under the piston: food for thought. Very good.

Most would have thought (those that kickstart two strokes anyway), that it was the mixture firing BTDC making the engine try to reverse, because there was insufficient rotational speed (and foot force) to energise the flywheel to go past TDC.

[rodbolt17]

and incorrect timing or lack of rotational speed can cause a 2 stroke to start and run backwards if the ign system allows it.
ask anyone who now uses a chicken stick on two stroke model airplane engines.
yea I still have marks on some fingers from 40+ yrs ago.

the old v4 and inline 3 pulse pack amp ign system on the OMC stuff used an anti reversing spring.
leave it out or the occasional wearing out and the engine may start and run backwards.


but in the lean sneeze case the engine is already running and the A/F mix explodes in the crankcase NOT the cylinder.

remember 2 strokes use PRIMARY then SECONDARY compression first moves the A/F mix the second makes power.

[99yam40]

Only motor I ever had run backward on me was a Case Diesel iron wheel and lug Rice field tractor.
tried to run up out of a ditch without enough throttle.
Rolled back and refired.
the oil bath air cleaner turned into the exhaust pipe blowing oil everywhere.
I was young and had no idea what i had done.
A simple shut off of fuel to tuen off motor and a restart along with a bunch of cleaning and refilling the oil bath and all was good again

[tassingh]

Red lever is in the up or full counterclockwise position. I had pulled the fuel pump to check if the diaphragm was leaking fuel into the lower cylinder, it had a good seal and the diaphragm was dry, however if the diaphragm was leaking this would have given the motor a rich not lean mixture.
I order new reed plate gaskets and lower seals, will try changing the reed gaskets and if that doesn't solve it, I will be pulling the power head to replace the lower seals and gaskets. .............I'm pretty sure that the carbs are not the issue but will go back there if this don't remedy the problem ....... to be continued ..... thanks

[zenoahphobic]

and incorrect timing or lack of rotational speed can cause a 2 stroke to start and run backwards if the ign system allows it.
ask anyone who now uses a chicken stick on two stroke model airplane engines.
yea I still have marks on some fingers from 40+ yrs ago.

the old v4 and inline 3 pulse pack amp ign system on the OMC stuff used an anti reversing spring.
leave it out or the occasional wearing out and the engine may start and run backwards.


but in the lean sneeze case the engine is already running and the A/F mix explodes in the crankcase NOT the cylinder.

remember 2 strokes use PRIMARY then SECONDARY compression first moves the A/F mix the second makes power.

Those marks on your fingers?
You no doubt have lasting cuts on the inside. But how about the topside?

My cuts on the inside are from pushing the prop. the ones on the back are from the rapid fires, the other blade coming around very swiftly.

Usually this happened when ever slowly turning the prop not intentionally spinning it to start, and the engine pops! It wasn't trying to run backwards.

Pilots still manually flip full sized props! (what happened to that golfer years ago?)

[boscoe99]

Those marks on your fingers?
You no doubt have lasting cuts on the inside. But how about the topside?

My cuts on the inside are from pushing the prop. the ones on the back are from the rapid fires, the other blade coming around very swiftly.

Usually this happened when ever slowly turning the prop not intentionally spinning it to start, and the engine pops! It wasn't trying to run backwards.

Pilots still manually flip full sized props! (what happened to that golfer years ago?)

You mean "stubby"?

[rodbolt17]

that was a wonderful difference between the testors .049 and the cox .049 motors.
the testors had a built in starter spring.
the cox you had to slip the spring over the prop and wind it.

sometimes even with the glow plug not attached the cox would pop,start backwards and eat up the fingers long before reflexs could get them out of harms way.

I leaned about chicken sticks back in the late 60's before interwebs and chicken sticks.

called them broom handle chunks.