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4JH4 HTE Fuel primer behavior

M

M0nster

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Joined
May 13, 2025
Messages
5
Quick question, is the manual priming pump plunger supposed to get sucked down while the engine's running? or should it stay up and useable? On my Hunter 49, after bad fuel drama and lots of filter changes, I couldnt get over 1500 RPM without issues until I add an electric Yanmar lift pump, which fixed everything. Ive now replaced the manual pump, pulled the electric one, and the engine runs fine in neutral, but the plunger still sits about 3/4 down at idle. Is this normal at all? Full power test run tomorrow.
 
Yeah, it's normal for the plunger to sit partway down while running, it's not meant for use during operation...if your engine runs smooth now, you're all set
 
Sorry for jumping in late. Agree, what you're seeing is how the system usually works. I'm pretty sure the position of the plunger when it's running doesn't mean there's a problem
 
M0nster said:
Quick question, is the manual priming pump plunger supposed to get sucked down while the engine's running? or should it stay up and useable? On my Hunter 49, after bad fuel drama and lots of filter changes, I couldnt get over 1500 RPM without issues until I add an electric Yanmar lift pump, which fixed everything. Ive now replaced the manual pump, pulled the electric one, and the engine runs fine in neutral, but the plunger still sits about 3/4 down at idle. Is this normal at all? Full power test run tomorrow.
Click to expand...
I wanna add one tip. For your full power test, keep a close eye on the fuel pressure if you have a gauge, or just watch for any hesitation or surging. If you had an air leak somewhere, the plunger would likely sit fully up and you'd lose your prime,
so the fact that it's getting pulled down is a good sign. It sounds like you've fixed the issue
 
syrupfan_ said:
I wanna add one tip. For your full power test, keep a close eye on the fuel pressure if you have a gauge, or just watch for any hesitation or surging. If you had an air leak somewhere, the plunger would likely sit fully up and you'd lose your prime,
so the fact that it's getting pulled down is a good sign. It sounds like you've fixed the issue
Click to expand...
I agree with the tip, and yes, its normal for the manual priming pump plunger to sit partway down while the engine's running,, that just means the fuel system is drawing through it properly. As long as the engine holds power under load on your test run, you should be fine
 

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