1985 K100 RT Compression

[kylemb]

78,000 miles.

when i got the bike it had a pretty bad air leak in the throttle body inlets causing it to run very lean. i assume the previous owner road it this way for 15-20k miles. the spark plugs showed signs that it was too hot but it has never overheated. i ended up replacing the inlets and the air leaks are gone, re-tuned the bike doing a lean drop, adjusted the valves, etc.
i just did a compression test:

https://goo.gl/photos/eBLEeciXWWikeRqM8

cylinder 1: 150 psi
cylinder 2: 145 psi
cylinder 3: 135 psi
cylinder 4: 158 psi

the symptoms of which you can feel. the engine just isn't quite in sync with itself. fuel pressure is 35 psi right on the money (gas tank is squeaky clean / new gas filter). coils test well and no air leaks but i still can't quite get a good throttle response and it seems like i have to tune the bike to be a bit more on the rich side to keep her from studdering. the low end torque is just not there either. this is how she sounds:

https://goo.gl/photos/za1g76n5H2B6qMvR8

i've replaced the airflow meter and it didnt really help, although i suspect that the springs in both are a bit lax from age as they both meter well.
when i lean the bike to the left the bike starts to stall, when i lean the bike to the right the idle increases, demonstration:

https://goo.gl/photos/cFHcCsApBfApsQdy6

this is why i suspect the spring being loose causing the vane to open and close more with the lean of the bike.

but other than that i can only guess the engine is a bit off due to the discrepancy in the compression; causing an uneven vacuum and making the vane in the AFM wiggle a lot more than it should (especially if it isn't as tight as it needs to be). i was under the impression that the vane should be fully closed at idle whereas mine is moving; demonstration:

https://goo.gl/photos/tq9aJCECQEtVALDD8

i also suspect that perhaps the exhaust valves in cylinder 2 & 3 may have gotten a bit worn from being ridden in the excess heat for so long.

thought'd i'd share my discoveries. i love feedback!

i thought about adding some

[Martin]

Doing a wet compression test will show whether it is rings or valves causing the low readings. To do a wet test squirt a couple of pumps from a oil can into the cylinder and redo the test. The oil should seal the rings, if the reading is still low it points to the valves as a problem. Do it a couple of times to make sure that you have sealed the rings.
Regards Martin.

[kylemb]

Doing a wet compression test will show whether it is rings or valves causing the low readings. To do a wet test squirt a couple of pumps from a oil can into the cylinder and redo the test. The oil should seal the rings, if the reading is still low it points to the valves as a problem. Do it a couple of times to make sure that you have sealed the rings.
Regards Martin.

will do

[Martin]

If you have access to a compressor and a fitting to attach the hose to the spark plug hole with a shut off valve and a gauge to monitor you can do an even more definitive test called a leak down test. It involves placing the cylinder on TDC filling the cylinder with air  and seeing if it drops. if it does drop you can listen at the crankcase the exhaust and inlet to determine where the leak is. Unfortunately not everyone has the equipment to do this, although you might find someone able to lend you the equipment or do it for a reasonable price.
Regards Martin.

[Nine80seven]

 :2thumbup: on martin's air test.  Just did it to 85KRS, 84k miles, has a problem, was gonna pull the head, have another head ready to go, and then everything checked out OK. 

[kylemb]

If you have access to a compressor and a fitting to attach the hose to the spark plug hole with a shut off valve and a gauge to monitor you can do an even more definitive test called a leak down test. It involves placing the cylinder on TDC filling the cylinder with air  and seeing if it drops. if it does drop you can listen at the crankcase the exhaust and inlet to determine where the leak is. Unfortunately not everyone has the equipment to do this, although you might find someone able to lend you the equipment or do it for a reasonable price.
Regards Martin.

yea, i have sorta considered these things, but i was hoping that someone would tell me something i hadn't thought of yet or maybe that these compression figures arent that far out. to repair rings or valves is a hell of a job i figure almost worth finding another engine over and i feel like even though this one isnt that bent out of shape, it isnt going to perform the way i can tell it should unless i do a major overhaul. guess ill keep lookin until i find out exactly what it is and go from there.

[Martin]

Bricks don't like to sit, a lot of problems can be resolved by just riding them, especially if they have been sitting for long periods. If you haven't done a oil change since getting it do so and then just ride it it might settle  down. A mate bought a k100 which smoked prodigiously, he was going to rebuild it. But as it had been sitting for at least a couple of years he decided to just ride it and it eventually settled down.
Regards Martin.

[kylemb]

Bricks don't like to sit, a lot of problems can be resolved by just riding them, especially if they have been sitting for long periods. If you haven't done a oil change since getting it do so and then just ride it it might settle  down. A mate bought a k100 which smoked prodigiously, he was going to rebuild it. But as it had been sitting for at least a couple of years he decided to just ride it and it eventually settled down.
Regards Martin.

yea i got everything tuned up the best i can, doesnt sound or ride half bad. engine feels like its pulling about 80%. may ride her to the beach and back and see if i get any improvements.

[bizzaro]

Have you tried the magic juice? Techron complete fuel system cleaner.  Really, give it go. Full bottle to less than a tank full. Do it again. Then tell me you didn't see an improvement!   It is like a tune up in at bottle. And cheap at that effin store I hate to support.....................Freaken Wal Mart.................... :mbird

[kylemb]

Have you tried the magic juice? Techron complete fuel system cleaner.

Yessir. Just ran that through 2 tanks. I have a bottle of sea foam that I may put in next. As well as that oil additive.

[bizzaro]

I wouldn't put restore in anything but the garbage, but that is just me.  Unless your just trying to extend briefly the life of an engine.  I just don't believe it works, other than temporarily.  It may postpone the inevitable, but it will not fix "anything".

[kylemb]

I wouldn't put restore in anything but the garbage, but that is just me.  Unless your just trying to extend briefly the life of an engine.  I just don't believe it works, other than temporarily.  It may postpone the inevitable, but it will not fix "anything".

yea starting to second guess that stuff myself. may just stick with the seafoam for now