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'81 XS400 bike died, motor filled with gas, now what?

Discussion in 'The Garage' started by MGXS400, Aug 2, 2015.

  1. MGXS400

    MGXS400 XS400 Member

    A little background:

    I've had this bike for a little over a year, bought it running on one cylinder and replaced a carb with a broken float tower(?). While I had the carbs torn apart, I rejetted and cleaned to the best of my abilities.

    That was about a year ago and I have been riding the bike ever since. I regularly ride canyons out here in Utah with the occasional 20 minute highway cruise to work. Its always ran pretty well but a couple weeks ago it started running poorly. Its always leaked a little bit of gas around the front sprocket(?).

    I haven't been riding much because we're currently in the process of moving and work has been crazy. The bike has been sitting without being regularly ridden for the last month. Maybe 2 or 3 times in the last month or month and a half.

    Jump to a few days ago:

    Mid move, I went to ride the bike to a friend's house where I will be storing it. It started up fine and I put it into 1st, I got into 2nd, maybe 3rd and the bike just died in the middle of our neighborhood. I hit the electric start button and it sound normal, a little more gritty, not as smooth.

    Today I pulled the carbs, looked at the floats, everything is looking normal. Petcock seems to be holding the gas just fine.

    This is my guess:

    I think as the bike sat, gas must've leaked down into the cylinders and thinned the oil. My leak had gotten pretty significant due to the thin oil and I shouldn't have tried riding it but I was only going 4 blocks no faster than 30mph so I risked it.

    I started it up and then 1 block later, boom, failure. I drained the oil today and there must've been a full motor's worth of gas in there mixed with the oil. I drained it, flushed it a couple times and went to try to get it to turn over with starter fluid and no gas. I didn't want to hook up the tank and refill the motor with gas.

    It's never blown fuses but it blew a couple and I couldn't get the lights or anything to work. I don't know if this is related to the gas in the tank but its a new problem. I couldn't get the bike to turn over but the crank turns freely with the kickstart. It still feels a little gritty but it was better than before. That's where it stands as of today.

    I'm relatively new to motorcycles but I'm pretty confident with motors, tools and bolts. I'm hoping I don't have to tear the heads off and the pull the cylinders/replace piston rings. I'd probably consider paying someone to do that if it's not crazy expensive but we'll see.

    What do you guys think? Where do I look next? Could this be a quick fix or a major problem.
  2. bcware

    bcware Well-read Top Contributor

    First off, the gas in the oil is bad, but if it only ran for a short time you may be fine. I have killed a snowblower engine by thinning the oil with gas (flooding) but it ran for quite a while and eventually started knocking very loudly; then it stopped suddenly and basically blew up.

    It sounds like you're flooding. Your float tower repair may have altered the way the floats work causing the flooding or it may be another problem with the floats.

    The fuses are not likely related in my opinion.

    I don't know what you mean by "boom, failure" does this mean it just shut off or did it make horrible noises?

    Having someone else do the work is out of the question if the motor has internal damage; you could buy 2 or 3 new complete motorcycles with what it would cost; also this sort of incident can easily cause bottom-end damage; if there is an issue it is not likely isolated to the top of the engine.

    You may have just been too rich to run any further, you may have "hydro-locked" the engine with gas, or you may have internal damage (essentially the motor overheats when there is gas in the oil); the overheating due to lack of oil viscosity can damage ANY part of the engine or ALL of the engine.

    If you got lucky, however, you may have minimal or no damage in the case of a short excursion, "hydro-locking," or just being plain too rich (fouling out). These things CAN cause damage (they are not benign), but you may get away without any.

    A lack of horrible noises when the engine died is a good sign. The engine turning over smoothly is a good sign.
    Last edited: Aug 3, 2015
  3. MGXS400

    MGXS400 XS400 Member

    BC, I just meant it was an abrupt failure when I said "boom".

    The float tower was never repaired, I replaced that whole carb so I don't think the floats are the issue. Is there any reason gas would leak into the cylinders with a good petcock and good carbs?

    Thanks for all the information, that should give me somewhere to start. I'm going to work on the electrical issues and then see if I can get the bike running.

    Off note, did you ever surf any Jeep forums? The username sounds familiar.
  4. bcware

    bcware Well-read Top Contributor

    No Jeep forums for me!

    It is possible for carbs to flood with no obvious cause. I have had it happen a few times on motorcycles, snow blowers, etc. After opening the offending carbs there was no apparent cause yet the floats must have become stuck leading to the flooding. I ended up installing manual cut off valves for insurance but I have never had a repeat occurrence. Sometimes it's just a fluke.

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