Hi all,
Over the winter I rebuilt the carbs in my 2003 Sportster LE 951. I purchased the boat early 2023, and the boat ran pretty bad. Rough idle, stalled when giving it gas, and would run at high rpm great for about 20 minutes, die, and not start back up until you changed the plugs. Plugs would come out dripping wet with oil/fuel.
When I rebuilt the carbs, I surprisingly discovered they were open before, and they were very clean inside. The settings were quite off from spec... Low was 1 turn on each side, high was 1 turn, 1 1/2 on the other side... I also discovered that the wrong pop off spring was used, as it had a silver spring that was popping off around 30psi. I cleaned every nook and cranny, inspected and cleaned the jets, replaced the needle valves and seats, the metering assembly, and put the proper black spring in, all genuine Mikuni parts. I tested the carbs afterwards and got a perfect pop off pressure of 20psi. I set all the carb adjustments back to factory specifications: 1 1/2 low, 0 high, and used the recommended idle set of 1/2turn after touching plate. (Trying to remember without the shop manual in front of me at the time of writing this)
I also discovered the oil injection pump was set way too rich, so I properly adjusted that back to specs.
Took it out on the water and idles perfectly smooth, and idle to 1/4 is crisp, smooth, and responsive. 1/4 to 1/2 has a slight hesitation but cleans up pretty quick. My problem is anything over 1/2. When giving it gas, the motor just bogs out. You can go from 1/2 to WOT and nothing happens, just the motor sounds like its running out of breath. Now, if you quicky pump the throttle up and down while going above 1/2, the motor runs great and will eventually get to WOT running great until you let off the throttle again.
1/4 throttle plug chop looks mocha brown, 3/4-WOT plug chop plugs have a reddish tint(fuel additive from the winter storage??)
I tried to richen the low speed adjusters and did not seem to have any effect. I turned the high speed adjusters out about 1/4 and now the boat had a hard time running around 1/4 throttle...
I have done so much research and time learning about these carbs and boats I am beginning to get burned out. What do I need to do here? I'm assuming this sounds like a very lean condition over 1/2 throttle, but why does pumping the throttle make it run fantastic? From what I have read on here, the accelerator pump is useless after 1/4 throttle, and I can see it squirting fuel into the carbs when giving it gas. I don't remember the exact compression test results I got, but I do remember that they were well within specs. I am not expecting someone to diagnose this over the web, but if someone could point me in which direction I should be taking from here I would greatly appreciate the help!
Over the winter I rebuilt the carbs in my 2003 Sportster LE 951. I purchased the boat early 2023, and the boat ran pretty bad. Rough idle, stalled when giving it gas, and would run at high rpm great for about 20 minutes, die, and not start back up until you changed the plugs. Plugs would come out dripping wet with oil/fuel.
When I rebuilt the carbs, I surprisingly discovered they were open before, and they were very clean inside. The settings were quite off from spec... Low was 1 turn on each side, high was 1 turn, 1 1/2 on the other side... I also discovered that the wrong pop off spring was used, as it had a silver spring that was popping off around 30psi. I cleaned every nook and cranny, inspected and cleaned the jets, replaced the needle valves and seats, the metering assembly, and put the proper black spring in, all genuine Mikuni parts. I tested the carbs afterwards and got a perfect pop off pressure of 20psi. I set all the carb adjustments back to factory specifications: 1 1/2 low, 0 high, and used the recommended idle set of 1/2turn after touching plate. (Trying to remember without the shop manual in front of me at the time of writing this)
I also discovered the oil injection pump was set way too rich, so I properly adjusted that back to specs.
Took it out on the water and idles perfectly smooth, and idle to 1/4 is crisp, smooth, and responsive. 1/4 to 1/2 has a slight hesitation but cleans up pretty quick. My problem is anything over 1/2. When giving it gas, the motor just bogs out. You can go from 1/2 to WOT and nothing happens, just the motor sounds like its running out of breath. Now, if you quicky pump the throttle up and down while going above 1/2, the motor runs great and will eventually get to WOT running great until you let off the throttle again.
1/4 throttle plug chop looks mocha brown, 3/4-WOT plug chop plugs have a reddish tint(fuel additive from the winter storage??)
I tried to richen the low speed adjusters and did not seem to have any effect. I turned the high speed adjusters out about 1/4 and now the boat had a hard time running around 1/4 throttle...
I have done so much research and time learning about these carbs and boats I am beginning to get burned out. What do I need to do here? I'm assuming this sounds like a very lean condition over 1/2 throttle, but why does pumping the throttle make it run fantastic? From what I have read on here, the accelerator pump is useless after 1/4 throttle, and I can see it squirting fuel into the carbs when giving it gas. I don't remember the exact compression test results I got, but I do remember that they were well within specs. I am not expecting someone to diagnose this over the web, but if someone could point me in which direction I should be taking from here I would greatly appreciate the help!
