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Briggs-Fan
Briggs-Fan, Small Engine Technician
Category: Small Engine
Satisfied Customers: 1264
Experience:  over 15 years experience in small engine repair, multiple certifications
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I have strong experience with Briggs & Stratton small

Customer Question

Hello. I have strong experience with Briggs & Stratton small engines, but not much with Honda. I have a GX390 on a pressure washer system. Won't start (or fire) at all. I cleaned the carburetor thoroughly and changed spark plugs. I have ignition (tested with plug grounded to engine and pulled starter), and when trying to start, the plug gets wet with fuel. I got a compression tester and it reads barely 20 psi when cranking hard. How do I tell if I have an automatic compression release that may be malfunctioning? Otherwise, I assume valves are misadjusted, or possibly the rings are frozen on the head? Thank you for any help you can provide me. I want to fix this myself rather than head to a Honda shop.
Submitted: 2 years ago.
Category: Small Engine
Expert:  Briggs-Fan replied 2 years ago.

Hi my name is ***** ***** welcome to just answer.

Expert:  Briggs-Fan replied 2 years ago.

20 psi is terribly low so I would remove the ohv cover and check the push rods and rocker arms

Customer: replied 2 years ago.
Hello John. I did that when cleaning the engine. I verified the valve rockers are moving up and down. I don't have much experience with OHV. What am I looking for when I inspect again?
Expert:  Briggs-Fan replied 2 years ago.

I would check for valve clearance . I can try to get the specs on valve clearances , 20 psi is terribly low

Expert:  Briggs-Fan replied 2 years ago.

Here is your valve clearances for your engine i

ntake 0.20 +/- 0.02mm ( 0.008 +/- 0.001in )

Exhaust 0.20 +/- 0.02mm ( 0.008 +/- 0.001in )

Customer: replied 2 years ago.
Just pick up a standard feeler gauge and inspect between the valves and rockers?
Expert:  Briggs-Fan replied 2 years ago.

Yes , this video will help you with checking ohv engines

https://youtu.be/xmXr4U5R8ak

Customer: replied 2 years ago.
Thanks. That was a terrible video. I certainly didn't hope you filmed it. But I get the point. I'll be getting a feeler gauge later today and checking it out. I also asked how to tell if there is an automatic compression release feature on the model?
Expert:  Briggs-Fan replied 2 years ago.

No I didn't make the video, it was just to give you a general idea , the compression release is on the camshaft and has a spring attached

Customer: replied 2 years ago.
John, what is the likelihood of this becoming damaged?
Expert:  Briggs-Fan replied 2 years ago.

Usually when they break they won't release compression , your 8n at 20 psi which is way low almost like a broken connecting rod and the piston isn't moving type thing . I can't see how it would get your compression that low unless the cam came apart and isn't pushing the valves

Customer: replied 2 years ago.
Hi John. I got a feeler gauge and properly adjusted the gap. Turns out the previous owner took the engine to a not-so-skilled mechanic and he completely adjusted the exhaust valve completely open. So now it is up to about 50 psi and started right up. It smokes badly and I believe that is because of too much oil in the crankcase. This pressure washer was badly abused in its past life. So to conclude the support, I'd like to know what is my target cylinder pressure? Is 50 psi adequate? And where can I find the oil capacity? I'm going to drain and refill exactly. Thank you John.
Expert:  Briggs-Fan replied 2 years ago.

You need 60 psi for 4 cycle engines and 90 psi for 2 cycle engines . So your still low , they may need a little more adjusting , make sure your oil isn't thin or smells like gas , if so don't start it until you fix it . The carburetor could be allowing gas to get down into the crankcase and mix with the oil . After emptying the oil add 3/4 of a qt . It should have a measuring stem almost like a dip stick on one of t g e caps , but make sure the oil isn't thin or smells like gas