Brand new 8gpm engine troubles

Hi all,

I have a brand new 8gpm Pressure-Pro cold skid with a Honda GX630 engine that has been giving me trouble. Well, it’s not brand new, but only has 20 hours on it.

Most recently it went to the shop because it wouldn’t run without choke. The shop said it was water in the gas, (which must have come from the gas station because there’s no way I got water in the tank!) and so I drained out all the old gas and bought new, premium gas. I didn’t drain the carburetor cup, but since then I’ve run the machine for about 3 hours and so I would assume that all of that gas has been replaced(?)

Anyway, it seems to work great when I’m on the trigger, but once I release the trigger and it goes back into bypass mode it exhibits some issues. Usually it will just run a little rough and backfire every few seconds - not loudly, but noticeably. But sometimes it does what you see in the video:

GX630 in bypass mode - YouTube

As you can see the governor is working overtime trying to regulate the speed of the engine. I don’t think this is normal. Do you have any ideas as to what might be going on? Is this still a fuel issue? I would have guessed that if it was going to have problems it would be while on the trigger, right? Isn’t there more load on the engine when I’m spraying? In bypass mode there is almost no resistance as the pump just pushes the water back into the tank… or at least that’s what I’m imagining.

I’d appreciate any kind of help.

I noticed this with my machine when I was tuning it and manually pushing on the governor but it smoothed out. There is a spring over the governor linkage is it connected. Is the linkage free? Just a few things to check before you dig deeper.


Subscribing. I have a GX 630. When I’m spraying water it seems to run fine. When I release the trigger, the motor runs erratically and backfires. Been through the whole fuel system and a few other things. I’ve dug through the inter webs and it seems there have been more than a few instances with this. I haven’t found a thread with a solution yet. I’ve taken it to a mechanic and they have given up on it.

I found this link to some information about the engine.


Have you guys tried non ethanol gas?? thats all I run in my machines, that ethonal is really bad for these small engines. John I know you should be able to get some at the beach that all boats use.

I had the coil go out on mine, and when you pull the trigger the engine seems like it will almost shut off, you check that by pulling off the spark plug wire while the motor is running see if you notice a change.

Timing I had some guy yesterday tell me he has been fixing the timing on these engines, I think he is full of crap but you never know.

Timing could very well be it dave. The entire fuel system has been cleaned or replaced. It’s unburnt fuel in the combustion chamber at the wrong time. I’ve had it at a pressure washing place that builds trailers and sells chems. I need to take it to a more qualified small engine mechanic.

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Mine works great when I’m pulling the trigger. It’s when I go into bypass that it happens.

Mark, thanks for the download. It goes through maintenance, but doesn’t have anything from the troubleshooting chapter forward.

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sounds like your unloader may need adjusting

It also stops before the end of the book the cylinder cleaning references chapter 14.

I’ll keep looking and will post if I can find it.

I just got this machine about two weeks ago and adjusted the valves yesterday. This is an exaggeration but there was enough clearance to put my finger through it. It was bad. It starts much better now.

As far as timing go it’s veritable controlled electronically for what I understand. If it’s not please let me know.


I’d like to know how you adjusted the valves?

Hey I thought I’d post an update on my situation:

The engine seemed to stop hunting about halfway through a job last week, and go back to it’s “normal” backfiring and rough running. The small engine mechanic suggested I put some Heet in there to dry out the gas, or in other words, get rid of the water which might have collected in the bowl.

Failing that, I was talking to Bob at Pressuretek about it, and he thinks it could be an ethanol problem, as was mentioned on this thread. I can’t get non-ethanol gas anywhere around where I live, but instead he recommended Star Tron, which is some kind of enzyme additive which can “eliminate” the ethanol problem. He suggested doing so at every fill up. After I’ve tried the Heet I’m going to try the Star Tron. I’ll let you know if any of those things solve my problem.

…though I wonder if everything I just said has already been tried by Ultimate House Wash?

Let us know how this works out for you. Hopefully it’s the answer because I was starting to think just maybe you got a lemon for an engine. It does happen sometimes with any engine and it’s reasons like this there is the “Lemon law”-- best of luck.

That much trouble on a new machine = warranty claim in my book.

Ok just cleaned my carb and had the same issue. I had the nut on the carb linkage on the carb to loose. There is a nut the opposite side of the carb on the shaft that to governor opens and closes. Mine is a GX620. maybe your problem.


I have a GX 390 with the same issue. I have to run it at half choke until it warms up and then it does ok but cold it oscillates like that every time.

I have a GX 690 with an 8 gpm stealth skid unit- I notice you have the same fuel tank and fittings as I do. There are a lot of posts around the net concerning the tank vent valve not working and starving the engine of fuel. The tank vent has a valve that is supposed to open but doesn’t. I will let you know if this improved the way mine runs, you might want to try opening the tank vent (pulling it out) and see if it still runs bad. Just a thought while looking for tank vent info on the net.

Depending on the age of the machine…and I know this sounds crazy…but it’s probably your fuel cap not venting properly.

Actually it doesn’t sound crazy at all. Once I went over to the machine when it was doing the oscillating thing and I took the gas cap off to see if it was running out of fuel and it started running normally. I thought I found the problem but the gas cap removal doesn’t correct it every time so maybe its a combo of problems.

These are the problems you can get when buying something used. Did you buy this from a person or a distributor? Hopefully they’ll work with you in getting this fixed. 2 weeks with the same problems is 2 weeks to long. Good luck.

Hey guys, thought I’d update you on my situation:

I ran a full tank of gas with Heet added to dry out the gas, and it helped a bit. The machine doesn’t hunt any more, but was still backfiring a bit.

Well, today I started running gas with Star Tron in it, which Bob from Pressuretek recommended I try. It seems to have cleared up all the problems! So my issues were at least partly due to ethanol in the gas, it seems. It ran flawlessly today!

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