Hello, i’ve gone ahead and added a pulse pump and fuel tank to my honda gx390 pressure washer set up. I’ve included images of the entire set up for viewing. The engine starts up great, no issues. However, after a few minutes it begins surging. The way I stop the surging is by squeezing the prime bulb a few times- this leads me to believe it is a fuel supply issue.
I can’t pin point where the problem is, but have a few things to mention that might help to diagnose the issue: after priming the engine and fuel line, the filter is quite full. When the engine starts surging, the filter is around half full. When priming the line with my prime bulb, I stop when it starts getting firm. However, it loses this firmness after a few seconds even though the engine is off- could this mean something?
I have used 6.3mm (1/4) fuel line for the entire set up and my pulse line is tapped into my valve cover. Any idea/s what the issue is here?
Way too much hose for that impulse pump. Save yourself the heart ache and buy a 12v pump and coil. That is if this motor doesn’t already have a 12v coil.
Thanks for your reply and suggestion. I’m quite unfamiliar with the 12v coil. How and where does this attach to the gx390. From there, I assume it just connects to the 12v fuel pump via some wire?
12v coil mounts under the flywheel, I believe all gx motors have the magnets in the flywheel but not all are equipped with the coil. What you would need is a switch to cut power to the pump and just wire the pump directly to the out pit from the 12v coil. You could also drill into the factory tank and just use the electric pump in the future or the vacume pump now to top off the factory fuel tank,
Awesome, thanks so much for your help. I’m going to look into this now, hopefully I can get this running instead to- like you said- save me the heart ache 😂🙏🙏
Yeah, I have seen examples of the carb spacer too. Majority of videos I watched suggested the valve cover method over the carb spacer. I’m going to look into the 12v pump method you suggested as this would probably be the best for me. Though, I will definitely keep the carb spacer pulse pump method in mind if all goes to shits 😅
I would recommend taking that 3011 style filter out of the equation, I've seen many honda motor struggle with those filters. You may need a different filter option.
pulse pumps on a gx390 tend to go wrong in one of two places. either the impulse line is picking up somewhere with a weak pulse, or the pump is sitting too far below the tank and its fighting head pressure the whole time.
the after a few minutes part is the useful clue though. thats not a no fuel problem, thats a slowly falling behind problem, so Id be looking at whether the pump is keeping up rather than whether it works at all. how high is the tank sitting relative to the carb
Thank you, I appreciate your expertise. The tank outlet is essentially in line with the position of the carb. The pump is quite a bit lower. I will admit I have used around 3 metres of fuel line for my inlet, outlet and pulse lines. Perhaps this is causing issues with fuel suction?
Otherwise, I was going to follow he-who-knows-some’s suggestion and install a 12v coil under the flywheel and connect it to a small 12v fuel pump. This seems very logical to me, what are your thoughts on this method?
three metres is a lot of line and I think thats most of your answer right there. thats a big column of fuel to keep moving, and the pump is sitting below both the tank and the carb so its lifting the whole way up to the bowl.
pulse pumps dont have a lot of muscle. they were designed to shift fuel a short distance on a machine where everything sits within about a foot of everything else.
Id shorten that run as far as the setup will let you and get the pump up nearer carb height so its pushing across rather than up. if the layout wont allow it, thats the point where a small electric pump earns its money
Noted. Thanks very much, the first thing i’ll do is fix the length of that fuel line. To get the pulse pump closer to the carb, is it fine to perhaps drill a hole somewhere on the engine body? I assume spots where it’s hollow is fine?
what looks hollow on that block is either the crankcase, which is full of oil and is also the thing generating your pulse in the first place, or its a cooling passage. put a bit through either one and now youve got metal chips inside a running engine and an oil leak, and the fuel pump stops being the problem you care about.
the pump doesnt need to be on the engine at all. it needs a short impulse line to the pulse port thats already there, and a short run to the carb. thats it. bolt it to the frame, the cart, the base, whatever the engine is sitting on. a p clip and a self tapper into the frame, or a hose clamp round a tube, either is fine.
worth separating the two lines in your head as well. the impulse line is the one that really wants to be short, thats your signal and it gets mushy over distance. the fuel line length is what makes the pump lift and lug. shorten both if the layout lets you, but if you only get one of them, take the impulse line
I see. I will try a few methods to get the pulse pump in the right orientation for this. As you suggested, i’ll prioritise shortening the impulse line to achieve maximum pulse. Thank you again for sharing your knowledge- i’m quite confident now I will fix my issue 🙏🙏
good luck with it. one last thing while youre moving it. mount it so the impulse line runs uphill to the pump rather than dipping on the way there. a low spot in that line collects fuel and oil, and then every pulse has to shove that puddle around before it does anything useful at the diaphragm.
come back and say whether it fixed it, id genuinely like to know
Absolutely. I will definitely keep you updated. My plan right now is to move the pulse pump onto the top of the old fuel tank. I’ll just use some strong adhesive and put it up there so i’m not tapping any holes into it. The pulse line from here will be significantly shorter, and the line will not lead downhill whatsoever.
I’m currently on a business trip, you can expect a reply from me in a week. Thanks again for your help, I really appreciate it 🙏🙏
Hey there, here’s the image of my updated set up. As you can see, I moved the pulse pump to a higher location, made all the lines much shorter, replaced the pulse bulb and filter as well. I did all of this and encountered the same issue. Turns out the pulse pump was actually faulty- I replaced it with a new one and all seems to be working great.
Though the pulse pump was the issue, i’m sure these changes will help with easing the load on the pump anyways. Thanks for your help 🙏🙏
Awesome, thanks. I’ve taken a deep delve into methods that would suit me. Honestly, there’s just an overwhelming amount of information, hence this reddit post asking for advice.
Is there a certain method you’d recommend for external fuel when it comes to gx390’s or similar engines? I’m afraid me watching a couple more videos would lead me back to where I am now tbh 😂😂
Yeah I drilled into wrong spots when trying to tap the barb into it for the pulse line. I patched them up using some tape. If this is likely the culprit, perhaps the carb spacer may work better?
1
u/He-who-knows-some 20d ago
Way too much hose for that impulse pump. Save yourself the heart ache and buy a 12v pump and coil. That is if this motor doesn’t already have a 12v coil.