Topic: CB550 RPM issues

[natron602]

Just finished the top end rebuild on my 1975 550k and still having issues. It seems to run fine until I get to about 60 mph then the tachometer jumps and buries itself in the high end. I dint notice anything changing in how it runs at this point but obviously I slow immediately. RPMs are probably higher than supposed to be up until then too. About 1500 over speed I'm at so 50mph =6500. What's the likely cause? Air leak? Clutch? Could it be a spark plug wire? The tachometer maybe? I'm new at this so any ideas are helpful.

[C5paul]

Your engine stays at steady rpm but just the tach jumps up? Or were you stating that your engine revs up?

[goldarrow]

What's front and rear sprockets sizes?   550s are high rev beasts. 

[natron602]

Your engine stays at steady rpm but just the tach jumps up? Or were you stating that your engine revs up?

The engine doesn't seem like it's revving. I'll linger there an extra moment to double check on my way home though.

[natron602]

What's front and rear sprockets sizes?   550s are high rev beasts.

Stock. I know they run high but I should be able to do more than 55.

[flatlander]

test it a bit more systematically and report back. from the above it's not quite clear what the engine is doing vs. what the tach is showing. don't be afraid - 6500rpm (if correctly indicated) is not going to hurt your engine, that's just where the fun begins with the 550. just don't stay too long in the red area of your tach.

and... you're saying you can't go faster than 55mph? you run out of power?

[natron602]

test it a bit more systematically and report back. from the above it's not quite clear what the engine is doing vs. what the tach is showing. don't be afraid - 6500rpm (if correctly indicated) is not going to hurt your engine, that's just where the fun begins with the 550. just don't stay too long in the red area of your tach.

and... you're saying you can't go faster than 55mph? you run out of power?

Nono. That's just it. I have power left and it doesn't noticeably rev the engine but at 60 mph the tach rockets past the red and buries itself. If I slow quickly it will fall back to about 7k rpm at 55 mph but if I get it up there again, BAM. Buried needle again.

[flatlander]

so only the tach needle moves up suddenly, the engine doesn't jump to higher revs - is that right?
what gear are you in when it shows 7k at 55mph?

[natron602]

so only the tach needle moves up suddenly, the engine doesn't jump to higher revs - is that right?
what gear are you in when it shows 7k at 55mph?

5th gear and if the engine is revving harder, I'm not noticing. I slow down rather than risk it though as I don't see any way a mechanical Tach could malfunction in that way. But again, I'm pretty new to all this so who knows?

[flatlander]

5th gear with stock sprocket sizes you should be around 4k at 55mph - not exactly sure now as my memory might not be too exact but 7k is not normal. check here for reference: http://cb550.nl/wp-content/uploads/2008/12/vermogengrafiek.jpg

are your revs consistently hight for the speed your going in any gear?
is the clutch engaging properly?

[C5paul]

test it a bit more systematically and report back. from the above it's not quite clear what the engine is doing vs. what the tach is showing. don't be afraid - 6500rpm (if correctly indicated) is not going to hurt your engine, that's just where the fun begins with the 550. just don't stay too long in the red area of your tach.

and... you're saying you can't go faster than 55mph? you run out of power?

Nono. That's just it. I have power left and it doesn't noticeably rev the engine but at 60 mph the tach rockets past the red and buries itself. If I slow quickly it will fall back to about 7k rpm at 55 mph but if I get it up there again, BAM. Buried needle again.

What I am reading is that your engine does not suddenly increase in rpm, but just the tachometer pegs. Is that correct?
Your description leaves a bit of uncertainty as to what is happening. If the engine doesn't "rev up" when the tach begins to climb rapidly I'd say your tach is failing. If the engine rpm suddenly pegs along with the tach I'd be sure your clutch is not slipping.

[natron602]

test it a bit more systematically and report back. from the above it's not quite clear what the engine is doing vs. what the tach is showing. don't be afraid - 6500rpm (if correctly indicated) is not going to hurt your engine, that's just where the fun begins with the 550. just don't stay too long in the red area of your tach.

and... you're saying you can't go faster than 55mph? you run out of power?

Nono. That's just it. I have power left and it doesn't noticeably rev the engine but at 60 mph the tach rockets past the red and buries itself. If I slow quickly it will fall back to about 7k rpm at 55 mph but if I get it up there again, BAM. Buried needle again.

What I am reading is that your engine does not suddenly increase in rpm, but just the tachometer pegs. Is that correct?
Your description leaves a bit of uncertainty as to what is happening. If the engine doesn't "rev up" when the tach begins to climb rapidly I'd say your tach is failing. If the engine rpm suddenly pegs along with the tach I'd be sure your clutch is not slipping.

I don't feel any change in performance. Just the tach. What would cause a mechanical tach to fail like that? Is there a way to check or anything I can clean or adjust?

[goldarrow]

First to do Clean or replace tach cable, cheapest option

[scottly]

Did you install a 650 cam when you re-built the top-end?

[natron602]

Did you install a 650 cam when you re-built the top-end?

No. The rebuild was admittedly half-assed in that I didn't do everything I should because I hadn't gotten the money or plan together when the oil leak got too bad too deal with. The cam lobes do have some wear and I'd like to replace soon. Is that the way to go? Could that be related? Possible the PO did?

[scottly]

How much running time did you yourself have on the bike before the rebuild?

[natron602]

How much running time did you yourself have on the bike before the rebuild?

Daily rider. About three months with occasional weekend down time for carb cleaning and such.

[scottly]

You had the same tach before the rebuild and it worked normally?

[natron602]

You had the same tach before the rebuild and it worked normally?

Nope. Same problem before the rebuild. Kind of hoped it would be solved. Replaced gaskets and o rings cleaned and lapped valves cleaned cleaned cleaned and painted. The timing and carb sync are left on my list but can't think of any reason those would do that.

[natron602]

First to do Clean or replace tach cable, cheapest option

I'll order one now. Can't hurt.

[scottly]

You had the same tach before the rebuild and it worked normally?

Nope. Same problem before the rebuild. Kind of hoped it would be solved.

Is the tach a stock 550 part?

[natron602]

Yep. Like I said, seems like probably just the tach but can't imagine what could make it do that. I'm stumped. I'm down with replacing inexpensive things like tach cable to see, my brain just insists on knowing what's going on and planning attack over trial and error replacing, if that makes sense.

[scottly]

I hope you didn't do the rebuild trying to "fix" a faulty tachometer!

[natron602]

I hope you didn't do the rebuild trying to "fix" a faulty tachometer!

Haha! No. Had to replace the head gasket. When I got in there, there was so much carbon built up (and really neat moving parts to play with) that I couldn't bring myself to just slap it back together.

[seanbarney41]

You had the same tach before the rebuild and it worked normally?

Nope. Same problem before the rebuild. Kind of hoped it would be solved. Replaced gaskets and o rings cleaned and lapped valves cleaned cleaned cleaned and painted. The timing and carb sync are left on my list but can't think of any reason those would do that.

Is that an oreo cookie in your hand?  Those go in your mouth, not a 550 engine!