Honda GX390 carb settings on pressure washer.

[i6pwr]

This is on a pressure washer I just bought used, it appears to have new gaskets between the carb and the engine. The engine starts on the first pull and runs very smooth, but it seems when I use the washer under full pressure, around 3600 PSI, it slows down a little more then I would think is normal but I understand this is a heavy load for the engine.

I just put a new AR pump on it and everything seems to be working fine, but when I shut it off there was a pop from the exhaust so I want to speculate something is slightly out of adjustment.

What should I look for with adjustments and operating speed? I assume the engine runs at 3600 at no load and is it 3400 RPM under load?

I have a non-contact tachometer I could use.

Fuel is fresh, but the fuel that was in there smelled a little like varsol. I haven't checked the plug but I did change the oil.

I'm good with small engines but I would like some pointers since this is my first GX390.

 

[Quest]

popping sounds like engine run-on after shut off; most likely due to 1 or more of the following:

-carb doesn't have proper fuel shutoff (engine still sucking fuel+air mixture after shutoff), which may lead to popping if the mixture is strong enough to self-ignite.

-spark may not have been completely grounded (short) when the engine shut off. Because almost all OPE engines rely on a magneto (with electronic ignition) to generate the sparking energy, shutting down the OPE engine and the magneto still spins == spark keeps coming into the plug, which may still ignite the fuel+air mixture that the engine suck in during intake stroke.

-some carbon-like hot deposits within the combustion chamber.

W/o knowing precisely what model (need model/serial number to identify), we can only guess if your carb has been retrofitted with a slightly different type or so, which is possible.

I'd drain the carb + fuel tank, pull off the carb bowl to inspect for gums, varnishing and debris and refuel the system with fresh new fuel.

Running old, rancid fuel will not do anyone any good anyways( esp. being cheep), for the rancid gas will cause carboning of combustion chamber and more.

Q.

 

[hatt]

I think the governor should keep it at a pretty steady RPM unless the pump is too big. I've never tested the RPM of my washer with a 390. It may just need a couple tanks through it.

 

[spackard]

I have one of these pressure washers, bought from a home improvement store closing in 1995. (Honda GX390 bolted to a pro-quality pump). It also pops once when shutting down from use at max pressure. I think it runs at the max output of the engine when on max pressure and the muffler gets so hot that when you shut it down a little unburnt fuel flows into the muffler, heats to the flash temperature, and flashes. The sound definitely is from the muffler, and is repeatable if you give it time to reheat the muffler again for a couple of minutes.

It won't pop if run at about 1500PSI. I don't know about the other PSIs, either I have it dialed somewhat low or at max. Anyway, normal condition, nothing need to be done to correct it.

 

[i6pwr]

Originally Posted By: spackard
I think it runs at the max output of the engine when on max pressure

I agree, it's definitely giving all it can.

The serial # is GCAA-2880714

I also noticed some fuel seeping where the line meets the tank, not sure exactly where though....hopefully it's an easy fix.

 

[Merkava_4]

If the engine slows down under load, you might need to richen the carb up a little bit.

 

[The motor guy]

Originally Posted By: Merkava_4
If the engine slows down under load, you might need to richen the carb up a little bit.


I don't think a 200rpm drop under load is abnormal. Also letting it run without a load for 30 seconds or so will eliminate a backfire after shutdown, don't shutdown an engine immediately after running a heavy load.

 

[bubbatime]

Yeah drop the engine RPM to low and let it cool off for 30 sec before you shut it off. Dont let the pump over heat though.

 

[i6pwr]

I slowed it down but not to an idle, maybe 1/4 throttle at most also allowing some water to circulate by pulling on the wand.

That's another question I had.....when starting the engine with the water on, it seems to pull easy but if it doesn't start on the first pull, then I have to fight the water pressure...almost like it's not unloading the pressure and I thought I was going to break the starter rope.

If I pull the trigger on the wand and relieve pressure, I can pull it again.

Maybe this is normal for such a large pump?

 

[spackard]

I've always pulled the wand trigger and kept it pulled in order to start the engine. I don't put any spray nozzles into the wand until the engine has run a minute or two. It makes for a bit awkward starts but what else makes sense? I've always tried to keep the time run without water running out of the wand to under 60 seconds, mostly under 30 seconds though. Even with an auto-unloader the water heats up quite a bit in 60 seconds.

I'm starting an engine, warming it, then starting to use it for work. People don't load up air compressors nor arc welders until the engine's started and warmed a little. Same with cars, come to think of it.

 

[bubbatime]

Originally Posted By: i6pwr
I slowed it down but not to an idle, maybe 1/4 throttle at most also allowing some water to circulate by pulling on the wand.

That's another question I had.....when starting the engine with the water on, it seems to pull easy but if it doesn't start on the first pull, then I have to fight the water pressure...almost like it's not unloading the pressure and I thought I was going to break the starter rope.

If I pull the trigger on the wand and relieve pressure, I can pull it again.

Maybe this is normal for such a large pump?


Completely normal. Have someone hold the wand handle as you pull the cord. I get creative and hold the wand handle myself, which makes it a lot easier to start.

 

[i6pwr]

Originally Posted By: bubbatime

Completely normal. Have someone hold the wand handle as you pull the cord. I get creative and hold the wand handle myself, which makes it a lot easier to start.


Good to know, wanted to be sure I didn't have a faulty unloader.

So I pulled the fuel tank and carb and the tank has a lot of debris in it, looks like bits of leaves so I will clean that all out. The carb wreaks of bad gas still and the inside of the float is pretty rusted up. I'll take a wire wheel to it and see if I can get it all out, but I will throughly clean the carb and get new gaskets and fuel line. The fuel filter at the tank is leaking or maybe the old line but I may as well replace the filter.

Float assembly looks ok, haven't checked the needle yet.

Any recommendations on where to get the carb kit from? I imagine they are everywhere but if anyone has a good source please let me know....thanks.

 

[DSparks]

Go to gxparts.com and buy a carb. Chinese yes.but work good and cheap...used many of them...the teeny tiny holes in the main jet are about impossible to clean correctly...been there done that..

 

[i6pwr]

Originally Posted By: DSparks
Go to gxparts.com and buy a carb. Chinese yes.but work good and cheap...used many of them...the teeny tiny holes in the main jet are about impossible to clean correctly...been there done that..


I did order a carb but I caved and went OEM. It was about $20 more but what the heck...my track record this past year with a lot of non-oem I figured it's only $20.

You're right..for that price it's not worth the hassle right now, maybe I can tinker with this one later but I have a bunch of stuff to clean. Picked up the gaskets also and a new fuel line and filter.

 

[i6pwr]

Installed the new carb Friday, it fired on the first pull and has ran perfectly...what a difference. Thanks for the tip on the new carb.

 

[bubbatime]

Originally Posted By: i6pwr
Installed the new carb Friday, it fired on the first pull and has ran perfectly...what a difference. Thanks for the tip on the new carb.


Good job. It's always feels good when you fix and repair things yourself instead of having someone else do it.

Now be sure and run a double dose of Stabil fuel stabilizer in that thing so that you don't have that problem again.