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I need some serious help. I fightered my 2001 Yamaha YZF 600r. I ran the bike for a while without filtering the big air holes in the frame. I also took the exhaust off and ran without that for a few days. (that was like 2 weeks ago) Ive since put the exhuast back on and made filters for the air holes in the frame. But the bike is missfiring like crazy. It started off just miss firing in 5th gear. Now it is doing it in third and fourth gear. It idles fine. ANd first and second gear it runs perfect. But when I get to third and give it gas it does not want to respond. I may have did something to it but not sure. Does anyone have any idea what could be wrong. i'm thinking maybe spark plugs or it may need a retuning but I dont' know?
 

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GURU of da poo poo
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If you changed up your exhaust there's a good chance you'll need to re-jet to compensate.
 

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Discussion Starter #3
Thanks, I did put the original exhaust back on. Do you think I would still need to rejet?
 

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hi m8,i have a yzf 600 ive done up & can tell u that the holes you refer too are not filtered anyway,your filtering is all inside the airbox.those pipes pressurise the airbox which may be your problem(airbox not pressuring yet carbs are set for it),although if yo have put extra filters over those holes in the frame that could put the carb set up out.
i would: retrace my steps 1 by 1 back to when it was running good whilst checking i havent/didnt knock off anything etc
ps you notice faults more under load/strain thats why not so noticable in 1 & 2 i would say
(prop not noticable at all in neutral reving it?)
im no expert so stand to be corrected but hope this helps.
ps mine is still running like shite grrrrrrrr
 

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I've brought a CBR600 FM 1991 from my nephew who never had it running right. But the similarities of your fault on your bike is 95% the same as mine. First, second gear are fine but when I get to 55-60 mph it then is affected by it's fault. but if I nail it from the off and stay hard on it I can get to 100 mph but as soon as I let the power off it will never pick up until I drop to 60 mph.

My nephew got the bike cheap with the plastics missing, and never really used it. He knackered the air box by drilling holes in it, so I went one stage further and cut the top off the air box which made no change, I've rebuilt the carburettors twice and used a hole tin of carburetor cleaner though it. also taken the K&N air filter off and fitted original the exhaust is baffled and the jetting seems standard. New inlet rubbers. All to no positive out come.

I'm going to get a replacement air box with air snorkels fitted. I'm thinking it might be air flow related.

Post up your results if you get to the bottom of the fault.

Thanks Dave
 

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hi m8,i have a yzf 600 ive done up & can tell u that the holes you refer too are not filtered anyway,your filtering is all inside the airbox.those pipes pressurise the airbox which may be your problem(airbox not pressuring yet carbs are set for it),although if yo have put extra filters over those holes in the frame that could put the carb set up out.
i would: retrace my steps 1 by 1 back to when it was running good whilst checking i havent/didnt knock off anything etc
ps you notice faults more under load/strain thats why not so noticable in 1 & 2 i would say
(prop not noticable at all in neutral reving it?)
im no expert so stand to be corrected but hope this helps.
ps mine is still running like shite grrrrrrrr
+1, unblock the air holes.
 
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