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13 HP (GX390) Honda Engine Problems


Big Jon's Avatar
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08-26-09, 09:25 AM   #1  
13 HP (GX390) Honda Engine Problems

I use my machine for pressure washing. I would appreciate any advice you folks might have. I have looked at some current treads and don't see my exact problem, so here it is:

When I start my machine it idles a little rough, but can stay running on its own fine. In fact when I'm not gunning it isn't obvious there is a problem (it almost sounds like a small timing problem). However, once I pull the trigger the machine can't produce any real horsepower. The engine sounds like it struggles, and it wavers. The pressure goes up and down, but even at its strongest the psi is very low. I looked at it closely with the trigger pulled and the thing I noticed was the wire and spring under the throttle bar were moving back and forth.

Any ideas? Thanks in advance.

Also... until this happened the machine was working perfect. This whole year I have been keeping very close tabs on it.


Last edited by Big Jon; 08-26-09 at 09:27 AM. Reason: Additional Information
 
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08-26-09, 07:04 PM   #2  
Well Jon,

Have you replaced the spark plug ?

Could be one of two things or both causing this, Start the unit and give it full power. As it's pulsing ("the wire and spring under the throttle bar moving back and forth") start slowly applying the choke, If the "wire and spring" stops moving and it starts putting out full pressure the carb is leaning out. It needs to be removed/taken apart and cleaned making sure all ports/passages and jets are fully clean/open, Then check the tank for trash/water.

If there's no change applying the choke, It could need the valves checked/adjusted. This is done with the engine cold and the piston set at top dead center compression stroke;







Good Luck

 
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08-26-09, 08:50 PM   #3  
Thanks a lot for replying 31YTeck. I will try your first idea tomorrow. The engine not getting enough fuel could be the problem. I'll let you know how it goes. Thanks again.

Now that I think of it I did have some minor problems starting the engine a few times this summer. It was after I ran out of gas and refilled it. Maybe some dirt got into the carb. Anyway, I'll see how it goes tomorrow.

 
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08-27-09, 02:12 PM   #4  
31YTeck, I tried your first idea. I started the machine and slowly applied the choke and left it half way for at least 10 minutes. No change... unfortunately. So it probably isn't a lack of fuel. Nevertheless, I think I will clean the carb since your suggestion about the valves seems pretty challenging to me. It can't hurt and maybe it will help. I will also get a new spark plug even though I changed it 3 months ago (with little use in between)... again can't hurt and cheap. Any suggestions about cleaning the carb? I have never done it before, but will get some basic advice before cleaning it tonight.

If none of this works I will try to do what you suggested about the valves. I have a feeling this is probably the problem. Today after I started and stopped the machine a few times it became very difficult to pull start and almost ripped my arm off. That sounds like a compression issue (but what do I know?).

Anyway, I continue to update about how it goes. Thanks.

 
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08-27-09, 03:13 PM   #5  
Here is a basic carb cleaning procedure;


Take the carb. off then tear it down, Spray carb. & choke cleaner with the straw through ALL ports, passages and jets then blow it out with compressed air if available then re-assemble, Check/clean the fuel tank.

Here is a LINK to a GX390 carb breakdown should you need it.

Make sure #33 main jet is fully open and the port #39 adjuster screws into, Also make sure the O-ring on #34 pilot jet is in good condition and not cut.


Good Luck

 
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08-31-09, 07:12 AM   #6  
31YTech, I finally took off the carb last night. I was a little nervous, but it worked out. It was a little difficult since the frame for the pressure washer was kind of in the way. Anyway, it didn't take long to see something odd. As I took off the plastic air inlet (after taking off the filter etc), a small flat brass piece fell into the ground. Unfortunately I wasn't able to see where it was in the carb or inlet prior, but it fell out loose. It wasn't until I took off the whole carb and had a look that I realized it was a part of the choke (#8 on the diagram you included). I don't think I broke that when I took off the air intake, it was probably broken all along and could be the problem. What do you think?

I thought about cleaning the carb like you said, but I remembered I paid to have it cleaned last year (I spent a lot on repairs last summer). It still looks clean so I left that until seeing if the choke "flap" is the problem. [There was no visible impediment to the main jet (I tried weakly to remove it, but didn't want to damage it, so never got it off), but had trouble finding #34 pilot jet. Again I thought about waiting before messing with the #39 adjuster screw... would I remove this?]

I tried to gently force the flap back into the slit on the choke, but one of the sides on the choke "peg" is broken. I don't want to damage it more.

Any ideas? Thanks again for your help, I would be lost without it.

 
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08-31-09, 09:11 AM   #7  
I'd say it a fair chance that is your problem, at any rate it should be replaced. With the butterfly (flap) out of the shaft, the shaft should pull out of the carb body.

#8 choke set, on the diagram should be the part you need. If any foam or other washers are included or on original, be sure to replace them in the same order.

With the new shaft, simply install it in the body reverse of removing the old one, then insert the new butterfly (flap) into the slot in the shaft. It appears that this one simply "clicks" into place with friction locks....might look for screw holes in the shaft to make sure.

The parts list does not specify and is a bit vague, perhaps 31Y knows for sure if the shaft is included with the choke set. My assumption is it certainly should be.

 
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09-04-09, 10:08 AM   #8  
I want to thank you guys for the help you gave. I sure appreciate you spending your time to help me.

Here's my last update: I put the carb back on without the butterfly air "flap" and the machine was able to pump out the power I needed. However, it still ran rough so I only used it for about 30 minutes. I was going to check a couple of things when I noticed it leaking some gas around the seal between the carb and the engine. I tried tightening the lower screw on the float chamber, then tried to start the engine. I couldn't turn the engine over... period. It still was leaking gas so I tried messing with the machine a little more and overtightened the screw that pushes the air intake onto the carb. I broke the bolt. At this point I gave up and left it for a local professional to do.

It was a learning experience I guess. Thanks again.

 
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09-04-09, 10:35 AM   #9  
Sounds like your float and or needle and seat are not shutting off fuel flow to the carb. The leaking fuel is probably fuel overflowing from the bowl into the intake and in to the cylinder causing a hydro lock. Likely the oil is now overfull as well and diluted with gas.

Good luck with your mech, thanks for the update.

 
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