Stalling when throttling up too fast

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BuildItOnce

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My wife and I took out our boat yesterday for its maiden voyage (and to do a little fishing). After we got out of the marina I started to throttle up the twin honda 50s to head out toward the fishing grounds. At around 2k RPM on the starboard engine it started to stall and then died. Starts right back up just fine. I kept trying to throttle up and got the same results, so I asked my wife to head back and pump the fuel priming bulb. That seemed to have fixed it and I was able to throttle up to full throttle without stalling.

And then it started its stalling business again. I figured out that if I throttle up to 2k RPM and hover there for 3-4 seconds it seems to catch its breath and will then let me throttle up higher to max RPMs without stalling. Anytime I try throttling up from idle to full throttle quickly (and by quickly, I don't mean slam down to full throttle) the starboard engine will stall. If I bring the RPMs back down when I notice it stalling it'll catch itself and not die. Otherwise I have to restart it again. The stalling problem continued through the 4 or so hours we were out on the water yesterday. I did notice that one time when I was up in the 4k RPMs the tach bounced around a little like it was having trouble maintaining it (not so on the port engine) and at 5k+ it was holding steady. It wasn't bouncing around wildly or anything, but might hold steady for a few seconds or more and then bounce a bit... repeat.

There's never a problem at 2k RPM or below.

I guess I should have had my wife do a little more testing back there with pumping the fuel priming bulb to see if that indeed made the problem go away entirely. It seemed to when I had her pump the bulb the first time.

When we took the boat out for a test drive 3 weeks ago no such problem occurred. Everything was running great and I was able to throttle up and down at any rate without issues.

The port side engine has no issues. Never stalled and behaves normally.

On the bright side we pulled in 2 silvers near Shilshole last night... 4lbs and 10lbs!

Any ideas? Do I have a fuel feed problem? Or do I have a gummed up carb problem? The fuel in the tanks is NOT ethanol free. The previous owner would dump a can of sea foam into each tank every other fill up to keep things going smoothly.
 
Start at the engine fuel filter and and clean all lines and filters back to the filter. Drain the carburetors. Give them a good dose of Sea Foam. Add a double dose conditioner to the gas.
Good luck
 
What year are the motors? carbs or FI?


Several items to check
Check prime rbulb is vertical (up) and connections are tight. Better ones have 2 check valves, Easy to replace with a better one

Check all fuel hose bends. Inner hose can separated esp at sharp bends yet the outer side looks looks great. Usually there is a sharp bend inside the rigging tube going inside the motor and the under cowling fuel filter which is another item to inspect and check for water and debris. Easy to replace, too

replace and inspect filters and look for debris and water

I have an external Racor fuel and water filter with a clear inspection bowl on the filter bottom. Easy to check for water and debris

Check fuel tank vent on hull is clear.

Maybe tank needs cleaning and fuel pickup tube replaced

Fuel pressure on injector rail and can be checked easily with fuel pressure tester and will tell you the pressure going to injectors and how well the high pressure fuel pump is working

I highly recommend buying the factory shop manual.


or locate a good shop to look at it..If carbs, I agree with the other replies. ethanol gas isnt that awful just to burn it quickly and keep it fresh. Yamaha has Ring Free gas additive maybe Honda the same
 
Sounds like a gummed up high speed jet in the carburetor to me. At least worth a shot to look at. We had the BF40s on our first c-dory with the same symptoms on the port side motor. Carl at EQ marine showed us how to get it clear with sea foam.
 
PaulNBriannaLynn":1fpsi986 said:
Sounds like a gummed up high speed jet in the carburetor to me. At least worth a shot to look at. We had the BF40s on our first c-dory with the same symptoms on the port side motor. Carl at EQ marine showed us how to get it clear with sea foam.
Click to expand...

What was the procedure with sea foam? I tried a sea foaming on Friday and it seemed to work. When I initially started it and let it warm up for a few minutes and tried throttling up it was doing the same thing.. stalling at just above 2k RPM if I didn't stop at 2k and let it "catch its breath". So I was at least able to verify the problem was still there, even with the boat on the trailer without pushing a load.

I mixed about 2/3 a gallon of ETHANOL FREE fuel with 2 cans of sea foam and ran that through the motor using a separate primer bulb, fuel line, and fuel tank. I'd say 15 minutes or so of doing this and eventually I was able to throttle up and down at any rate and it wouldn't stall at all. Aha! I thought I had fixed the problem.

I took the boat out into the water the next day... ugh... problem is back. FYI, I siphoned out all of the ethanol laced gas from the tanks and replaced it with ethanol free, along with a can of sea foam in each tank... so it was running new ethanol free + sea foam blend.

The only difference I can think of is the small amount of ethanol fuel in the fuel line + fuel/water separator, along with the primer bulb + fuel line itself... so I am thinking maybe it's the fuel line and primer bulb that's giving me a problem? Or maybe I need to run a high concentration of sea foam through the motor for a longer period? I probably only ran it 15 mins or so... or maybe Carl has a better procedure?
 
Ah the dreaded fuel delivery problem on carb’d Hondas. , I believe your fuel pumps need replacing.

Best way to test it: If a partner pumps the bulb does the engine start running like a champ? Above a certain RPM does the engine keep in chuff? Is it primarily when accelerating from 2k RPM to 4K RPM that the engine chokes and dies?

I had this problem for about six months and tried all kinds of gypsy magic to fix the problem. Seafoam. New gas. Incantations. Carb adjustment.

It turns out the diaphragms on the Honda fuel pumps afe very fragile, and go to pot under the right conditions.

Thankfully this is about the easiest repair you can ask for. 1 hour tops to replace them. Easily accessible. And the parts themselves are inexpensive. $80-100 a piece.

For more details:

https://www.thehulltruth.com/boating-fo ... -pump.html
 
BuildItOnce:

If you send me a PM with your phone and email, we can discuss the problem in more detail, and share anything we learn with the others.

Almas Only
 
The way I do it is similar to you, a heavy concentration into the tank. To clear up an injector problem with the current EFI 90 Honda when we bought the boat, I added a half gallon of seafoam (I buy it in the gallon tin, its cheaper) to one of the tanks, so 20 gallons or so of fuel. After running on that tank for a day the problem was clear.

With the twin 40 Hondass, he straight up poured seafoam down the fuel line, so what went into the carb was basically pure seafoam. It cleared out those jets. Honestly, I never had to do it after that because I religiously used non-ethanol fuel, and always unplugged the fuel lines while idling to burn up the remaining fuel in the carbs, plus draining the float bowls on the carbs if it was gonna sit for more than a day. It became my routine and may seem extreme but for years never had another problem with the twins.
 
Getting in here late but let me talk about what I hear. You are stalling when you throttle up. You replaced the fuel line so you could run fresh fuel and the problem went away. you switched back and the problem came back, right? If that is wrong tell me. You still think you have a fuel problem, you dont, you have a fuel delivery problem. You have a old fuel line or bulb that is allowing air in when you throttle up and increase the suction. try replacing all the fuel line and bulbs first. that is my take. You are chasing the ethanol delusion that is just not as bad as people think it is. After the fuel line i would take the advice above and check the fuel pump..
 
oh and if you are running carbs please do what we have always done with carb motors both 2 and 4 stroke. If you are not going to run the boat with in a week disconnect the fuel line and let the motor run out of fuel when you flush the motor or if in fresh water at the dock. you will have to restart a few times to get it all. if you are not going to run for a few month also drain the fuel bowl. If you do this then ethanol can not harm your motor because their is not ethanol in the motor. I was taught to do this with small out boards when I was young. old fuel is only problem if its in the motor. So use your fuel and then then drain the rest and it can not harm or gum up your motor.
 
one other thing that I do is to add Marvel Mystery Oil. The thing that this does is to provide an "oil" to the gas to both give more lube to the rings, but coats the aluminum parts in the fuel system (carbs) with the oil, which helps inhibit the oxidation of aluminum when the fuel sits in the carb bowls and other parts. I also mostly run non-ethanol fuel and use marine stabil in the gas. I also drain the carb bowls when the motor sits for an extended time, such as over the winter. I started doing this when I noticed that the two strokes with fuel oil mixes did not seem to oxidize the aluminum in the carbs, and showed pretty clean systems compared to the 4 stroke without the oil. I realize that the jets in the 2 strokes were larger also, so jet plugging is less with these motors, but the small kickers still have pretty small openings. All these things help prevent the plugged jets -- something that can destroy a motor if it is running with a lean running cylinder(s) or one that is getting no fuel at all.
 
busski":gcr6jtg2 said:
Ah the dreaded fuel delivery problem on carb’d Hondas. , I believe your fuel pumps need replacing.

Best way to test it: If a partner pumps the bulb does the engine start running like a champ? Above a certain RPM does the engine keep in chuff? Is it primarily when accelerating from 2k RPM to 4K RPM that the engine chokes and dies?

https://www.thehulltruth.com/boating-fo ... -pump.html
Click to expand...

Yeah, it only happens when I start throttling up and it hits about 2.2K ... if I go too fast past 2.2K it chokes and dies... unless I back off the throttle quickly.. then I can catch it and keep it from dying. Once I let it sit at 2.2K for some seconds I can throttle up and normally have no issues. Every once in a while the RPM needle will start bouncing around up high, but usually that doesn't happen. Once beyond 2.2K it normally runs great.

I swapped out the fuel line and primer bulb the other day and took the boat out... it seemed to be behaving a little bit better, but the problem persists... when I got out this weekend I'll do a bunch of testing and have someone pump the bulb continuously while I try to see if I can make the problem happen.... much thanks for the fuel pump suggestion and info... I am thinking this is probably the issue too. If pumping the bulb does the trick then I'll just go ahead and order a pump.. maybe a second to have on hand in case the other motor ever develops the problem.
 
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