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Author Topic: 73 CB 500 Engine Surge  (Read 640 times)

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Offline toobad

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73 CB 500 Engine Surge
« on: August 11, 2015, 08:34:03 PM »
I have a 73 CB500 K2 which until up to this point was running perfectly.  About two weeks ago when shifting between gears, I noticed a quick surge in RPMs.  It only lasts about a 1/10Th of a second and then quits - resuming to a smooth operation.  I didn't think too much about it then but it is now occurring about once a ride.  I am thinking it is a carb issue and needs to be resync'd or maybe a piece of debris in one of the jets. Has anyone experienced this issue and what did you do to resolve?  Thanks for your assistance.
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Offline PeWe

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Re: 73 CB 500 Engine Surge
« Reply #1 on: August 11, 2015, 10:20:18 PM »
Have you read this? The Thoughts of Hondaman. / Dealing with the 500/550 "flat spot"
http://forums.sohc4.net/index.php/topic,7401.msg67251.html#msg67251
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CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline calj737

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Re: 73 CB 500 Engine Surge
« Reply #2 on: August 12, 2015, 04:31:20 AM »
It may also be indication of clutch slippage. Momentary peak of RPMs during gear changes is the motor spinning while not friction is present (clutch plates not engaged) despite the clutch lever being released. Suddenly, the plates stick, and the bike accelerates normally, and RPMs drop. Is it almost like you pulled in the clutch lever, but did not move the gears or release the throttle? If so, I'd suspect a thorough adjustment and inspection of your clutch cable is in order.
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'74 550 Build http://forums.sohc4.net/index.php?topic=126401.0
'73 500 Build http://forums.sohc4.net/index.php?topic=132935.0

"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline toobad

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Re: 73 CB 500 Engine Surge
« Reply #3 on: August 12, 2015, 02:02:00 PM »
Good point!  I will check it out.  Thanks for your comment.
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