250 Pro XS back firing?

[Champlainbassman]

Engine 2018 250 Pro XS 2 Stroke
serial number 2B532093


Recently had an issue with what I thought my pro xs was doing. Sounded like it was back firing. Here’s the story just wondering what are some thoughts. I ran through
some extremely shallow water and churned up some sand I believe and after I got out of the skinny stuff I ran 20
miles no problem. The next day I ran 70 miles no problem. I got up to make a move and all of the sudden while running my motor would cut out and make a loud over revving sound while my rpms hiked way up then it would correct itself and then periodically happen every 2 minutes. This happened about 10 times and I believe it was due to running in the shallow stuff the day before but I have a hard time believing after running around for 70 miles it didn’t act up prior to. After this happening 10 times or so I ran about 70 miles back to the ramp and it never happened again while we ran back. Has anyone ever had anything like this happen? It seemed like it might have been close to blowing up or something but now appears to be running fine. Is it possible that the skinny water did this or is it a coincidence that this happened and there may be a larger issue? Any insight would be much appreciated! Thanks guys

[OldTimer57]

Your description sounds confused "cut out and make an over-revving sound..." Can't do both. I had a family member that had something similar years ago. Turned out to be a couple of broken teeth on the main forward gear, and a broken tooth on the pinion gear. He was hearing a loud tick-tick-tick that varied based on RPM. And at the right speed/load it would rev-up for a fraction of a second then sort of slam back into gear and go again. Can't say that is your problem, but it certainly sounds like a gear case problem. Backfiring will almost always blow reeds out as they are not made to deal with that kind of pressure. Hard to get a direct injection motor to backfire, thank goodness. You ought to pull the drain plug and see what it looks like. And big chips of metal and the L/U needs to come apart. I'd almost bet that is where your problem lies... Other possibilities include driveshaft splines but I'd think they would wear out once they slipped, rather than slipping and then re-catching.

Good luck with it.

[Savage]

Any alarms?

[Mon Mariner]

My Standard answer: Check the Tracker Valve, then check everything else.

[Champlainbassman]

Thanks guys. No alarms. The other thing is it happened in an area of pea soup colored water. Not sure that matters or not

[EuropeanAM]

Almost makes me wonder if you were in some type of vegetation that got into the prop (or shallow enough water that it caused ventilation).

[haus9393]

DON PLEASE READ MY COMMENT AS IT HAS MORE DESCRIPTION AS TO WHAT WAS HAPPENING!!!!!


I was in the boat with Champlainbassman as it was a team event. The motor was running perfectly fine as normal. We made about a 10 mile run. Towards the end of the run he was going about 50mph when I heard a loud “pop”. I thought he had hit a log as it made a very similar sound to when you crack a underwater log at that speed. He said it was not a log. I was watching the motor as he slowed down it made the pop noise again and it began to somewhat “chug” almost like when it’s running out of fuel. (I had a fuel rail diaphragm go out on my pro xs last year and it was a minor version of the sound that makes). As we came off plane he shut down and we trimmed up. Everything looked ok with the lower unit. We fished and then took off running again. When he started the motor it was ok sounding until he hit the gas to take off. The motor made the pop noise again and he let off the gas. The pop noise is extremely similar to a back fire. Now we got back on plane and started running again. Once he reached 50 mph it back fired again but it also sounds like the motor is Reving as if the hub is spun on the prop and this all occurs at the exact same time. He let off throttle and ran about 35mph and 3k rpm via a smartcraft sc1000. I said watch your rpm and see if the Rpms rapidly increase when it back fires. Immediately after it back fired again and the rpms instantly jumped to 3900 and back to 3000 again. We shut down and the motor started “chugging” again. After this we fished a spot and took off to run 70 miles back to the ramp. The rest of the day the motor did not act up a single time. I can verify I heard the back fire sound 8-10 times over a 5 minute period and 3-4 mile run. I suspected the motor might be flooded out and misfiring on a cylinder. The motor did not throw any codes which is amazing to me. He said he has full range of rpms. The plugs have never been changed and it has about 300 hours on it so that needs to be done ASAP.

One thing that I said might be contributing to this issue was the fact that during the day he was starting the motor and as soon as it was started he would instantly jump on plane. Like turn the key and put it in gear within 1-2 seconds and punch the hot foot wide open. Almost like the smart craft was still showing the amount of hours on the motor and we were already on plane. He said he does it all the time but this was extremely fast. I know I always wait at least 10-20 seconds before hitting the hot foot on my engine to verify it’s at 120 degrees. I was thinking even though these motors are extremely smart, that during this time it could be dumping an excessive amount of gas during this time causing a rich condition and misfires. Maybe not and maybe it’s just a coincidence either way it’s not good practice at all. I’ve heard efi mercury motors running for the last 12 years (which is not long) and personally listened to my pro xs for 800 hours and have never heard a noise like what was coming from this motor. I’ve had my arctic cat snowmobile which is efi foul plugs and make a similar sound as it was misfiring.

[EuropeanAM]

Strange to say the least. I'd get this in and have it checked (prop, hub, gearcase, etc). Can't say I've ever heard of a description exactly like this one!

[billspence]

DON PLEASE READ MY COMMENT AS IT HAS MORE DESCRIPTION AS TO WHAT WAS HAPPENING!!!!!


I was in the boat with Champlainbassman

Problem identified.

[haus9393]

Problem identified.

Hahaha always.

[haus9393]

I wanted to update this thread since Champlain bass man hasn’t. He pulled the prop and found the hub was spun. All 4 of the black strips on the flo torq ll hub were falling off. The sounds we heard must have been result of the prop slipping and the motor over spinning.

[Savage]

I have yet to see a "Racing Hub" be "spun" because the snubber strips came unglued.....Better look elsewhere.

[haus9393]

I have yet to see a "Racing Hub" be "spun" because the snubber strips came unglued.....Better look elsewhere.

Thanks I’ll let him know that it may not be 100% resolved yet. I haven’t heard of anyone spinning these as well but supposedly it does happen when hitting objects to keep the prop shaft from bending or breaking.

[JOE54]

I have yet to see a "Racing Hub" be "spun" because the snubber strips came unglued.....Better look elsewhere.

+ another motha, cant remember last time I had um in mine, think they are rated over 1000 HP

[haus9393]

He dragged it through the sand running wide open

[EuropeanAM]

Those "strips" are a rattle-absorption device. The part that might "spin" is a small layer of material that is only visible from the GEARCASE end of the prop. If unsure, PAINT a mark on the center (splined) hub, and the outer (square) portion, aligned with each other.

Run engine... and recheck. The marks will "move" if the hub is spinning.