august
Member
My motor is a new NE-R. Cam is one tooth advanced.
I think I have blowback through the carbueretor, as the carb throat and air cleaner always have some raw gas laying in them after running, and it kind of sounds like air is being pushed backwards through the carb when running.
I took the head off and watched the timing of the valves and piston when rotating the engine by hand and noting the position of the piston and valves during the four strokes.
On the power stroke,the ex valve starts to open when the piston still has about a 1/4 inch of travel before bdc.
On the exhaust stroke, the int valve is opening when the piston still has a 1/4 inch of travel before tdc. I think this is where I am getting some blow back through the carb.
On the intake stroke,the piston goes down about 3/4 of an inch before the ex valve closes.The int valve is open from the top of the intake stroke until the piston is at bdc and then still open until the piston is 1/2 inch into the compression stroke.
On the compression stroke, the piston goes up 1/2 inch before the int valve closes completely closed. I think I am getting some carb blowback on this stroke also.
I tried the cam at the dot to dot alignment position, and it lessens the amount of time the valve stay open during opposing strokes, so there is less time that compression and power strokes are losing pressure through valve being open too early or late.
I know there has to be some time for air to change directions and all that, but does this sound like maybe the cam is advanced too far?
The engine does run with the cam one tooth advanced, but doesn't start as easily as I think it should, and I was only able to get 50 lbs on the compression tester.I had the head changed under warranty, as it was leaking,so I don't think head leaking is the problem.
Would like to hear some ideas as to whether this amount of piston valve overlap is right, or should I put the cam back to dot to dot.
Hope my description is not too confusing. I did compare my cam timing with the article that Quenton put into the Whizzer news letter, but couldn't come up with the settings that he described.
Any help is appreciated Thanks August
I think I have blowback through the carbueretor, as the carb throat and air cleaner always have some raw gas laying in them after running, and it kind of sounds like air is being pushed backwards through the carb when running.
I took the head off and watched the timing of the valves and piston when rotating the engine by hand and noting the position of the piston and valves during the four strokes.
On the power stroke,the ex valve starts to open when the piston still has about a 1/4 inch of travel before bdc.
On the exhaust stroke, the int valve is opening when the piston still has a 1/4 inch of travel before tdc. I think this is where I am getting some blow back through the carb.
On the intake stroke,the piston goes down about 3/4 of an inch before the ex valve closes.The int valve is open from the top of the intake stroke until the piston is at bdc and then still open until the piston is 1/2 inch into the compression stroke.
On the compression stroke, the piston goes up 1/2 inch before the int valve closes completely closed. I think I am getting some carb blowback on this stroke also.
I tried the cam at the dot to dot alignment position, and it lessens the amount of time the valve stay open during opposing strokes, so there is less time that compression and power strokes are losing pressure through valve being open too early or late.
I know there has to be some time for air to change directions and all that, but does this sound like maybe the cam is advanced too far?
The engine does run with the cam one tooth advanced, but doesn't start as easily as I think it should, and I was only able to get 50 lbs on the compression tester.I had the head changed under warranty, as it was leaking,so I don't think head leaking is the problem.
Would like to hear some ideas as to whether this amount of piston valve overlap is right, or should I put the cam back to dot to dot.
Hope my description is not too confusing. I did compare my cam timing with the article that Quenton put into the Whizzer news letter, but couldn't come up with the settings that he described.
Any help is appreciated Thanks August
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