Tim Morris 3 #1 Posted July 13, 2023 I have a C-121, with the original Kohler k301. It runs rough at high speed. And will not Idle. I replaced the carburetor with new one. That didn't help. I tried taking compression test. I only had a older tester. One that I hold into the spark plug hole. I'm only getting about 40 psi. At best. I tried bypassing the fuel system. A new fuel line from the fuel pump. Into a fuel can of fresh gas. No difference. Thinking that with the low compression. My motor isn't drawing enough fuel? ? Share this post Link to post Share on other sites
Achto 26,610 #2 Posted July 13, 2023 (edited) 2 hours ago, Tim Morris said: I tried taking compression test. Your engine has an automatic compression release for easier starting, so it is hard to take a compression test. One other possible issue to try would be the condenser. A bad one will cause the same symptoms. Edited July 13, 2023 by Achto 2 Share this post Link to post Share on other sites
TonyToro Jr. 1,164 #3 Posted July 13, 2023 1 hour ago, Achto said: Your engine has an automatic compression release for easier starting, so it is hard to take a compression test. One other possible issue to try would be the condenser. A bad will will cause the same symptoms. or clean and regap the points. 1 Share this post Link to post Share on other sites
Tim Morris 3 #4 Posted July 13, 2023 I did adjust the points . How and where do I check the automatic compression release? Share this post Link to post Share on other sites
Achto 26,610 #5 Posted July 13, 2023 6 minutes ago, Tim Morris said: How and where do I check the automatic compression release? The compression release is on the cam shaft. It is a spring loaded mechanism that holds the exhaust valve open a little bit on the compression stroke at low RPMs, (crank speed). Once the engine starts it retracts and allows the exhaust valve to close all of the way so that the engine will run properly. It is seldom an issue on Kohler engines, but it does make it impossible to take a correct compression reading. A leak down tester is the only good way to look for compression leakage on these engines. In order to do a leak down test you have to position the engine either just before or just after the compression release opens the exhaust valve. 1 Share this post Link to post Share on other sites
gwest_ca-(File Mod) 10,513 #6 Posted July 13, 2023 They don't need it very often but good practice is to check the valve tappet clearance. If it is changed much it should be redone after a few hours of running. A shot of Marvel Mystery oil in the fuel helps which lubes the valve stems so they are more apt to close every time. 2 Share this post Link to post Share on other sites
