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atf8611

What did I break?

10 posts in this topic

99 WR400..... It has been sitting for a while and i wanted to start it... About a week and a half ago, I went outside and started it on the first kick. ran it for about 2 minutes, and it stalled shortly after i took the choke off. I didnt try to restart it after that. The next day I tried to start it again, but couldnt get it to start after about 10 minutes of trying. Yesterday i went at it again, but with some starting fluid. I sprayed some in the airbox, set the seat on it, and tried to start it... still no go. I then held in the decomp and kicked it through a few times and after about the third time, it backfired very loudly and the air filter cought on fire. I poured some water on it to put it out. fortunatly, the only thing that was hurt was the air filter, nothing else got burnt. my problem is that now there seems to be little compression. there is very noticable resistance, but i can push past tdc with my hand. I can hear air slowly seeping through somewhere although im not sure where. what could have cause my no start, and now my low compression problems? Thanks for any help.

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aft8611

I have the same bike, and early in my ownership i had similar problem and posted it here and was asked the following.

Was the backfire like a rifle shot or shotgun? hissy type backfire or loud percussive blast?

if its a 'rifle' style backfire, change the plug and start again. I'd make sure i clean everything out of airbox. i had a couple of times where i would kick for days and was advised here to just get new plug. worked each time. i now use iridium plug, no probs since.

except after leaving bike for about two or three weeks i found that if the outside temp went up and down a bit it caused condensation in my tank ( at least thats what i think).

try the following ( i know it seems very basic)

drain carb into something you can check fuel for water.

clean airbox of anything flammable

try iridium plug ( about twice cost of normal)

if no go, ask others on here that know what their talking about.

good luck

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aft8611

I have the same bike, and early in my ownership i had similar problem and posted it here and was asked the following.

Was the backfire like a rifle shot or shotgun? hissy type backfire or loud percussive blast?

if its a 'rifle' style backfire, change the plug and start again. I'd make sure i clean everything out of airbox. i had a couple of times where i would kick for days and was advised here to just get new plug. worked each time. i now use iridium plug, no probs since.

except after leaving bike for about two or three weeks i found that if the outside temp went up and down a bit it caused condensation in my tank ( at least thats what i think).

try the following ( i know it seems very basic)

drain carb into something you can check fuel for water.

clean airbox of anything flammable

try iridium plug ( about twice cost of normal)

if no go, ask others on here that know what their talking about.

good luck

It was pretty damn loud. hard to say if it sounded more like a rifle or a shotgun because i was more occupied with the fire....

I almost definatly have water in every part of the intake system now b/c i poured a decent amount into the airbox. I was planning on draining the carb anyway, and a new plug never hurts.

The thing that does concern me is the loss of compression. any idea what that might be? Could a backfire like that screw up the rings, or the valves or somthing?

Thanks for any help!!

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1 other question regarding compression.... is it normal to be able to slowly push through it, or should it be complely air tight?

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1 other question regarding compression.... is it normal to be able to slowly push through it, or should it be complely air tight?

come on, I know someone can at least answer this question.... Thanks!

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come on, I know someone can at least answer this question.... Thanks!

I am no expert but mine is solid as a rock without the compression release pulled, it won't move at all.

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yes my compression is rock solid too, and i am no expert either.

sound like a question for toyota.

have you checked whether the decomp lever is releasing or stuck?

if it's more than that, keep the post fresh for the technos.

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99 WR400..... It has been sitting for a while and i wanted to start it... About a week and a half ago, I went outside and started it on the first kick. ran it for about 2 minutes, and it stalled shortly after i took the choke off. I didnt try to restart it after that. The next day I tried to start it again, but couldnt get it to start after about 10 minutes of trying. Yesterday i went at it again, but with some starting fluid. I sprayed some in the airbox, set the seat on it, and tried to start it... still no go. I then held in the decomp and kicked it through a few times and after about the third time, it backfired very loudly and the air filter cought on fire. I poured some water on it to put it out. fortunatly, the only thing that was hurt was the air filter, nothing else got burnt. my problem is that now there seems to be little compression. there is very noticable resistance, but i can push past tdc with my hand. I can hear air slowly seeping through somewhere although im not sure where. what could have cause my no start, and now my low compression problems? Thanks for any help.

sounds like your spark plug failed to ignition the engine first, and with the fluid it blast!

maybee your spark plug blast/broke, and compression is leaking through their.

if it is broken, be careful to remove all parts away (by blowing compress air through the side hole in the right side of the head)

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sounds like your spark plug failed to ignition the engine first, and with the fluid it blast!

maybee your spark plug blast/broke, and compression is leaking through their.

if it is broken, be careful to remove all parts away (by blowing compress air through the side hole in the right side of the head)

I figured that the compression should be rock solid, because I thought it was before..... I guess I will have to pull the spark plug, and take it from there. now here is another question: What tools do I need to remove the plug without taking off the valve cover?

Thanks for all the info!

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The easiest way to get the spark plug out is to buy the Yamaha tool. It goes right in there and takes care of it. I pulled the gas tank and used a spark plug socket with a small extension and a knuckle extension to get mine out. I also had to cut a few wire ties and spread the wires out to get proper clearance.

You definitely have a compression leak. Without using the decomp. lever, it should be rock solid. Start with changing the plug and see what happens. If it still leaks, update this post and someone will jump on it.

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