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2016 Honda (tohatsu) 150 stalling and surging over 3500 rpm....sometimes

S

Swampsquash

New member
So I've been fighting this issue for a few months now.

When I keep it under 3500 rpm the motor seems to do fine. But when I go over and run it harder it will sometimes stall and surge and I back off and it then shuts down. It will refire after I cycle the key a few times and pump the bulb. I Even had to put in neutral and gas it a little to get it to start once. This doesn't happen all the time. 2 trips ago I fished all day and it ran just fine then it stumbled on the run back to the ramp at the end of the day.

So I've felt this was a fuel issue and I figured it was full of crud. Well I haven't found anything gummed up or dirty.

I've replaced all the outboard fuel filters under the hood. I've replaced the Boat Racor filter also

I took apart the vst and it was basically spotless. I unfort cracked the plastic on the high pressure fuel pump removing it and now it and it's filter screen are brand new.

The outboard isn't throwing up any engine lights.

I also did a compression test just to make sure the powerhead was doing ok (190-190-191-200)


Any ideas?
 
Hi,

I'm not expert on these so just an idea or two.

When you had the VST apart, did you make sure there's no blockage in the fuel cooler water passage? Item 12 in link below.
The intermittent nature of the issue makes me wonder if the fuel is sometimes getting overheated and causing a vapor lock condition.


Another thought is that I think this engine has an intake manifold "runner" to modify the incoming air.

It's actuated by a vacuum diaphragm controlled by a solenoid valve. See items 16, 17 and 18 in link below.

I don't have any experience with this nor the manual so I can't tell you how to diagnose or troubleshoot that. The reason I'm mentioning it is because of your saying that the problem seems to be associated with 3500 rpm. I think that is likely around the rpm that system would activate and deactivate. Meaning the runner arm in the manifold moves when commanded then returns when vacuum is removed.

I know that, on cars that utilize those manifold runner systems, sometimes you can hear the runner making a rattling or crackling sound if it has broken or come loose inside the manifold.

You could try applying vacuum to the diaphragm with the engine off to see if it makes unusual noises as you apply and release vacuum.


Good luck.
 
Howl about the boat’s fuel system like the fuel pick up tube in the tank & the vent? These can be hidden problems that can cause the same problem. Based on experience with my 4.3 V6 I/O I’d always check and rule that out first. Easy to do by running the boat temporarily on a portable outboard tank….
 
nanserbe said:
How did the float and seat look in the VST? It almost sounds like it could be getting stuck
Click to expand...
The float and the seat looked pretty good, the tip still seemed supple. it moved freely. I took it apart and sprayed some cleaner in the hole to make sure no crud was in there. I wish I was smart enough to order a new needle (I'm not sure it's actually called that) but I forgot.
 
jgmo said:
Hi,

I'm not expert on these so just an idea or two.

When you had the VST apart, did you make sure there's no blockage in the fuel cooler water passage? Item 12 in link below.
The intermittent nature of the issue makes me wonder if the fuel is sometimes getting overheated and causing a vapor lock condition.


Another thought is that I think this engine has an intake manifold "runner" to modify the incoming air.

It's actuated by a vacuum diaphragm controlled by a solenoid valve. See items 16, 17 and 18 in link below.

I don't have any experience with this nor the manual so I can't tell you how to diagnose or troubleshoot that. The reason I'm mentioning it is because of your saying that the problem seems to be associated with 3500 rpm. I think that is likely around the rpm that system would activate and deactivate. Meaning the runner arm in the manifold moves when commanded then returns when vacuum is removed.

I know that, on cars that utilize those manifold runner systems, sometimes you can hear the runner making a rattling or crackling sound if it has broken or come loose inside the manifold.

You could try applying vacuum to the diaphragm with the engine off to see if it makes unusual noises as you apply and release vacuum.


Good luck.
Click to expand...
I actually had that vst water cooler plug up before, the tell tale wasn't squirting water out. It seems to be passing waster no problem now. I'm not a fan of that design,it really seems to get a little crusty.

I will take a look at the vaccum diaphragm and see if everything seems ok
 
louc said:
Howl about the boat’s fuel system like the fuel pick up tube in the tank & the vent? These can be hidden problems that can cause the same problem. Based on experience with my 4.3 V6 I/O I’d always check and rule that out first. Easy to do by running the boat temporarily on a portable outboard tank….
Click to expand...
Yeah thats my next move. I guess I should get a secondary tank

I'm trying to figure out how to check the hose in the tank.. All of the fuel hose that I've checked to this point still seems in good shape and supple. The fuel line is about 8yrs old. So Possibly time to replace it

Something I failed to add is in Jan I used the boat for the first time in 6 months (damn hurricanes last yr) And the motor was running really rough, really surging, vibrating and struggling even at idle. But it worked through it and improved alot by the end of the trip and it was running basically normal.. It literally runs normally most of the time but when I push it in higer rpm it has the issue I described in the orginal post
 
Last edited:
Outboard fuel tank for testing.jpg

I added a shut off valve for safety.
I wonder if you removed the sending unit cover and looked inside the tank, what'd you'd see in there. Some pick up tubes have a screen on the end of them and gunk can get stuck to it and cause the fuel starvation problem you might be having. In my case (same problem) the clue was the center electrode porcelain insulators were white, suggesting very lean fuel mix. When I hooked up the portable tank it was like a totally different boat. Jumped up on plane and revved right up to 4900 rpm which is about as high as you want to go with a pushrod inboard....
So my problem is either the anti-siphon valve or pick up tube....
 
louc said:
View attachment 36367
I added a shut off valve for safety.
I wonder if you removed the sending unit cover and looked inside the tank, what'd you'd see in there. Some pick up tubes have a screen on the end of them and gunk can get stuck to it and cause the fuel starvation problem you might be having. In my case (same problem) the clue was the center electrode porcelain insulators were white, suggesting very lean fuel mix. When I hooked up the portable tank it was like a totally different boat. Jumped up on plane and revved right up to 4900 rpm which is about as high as you want to go with a pushrod inboard....
So my problem is either the anti-siphon valve or pick up tube....
Click to expand...

Yeah unfort my tank is pretty long and everytime I've looked inside I can't really see anything. It's unfort not an easy process to remove the sending unit. My tank sending unit screw threads crapped out years ago and I had to install one of those "rings" that goes underneath for you to tighten it to. I need to check my pickup tube and see if maybe it'll unscrew out, but I'm guessing no. That wld be much too convienent. I removed the anti siphon valve and replaced it with a plain old fuel line fitting yrs ago and forgot to eventually install a new anti siphon....whoops


How do you tie in that tank to your boat? A 3 way valve? Or just attach it to your water sep fuel filter?
 
Attach it to the in-side of the water separator, I assume you have the spin on?

When you do that, check the condition of the fuel hose, see if it’s old and cracked looking or breaking down inside the hose.
 
That’s what I did, I just hooked the hose from the outboard tank to the barb on the fuel filter. Just make sure to add a shut off valve if you choose to do this so you can shut off the fuel flow in case of leaks; don’t want fuel in the bilge even in an outboard boat….
 
Okay did some looking around and found well nothing lol.

I unhooked a bunch of fuel lines. The line I installed 7 or 8 yrs ago was shields 368. It honestly still looks like it's in pretty great shape. No obvious flat spots, fuel flows through without hestitation etc. I bought new 368 from amazon but can't decide if I want to install it or not.

I found a 6 gallon tank, I will run it on that the next time I can get it to the water for a trial and error.

The only thing in the fuel system that I have yet to touch is the low pressure fuel pump. I kinda heard they never really went bad. I'm assuming if there was a problem with it there wld'nt be any fuel priming after I replaced the onboard fuel filter.

What about fuel injectors? Is there a possibility some crud clogged in a a fuel injector could cause an issue like this?
 
The injectors are certainly a possibility, there’s usually a shop near you that can clean them if you bring them in. I’ve found people with the injector machines via Facebook too. There’s also the at home carb cleaner method you can find on YouTube.

Have you also tried having someone pump the bulb while you try and accelerate?

Also try unplugging the fuel pressure regulator vacuum hose (cap it off) and see if that changes your symptoms. If there’s fuel in that regulator it’s bad too.

The next step might be to have someone scan it or data log it with you.
 
nanserbe said:
The injectors are certainly a possibility, there’s usually a shop near you that can clean them if you bring them in. I’ve found people with the injector machines via Facebook too. There’s also the at home carb cleaner method you can find on YouTube.

Have you also tried having someone pump the bulb while you try and accelerate?

Also try unplugging the fuel pressure regulator vacuum hose (cap it off) and see if that changes your symptoms. If there’s fuel in that regulator it’s bad too.

The next step might be to have someone scan it or data log it with you.
Click to expand...

Yah there's a guy in Naples I've used before for injectors. I may just mail them to him. I'm just not sure they really need it or are the issue. LOL But whats another $100 thrown at it :D

I've only been solo the last few times out so I didn't have someone to pump unfort. But the next time I will make sure I have someone to try that.

I will investigate that fuel pressure regulator

Yeah I really wish it was easy to scan like a car
 
You run it on a hand tank of a belly tank? I've had the fuel pickup hose inside my maintenance hand tank spilt and cause similar issues you describe.
Try a new hand tank. its definitely not the VTEC airbox diaphragm, that kicks in at over 4000 rpm and just provides different airflow not fuel.
 
HonDan said:
You run it on a hand tank of a belly tank? I've had the fuel pickup hose inside my maintenance hand tank spilt and cause similar issues you describe.
Try a new hand tank. its definitely not the VTEC airbox diaphragm, that kicks in at over 4000 rpm and just provides different airflow not fuel.
Click to expand...

Yeah I have plans to run it on an external tank. Just haven't had a chance yet.

I wanted to take out the pickup hose. But I'm not 100% sure that it actually unscrews and def don't want to break it. But I'm guessing it has to unscrew, otherwise it wld have to be welded into the tank permanently and that seems not very smart
 
Most screw in but there are some that just push in and are sealed with an O ring. Post a pic of what you have…
 
I downloaded it and magnified it, you might be right, that looks like it's welded in! I would guess (but I could be wrong) that if they did that, the tube doesn't have a screen at the end of it, or at least I would hope the builder had the sense make it that way if they were permenantly installing it. The only other thing you can do, is to carefully try to remove the barb and make sure it's open, clean and also see if you can blow into the tank (careful, no sparks etc) to make sure the tube isn't blocked.
BUT that's all getting ahead of where you are. First do the outboard tank test, if it runs like it should, then you're back to that, if it doesn't, then the pick up tube & barb aren't your problem. Due to the trouble you can have with removing these things, I would advise making 100% sure that you actually have to deal with that to solve the problem!
 
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