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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 12592
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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I have a Honda Gx390 engine on a pressure washer that cuts

Customer Question

I have a Honda Gx390 engine on a pressure washer that cuts out at high speed but runs fine at low speed. I have replaced the coil , carb, plug, oil, and air filter. Cleaned the fuel tank and installed fresh fuel. Adjusted the valves to specs. I don't know what else to do to correct the high speed issue.
JA: I'll do all I can to help. Is there anything else the Small Engine Technician should be aware of?
Customer: No i think that I covered all of it.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Small Engine Technician about your situation and then connect you two.
Submitted: 9 months ago.
Category: Small Engine
Expert:  Curtis B. replied 9 months ago.

What is full engine model number? Honda usually puts in low oil level sensor or oil pressure sensor. Is oil level full and not thinned from gas contamination? Locate the oil sender and bypass it. Then run test.

Customer: replied 9 months ago.
I also disconnected the low oil switch. No change.
Expert:  Curtis B. replied 9 months ago.

Will it die if you keep it at full throttle?

Customer: replied 9 months ago.
Honda GX390 QAPW GCBDT-1094835
Expert:  Curtis B. replied 9 months ago.

Does it have a sediment trap/filter? Have you bypassed it?

Customer: replied 9 months ago.
At full throttle it runs and will not die but will miss and cut out. when I back off to half speed its fine. I checked the fuel system and filter and its fine. I also applied the choke to see if it would improve but did not.
Expert:  Curtis B. replied 9 months ago.

Did you remove the fitting from the fuel tank with the screen on it and check the screen?

Customer: replied 9 months ago.
fuel system is all new. New carb,fuel lines and tank filter.
Expert:  Curtis B. replied 9 months ago.

Have you tried a raised fuel tank for test? Sounds like just a lack of fuel.

Customer: replied 9 months ago.
I disconnected the fuel line to the carb to check the flow and it was very good no problem.
Expert:  Curtis B. replied 9 months ago.

OK,let me opt out, maybe someone else can help.Sorry.

Expert:  Briggs-Fan replied 9 months ago.

Hi my name is ***** ***** welcome to Just Answer . This may seem like a odd question but since you have covered most bases have you checked the timing key that holds the flywheel in place ?

Customer: replied 9 months ago.
No not yet due to I have never had that happen. I will check. That is probably the only thing that I did not check. Will let you know.
Expert:  Briggs-Fan replied 9 months ago.

Looking at everything you covered it is one of the few culprits that could cause the problems you are having , the other thought would be if your engine had a fuel pump

Customer: replied 9 months ago.
No fuel pump. Fuel tank on top of engine.Honda GX390 13hp without Elec start. Xstream pressure washer 4000 3.5 model.
Expert:  Briggs-Fan replied 9 months ago.

Ok , let's see if the key is sheared ,

Customer: replied 9 months ago.
The key is not sheared. All ok. ???
Expert:  Briggs-Fan replied 9 months ago.

Ok , your pump is a direct drive as in bolts directly to the engine right ?

Customer: replied 9 months ago.
Belt drive.
Expert:  Briggs-Fan replied 9 months ago.

It's doing this with the belt disconnected from the pump right ?

Customer: replied 9 months ago.
No. It is in normal operating condition with the belt connected. It starts fine and runs fine until you go to full throttle. It will start cutting out or missing at about 50% throttle. Changed the carb, coil, spark plug, fuel line and tank filter, fresh gas and flywheel key. Changed all of the gaskets with the carb and intake. Adjusted valves and disconnected the low oil switch. After all of that it still runs the same way. ????
Expert:  Briggs-Fan replied 9 months ago.

Ok , have you tried the motor with the air filter off ? . I'm trying to think of anything you haven't already checked , another concern is the cam. I was asking if you tried the motor with the belt off to eliminate the pump being the culprit

Customer: replied 9 months ago.
I did run the engine without the belts and air filter and it runs the same.
Expert:  Briggs-Fan replied 9 months ago.

Ok that would eliminate any air restrictions or the belt or pump being the issue . It's hard to say it's the carburetor because it's done this with 2 different carburetors right ? . It could be the cam itself in the motor

Customer: replied 9 months ago.
I am done.
Expert:  Briggs-Fan replied 9 months ago.

The only probable cause that we haven't checked is the cam , how much wear does the engine have on it ?