'77 Kz650c Potential Valve Issues

Hey, this is my first post. This is a rad community and I'm stoked to be a part of it!





I've got a 1977 KZ650C chop. It ran fast and loud before I started having some issues a few weeks ago. One day I started it up and after a brief warm up and ride it felt like it was running poorly and wouldn't stay running at an idle. I parked it at home and let it sit. It was just after dark and while trying to get it to run again I realized it wasn't firing correctly on the number 3 cylinder. The exhaust tube coming from number 3 wasn't cold, however, it was searing hot. If I gave it some throttle (while running) it would smell like hot and the pipe itself started glowing a dull orange. I immediately turned the bike off. I cleaned the carbs, jets, float needles, made sure floats were adjusted correctly, etc. The problem has persisted though and I won't let the bike run for more than needed to try out little fixes.

Does this sound like a stuck valve on the exhaust side of cylinder 3? If not, what should I look at next? If it is, should I remove the cylinder heads and start there? I have the Clymer manual and have taken the bike apart a few times, but I don't want to get into the block before I get a second opinion.

I appreciate any help.

Welcome. If you have a stuck/bad valve,... have you run a compression check?

Glowing red exhaust pipes are NOT good. Not sure what to suggest other than the basics like making sure the carbs are clean, no intake boot leaks, the choke isn't sticking open, and adjust the valves. Valves rarely stick, but a lot of people don't adjust them which causes them to burn.

I haven't run a compression check. Should I? And what would poor compression indicate for the situation? And I haven't done a valve adjustment since I've owned the bike, I should probably take a look at that.

If not already done, would also inspect and assure serviceable condition and proper functioning of the ignition timer advancer unit, especially that the weight arms move freely on their pivots.

The advancer might be rusted and stuck in position, or the pivots might simply need lubing.

The advancer isn't supposed to look like this:




Where lubing is desired, may sometimes reach the pivots through the timing inspection window (without needing to remove the points plate in order to gain full access to the entire advancer).





Good Fortune!

rage_rides wrote: I haven't run a compression check. Should I? And what would poor compression indicate for the situation? And I haven't done a valve adjustment since I've owned the bike, I should probably take a look at that.

Could mean a valve adjustment or other compression leak problems... let us know what you have here, before tearing into the engine. Helps to diag the problem before tearing in and not knowing some baseline.

rage_rides wrote: Hey, this is my first post. This is a rad community and I'm stoked to be a part of it!

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I've got a 1977 KZ650C chop. It ran fast and loud before I started having some issues a few weeks ago. One day I started it up and after a brief warm up and ride it felt like it was running poorly and wouldn't stay running at an idle. I parked it at home and let it sit. It was just after dark and while trying to get it to run again I realized it wasn't firing correctly on the number 3 cylinder. The exhaust tube coming from number 3 wasn't cold, however, it was searing hot. If I gave it some throttle (while running) it would smell like hot and the pipe itself started glowing a dull orange. I immediately turned the bike off. I cleaned the carbs, jets, float needles, made sure floats were adjusted correctly, etc. The problem has persisted though and I won't let the bike run for more than needed to try out little fixes.

Does this sound like a stuck valve on the exhaust side of cylinder 3? If not, what should I look at next? If it is, should I remove the cylinder heads and start there? I have the Clymer manual and have taken the bike apart a few times, but I don't want to get into the block before I get a second opinion.

I appreciate any help.

WTF is that?

Id tear back into the carbs again if it just started getting hot all the sudden on one cylinder,maybe try swapping a different set of carbs on there just to see if it makes a difference.

Could perform a quickie clear-tube test on #3 carb to rule out possible fuel starvation due to a too low fuel level being caused by whatever reason.

Good Fortune!

rage_rides wrote: I haven't run a compression check. Should I? And what would poor compression indicate for the situation?.

That the valve is not fully closing or is not seating well.

Thanks for the help guys, I've got some good places to start. I'll hit it this week and let you guys know how it turns out.

bountyhunter wrote:

rage_rides wrote: I haven't run a compression check. Should I? And what would poor compression indicate for the situation?.

That the valve is not fully closing or is not seating well.

...or rings that are no longer sealing. But a leakdown test helps, in this regard.


Yes RR, please do keep us posted with what you discover.