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33cc Asian two stroke will not run

#1

T

Teedee

I have a small 33cc two stroke that will only run if I put some fuel in the sparkplug hole directly on the piston. Dies as soon as this fuel is gone. I have replaced fuel filter in tank, fuel lines, cleaned the carburetor, installed new plug, tested cylinder pressure (120 psi), checked crankcase seals and even tried a New carburetor. Cyclinder leak test holds its pressure. I have examined intake and exhaust ports and all are normal. There is no reason for this engine not to run. What have I missed?


#2

R

Rivets

You missed crankshaft seals. If one or both are leaking you will get no fuel to cylinder.


#3

StarTech

StarTech

As said do a crankcase vacuum test. Vacuum test at .5 bar (7.25 psi). Also is the impulse port clear?


#4

T

Teedee

Rivets said:
You missed crankshaft seals. If one or both are leaking you will get no fuel to cylinder.
Click to expand...
I pressurized the cyclinder to 120 psi, blocked off the intake and exhaust and let it sit for 10 minutes. No pressure drop.


#5

T

Teedee

StarTech said:
As said do a crankcase vacuum test. Vacuum test at .5 bar (7.25 psi). Also is the impulse port clear?
Click to expand...
This engine has no apparent impulse port unless it is built into the carburetor. There is no separate line. I will remove the carburator and see if there might be something cast into the carburator. So if I block off the intake and exhaust and pull a vacuum through the spark plug, is this significantly different than the cyclinder leak test I have already performed?


#6

R

Rivets

You need to pressurize or apply a vacuum to the crankcase, not the cylinder.


#7

T

Teedee

Rivets said:
You need to pressurize or apply a vacuum to the crankcase, not the cylinder.
Click to expand...
Thanks. I will take a look and see what I have for access. I am beginning to think these are throwaway engines. What a shame.


#8

B

bertsmobile1

You test the crankcase seals under both compression & vacuum by fitting an adapter plate with a spiggot in it over the carburettor port if it has no external impulse line .
In theory you can do the testing via the plug hole but that relies on you making sure the internal induction port is open and remains so during the testing.
I find this need 5 hands as the piston does not want to stay there and on a lot of engines exactly where the port is is difficult to determine .
So the easiest thing it piston at TDC and crank locked then leak down test.
While the cylinder is sitting there pressureised you can pull off the carb and hook up the crank testing gear.


#9

T

Teedee

bertsmobile1 said:
You test the crankcase seals under both compression & vacuum by fitting an adapter plate with a spiggot in it over the carburettor port if it has no external impulse line .
In theory you can do the testing via the plug hole but that relies on you making sure the internal induction port is open and remains so during the testing.
I find this need 5 hands as the piston does not want to stay there and on a lot of engines exactly where the port is is difficult to determine .
So the easiest thing it piston at TDC and crank locked then leak down test.
While the cylinder is sitting there pressureised you can pull off the carb and hook up the crank testing gear.
Click to expand...
Thanks. I will give this a try. I learn something new everyday.


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