robinsbd
Petty Officer 2nd Class
- Joined
- Dec 7, 2013
- Messages
- 138
A little bit of background: I was having an issue with my engine not being able to idle last year. I did a complete carb rebuild last year and I also did an initial tune up (plugs, wires, cap, rotor, ignition coil). After the carb rebuild, I had the boat out on the water last fall (warm 60 degree days during the first week of November). When I did the carb tuning, I was able to get it to idle pretty decent. I took it for a long run and didn't have any issues bringing it back to idle and docking was great.
This year, first time out, I ran into a similar issue. I could run up the river no problem at speed, but as soon as I want to idle, it just stumbles and dies. While in forward gear, I was only able to get the RPMs down to about 1200 steady. Anything below that, and it would stumble and die. My first thought was that the fuel is getting old (a little over 2 seasons old w/ one treatment of stabil). I know this ethanol gas goes bad fast, so I pumped all the gas out and filled a fresh tank of gas and I also added seafoam in the correct proportion with maybe 5 or 6 gallons untreated so the mix is a little weak on the seafoam, which is fine. I just figure it helps stabilize the gas a bit and maybe cleans a little bit as it passes through the carb.
The engine still wouldn't idle. So, I went through the carb tuning procedure from the Merc manual the same as I did last year. I have the Thunderbolt V in base timing mode and set the idle mix and speed screws to their default settings. I was finally able to get it to idle steady after backing out the idle mix needle more than 2 turns. That seemed pretty normal and I think that was close to the same as last year. It's idling in neutral at about 700 RPM according to the dash tach. Seems a little rough. I backed the idle mix screw out more and more and the idle kept going up. I was able to back it out at least 5 turns and she still runs. That's how I got the idle all the way to 700. I never touched the speed screw and left it at the default setting (2 turns in).
Now, when I try to rev the engine slowly, it hesitates and stumbles and acts like it wants to die. If I punch the throttle, she revs way up to 3K no problem and then I let it back down to idle. It stays idling, but as soon as I try to accelerate gradually, it just stumbles and stumbles. Also, I got it to back fire once through the carb. I turned the idle mix screw back in to somewhere around 3 turns out, but the acceleration issue is still the same. When I push the accelerator forward, it just hesitates, starts to hiss a little louder and then stumbles and it will back fire if I do that too much. I also tried the same thing in normal mode (not base timing mode), and it still acts the same. Again, if I punch the throttle, it will stumble some and then accelerate way high, but it's definitely not working right.
Somethings going on here, but I just don't know where to look next. I did all my testing in the water tied up to a dock. I don't want to leave the dock in this condition, so I'm back on the trailer again.
Thanks for your help!
This year, first time out, I ran into a similar issue. I could run up the river no problem at speed, but as soon as I want to idle, it just stumbles and dies. While in forward gear, I was only able to get the RPMs down to about 1200 steady. Anything below that, and it would stumble and die. My first thought was that the fuel is getting old (a little over 2 seasons old w/ one treatment of stabil). I know this ethanol gas goes bad fast, so I pumped all the gas out and filled a fresh tank of gas and I also added seafoam in the correct proportion with maybe 5 or 6 gallons untreated so the mix is a little weak on the seafoam, which is fine. I just figure it helps stabilize the gas a bit and maybe cleans a little bit as it passes through the carb.
The engine still wouldn't idle. So, I went through the carb tuning procedure from the Merc manual the same as I did last year. I have the Thunderbolt V in base timing mode and set the idle mix and speed screws to their default settings. I was finally able to get it to idle steady after backing out the idle mix needle more than 2 turns. That seemed pretty normal and I think that was close to the same as last year. It's idling in neutral at about 700 RPM according to the dash tach. Seems a little rough. I backed the idle mix screw out more and more and the idle kept going up. I was able to back it out at least 5 turns and she still runs. That's how I got the idle all the way to 700. I never touched the speed screw and left it at the default setting (2 turns in).
Now, when I try to rev the engine slowly, it hesitates and stumbles and acts like it wants to die. If I punch the throttle, she revs way up to 3K no problem and then I let it back down to idle. It stays idling, but as soon as I try to accelerate gradually, it just stumbles and stumbles. Also, I got it to back fire once through the carb. I turned the idle mix screw back in to somewhere around 3 turns out, but the acceleration issue is still the same. When I push the accelerator forward, it just hesitates, starts to hiss a little louder and then stumbles and it will back fire if I do that too much. I also tried the same thing in normal mode (not base timing mode), and it still acts the same. Again, if I punch the throttle, it will stumble some and then accelerate way high, but it's definitely not working right.
Somethings going on here, but I just don't know where to look next. I did all my testing in the water tied up to a dock. I don't want to leave the dock in this condition, so I'm back on the trailer again.
Thanks for your help!