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so i changed my spark plugs yesterday and...


mrmako777

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i noticed that when i took my airbox off, i have gas blow by on the #4 stack inside the airbox. all my plugs looked good for normal wear except #4 is running rich (timing chain is on the left side?, so the #4 cylinder is where the blow by is coming from). i am running a pc3. what is the problem here? i dont understand why one cyclinder would be running richer than the other 3. is this something i need to address right now or is it not that big of a deal?

Edited by mrmako777
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Im pretty sure my PC has a cylinder balance setting that lets you adjust individal cylinders yours is prolly the same should be able to lean out #4

are you running a pc5? pretty sure the pc3 does not allow each cylinder to be mapped individually

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the real question is, do you know what you are looking at.

the cams go all the way across the engine. they are not on one side.

this is also why I'm so against people just buying a pc and have no idea how to use it. you can't just slap one in and load a map into it and call it good.

you need to get on a dyno and tune it for your bike. no 2 bikes are exactly the same, so using someone elses map is a waste of time and could potentially cause problems..such as yours.

Edited by serpentracer
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the real question is, do you know what you are looking at.

the cams go all the way across the engine. they are not on one side.

yes i do realize what im looking at and i realize the cams go across the motor. what i was referring to when i said the left side was the timing chain as a starting point as to which to label the cylinders in succession, 1-4. i misstated that, my fault :cool:

this is also why I'm so against people just buying a pc and have no idea how to use it. you can't just slap one in and load a map into it and call it good.

you need to get on a dyno and tune it for your bike. no 2 bikes are exactly the same, so using someone elses map is a waste of time and could potentially cause problems..such as yours.

yes im also aware of the need to have it tuned. a generic map, while not preferable, will allow me the leisure of time until i can have the bike dynoed and tuned accordingly. this thread also is not about me putting a pc on or a specific question about one. its about me trying to figure out why one cylinder is getting more gas than the others. it may or may not have anything to do with the pc. thanks for your input tho

Edited by mrmako777
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Back to basics. Blow by into the intake would be possibly:

A. intake valve leaking on the compression stroke

B. exhaust valve not opening or exhaust restriction on the exhaust stroke

C. cylinder not firing allowing fuel/air mix to blow everywhere when the valves open.

D. fuel injection timing very wrong on that cylinder

E. vacuum leak in or around the #4, between valve and injector.

I'll take A or E, that's my guess. Question is the blow-by carbon or fuel.

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Back to basics. Blow by into the intake would be possibly:

A. intake valve leaking on the compression stroke

B. exhaust valve not opening or exhaust restriction on the exhaust stroke

C. cylinder not firing allowing fuel/air mix to blow everywhere when the valves open.

D. fuel injection timing very wrong on that cylinder

E. vacuum leak in or around the #4, between valve and injector.

I'll take A or E, that's my guess. Question is the blow-by carbon or fuel.

thanks recon for some plausible theories. im goin to talk them over with my mechanic neighbor and see what he thinks and what we should do about it. as far as the blow-by, its most certainly gas. the weird thing is tho its like a gummy gas like its been sitting there for awhile. the first time i noticed it i thought it was oil but according to my neighbor, its fuel

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Now I'm also wondering if a bad injector signal or bad (leaky) injector might be putting excess fuel in there. I remember that now from aircraft and car injector trouble shooting charts.

Edited by ReconRat
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Now I'm also wondering if a bad injector signal or bad injector might be putting excess fuel in there. I remember that now from aircraft and car injector trouble shooting charts.

i talked over your theories with him and it seems like the most plausible one may be the exhaust valve. i have no loss of power from the motor and now that i have new plugs in, she feels like shes running a bit smoother. my initial thoughts were a bad plug or the secondary to that cylinder was spraying too much fuel, which sounds along the lines of your last post. im hoping that it was the plug, but somehow i feel i will have to revisit the injector theory

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If an exhaust valve or exhaust restriction or even a proper combustion problem exists, the temperature on that pipe should be lower. Enough to notice, I would think. At least when it's warming up, that pipe would do so slower.

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