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Can a muffler plug blow a top end?

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Alright guys,  First off I'd like to say that i am new to posting but not new to TT as i read it all the time at work.  Anyhow,  Recently i left my muffler plug in my 2008 YZ250 after washing it, and when i took it out riding the other day i forgot that it was left in and kicked the bike about 10 times until realizing that i left it in.  Since then the bike has been acting really weird.  After starting it for the first time since the muffler plug was taken out it felt very sluggish and the throttle response was so horrible it made me not want to ride.  I shut it off after about 2-3 minuets of it running.  I put it back in my garage and went on vacation figuring that i would deal with it when i came back.  I decided to kick it after a week after being gone and it started right up and ran great like it usually did.  So i went to the track the next day and it wouldn't start no matter how many times i kicked it.  I even tried to bump start it and that failed.  But i did notice that while trying to bump start it, with it in first gear it was extremely hard to push. (yes the clutch was held in all the way...).  Sometimes it will turn over for a few seconds and then it red-lines itself for a brief second with no throttle given and then shuts off.

 

Anyways, my thoughts is that maybe a gasket was blown when kicking it with the muffler plug in?  Or does anybody else have any ideas or opinions on this would be much appreciated!  I am going to tear it down and do a new top end rebuild and hoping that it solves the problem.  I didn't know that a little 6 dollar muffler plug could cause so much trouble.

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Shouldn't hurt anything. I forgot and left the butt plug in my '03 more than once. Bike would actually start and run for a second or 2 with it in, never had a problem afterwards. Have did the same thing on my KDX, no problems there either.

Have you checked/changed the plug? Also may need to clean the carburetor good if it's been setting quite a bit. And yes, it's going to be hard to push in first gear due to common clutch drag. Usually roll start them in second or third gear.

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i left mine in for a good wile on a 2 smoker. it blew out once i cracked on the throttle to try to pull a wheelie.

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Maybe the washing was the cause and the plug is coincidental. Some symptoms sound like maybe water in the gas. Red lining sounds different, though, like you are going way lean. Might be better off draining the bowl and tank and trying with new gas. Cleaning the carb would be the next step. That plug did no harm at all.

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Dude, it's a smoker.  Start with the easy stuff.  Replace the spark pug. Put in fresh gas. Clean the air filter.  It will run.  If you don't want to mess with it, I'll give you $500 cash!

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I regularly leave my plug in on my 04 yz250, and it has a shitty seal on where the expansion chamber meets the muffler, so when I start it with the plug in it one of two things happen: #1, if I just sat the plug in, and the bike starts first kick, the plug flies out into my garage(what better way to put it away) or #2, if I have really pushed it in there to wash the bike, it will hiss out the gap for a few seconds before stalling and not starting until the plug is out :), it'l be a problem somewhere else, like rpt50 said, start with a new plug, they are like 5 bucks each! air filter may also be blocking high air flow, starving the engine OR your gas could be too old, if it is full synthetic like mine it only lasts about a month, also leave it for a while before trying to start it again(overnight) as I am assuming like my yz, it has no drainage screw in the carby, very frustrating!!!

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Sounds like your having carb issues, you need to take it apart and look everything over and clean it up while your at it. That would explain the shitty throttle response, and your slide is probably stuck open causing it to be hard to start and running at wide open throttle when it does start.

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Knock on wood, leaving the plug in mine didn't seem to hurt it any. I kicked and kicked, even used the electric starter, until I realized the damn thing was still in. Felt like a newbie. :banghead:

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I've done this also, and it blew a reed. I had a boyesen rad valve with 3 stage reeds. The first stage is very thin and a hairline crack formed from the back pressure.

Boyesen did warranty the reeds, as they said they had never seen them break that way before. Great product, better company.

Edited by GMO397
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Shouldn't hurt anything. I forgot and left the butt plug in my '03 more than once. Bike would actually start and run for a second or 2 with it in, never had a problem afterwards. Have did the same thing on my KDX, no problems there either.

Have you checked/changed the plug? Also may need to clean the carburetor good if it's been setting quite a bit. And yes, it's going to be hard to push in first gear due to common clutch drag. Usually roll start them in second or third gear.

 

Same here with my KTM 300, I've forgotten about the muffler plug more than once and it's never caused a problem.

 

Could it be that the OP's top end needed a rebuild anyway??  The plug would cause more backpressure for sure, but not to the extent that it blows the top end--just consider how much stress is put on the piston and motor at 9,000 RPMs, and that doesn't cause problems unless the piston is worn out.

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Sounds like you flooded it the first time around then you let it sit for awhile which probably gunked the carb up, sounds to me like you need to crack that carb open and check your jets and what not make sure they arent clogged

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So i found out that the spark plug was fouled. :banghead:   I kinda feel dumb, but at least my bike is running normal again.  I didnt think it would of been something so simple becasue of the way it was acting.  thanks guys!

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So i found out that the spark plug was fouled. :banghead:   I kinda feel dumb, but at least my bike is running normal again.  I didnt think it would of been something so simple becasue of the way it was acting.  thanks guys!

 

Sometimes its just the simple things, I overlooked it myself and didn't suggest you change the plug. Glad its running for you though!

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