Crankcase creates vacuum?

[chubcobear]

Does the crankcase create a vacuum for the return of fuel mix in the recirculation system? (J90TLCUR) Two one-way valves (below top carb) feed one return line starboard side which goes into crankcase. Does it suck the fuel mix in? Thanks.

 

[F_R]

Re: Crankcase creates vacuum?

Does the crankcase create a vacuum for the return of fuel mix in the recirculation system? (J90TLCUR) Two one-way valves (below top carb) feed one return line starboard side which goes into crankcase. Does it suck the fuel mix in? Thanks.

Not familiar with that particular motor, but yes, there is a vacuum in the crankcase of any two-stroke when the piston is on the up-stroke. The vacuum alternates with a pressure on the down stroke of the piston. That vacuum/pressure cycle is essentional to a two stroke being able to run.

The one-way check valves you mentioned are evidently to let it "see" the vacuum pulse and block the pressure pulse.

 

[ezeke]

Re: Crankcase creates vacuum?

That's correct for your engine except that there are 4 recirculation check valves in the intake manifold rather than two; one for each cylinder.

 

[chubcobear]

Re: Crankcase creates vacuum?

F R and ezeke thank you for the info. Yes, there are four. I am only re-hosing the upper two (going to starboard side) because the hose was brittle and cracking. I wanted to make sure fuel/oil mix was going to get sucked into the crankcase. Two upper feed to a "T" and then single hose to the CC.