Hello this is a tough one for me to figure out. I have a 1998 C40TLRX with 307 hours. Compression is 129/128/129 (T-B) and it has a clean and strong flow of water through the indicator.
When I run the motor it will idle perfectly, hole shot well and then somewhere between 2700-3500 rpm it has a miss that makes it run just a bit off with intermittent small surges which during the 3-6 second surge it runs perfect. Also if I punch it it responds well and will run up to 5500rpm but still seems a bit off in performance. It has from time to time bogged down with a harsh vibration, when this happens I bring the rpm down to idle speed 7-800 rpm while still in gear. Give it gas and it runs fine but still has a slight miss. At idle or sub 1200rpm, in or out of gear it runs flawlessly. Starts perfect also every time. It seems to also be using a lot of fuel, while I haven't analysed it yet, an educated guess would be about 8 gallons an hour. I have cleaned the tank and filters, drained the carbs, checked the gap on the plugs and replaced the fuel pump. Ran it at night to look for dancing spark and it is good. One thing I did notice, when it started to act up I pumped the primer bulb on the tank and while it did not affect the performance of the engine, the bulb itself seemed soft and easy to pump, not rock hard and feeling full (Your welcome if that comment made you snicker) I did check all the clamps on the fuel lines and they were tight. Any ideas? I have not pulled the carbs yet for a cleaning. wanted input before doing surgery. Thanks. I always do followups for future readers when I ask a question.
When I run the motor it will idle perfectly, hole shot well and then somewhere between 2700-3500 rpm it has a miss that makes it run just a bit off with intermittent small surges which during the 3-6 second surge it runs perfect. Also if I punch it it responds well and will run up to 5500rpm but still seems a bit off in performance. It has from time to time bogged down with a harsh vibration, when this happens I bring the rpm down to idle speed 7-800 rpm while still in gear. Give it gas and it runs fine but still has a slight miss. At idle or sub 1200rpm, in or out of gear it runs flawlessly. Starts perfect also every time. It seems to also be using a lot of fuel, while I haven't analysed it yet, an educated guess would be about 8 gallons an hour. I have cleaned the tank and filters, drained the carbs, checked the gap on the plugs and replaced the fuel pump. Ran it at night to look for dancing spark and it is good. One thing I did notice, when it started to act up I pumped the primer bulb on the tank and while it did not affect the performance of the engine, the bulb itself seemed soft and easy to pump, not rock hard and feeling full (Your welcome if that comment made you snicker) I did check all the clamps on the fuel lines and they were tight. Any ideas? I have not pulled the carbs yet for a cleaning. wanted input before doing surgery. Thanks. I always do followups for future readers when I ask a question.