Johnson 20HP wont rev under load, have paid to have water pump, spark plugs and check carbi but will rev with the ears in and for about 30sec in water then nothing then drives at about 2knotts

The float may be stuck or the brass metering jet in the carburetor is plugged

Hi if it stop when the trigger is pulled the issue is with the motor.
stopping is caused by , low revs on motor or low compression or poor spark, sometimes faulty carby.
change spark plug , adjust valve ( when valve has some slight side movment it is ok if up and down , it should be tighter (valves usually under side cover near top ) increase revs a little ( make sure revs dont get rough when running high) set max revs to when the engine still runs smoothly at max.

Check that the fuel pump is working and pumping fuel (fuse or burnt out) as it sounds like there is no fuel in the carby. To check if the engine is going to run remove the air filter from the top of the carby and pour about a table spoon of fuel directly into the carby throat. Replace the air filter and crank the engine. If is going to run it will fire and then stop

have the carby overhauled and cleaned out
check all rubber components for failure inside hoses and fuel pump

Check for a shorting spark plug wire when the engine is under load. Get a spray bottle of water, and mist some water on the plug wires from the dist. cap to the spark plugs. Rev the engine, and you might see a blue spark shorting to the outside of the spark plug or to the cylinder head. If that checks out, check under the dist. cap for any oxidation on the contacts, or hairline cracks in the cap. Any of these things will give you a misfire under load.

hi there jaybolt

here is a website for parts

http://www.partstree.com/parts/?lc=echo&mn=SRM-2100+Type+1+S%2FN%3A+001001+-+159490

all being well and compression and spark and timming , muffler is clear , carby is clean , and diaphrams are all ok you mention carb rebuilt , fresh mix , and fuel filter and lines are good

does the unit run with 2 stroke mix in the plug hole - then stop ?
if yes assume compression and spark are ok,, if no check compression and spark and muffler

will the unit run with 2 stroke mix sprayed into the carby throat, then stop ?

if it does sounds like you have a air leak somewhere in the intake system

could be at barrel base gasket, c/case joint, manifold boot/ block gasket, carby gasket , impulse hose ,if this unit has one , c/case main seals leaking

2 strokes need air tight c/cases in order to pump fuel / air / oil mixture from c/case to cylinder
and to create a vacuum for entry of fuel/ air / oil mix from carb to c/case

symptoms of air leak are -: hard to start, wont idle, stalling, low power, inconsistant idle, over rev
overheat

pressure and vacuum testing can be done by blocking off intake and exhaust with rubber and metal plates , then fitting adapter to spark plug hole , and placing piston at bdc , pressureise cylinder to 7 to 8 psi of pressure and check areas , base gasket, manifold joint, main seals, , impulse hose ? for leaks with soapy water - if leaking bubbles will be evident

if no leaks and pressure is held at 7 psi for at least 2 minutes with dropping - presure test is good
next do the same test using vaccuum again go to 20 - 30 inch / vaccuum

if vaccuum held unit is ok

suggest take a good look at carby and recheck its rebuilt correctly and setup particularly if P and V test are good and spark coil tests good with a coil load test using a spark gap of 6.00 mm to stress the coil ( simulates spark under compression load)

have a look and let me know what you find

cheers pauly46

hi there

paul 46 here.

all being well and compression and spark and timming , muffler is clear , carby is clean , and diaphrams are all ok , fresh mix , and fuel filter and lines are good

does the unit run with 2 stroke mix in the plug hole - ?
if yes assume compression and spark are ok,, if no check compression and spark and muffler

will the unit run with 2 stroke mix sprayed into the carby throat ?

if it does sounds like you have a air leak somewhere in the intake system

could be at barrel base gasket, c/case joint, manifold boot/ block gasket, carby gasket , impulse hose ,if this unit has one , c/case main seals leaking

2 strokes need air tight c/cases in order to pump fuel / air / oil mixture from c/case to cylinder
and to create a vacuum for entry of fuel/ air / oil mix from carb to c/case

symptoms of air leak are -: hard to start, wont idle, stalling, low power, inconsistant idle, over rev
overheat

pressure and vacuum testing can be done by blocking off intake and exhaust with rubber and metal plates , then fitting adapter to spark plug hole , and placing piston at bdc , pressureise cylinder to 7 to 8 psi of pressure and check areas , base gasket, manifold joint, main seals, , impulse hose ? for leaks with soapy water - if leaking bubbles will be evident

if no leaks and pressure is held at 7 psi for at least 2 minutes with dropping - presure test is good
next do the same test using vaccuum again go to 20 - 30 inch / vaccuum

if vaccuum held unit is ok

suggest take a good look at carby particularly if P and V test are good and spark coil tests good with a coil load test using a spark gap of 6.00 mm to stress the coil ( simulates spark under compression load)

have a look and let me know what you find

cheers pauly46

check basics 1st fuel , air, compression, spark , timming
then secondary compression ie crankcase air tightness
2 strokes need air tight c/case in order to draw in & pump mixture

check your tank breather is working,

has this saw been sitting a while ? if so might pay to rekit carb

check your carby diaphrams are pliable and inlet screen is not blocked and metering needle is set flush with chamber floor,
are hi / lo needles set base settings are 1-1/4 turns out from lightly seated , final hi setting is done while @ full rev and needs to 4 stroke slightly

check ignition spark under load ie while under compression load- could be a weak spark

check timming key

check for a air leak at cylinder / manifold block gasket or carb joint

check barrell bolts are tight everything been = engine should run

cheers

check gap on plugs and check mixture of gas and oil.