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hey guys, New owner here. i recently just got a 1974 cb360 for $600. the lady told me the carbs were rebuilt and everything a few months ago with the receipts to prove. i'm having an issue where I'll be riding and itll run amazing cold. once it warms up, it runs rough. it misfires, loses power, but has random surges of wanting to gain full power back, but never does. let it cool down, start it up and its back to normal until its warm again. Is this a carb sync issue or something else? I should mention i just had the air filters slid into the carbs but not hose clamped down, would this cause the issue? Thanks, any help is appreciated
 

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Welcome - lots of missing info in order to form a complete picture, starting with the exhaust on the bike - stock or aftermarket? Have you checked the plugs color after it runs poorly? If it doesn't need the choke to start when cold, it could be too rich and thus run worse when hot. Pictures of the bike and your current setup will help
 

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bike is completely stock. i swapped in new plugs yesterday that are properly gap. i use the choke to start, but i can turn it off a few seconds after it starts running.
 

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this is the only photo I have at the moment. also has a brand new battery that i keep on a tender.
Looks to be in pretty decent shape for its age, original paint is rare after this amount of time. Yes, air filters unclamped could make a bit of difference but not that much, and it would be leaner anyway. Sounds like you have a larger issue. Did you go through the points and timing yet? Do you have a Factory Shop Manual (FSM)? There are many people here who will have one available for you, someone will come along soon and send you a private message (PM) to arrange getting one to you
 

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i haven't checked the points or timing yet. i do not have a manual. i was thinking it could be the coil/condenser.
 

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I would look at the Rubber Intake Boots that connect the Carbs to the Intake on the Head.

If original the rubber may be dry rot and cracked. Once they warm up and soften they may be leaking raw air behind the throttle plates.

Buy some carb cleaner. and give the boots a spray when the symptom is acting up.

ANY - change in idle speed indicates they are leaking air.

Simple replacement and may be worth it anyway, as if they aren't leaking now they will if they are old.

Also go the MISC Section for the 25035/360's
At the TOP is a Sticky POST - that new to you bike checklist.

If you have not read the yet it is VERY informative and will get you up to speed with the many adjustments and systems for your bike.
 

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Discussion Starter #9
i think the carbs may be off. with the air cleaners on, it has no power after it warms up. take the filters off, has power but hesitates before it starts to go with full power. I'm borrowing a carb sync tool, so, i'll give that a shot.
 

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There will always be hesitation when the filters are off unless someone has taken the time to rejet for it, and remember that the engine's needs change as it gets warm - colder needs more fuel, warmer needs less. As Yendor mentioned, it couldn't hurt to invest in a new pair of intake boots... they are notorious for cracking with age and since you probably don't know if they have been changed or not, best to err on the side of caution. If you buy them now, you'll probably never have to do it again
 

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A few years back I had similar symptoms on a Yamaha XT500. The fault turned out to be the generator flywheel - over time the magnetism had dropped, but apparently these magnets are also affected by heat - the two combined meant that when the engine was warm, power was low. I guess it could be a bunch of things, so just throwing this out there...
 

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hey guys, New owner here. i recently just got a 1974 cb360 for $600. the lady told me the carbs were rebuilt and everything a few months ago with the receipts to prove. i'm having an issue where I'll be riding and itll run amazing cold. once it warms up, it runs rough. it misfires, loses power, but has random surges of wanting to gain full power back, but never does. let it cool down, start it up and its back to normal until its warm again. Is this a carb sync issue or something else? I should mention i just had the air filters slid into the carbs but not hose clamped down, would this cause the issue? Thanks, any help is appreciated
After a quick read, my instinct tells me it's running rich. Main jet too large.
 

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Check float height, 19~21mm. You'll probably find its below 18mm?
Personally, I prefer to use 21mm even with stock bikes, not sure if 'E' fuels have less density so float doesn't 'float' as well as in unleaded?
You should have 68 primary main jet and 100 secondary main jet. If it's had a rebuild kit fitted, check te pilot jet is Kei-Hin, aftermarket ones need work to make them Kei-Hin spec
 
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