Peaceful Pirate
Seaman
- Joined
- Aug 26, 2007
- Messages
- 71
I need to get this boat finished and then ready for winter, so before I start tearing things apart (or pulling what is left of my hair out!) I would appreciate a bit of wisdom from anyone who might care to comment. I am confident that the answer is something we are overlooking:
The original engine in this boat was a ?69 120hp. It had an old outdrive that died, so we put the 140 1.98 outdrive in its place. Together they developed good WOT at 3900-4000 RPM. The 140hp came out of a ?72 Starcraft we recently acquired.
Problem: ?72 140hp Mercruiser mated with a ?74 1.98:1 140 outdrive, will develop only +/- 3000 RPM at WOT in open water. Obvious lack of power at WOT.
1. Will run-up well over 4000 RPM in natural - Advances smooth.
2. Outdrive was just removed from 120hp unit and ran well ? Developing full WOT to +/- 3900-4000 RPM.
3. Started out with a 15 1/2 X 19 prop ? Changed out to a 14 1/2 X 17 ? No noticeable change in RPM.
4. Running a mechanical fuel pump with an electrical in line pump. Fuel flow to carb is strong.
5. Compression check ? Warm with carb open - 122/118/125/125.
6. Rechecked/Readjusted valves ? Did a running valve adjustment ? Back off to chatter then turned down slow, quarter at a time, to 3/4 down.
7. Ran open water again ? Still only +/-3000 RPM, only this time noticed what appears to be an intermittent ?miss??
8. Rechecked timing. OK. Ran-up in gear tied off to dock and noted that distributor appeared to be advancing as required.
9. Mercruiser manual call for 3/4 turn down from lash. I note that Selco calls for one full turn down from lash. My gut is to always go with Mercruiser, but thought I would mention it.
10. The boat tach has been checked against a handheld unit and is well within tolerance (+/-200 RPM in the 3-4000 range). The intermittent miss is first started to show up after the valves were readjusted (hummm!). Timing was set in gear at 650 RPM to 6 before TDC.
11. An after thought: As a kid, we use to run an old dirt track hard by advancing timing to the point of max RPM and then if the engine kicked back at start, we would retard the timing just to the point it would start. Any logical comparison to this?
With compression well within range, and valves readjusted, we can only lean towards the distributor or the carb, but again, we am listening!!!!! Thanks in advance for your help.
The original engine in this boat was a ?69 120hp. It had an old outdrive that died, so we put the 140 1.98 outdrive in its place. Together they developed good WOT at 3900-4000 RPM. The 140hp came out of a ?72 Starcraft we recently acquired.
Problem: ?72 140hp Mercruiser mated with a ?74 1.98:1 140 outdrive, will develop only +/- 3000 RPM at WOT in open water. Obvious lack of power at WOT.
1. Will run-up well over 4000 RPM in natural - Advances smooth.
2. Outdrive was just removed from 120hp unit and ran well ? Developing full WOT to +/- 3900-4000 RPM.
3. Started out with a 15 1/2 X 19 prop ? Changed out to a 14 1/2 X 17 ? No noticeable change in RPM.
4. Running a mechanical fuel pump with an electrical in line pump. Fuel flow to carb is strong.
5. Compression check ? Warm with carb open - 122/118/125/125.
6. Rechecked/Readjusted valves ? Did a running valve adjustment ? Back off to chatter then turned down slow, quarter at a time, to 3/4 down.
7. Ran open water again ? Still only +/-3000 RPM, only this time noticed what appears to be an intermittent ?miss??
8. Rechecked timing. OK. Ran-up in gear tied off to dock and noted that distributor appeared to be advancing as required.
9. Mercruiser manual call for 3/4 turn down from lash. I note that Selco calls for one full turn down from lash. My gut is to always go with Mercruiser, but thought I would mention it.
10. The boat tach has been checked against a handheld unit and is well within tolerance (+/-200 RPM in the 3-4000 range). The intermittent miss is first started to show up after the valves were readjusted (hummm!). Timing was set in gear at 650 RPM to 6 before TDC.
11. An after thought: As a kid, we use to run an old dirt track hard by advancing timing to the point of max RPM and then if the engine kicked back at start, we would retard the timing just to the point it would start. Any logical comparison to this?
With compression well within range, and valves readjusted, we can only lean towards the distributor or the carb, but again, we am listening!!!!! Thanks in advance for your help.
