sumyunguyz
Recruit
- Joined
- May 29, 2012
- Messages
- 5
Iv'e been battling this issue for several months now and at my wits end!
Symptom: No increase in RPM's from 3/4 throttle to full throttle. Maximum RPM @ 4200.
Boat: 18ft. Tracker bass buggy pontoon.
Engine: 2000 75 hp Mercury w/ approx. 100 hours on it. S/N 0T160329
Last season I took it to a Mercury dealer and they had it for 3 months. Picked it up twice, took it to the lake and still had the same problem. Mechanic replaced the battery, fuel tank, prop, cleaned carbs, changed plugs. The third time I took it back they admitted they really got frustrated with working on it and didn't know what exactly was wrong with it. Fortunately they refunded some of my money back and I felt like they really did try to figure it out but the Mercury associate rep. that came by while it was in the shop wasn't able to nail it down either. Since I don't have a trailer for my boat and it sits in my boathouse it's really hard finding a mechanic that makes house calls.
Since then I have done a number of things since I personally felt it was a fuel delivery problem. The engine idles fine @ 850-900 rpm, takes off out of the hole very fast but 4200 RPM is max throttle. Pulling back from full throttle to 3/4 throttle has no change in RPM. Sometimes it does sound like one of the cylinders is misfiring when I slowly pull back on the throttle. Before this problem began it used to run 5200 @ WOT and cruise around 27 MPH on gps.
So this is what been done recently that really hasn't been any help:
1. New fuel pump
2. New external and internal engine compartment fuel lines, including quality fuel bulb.
3. Racor R-12 external fuel\water separator filter. New engine compartment fuel filter.
4. New plugs NGK - BUHW-2. Condition of plugs seem to be slightly wet after 15 minutes of run time.
5. New carburetor kits. Floats are good and set correctly. (Have never run ethanol fuel in this or any of my engines. When overhauling carbs they were like new inside). 87-89 octane no ethanol fuel. Quicksilver 2 stroke oil. Air test on carbs indicate no leakage around needle valve while closed.
6. Compression test dry @ 5 sec. 112# on all 3 cylinders.
7. Synchronized carburetors. Inspected butterfly valves for full opening closing from idle to WOT. Fuel pressure running 5-6# at inlet of carburetors while running between 900 - 1200 RPM. No change in engine speed or performance while pumping fuel bulb.
8. Checked all electrical connections. Bought a new CDM and moved it around to different cylinders to see if it made any difference. (None)
Hopefully I've ruled out all possible fuel problems so now I think it could be ignition.
Have a Mercury service manual on this engine and think I have ruled out just about everything that would attribute to a fuel performance issue that I can think of so thought I would reached out to some of the best here to see if you guys can help me out.
Symptom: No increase in RPM's from 3/4 throttle to full throttle. Maximum RPM @ 4200.
Boat: 18ft. Tracker bass buggy pontoon.
Engine: 2000 75 hp Mercury w/ approx. 100 hours on it. S/N 0T160329
Last season I took it to a Mercury dealer and they had it for 3 months. Picked it up twice, took it to the lake and still had the same problem. Mechanic replaced the battery, fuel tank, prop, cleaned carbs, changed plugs. The third time I took it back they admitted they really got frustrated with working on it and didn't know what exactly was wrong with it. Fortunately they refunded some of my money back and I felt like they really did try to figure it out but the Mercury associate rep. that came by while it was in the shop wasn't able to nail it down either. Since I don't have a trailer for my boat and it sits in my boathouse it's really hard finding a mechanic that makes house calls.
Since then I have done a number of things since I personally felt it was a fuel delivery problem. The engine idles fine @ 850-900 rpm, takes off out of the hole very fast but 4200 RPM is max throttle. Pulling back from full throttle to 3/4 throttle has no change in RPM. Sometimes it does sound like one of the cylinders is misfiring when I slowly pull back on the throttle. Before this problem began it used to run 5200 @ WOT and cruise around 27 MPH on gps.
So this is what been done recently that really hasn't been any help:
1. New fuel pump
2. New external and internal engine compartment fuel lines, including quality fuel bulb.
3. Racor R-12 external fuel\water separator filter. New engine compartment fuel filter.
4. New plugs NGK - BUHW-2. Condition of plugs seem to be slightly wet after 15 minutes of run time.
5. New carburetor kits. Floats are good and set correctly. (Have never run ethanol fuel in this or any of my engines. When overhauling carbs they were like new inside). 87-89 octane no ethanol fuel. Quicksilver 2 stroke oil. Air test on carbs indicate no leakage around needle valve while closed.
6. Compression test dry @ 5 sec. 112# on all 3 cylinders.
7. Synchronized carburetors. Inspected butterfly valves for full opening closing from idle to WOT. Fuel pressure running 5-6# at inlet of carburetors while running between 900 - 1200 RPM. No change in engine speed or performance while pumping fuel bulb.
8. Checked all electrical connections. Bought a new CDM and moved it around to different cylinders to see if it made any difference. (None)
Hopefully I've ruled out all possible fuel problems so now I think it could be ignition.
Have a Mercury service manual on this engine and think I have ruled out just about everything that would attribute to a fuel performance issue that I can think of so thought I would reached out to some of the best here to see if you guys can help me out.