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Author Topic: bike running lean??  (Read 2480 times)

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Offline enThrall

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bike running lean??
« on: December 16, 2009, 05:38:41 PM »
Hey there guys! I'm new to this forum and really new to working with motorcycles. So here I am inquiring about a problem with my bike after a small project with you knowledgeable fellow  ;D

I own a 1978 CB750K.

Did a small "project" over this winter break (i'm a college student) which consisted of new paint, side covers, crash bars, oil, oil filter, air filter, etc. I didn't go into the engine or mess with the ignition, though. Mainly cosmetic stuff.

I DID, however, pry off the air filter box to change the air filter. Then i realized that it had a foam (and dirty) air filter as the original one. I replaced it with an EMGO paper element filter. *Later I realized the filter cover boots didn't go onto the carbs as tightly as before, so now it's all tightened.*

Well, now the bike won't go past 3000rpm without some serious hesitation. This is when the bike is moving, that it hesitates, no matter which gear. The acceleration is far from good. When the bike is in neutral on the center stand, it revs nicely.

So I guess my question is, is it running lean? Does it make a difference whether the bike is under load or not? What kind of a problem do you guys think this is? And maybe, how do i fix it?

Thanks a ton guys  8) Appreciate it
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Offline TwoTired

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Re: bike running lean??
« Reply #1 on: December 16, 2009, 05:46:48 PM »
Combustion conditions lean/rich show up as deposits on the spark plug tips.

Install new plugs, go for a ride (or do a plug chop) and check the deposits.
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
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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.

Offline enThrall

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Re: bike running lean??
« Reply #2 on: December 16, 2009, 06:04:24 PM »
However, what confuses me is that it can rev without load and hesitate under load. Does it still mean that it's running lean?
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Offline TwoTired

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Re: bike running lean??
« Reply #3 on: December 16, 2009, 06:15:56 PM »
Probably.
It takes more energy to increase RPM under load than it does with no load.

Read the plug deposits and you don't have to play the guessing game.
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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.

Offline enThrall

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Re: bike running lean??
« Reply #4 on: December 17, 2009, 03:30:30 PM »
no doubt, turns out the bike was running lean. Taped the air filter partially to remedy that.  :)
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Offline fletcha221

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Re: bike running lean??
« Reply #5 on: December 17, 2009, 04:15:07 PM »
I'm going through the same issue right now. If you dont want to tape your air filter, try the next size jet.
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"Consistency is the last refuge of the unimaginative" -Oscar Wilde

1973 CB350f
1975 CB550k
1975 CB750 K5
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