I had an exhaust leak that made a similar sound. Came out at about 1/4 throttle. I worked over the header joints endlessly then traced it back to where the exhaust slips on.
Sounds like it to me. I'd go over the exhaust once more.
High pitched whistle or whirl from engineCurrent restoration: 1962 CB77
http://www.flickr.com/photos/1962_cb77_restore/ I will definitely check both the exhaust port mounting area as well as the slip joint for the muffler. Sure does not sound like it is behind me, but at speed and with a helmet, noises do funny things.
I pinged a friend who was a Honda mechanic back in the late 60's. Guy is working for us in Japan now. No luck in getting him to ask Honda R&D though. He thought it might be a worn bearing in the tranny causing a shaft to be cockeyed. I think If I take the bike down a big hill in neutral, I can simulate the partial load on the tranny since the engine will not be driven by the rear wheel. If the noise is there, it's the tranny. If it's not, it is not the tranny and engine/intake/exhaust related. Thanks, Rob Carb slides can make some noise too. If they're at all loose, they get a good workout being that close to the intake valves. Sounds like piston slap because well, it is piston slap - just not the ones in the engine. Good luck - I know how frustrating it can be to track down noises like that. I have 2 305's that I ride/wrench and with stock mufflers and baffles, you just have to learn to live with some mechanical noises.
Carb slides fit like new. But that's good input for future reference. I'm accustomed to mechanical noises from solid lifter engines. But this is too loud. The pitch is actually painful to my sensitive little ears at speed.
Riding with a half helmet, with all the wind noise and such, that noise from the engine tops them all and is downright annoying. Thanks, Rob UpdateI thought I found the source of the noise today. As I was pulling the exhaust, I noticed that the outside stud on the left pipe looked to be repaired. As I re-installed the exhaust, the stud started to crack as I tightened it. I quit, pulled the exhause, doublenutted the stud and removed it. Turns out somebody had welded the stud together. It gets better. I suspect this was done by the guy I bought it from becauses he does a lot of work on bikes. What he did was drill out the broken stud and missed center. So instead of getting the rest of the stud out and installing a heli-coil, he taps the hole for 1/4-20. Then he welds a 1/4-20 section onto the remaining 6mm section. I'd never seen a metric stud with coarse threads on one end standard threads on the other. So I checked and that was when I learned it was 1/4-20.
I tried a temporary fix with a standard 1/4 inch stud. But when I tighted it, the threads in the head pulled free. So I picked up an M6 Heli-coil kit and as I ran the tap into the hole, that was when I learned that a piece of the original stud was still in there. It came out with little effort. I finished tapping the hole, installed the heli-coil and picked up a new M6 stud at NAPA. I thought I had it licked. But, I took the bike for a ride with the air cleaners off and the noise was there, just not as pronounced. Next test was to put a set of straigh pipes I had on the bike and re-install the air filters and side covers. Noise is still there, but not quite as loud. I'm pretty convinced it is either an intake or exhaust noise because it is definitely throttle position sensitive. It's as I stated before, right at the point where the bike is neither accelerating or decelerating. I still need to take it up the mountain so I can coast in neutral with the clutch out and see if I hear it. I think that test is a waste of time because I really doubt it's the tranny. But better to eliminate it. Getting so I'm not really worried about it much. I'll just ride the bike and see what happens. Wild part is closing my legs up to the tank still makes it disappear. Maybe it is some strange harmonic. I can always stuff a couple piece of rubber in the fins to see if that changes it or elimates it. regards, Rob Re: UpdateThat sure does sound like some kind of loose exterior part vibrating. Tank mounts loose, tank badges, something under the tank touching the bottom, gas cap....??? 66 dream, 78 cb750k, 02fz1, 09 wing
Morning coffee maked for clear thinking. I'm wondering if it is not related to the primary chain. Part load condition would put the primary in a "loose" condition in that is it neither driving nor being driven. I should pull that cover off anyone if for nothing else than inspect the area and check the tensioner. Or it could be the oil filter chain is worn and loose.
The spare engine I tore into this summer had the oil filter chain sprocket on the chank off the crank and in the bottom of the engine along with the nut. Somebody reassembled it without the locking tab washer. Winter is right around the corner. Always need winter therapy projects. regards, Rob
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