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Author Topic: Flat spots in high rpms  (Read 1217 times)

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stanghater

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Flat spots in high rpms
« on: May 15, 2005, 09:05:37 pm »
greetings.... so check it out, when i ride my bike(it has no air filter BTW) it screams through 1st gear(unless its cold out) and every once and a while it has a flat spot in 2nd. third is worse and so on. sometimes it will run great up to 80-85. today i took a short freeway ride(about 15 min). the ride over was fine, ran good at 75mph, the way back, i couldnt get above 50. weird. my friends seem to think my bike is running way to rich. is this true? help me

Offline cben750f0

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Re: Flat spots in high rpms
« Reply #1 on: May 15, 2005, 09:32:41 pm »
if you aint got any filters on, then i would say that its running lean... jet it up... pretty sure that is you problem... it is ok till you are in the upper rev range, and relying on your main jet,and that when it gets flat, go up a size or 2 and see how it goes... it wont be running rich though... you have to remember that if it is cold you are pulling denser air into the bike, which makes it even leaner, thats why bikes that are running a bit rich, always seem to go better on the cooler days.

    go up a jet size, and take it for a spin, think you might be surprised..peace
you are never to old, to act like a kid... be safe
funny thing,chasing someone down hill on a bike 30 years older than theirs..
he said \\\\\\\'it was like watching a 250kg unguided weapon getting stuck up you bum\\\\\\\ http://www.bikepics.com/members/trixtrem/

stanghater

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Re: Flat spots in high rpms
« Reply #2 on: May 15, 2005, 11:02:59 pm »
how do i do the jet thing?

the flatness is sparatic.... i put a filter in it and it ran way worse, like it couldnt rev past 5k. somebody told me that the previous owner had tuned without a filter and now its running way rich

Offline cben750f0

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Re: Flat spots in high rpms
« Reply #3 on: May 16, 2005, 01:13:04 am »
you need to get a set of jets that are stock original for the bike, put them in, and work from there... i would also put filters on it... dont want to suck any #$%*e...go back to standard and work up, least then you have a base to work from... sorry i am not much more help...peace
you are never to old, to act like a kid... be safe
funny thing,chasing someone down hill on a bike 30 years older than theirs..
he said \\\\\\\'it was like watching a 250kg unguided weapon getting stuck up you bum\\\\\\\ http://www.bikepics.com/members/trixtrem/

Lumbee

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Re: Flat spots in high rpms
« Reply #4 on: May 16, 2005, 11:06:30 am »
...check u'r plugs...if they are sooty/oily, then u'r running rich...do that b4 you start screwing with the carbs...

stanghater

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Re: Flat spots in high rpms
« Reply #5 on: May 16, 2005, 12:09:52 pm »
...check u'r plugs...if they are sooty/oily, then u'r running rich...do that b4 you start screwing with the carbs...
speaking of that... what is the correct plug gap?

Offline TwoTired

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Re: Flat spots in high rpms
« Reply #6 on: May 16, 2005, 01:31:09 pm »
Well, I couldn't tell what bike or carb type you have.  But, if you are trying to change the mixture, it certainly is nice to know if you are currently running rich or lean.  One way to determine this is the yank the plugs and look at the tip/condition. Compare yours to the pics at:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
With this as a guide you can have some confidence that what you are changing is in the right direction.  Then, with some specifics about carb type you can address what part of the carbs need to be changed/adjusted.  I won't be able to help a lot with the CV type carbs.  But, I have some familiarity with the slide types.
In order to capture the chamber conditions, it is very nice to abrubtly stop the engine (Clutch in, spark off) while it is exhibiting the objectionable symptoms and look at the plug tips then to determine what is wrong.
Also, try to relate the problems to throttle position or RPMs rather than speeds, particularly if you have slide type carbs.  Let us know what you find.

Good luck,

Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

stanghater

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Re: Flat spots in high rpms
« Reply #7 on: May 16, 2005, 02:59:49 pm »
sorry i have a 81 cb 650. i will check the plugs today and get back

 

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