TOPIC:

Landlords CB750 16 valve DOHC.
65k miles.

1) Ran last fall but was never quite right and would lose power above 5K RPM.
2) Stored indoors and started monthly until about 3 months back when it wouldn't start.
3) Valve clearances are OK now. We checked and re-shimmed all the intakes because they were right at zero clearance.

Still no start so we get down to basics...
Compression jugs 1-4, 50, 0, 0, 60! WTF?
Measured dry with throttle full open and after valve adjustment.
Compression jugs 1-4. 180, 190, 180, 160
Measured with a squirt of oil in each jug.

Have never seen any exhaust smoke from this bike.

Since wet numbers are high I'm thinking cam timing is OK
it doesn't look like there's any slop in the timing chain. The cams don't rock. SO valve duration isn't way weird like on Marty's new xs650 I fixed last weekend.

Has anyone ever seen a bike with compression numbers like this that never smoked? I'm coming from low key car hobby wrenching and all this bike stuff is new over the past 9 months and have never seen anything like this.

I doubt we'll be able to get into it for a couple of weeks as
spouse Linda is visiting. But, I can't help thinking about it and what might be wrong.

The only thing I can think of that might make compression so low is that the rings got carboned up and stuck. Probably prejudiced because I just fixed the 2-stroke homelite leaf blower by unsticking the rings and cleaning them up. Any guesses. Will report back once we find the cause.

-Duck

Some kind of rings issue, I'd bet on that. The "no smoke" part has me scratching me head, tho.
Have seen (car) rings stick in the past....but usually with the telltale "poof" of ugliness out the exhaust.
Am interested to hear what you find......sorry cant offer any real help, tho.

I suggest doing the compression check all over again, even with no rings at all on the piston you will get some compression.

My guess is either a mistake on the part of the person using the compression tester, or a bad compression tester, those numbers make no sense whatever.

Hadnt thought off "pilot error"....comp tester a thread-in or a push-on?
Not to insult your intelligence....but we all been "bitten by the obvious" once or twice.
Keep the info on progress coming.

load the cylinders with marvell mystery oil or penetrating oil, if the compression rings are stuck it should free up, if the oil ring is working my be the reason for no or little smoke... let it set for a couple of days then crank it with out the plugs in, then put the plugs back and see how it runs

is it parked by your kawasaki?could explain compression problem,low self esteem.try counseling or park it next to a harley then it will start!

The only way you could have a running bike (albeit poorly) drop compression down to zero is to have holed the pistons. You would probably have noticed or smelled this much heat.

I suspect operator error of some sort but still believe that you have ring issues in any case. Yamaha Ring Free is the best product for freeing up rings that are not sealing as they stick inside the ring lans. Put some Ring Free down each cylinder and let it sit after turning the engine over a couple times.

Repeat your compression check.

Fresh gas, new plugs, double check all the plug wires/boots. Then jump it from the car.

Just my $0.02 worth.

BH-
Thanks.
BTDT.

WM-
No Harley.
Parked next to rusted out Plymouth Reliant.

No time for bikes for the next three weeks. If I did, I'd check comp one more time and if still zero, pull the head and have a look. Instead will have landlord squirt some MMO daily and then turn over. It will keep him busy and maybe the comp will come back after a week or two.