Author Topic: Can anyone hear the noise at idle? Any ideas?  (Read 1047 times)

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Offline 5thofhonda

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Can anyone hear the noise at idle? Any ideas?
« on: October 20, 2015, 02:46:54 AM »
I've known my 750 has running issues since I got it, but I'd like to see what the pros have to say about it now that I can finally record it.  Carbs have only been bench sync'd as life is kind of hectic right now, and I plan on tearing into it over the winter to punch it out and rebuild it.  The starting and warm-up process is a bit tiresome, but easier in the colder weather we've been having.  I can't remember if it does it in the video, but it will backfire out of the exhaust on decel, and lately out of the intake while it's warming up in the driveway.  Also there's a noticeable metallic sound at idle.  I'm thinking it's the cam chain, but there may be other parts involved.  I haven't done any tune-up work to it (I know, I know) because I had intentions from the start to tear it down once we get in the new house (short sale, going on 3 months now), and I only get out maybe once or twice a month for an hour or so.

SDP velocity stacks, drag pipes w/o baffles, 120 mains.  Everything else on the engine is stock as far as I know.

And the headlight issue is just loose crap in the electrical box.  The ignition may as well have came from GM, as the lights (and bike) have shorted out on me multiple times while riding if the key moves out of the right position.


Offline 70CB750

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Re: Can anyone hear the noise at idle? Any ideas?
« Reply #1 on: October 20, 2015, 03:50:49 AM »
There is a very good chance that the noise will go away with vacuum synchronization. 
Prokop
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Offline evanphi

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Re: Can anyone hear the noise at idle? Any ideas?
« Reply #2 on: October 20, 2015, 07:41:18 AM »
GO through the 3K tuneup. Your timing may be off, which could contribute to the backfiring and difficult warmup process.

I don't hearing anything funny at idle... but you have lots of tune-up work to do before you can say something is "wrong".
--Evan

1975 CB750K "Rhonda"
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K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

She's a mix-matched (former) basket case, but she's mine.

CB750 Shop Manual (all years), searchable text PDF
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Offline 5thofhonda

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Re: Can anyone hear the noise at idle? Any ideas?
« Reply #3 on: October 20, 2015, 11:25:02 AM »
I'll check those out when I get a chance. I've been putting off buying tools and trying to work with what I have, but it's comforting no one said anything like piston slap.