Slight metallic clanging from engine; bike's running fine

[vagabond]

Howdy all,

My 1979 XS650 Special II is running fine in its first few weeks of long-distance runs after years of storage and restoration (16000 miles). I thoroughly cleaned out the tank, petcock and tap valve, fuel lines and carburetors (the right pilot seems to be clog-happy; I probably need to re-treat the inside of the tank to get rid of the slight residue), adjusted floats to 27mm, and swapped out the old fuel filters for new ones. The bike's a bit slow to start up with pretty low RPM, and sometimes likes to hesitate a bit in low throttle as if the air/fuel mixture's not quite right (but smokes a bit if I enrich the mixture), but runs nearly perfectly once it warms up.

In the last couple days, however, I'm hearing a mild metallic clanging sound from the right side of the engine and am wondering whether it needs immediate attention and what it could possibly be.

I'd really appreciate any advice or insights. Thanks!

 

[retiredgentleman]

Slow to start up...................check that the orifice for the choke is clear............in the bottom of the float bowl. Should be able to see light from both ways...............may need to use a fine wire to probe it.

Noise in engine...............have you adjusted the valves and the cam chain adjuster correctly?

Another source of noise could be the cam chain adjuster. Its supposed to have a "damper" on it. The damper ( copper washer) was missing on my bike, and once I replaced it, the engine was quieter.

 

[jamesgs4]

My metallic clanging was the right side crankshaft bearing on an engine with 12k. Change your oil and check for bearing pieces. Mine ran perfect, albeit noisy, even up until I junked it.

 

[vagabond]

Great suggestions, guys. Thanks for that. Great illustrations, too. I'll go down the checklist tomorrow and see what I can find.

Retiredgentleman, do you know what size the copper washer is and whether you could find it at any auto parts store?

 

[xjwmx]

My right side metallic clanging was old Rotella plus a somewhat stuck clutch plus the po putting the pressure plate on in the wrong orientation. Sounded like an electric buzzer under the right side cover. Loose cam chain sounds a little bit like shaking a dog chain.

 

[vagabond]

What I've got sounds kind of like a wedding ring shaken up in an aluminum bingo ball down a hallway. Onomatopoeias are next...haha

 

[retiredgentleman]

No idea of the size of the copper washer. When I needed one, I just found one in my miscellaneous spare parts, and drilled the centre out to fit.

 

[5twins]

If you have '79 BS38 carbs, your floats are set wrong, too low or lean. Low fuel level in the bowls could be causing the hesitation and hard starting. Correct spec is 24mm +/- 1mm. Could also be causing your new noise. Running too lean might be making the engine ping.

 

[Tomterrific]

The idle speed adjustment screw is on the left of the carbs. This little screw is easy to access so I forced a tire valve cap over the screw to make a little knob. When I start my '77XS I screw in the idle adjustment to increase the speed of the idle. As the engine warms I back the idle down to 1200. Having a fast idle when the engine is cold keeps the idle stable. When I was new to teh XS some kind person gave me this tip and being able to quickly adjust the idle speed has made my XS very easy to live with.

Are your sure the idle jets have not replugged? Happens all the time. Small debris get through most coarse small gas filters but the debris is large enough to block an idle jet. Remove the mixture screw and blast the dirt back to the float bowl with spray carb cleaner.

The easiest way to keep down detonation and save an old engine is to use high octane premium fuel. Holed pistons vs. 20 cents more at the pump? I'll pay the 20 cents.

My cam chain slaps around and jingles. Careful adjustment minimizes the noise.

Tom Graham

 

[vagabond]

Thanks everyone for the suggestions.

I slightly tightened the cam chain adjustor, then readjusted the air/fuel mixture, and the bike's running perfectly. Since cam chain affects valves affects timing affects air/fuel mixture affects idling, I figured I would start with the cam chain first, which for the moment sorted everything out. Rotating the engine forward to check the pin going in and out of the threaded stud in the adjustor is no easy chore, thus is the compression...

5twins, I think the float level varies by carbs (even among BS38s) and bike. Some swear by 24 or 25mm, while I and others found that 27mm actually produces better results despite what the manual says. So 24 +/- 1mm is working for you?

Thanks again everyone!

 

[5twins]

Yes, 24mm works very well in my '78 carbs. I tried both extremes of the spec (23 and 25) and it runs best @ 24mm. A couple MM is a lot when it comes to float levels. At 27mm, you're set very lean. It could be contributing to all the problems you mentioned. You could also suffer fuel starvation at high RPMs and speeds.

 

[vagabond]

I'll give it a test run at 24mm this weekend. It's finally running well now, but I'd always be excited to get it running even better.

 

[vagabond]

After a thorough going-over this weekend, turned out my bike, after being in storage and hitting the road hard for the first time in years, is working out some kinks. The intake and exhaust valves on the right cylinder were tight, which eliminated the clanging noise from the cylinder, the cam chain was a bit tight, the points were slightly off, timing was advanced, and the voltage to the starter is around 12.5, still workable but not ideal. After warming up, now I'm getting better performance from dead starts and at low RPM, as well as much better performance at high speed. So I'm going to replace the alternator brushes to try to get that voltage up.

As a newbie to maintenance, the technology of these bikes is absolutely incredible. I have a newfound respect for all you old maintenance hands. Cheers again for the suggestions.