Surging Yamaha engine

[Tomc]

Hey All…
I have a Yamaha 115 VMax, on a 2019 Bennington. Loved the engine until I just dropped it in the water and coming home the engine was running a bit rough, and accelerating and decelerating on its own. I was scared to death as I brought it into my hoist, but it was relatively calm and I took a shot from about 30 feet out and was close enough to get er in.

Dealer where I bought it and have it serviced believed it was a kinked gas line, but I found none. Then they thought air in the line that needed to be purged, so I ran it (idle) for an hour and a half, and that did not help. They can’t come on site anytime soon, and the earliest they can see it with me bringing it in is 3rd week of June. So I want to check whatever else, and/or find an alternative place to get service.

Any suggestions from you-all on what else I can do and look for would be appreciated.

Thanks!

 

[Remediation]

By any chance is it old gasoline. That can make an engine run badly.

 

[Tomc]

By any chance is it old gasoline. That can make an engine run badly.

Gasoline from last days last year with stabilizer. My same routine each year. It should have been good.

 

[Pbakk]

Maybe bad spark plugs? On my Yamaha 115, it would surge and then fall back like it was cutting in and out. Changed spark plugs, added can of Sea Foam hoping it would help if an injector issue, and it worked. Not sure if one or both was needed, but cheap first try.

 

[fitz73222]

Surging is typically caused by fuel restriction either from plugged fuel filters or a fuel tank venting issue. Try running with the fuel fill cap removed to see if it's not venting correctly if it still surges replace your water separating fuel filter in the boat and the small fuel filter in the engine. That should fix it if it's a restriction issue.

 

[Tomc]

Surging is typically caused by fuel restriction either from plugged fuel filters or a fuel tank venting issue. Try running with the fuel fill cap removed to see if it's not venting correctly if it still surges replace your water separating fuel filter in the boat and the small fuel filter in the engine. That should fix it if it's a restriction issue.

Thanks for that. I did add some seafoam with a couple gallons of gas before the hour and a half running. I might try the spark plugs next. Thanks.

 

[Tomc]

Surging is typically caused by fuel restriction either from plugged fuel filters or a fuel tank venting issue. Try running with the fuel fill cap removed to see if it's not venting correctly if it still surges replace your water separating fuel filter in the boat and the small fuel filter in the engine. That should fix it if it's a restriction issue.

Thanks. I’ll run it with cap off. The other suggestions, I’m not quite confident in my ability not to screw things up, but I can probably phone a friend. Thanks!

 

[Tomc]

So I did replace the water separator fuel filter. That one looked like changing like oil filter, which it was, so easy enough. No difference. I did take the boat out again, and no surge, but it would not go over 4500 RPM. It got to 4500 RPM quick enough (about a third of the full distance of the throttle), but push it the rest of the way resulted in no change.

 

[Julianna]

If it's no longer surging and won't go over 4500, check your prop. The same thing happened to me with my other boat. I took it to the dealer and they did everything possible but never checked the prop. Once I had the correct one on, the boat flew like it should have.

 

[Tomc]

Thanks for the suggestion. I’ll check that out.

 

[Potomacbassin’]

Fuel issue. Lots of things that can cause this, most of the advice out there is to run the engine on a separate/portable tank so you can isolate if this is a fuel tank issue (bad fuel, fuel tank vent issue, crud in the pickup, fuel filter, etc) or if it's at the engine itself. You can cut your troubleshooting in half at that point.

Also another tell tale is looking at the fuel primer bulb, if it's sucked flat when surging that can indicate a tank issue as well. If troubleshooting the engine you have a few filters on your OB that should be checked as well as your lo/hi pressure pumps. These kinds of issues can be frustrating so either use a trusted and experienced mechanic or check a few of the more popular boating sites and do a search, lots of good info out there for DIY types.

 

[Tomc]

Thanks for this. I didn’t think about trying a separate fuel source. Way too much common sense for me!! Filters are good, I did take it out again with no surge, but limited RPM and an odd noise. Prop looks fine. I do have a mechanic friend coming over, as changing the filters and other checks were where my comfort level ended (well, a separate fuel source is something I’d try, but at this point, I’ll wait for the expert….also wanted to have him check other possibilities before changing spark plugs). Still not great boating weather here so not a big deal for us.