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Engine drops off under load after 10 seconds

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Beerman123

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Good day gentleman. 2002 175 johnson 60*. New bulb
new fuel pump from maxrules 06-150. Mix oil in gas. Compression 105-115. New plugs. Runnin on external tank to eliminate onboard tank, fuel filter clean. Choke solonoid clicking when choke pushed.
Runs fine off of plain. When throttle WO comes up on plain for 5-10 seconds then drops off to low rpm or dies. Restarts and idles fine. Throttle WO same thing again.
What would be next thing to look at.
Could vapor sep cause this. Seems to run out of gas. How to check pulse limiter section? Thanks
 
Have your assistant operate the manual pump while getting on plane.-------Report what happens then.----Does it keep running at full speed, yes or no ?
 
Before I changed the fuel pump the engine would not run over 3000 rpm wthout sqeezing the bulb. With sqeezing bulb continually it would run full speed. Will try sunday with new fuel pump.
 
Its very likely that your fuel pump was only part of your fuel supply problem. The stronger pump you have now has created more supply, but not enough. Has it used ethanol fuel or has it been stored with ethanol fuel? If so, you might be wise to check for restrictions in fuel lines under the cowling. Outside the motor you have likely eliminated any possibilities by trying the 6 gallon tank and different hose/primer.
 
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Hello gentleman. Compression 105-115. Ran external tank with new hoses and a pressure gage in discharge line where goes in vapor seperator. At idle 8#. At 3000rpm drops to 2#. Checked pulse limiter clean. Ran new hose with tee inline on pulse limiter. Good Pressure/vacuum at idle but drops off to vacuum at higher rpm using thumb gage. Would think it should still pulse pressure to drive fuel pump??? Ideas. Could not take on water today. Thanks
 
Can anyone tell me what kind of flow the pulse eliminator should have at higher rpm? Should both the pressure and vacuum to drive fuel pump go up as the rom's go up? Seems logical to me the more fuel you need the faster the fuel pump should run. If the pressure is supossed to go up with increasing rpm what would cause it not to increse with higher rpm. Thanks
 
Maybe for the same reason that your compression doesn't go up with higher RPM. it reaches a specific point and then levels off.
 
By the way, the compression is nothing to brag about. Was this warm or cold? Warm compression tends to produce more attractive numbers.
 
Good day gentleman. Ain't no bragging here. My job when asking experts for advice is to give out enough information good or bad for you to make an educated opinion. I appreciate and welcome any advice. Dad always said you can learn from someone who has done it or reinvent the wheel. Thanks
 
Okay, thats just my way of saying that the compression is a bit low. You could get a little higher with a warm engine test. I would like to see another 10 to15 psi. Its likely that you can gain only another 5 psi with a warm test. I believe that we are looking at a fuel delivery problem. Pressure may be okay but fuel "volume" is the "real issue". We have to have consider proper pressure while delivering fuel at WOT.
 
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I am taking to the mechanic today. I believe that the crankcase is losing the pressure side of the vacuum/pressure equation that powers the fuel pump at higher rpms. Do not know how to do a crankcase pressure test on an multi cylinder engine. It runs for 10'seconds under load until the vapor seperator goes empty I believe. When I find out what the problem is I will post it here. Thanks
 
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