Grum Man
Recruit
- Joined
- Apr 22, 2017
- Messages
- 5
First post, enjoy this forum.
I bought a 2005 30HP four stroke EFI Merc, new, to put on my '57 Grumman runabout that I redid, (the $250. boat that quickly turned into the $10,000 boat). The motor has been great, except for a chronic high idle that I recently remedied with a Dremel tool (no idle adjustment screw). A couple years ago while poking around the intake system, trying to figure out the high idle, I discovered a restrictor plate in the throttle body. A little research showed the only difference between the 40 HP and the 30 HP was that plate. All other parts are exactly the same, brain, sensors, camshaft, etc., etc. Of course I removed the plate (my wife's comment, "Do you have to turbocharge everything?") Wow, what a difference it made.
It would run quickly to 6000 RPM, I went up in prop size, and went from three blade to 4 blade. Much better. There is a throttle position that once you go beyond the motor stumbles and progressively bogs down, worsens with more throttle. Always exactly the same lever position where it starts. Never happened before the 30-40 conversion. With the new prop it starts at about 5100 rpm (it still runs quickly and smoothly to that RPM). Never noticed it before the prop change, I think because I didn't want to run above 5,500 RPM and never pushed the throttle to WOT position. I can fix it by adjusting the WOT stop, but of course I know there's a little more motor in there somewhere.
It seems obvious that fuel is not keeping up with the air at that throttle position. I read an old thread about Mercury chronic fuel pump problems in that motor series, a Merc mechanic commenting about pumps often putting out only 80%. Any ideas? I haven't tried squeezing the primer bulb when the stumble starts, would that translate to a boost through the pump, and smooth things out momentarily in an EFI system?
Again, the parts lists and diagrams for the 30 and 40 are exactly the same, with an asterisk by the restrictor plate (for 30 HP only). How much hassle is it to replace the pump? I'm a competent half ass amateur mechanic, but my worn out carpenter hands and eyes are more suited for low finesse work. I could easily shine on this problem and be happy, and don't want to go the trial and error route, but in the back of my mind I know I want to solve this.
Great forum. Any help, opinions, or comments would be appreciated.
I bought a 2005 30HP four stroke EFI Merc, new, to put on my '57 Grumman runabout that I redid, (the $250. boat that quickly turned into the $10,000 boat). The motor has been great, except for a chronic high idle that I recently remedied with a Dremel tool (no idle adjustment screw). A couple years ago while poking around the intake system, trying to figure out the high idle, I discovered a restrictor plate in the throttle body. A little research showed the only difference between the 40 HP and the 30 HP was that plate. All other parts are exactly the same, brain, sensors, camshaft, etc., etc. Of course I removed the plate (my wife's comment, "Do you have to turbocharge everything?") Wow, what a difference it made.
It would run quickly to 6000 RPM, I went up in prop size, and went from three blade to 4 blade. Much better. There is a throttle position that once you go beyond the motor stumbles and progressively bogs down, worsens with more throttle. Always exactly the same lever position where it starts. Never happened before the 30-40 conversion. With the new prop it starts at about 5100 rpm (it still runs quickly and smoothly to that RPM). Never noticed it before the prop change, I think because I didn't want to run above 5,500 RPM and never pushed the throttle to WOT position. I can fix it by adjusting the WOT stop, but of course I know there's a little more motor in there somewhere.
It seems obvious that fuel is not keeping up with the air at that throttle position. I read an old thread about Mercury chronic fuel pump problems in that motor series, a Merc mechanic commenting about pumps often putting out only 80%. Any ideas? I haven't tried squeezing the primer bulb when the stumble starts, would that translate to a boost through the pump, and smooth things out momentarily in an EFI system?
Again, the parts lists and diagrams for the 30 and 40 are exactly the same, with an asterisk by the restrictor plate (for 30 HP only). How much hassle is it to replace the pump? I'm a competent half ass amateur mechanic, but my worn out carpenter hands and eyes are more suited for low finesse work. I could easily shine on this problem and be happy, and don't want to go the trial and error route, but in the back of my mind I know I want to solve this.
Great forum. Any help, opinions, or comments would be appreciated.
