I think the stock compression is actually higher than that, like around 170-180 psi. What compression tester you use makes a big difference. For example, if you are also filling up the hose, that adds volume. You don't want to pick up any automotive tester and try to get accurate numbers. But with a fresh top end kit that you know has good compression, you cause that lower number for a reference for wear. I did a weird way to set compression once, but it worked well. A buddy of mine repairs bikes/quads/snowmobiles. etc, and he does have a very accurate gauge. I set the compression for one of his customers bike that was a Frankenstein RM125 with a stroked crank, a new top end and we oiled the rings. I had to modify the head to get the compression right. Since we knew his gauge was accurate, and after I cut a good squish clearance on the head (for the stroked crank), I lowered the compression (we were shooting for 185-190psi), by measuring the compression, taking the head off the bike, and me cutting the combustion chamber on my lathe. We just kept doing that in little bits, until we got the PSI he wanted. It ran great. Old RM smoked his neighbors newer bikes. :)
That was a monster of a bike. The 85 was the strongest. Honda de-tuned them a bit for 86-87 to make them a bit more rider friendly. I did not ride a 500 much, but they have a throttle you better respect. :) It was said that only a handful of people in the world could ride a well tuned 500 to its potential. It would be easier on the fast tracks of today though.
His explanation of anything lower than 125psi. Would have difficulty starting. Most who use a Head Decompressor will experience the same thing. But, because it is easier to kick they don't complain. Which is why I will never use a decompressor again ..
Not all compression gauges are created equal. I have one that reads about half what the actual PSI is. Small bore engines, automotive tester that also fill up the hose. The hose is about as much volume at the trapped volume of the head, so it reads 90psi with a new top end. :)
@EarthSurferUSA 500cc is not a small bore. Decompression valves are over rated. In my opinion because you need to kick more often using one. It causes more stress on the cases. When the lever slams into the peg at bottom.
I think the stock compression is actually higher than that, like around 170-180 psi. What compression tester you use makes a big difference. For example, if you are also filling up the hose, that adds volume. You don't want to pick up any automotive tester and try to get accurate numbers. But with a fresh top end kit that you know has good compression, you cause that lower number for a reference for wear.
I did a weird way to set compression once, but it worked well. A buddy of mine repairs bikes/quads/snowmobiles. etc, and he does have a very accurate gauge. I set the compression for one of his customers bike that was a Frankenstein RM125 with a stroked crank, a new top end and we oiled the rings. I had to modify the head to get the compression right. Since we knew his gauge was accurate, and after I cut a good squish clearance on the head (for the stroked crank), I lowered the compression (we were shooting for 185-190psi), by measuring the compression, taking the head off the bike, and me cutting the combustion chamber on my lathe. We just kept doing that in little bits, until we got the PSI he wanted.
It ran great. Old RM smoked his neighbors newer bikes. :)
That was a monster of a bike. The 85 was the strongest. Honda de-tuned them a bit for 86-87 to make them a bit more rider friendly. I did not ride a 500 much, but they have a throttle you better respect. :) It was said that only a handful of people in the world could ride a well tuned 500 to its potential. It would be easier on the fast tracks of today though.
His explanation of anything lower than 125psi. Would have difficulty starting. Most who use a Head Decompressor will experience the same thing. But, because it is easier to kick they don't complain. Which is why I will never use a decompressor again ..
Not all compression gauges are created equal. I have one that reads about half what the actual PSI is. Small bore engines, automotive tester that also fill up the hose. The hose is about as much volume at the trapped volume of the head, so it reads 90psi with a new top end. :)
@EarthSurferUSA 500cc is not a small bore. Decompression valves are over rated. In my opinion because you need to kick more often using one. It causes more stress on the cases. When the lever slams into the peg at bottom.
Told ya she was a fresh top end. runs awesome.