Crownline 202 BR backfires / pops through the carb, sometimes boat also smells of gas

[ibrw1]

Mercruser 1999 5.0L 2bbl Thunderbolt-5 engine serial #L345059 Crownline 202 BR
2 problems

Hi, I have a strong gas smell when I remove the boat cover. Issue just started. I've checked the gas lines from the tank to the electric fuel pump and all the way up to the carburetor. My gas tank is in its own compartment in the boat. I ran a 3/8" poly flow tube through the wall and down into the bottom of the fuel tank compartment. Applied a vacuum, had everyone sniff the of the air being pumped out. Imagine a pump used to inflate/deflate air mattress with a tube connected to it. Anyway, No gas smell at all. I don't see gas in bilge either.

I watched pressurized gas lines when underway. No drips, no wet spots no loose clamps, No smell of gas.

Parked boat, put cover, next day, removed cover, gas smell is back.

a) it's gas smell
b) it's strong

Problem 2, tied to problem 1????

Only after 30 plus minutes with 10+ people in boat, cruising along at 40 plus mph, engine stalls for 1/2 second. As if someone shut key off and right back on. Every 10 to 20 seconds, same thing. I slow to an idle for 10 minutes or so, problem disappears. I speed back up, after 20 plus minutes, issue returns.

Note, both issues started same day. I have 40 gallon gas tank. Had 16 gallons remaining when issue started. I have a fuel minder.

Ideas?

 

[Bondo]

Ideas?

Ayuh,.... Plugged tank vent,..??..??

 

[Scott Danforth]

Vent would be my first thought, bad float second

 

[cpubud]

same thing I was thinking plugged vent

 

[Watermann]

Gas smell under the boat cover is normally from the cover being over the fuel tank vent hull fitting. Daytime heating of the fuel causes fumes to come out and since is has nowhere to go it stays inside the cover.

So did the boat motor ever act up before when it wasn't maxed out on people?

 

[ibrw1]

Boat never acted up before. It's an older boat but I only run 2 to 3 tanks of gas through it a year. I was told by Mercruiser mechanic "Never ever adjust timing" so I don't even look at it. Special Timing and so forth. Thanks

 

[keith2k455]

Another one for the vent thought, but honestly I leave the cover open over 1 quarter of my boat in my heated garage because I think the smell is too much. By chance, what do the plugs look like....Specifically while this event occurs? 40 mph with 10 ppl....are you running wot here or what rpm? Might be running a tad rich or timing may be barely off so you only notice it when running it this hard.

 

[ibrw1]

First I want to thank everyone for all their helpful comments!!!!!!!!!!
Going to pull plugs tomorrow night. Plugs were new as of last fall. Also, going to check vent to see if plugged. My distributer cap, rotor and plugs are new as well as K&N marine air filter.

Anyway to answer some questions. Was at 7/8 throttle with rpm around 4500. The oil I use is as recommended but the gas, the gas is cheap stuff from local land lock shell station. How important is the good stuff? I know the 10% alcohol is low per unit vol btu. Would love to hear comments on that.

 

[Watermann]

Put fuel in your tank and you'll know if the vent is plugged, it will take forever and burp back up through the filler.You can also watch the mirage waves of fumes boil out of the vent while fueling.

So how do you like that K&N? I've seen them but the cost is crazy!

 

[ibrw1]

No Title

I got it because the thought of using a air strainer vs a air filter seemed unusual, anyway, they last forever and the carburetor looks clean as the day I got it. Most of my family has the K&N on their boats, never hear regret. Thanks again for all of your help..

 

[ibrw1]

Another one for the vent thought, but honestly I leave the cover open over 1 quarter of my boat in my heated garage because I think the smell is too much. By chance, what do the plugs look like....Specifically while this event occurs? 40 mph with 10 ppl....are you running wot here or what rpm? Might be running a tad rich or timing may be barely off so you only notice it when running it this hard.

Occurs with lots of people, going fast, over time.4500 RPM 7/8s of WOT
Will pull Plugs tonight, they are new so if rich then obvious.

 

[ibrw1]

Ayuh,.... Plugged tank vent,..??..??

Pretty sure on plugged vent. Gas blasts everywhere when full, gushes out. THANKS

 

[ibrw1]

Vent would be my first thought, bad float second

Thanks lots, I'm pretty darn sure of it now. Thanks

 

[ibrw1]

same thing I was thinking plugged vent

THANKS

 

[jkust]

Guys...where is the vent that you are all talking about?..reading about this it's donning on me I have the same issue with fuel blasting out suddenly while filling the tank plus the gas smell but the boat sits on a lift under a canopy.

 

[thedinz]

Guys...where is the vent that you are all talking about?..reading about this it's donning on me I have the same issue with fuel blasting out suddenly while filling the tank plus the gas smell but the boat sits on a lift under a canopy.

My outlet is the right rear of my boat, looks like a bilge outlet. This runs down into engine compartment and enters into gas tank along side the gas line running to the engine.

 

[ibrw1]

My Rinker was port side bow
My Crownline is port side stern. I have 1/2" or so hose that follows fill hose to / from tank to fill fitting

 

[Watermann]

My Rinker was port side bow
My Crownline is port side stern. I have 1/2" or so hose that follows fill hose to / from tank to fill fitting

Marine vent line is 5/8" but some boats don't have separate vent fittings, they have a vent incorporated into the filler neck.

 

[ibrw1]

No Title

Here is a picture of my vent. I removed it and applied a vacuum, it was clogged, I applied a pressure, now its not clogged. THANKS EVERYONE!

 

[ibrw1]

Ayuh,.... Plugged tank vent,..??..??

Vent WAS clogged! THANKS arrrrrrrrr