V8 250 Stumbles on cold start

[Dav0957]

2021 Pro xs 250
2B786374

Currently 250Hrs

Over the past year the start up crispness has declined I've changed plugs with properly gapped factory plugs. Known good fuel. Brand new XS cranking battery. When the engine is cold it seems to stumble to start up no longer has that crisp fire up. Once warm its better but still not like it was the first year of ownership. Also has smoke randomly on hot start up doesn't matter if it's been trimmed up or not. The oil level is correct with the FAQ section on here. Sounds almost like a miss then starts very quietly. Runs great plenty of power no missing or stumbling after that.

I have ran mercury fuel additives almost every tank since new as well.

Any Ideas?

[Dav0957]

I have been told its fuel vapor and to key on for 15 seconds then key off followed by starting?

Haven't tried it but seems odd to need to do this.

[Capt James]

How are your fuel filters and fuel connections? I would start there.

[Dav0957]

Filters are new connections are tight and leak free

[EuropeanAM]

Check the idle relief muffler boot inside the PORT side lower cowling. It may be dislodged from the muffler.

[Dav0957]

I removed cowlings and inspected all boots nothing was out of place. Id also imagine if it was it would affect every start not just the first start of the day.

[haus9393]

How does the turning the key for 15 seconds method work for you?

[Dav0957]

Im gonna give it a try tomorrow. Ill let you know

[EuropeanAM]

How does the turning the key for 15 seconds method work for you?

Please explain what you mean (and how it would benefit a Smart-Start engine).

[Dav0957]

He is talking about keying the engine on and letting the fuel pump run then returning to off before starting. Multiply People have these same symptoms and this seems to be the only way to get a normal start up. I'm going to see if it changes my cold start tonight. Im assuming its purging the "fuel vapor" that they claim is causing the start up hiccup.

[EuropeanAM]

That is definitely a possibility- especially if fuel being used is from a previous-season blend. Of course- the stuff we're getting in the summer here will just about evaporate in a sealed 5 gallon jug. I actually have an RVP test kit... won't even waste my time on summer blends anymore.

[Dav0957]

The fuel is fresh. Boat never sits more than 5 days at a time. I did try the key on for 15 seconds key off then start. It started and sounded just like it supposed to. Now the question is why. It was designed to do this so there has to be a root cause.

[mactlman]

The fuel is fresh. Boat never sits more than 5 days at a time. I did try the key on for 15 seconds key off then start. It started and sounded just like it supposed to. Now the question is why. It was designed to do this so there has to be a root cause.

might be a hot soak issues and the key on will run the fuel pump for a few seconds and move some hot fuel out and cooler fuel into the rail??

[Dav0957]

Hot soak? It does this on the first start of the day only.

[Pulsare2020]

might be a hot soak issues and the key on will run the fuel pump for a few seconds and move some hot fuel out and cooler fuel into the rail??

Maybe but it sounds like it is worse on cold starts? Perhaps you need to have a fuel pressure gauge connected and do the cold start the normal way and observe how long it takes to build fuel pressure and maintain it, and then check it again on a cold start by cycling the fuel pump before you try to start it and see if there are any differences and how it compares to spec?

[EuropeanAM]

The fuel is fresh. Boat never sits more than 5 days at a time. I did try the key on for 15 seconds key off then start. It started and sounded just like it supposed to. Now the question is why. It was designed to do this so there has to be a root cause.

Agree that pressure readings would be useful.

I do have another question related to your fuel: Do you commonly purchase your fuel from the SAME station, most of the time? What brand/grade?

IF you commonly purchase from one particular station, you might try a tank of fuel from a totally different brand/station (see FAQ section for fuel selection suggestions).

[Dav0957]

I purchase gas all over the state of VA and NC as I seem to travel a bit for tournaments. Always choose a busy Gas station and a full tank never seems to last more than 1-2 days of fishing. So it constantly sees fresh fuel along with quickleen. Brand changes depending on availability always 87 octane. My local dealers says its water not filling the exhaust belly. I didnt really understand what he was saying but he said to run it as it has no issue and doesn't seem to be willing to dig any further into it.

[EuropeanAM]

I'm with you on that because "water not filling the exhaust belly" is something I'm not following either.