ryanburns22
New Member
My issue is an off idle bog that I can’t seem to cure. I’ve tried everything I can think off but still can’t seem to get the bog tuned out. I picked up this 93 Seadoo XP end of April this year for cheap. It has the 657 Rotax engine with dual Mikuni BN-38 (SB) carbs. The ski is all stock with no aftermarket mods. Stock carb jets, stock air intake, stock everything. It had been sitting up about six years and needed some work. Compression is good at 150 psi on each cylinder. Here is a list of the things I done to get it back to where it needs to be:
- Pulled & cleaned fuel tank and baffle
- Replaced all fuel lines
- New fuel selector valve
- Pulled both carbs. Disassembled them, cleaned them (boiled them in lemon juice), and rebuilt them with new kits
- Made sure both carbs were synced correctly
- Verified no air leaks in the fuel system
- Adjusted pop-off pressure from 30 psi down to 22 psi. May have helped some but still did not cure the bog.
- Pressured tested needle and seat and both carbs hold up to 15 psi for 30+ seconds
The ski will start right up (once warm) and the idle is stedy and smooth dead on 1,500 rpm’s. I’ve tried adjusting the LS needled everywhere from 1 to 2 ½ turns out but still can’t cure it. As I turn them out (richer) it seems to get better with the best setting being around 2 full turns out. The engine still bogs at this setting but can pull through the bog without having to pop the choke. Anything below 2 turns out and you have to pop the choke to get through the bog or the engine dies out. Anything above two turns out and it becomes too rich and starts loading up and surging a bit.
Once past the bog the ski seems to run fine. Couple things to mention on this note. Not sure if any of this is abnormal or not but though I’d at least mention it. There is some slight hesitation in throttle response in the mid-range. This may be normal, not sure, but it’s definitely there. Also you can really feel the transition into the high speed circuit. Once you get between ½ and ¾ throttle the ski really jumps and takes off. It’s not a “smooth” transition.
So in regards to the off idle bog. Can anyone give me some idea of what may be causing this? Or any other ideas on what I may could do to cure it? At this point I’m about ready to chalk it up to the carbs themselves being the issue, which means I’d just have to replace them. I know that this can happen but I think it is pretty rare. I also don’t want to spend $300+ on a new set of carbs if there is something I haven’t though of or something else I can try to get these running like they should.
Any advice or help would be greatly appreciated. I’m just out of ideas at this point.
- Pulled & cleaned fuel tank and baffle
- Replaced all fuel lines
- New fuel selector valve
- Pulled both carbs. Disassembled them, cleaned them (boiled them in lemon juice), and rebuilt them with new kits
- Made sure both carbs were synced correctly
- Verified no air leaks in the fuel system
- Adjusted pop-off pressure from 30 psi down to 22 psi. May have helped some but still did not cure the bog.
- Pressured tested needle and seat and both carbs hold up to 15 psi for 30+ seconds
The ski will start right up (once warm) and the idle is stedy and smooth dead on 1,500 rpm’s. I’ve tried adjusting the LS needled everywhere from 1 to 2 ½ turns out but still can’t cure it. As I turn them out (richer) it seems to get better with the best setting being around 2 full turns out. The engine still bogs at this setting but can pull through the bog without having to pop the choke. Anything below 2 turns out and you have to pop the choke to get through the bog or the engine dies out. Anything above two turns out and it becomes too rich and starts loading up and surging a bit.
Once past the bog the ski seems to run fine. Couple things to mention on this note. Not sure if any of this is abnormal or not but though I’d at least mention it. There is some slight hesitation in throttle response in the mid-range. This may be normal, not sure, but it’s definitely there. Also you can really feel the transition into the high speed circuit. Once you get between ½ and ¾ throttle the ski really jumps and takes off. It’s not a “smooth” transition.
So in regards to the off idle bog. Can anyone give me some idea of what may be causing this? Or any other ideas on what I may could do to cure it? At this point I’m about ready to chalk it up to the carbs themselves being the issue, which means I’d just have to replace them. I know that this can happen but I think it is pretty rare. I also don’t want to spend $300+ on a new set of carbs if there is something I haven’t though of or something else I can try to get these running like they should.
Any advice or help would be greatly appreciated. I’m just out of ideas at this point.
