Alright folks, I've got a very odd but possibly simple motor problem. It's a long one, but bear with me. I have a 23 MB Mini with a Stage 1 from EVT spinning a big blade. For the past couple of years (didn't use it but a couple times last year) it has done the same thing. When I run full throttle, with the gas all the way down, it will run fine until about 5-10 minutes. Then all of a sudden it will die for a split second, skip a beat and keep going. If you remain on full throttle, the skips will become more frequent and it will start losing rpms, eventually dying. However, after it sits a little while, it will crank right up almost like it reset. HOWEVER, If I run 3/4 throttle and never dump it all the way, it doesn't seem to ever do it no matter how long I'm on it. It only does it about 5-10 min in from using full throttle. I have had the carb cleaned, full pumped replaced, gas tank cleaned, fuel lines inspected, etc etc twice since. It still does the same exact thing and only now have I been able to narrow down the sumptoms with the motor only doing it while at full throttle.

My initial guess is that the jets are dumping too much fuel at full throttle and it eventually floods the motor, thus letting it rest lets it get going again. What are yall's thoughts? Thanks for any help in advance.

If you were running rich enough to flood a running engine, you would be rollin' coal with that puppy up and down the river. Are you blowing smoke?

Sounds like fuel starvation. Is the breather on the tank open/working? I would start there. It could be letting enough air in to sustain 3/4 throttle but pulling too much vacuum at WOT and starts starving itself of fuel until you shut it down and it equalizes again.

Change the fuel bulb primer.

I'll grab a bulb and check it out. Does the vent have to be completely opened or do you have to play with it and find a sweet spot?

It doesn't have to be completely open just make sure that it's venting good and not holding any vacuum.

You running fresh water or salt water? Plug boots can cause a similar issue in salt water areas.

All fresh water. Also, if I replace fuel bulb and it continues, what could be some problems with the gas tank? This tank does not have a quick disconnect, just a straight fuel line to a valve/spout on the top of the tank. Is the problem from air getting in or a vacuum? Like where the valve touches the top of the plastic of the tank, if that isn't sealed properly would that effect it? Just trying to get a progression of steps going here. Just trying to see what problems a tank could present and how to service them.

If you don't vent the tank to allow air in, it will eventually pull enough of a vacuum to stop the flow of fuel. Most portable tanks have a bleed nipple on the cap. Open that bleed nipple all the way and make sure you are getting air into it. When you open it you should hear it hiss.

Yeh I've got the vent part. I'm talking about where the hose hits the tank, that fixture, and inside the tank. Does that have to be completely sealed or is it essentially just a fuel line dropped in a tank? Just trying to get more things to check on in case the bulb isn't the issue

It's not sealed for any reason beyond spill/leak prevention.

Gotcha, so the "air leakage" problems people speak of would only include the fuel bulb and any fixtures above the bulb then?

How many times have you ran it with that issue? or was that the first time?

how is your oil level?

do you experience a loss of rpms right before it dies?

I had the exact same thing happen to mine. The main bearing was going out on my PTO side and basically melted into the crank from excessive pressure on the crank. Running wide open, stuttered kept going then stuttered and died. When it cooled off you could get it going again. But this only happened once the next time the seal failed and pissed oil everywhere.

KS, it's done this repeatedly and very consistently over maybe 20-30 uses. Brstanle, I understand what you're saying now. I'll be looking into and will keep yall updated.

There is 1/4 x 7/16 fuel line on it now that was just put on. However, I can only find 3/8 and 5/16 ID fuel primer bulbs. Is this an odd size to have on a Stage 1 23hp? Should I be running larger fuel line?

Alright guys. Replaced the line, bulb, and filter. Problem still exists. When it starts puttering there is still fuel in the filter. Is it still possible to have air leaking in if it's still holding fuel? I did find the fuel line on the carburetor was loose and I tightened it but haven't run it since. I do notice when I pump fuel in, the level in the filter does fall to a point, and a few air bubbles come up through the filter. Thoughts?

That is next on the list. However, tightening up the fuel line on the carb has appeared to stop the bubbles for now. Would the air bubbles coming into the fuel filter indicate which side of the filter was losing the vacuum? Could it be determined if the leak is on the top side or the low side? Also, without any bubbles, the fuel in the filter still drops down to a level it sort of equalizes at. Is this normal or is it supposed to stay at where you pump it to?

I'll stop working on it and test it as soon as I can with the line tightening so I can isolate. If that fails, I'll move to gas tank. Thanks for help so far.

And bryce, I'm unable to tell if I have them while running. I do know when I'm not running and I pump the bulb and I watch it, a few bubbles would come into the filter from the tank end of the fuel line. Just by watching, the size of bubbles and frequency have greatly reduced after tightening that fuel line.

Hope so! There's not a real danger because it's never left me stranded mechanically speaking but it's just aggravating when I'm going through the skinny and can't touch full throttle. It has almost gotten me stuck multiple times by dying down at inopportune locations lol.

If you have a quick connect, Check the quick connection between the hose and the tank...... there is a o ring in there that can cause issues

It goes straight to a nipple that screws into the tank fixture. No quick connect which makes it a pain. Should I have some sort of tape on those threads as well?

Alright guys, sorry it has taken so long to get back. Having been going other places and using different boats. Took the boat out on a hunt today, the problem is not fixed but I do have some new data. So far I have replaced the threaded nipple screwing into the tank fixture, all fuel line up to pump, new bulb, new filter, and have tightened the clamps. The basic non electric fuel pump was replaced back in August. I recently found the fuel line to the carb was pretty loose and thought that was it. Took it out today and same thing happened. About 5 minutes in to full throttle it started skipping again, HOWEVER, I was able to get some more data. When the engine skips and tries to die, there is still fuel in the filter. It isn't completely full, but maybe half or 3/4. Also, I found if I pump the fuel bulb about every 5 seconds, it will run full throttle all day long. However, any time past about 5 seconds and it will start skipping again and dying down. Again, there is still fuel in the filter which would lead me to believe the problem is above the filter? Also I found some oil leaking out of my valve cover gasket. Should be a minor fix and unrelated. Ideas?

Replace the pump, move fuel tank closer, or run an electric pump

I'm having a similar problem but it just started today. I can run 1/2-3/4 throttle but it stutters, increasing as I give it more throttle. I checked my out of water rpms and it looks like I can't break ~3750 rpms. I have a mikuni with a rev limiter that keeps it at 4400-4600 rpms. Is there anyway that the problem could be with the rev limiter in my case? It also seems to not want to idle as smooth either. Any help would be great.


Sent from my iPhone using Tapatalk

Mine idles like a champ and the fuel tank is on a 4-5ft line. The distance shouldn't be a problem. However, the stock fuel pump did work with the mods in previous years. Is it possible that when I got one replaced last year, they put a smaller pump? How would I tell? I'm down for the e-pump but I don't just want to Band-Aid a problem that can resurface later.

These motors run on a very low PSI fuel system and any air in the system will cause issues. The issue you describe is isolated to running full throttle for a while when it starves seems to suggest you have enough pressure to run it but its just on the edge.

Check all your connections at the carb, fuel pump, and fuel filter. To try to eliminate variables, put a gas can at the transom with a short line straight from the fuel filter into the fuel can. If the problem goes away - its somewhere on your supply side. Primer bulbs, fuel pick-up tubes in the tank, adapters and connectors are all common points of loosing pressure in the fuel delivery system- any air bubbles in the filter indicate a leak somewhere.

Alright next question. Since I can't test if it's fixed without taking it out, what are some ways to test at the house? Should there be absolutely zero bubbles? Now, If I pump the bulb and fill the filter, every few seconds a tiny bubble will come from below the filter. Is this normal or is that the indication of the problem? Just need a way to test this at the house so I can go ahead and knock this out. My next culprit to chase down is the gas tank/drop line.

PS What auto parts store would be able to cross reference B&S Numbers to get a valve cover gasket? I hear CARQUEST carries more of that stuff, but I don't have one close. My main small engine store is closed on Sundays and Mondays.

Your problem is at sustained full load WOT- you can't test in the driveway.

Get rid of the primer bulb altogether - test with a short line to a can at the transom

Call BoatDr for gaskets or order them on-line.

Alright, however, before I begin back on the fuel problem, I believe the oil leak is now taking priority. With further investigation I believe the oil is coming out of the breather hose that comes out of the valve cover. I took the valve cover off to check seal and it all looks fine, however when I tightened it back down, I found a very small crack in the valve cover. Does one have to measure a certain tightness when putting the valve cover back on? Once I've taken it off once, does it all have to be readjusted? And past that, where do I need to start looking if its blow out from the breather hose? List of things to start checking to isolate?

This is turning into a nightmare...

Just did some more looking. The oil level looks high according to this dipstick. The guy I had working on it changed the oil back in August but the blowout from the vent hose looks to just now be happening. When I had my mods done a few years ago at EVT, my dipstick was broke and they made a new one with markings made by hand. Is it possible that I should be using much less oil after mods and the guy that changed the oil put in the factory amount?

Nope

If the blowout is from high oil level, shouldn't that have been apparent sooner (It was last changed in August)? And is there anything I need to watch for when putting a new valve cover on?