I have a 1996 HX. At any RPM over idle the ski runs great! However, the issue I'm having is...when riding the ski in the water and slowing all the way to idle the ski will sputter and not rev back up. It seems like the motor is running supper rich. When I go to full throttle there is no change at all. The ski will make just enough headway so I can stay balanced and have some forward momentum in the water. If I continuously pump on the throttle (or just leave it alone and idle, seems to make no difference) after maybe 30 seconds to a minute as I flounder in the water it will finally clean out and immediately pick up rpms again and I'm flying down the lake again. I have tried messing with the low speed air screws. It will seem to make a change...when I screw it in the mixture will be leaned out and the idle rpms will be high...then after a few seconds it goes back into the sputtering, barely running, super rich, idle just like before. I can kinda duplicate this when I run it on the water hose...after cranking and a few short revs I'll go to idle and after a few seconds I can see and hear the motor go from a nice smooth idle to a rough, rich sounding, bogging, shaking idle. It is much worse in the open water however. It will clean up and rev much quicker on the hose. I pulled the carbs twice to check the low speed screws (I previously rebuilt the carbs with a Mikuni kit) and the carbs are clean, the low and high speed screws have the rubber o-rings and springs like they should. One thing I do see when I have the ski on the trailer (and garden hose) with the air box and screen off, is a dripping of gas from the top of the pto carb. It looks like its coming from the round piece that the main jet supplies. I have checked both high speed screws and they both look fine with rubber o-rings and springs. I have both high speed screws turned to the zero spec and I started the low speed screws at 1 1/4. I hope I'm correct that screwing in these (clockwise) makes the motor run leaner. I am starting to think its an electrical problem. I did put a new MPEM module in the ski. Something I bought a few years ago off eBay. Could it be this module? I put a spark tester on both cylinders and they are both still sparking when the ski goes to idle and this bogging starts to happen. I have been trying to figure this out for over a year! I have been riding the ski but never slowing to an idle because of this. And, when I first crank the ski I have to keep it revved up so this doesn't happen as well. As long as it is at an RPM slighly over idle it runs clean and fine. Any suggests would be greatly appreciated as I am at a loss as what to do next.
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HX Issue I can't solve. Help!
- Thread starter bawray
- Start date
I did use a genuine Mikuni rebuild kit before and the ski has very little time on it since that was done. I installed new needles and seats as well. I used the black springs and checked the pop-off and it was within spec (its been over a year and I don't remember off the top of my head what the specs were, but I do remember checking it). I haven't done a leak down test or a compression test. Could an air leak around the motor or worn rings/low compression cause the issue I'm having?
The first thing I would address is the leaking fuel and then go from there
I took the carbs off and tried to see what was going on. It looks like the fuel must be coming from the main jet or the high speed air screw. I did replace the mylar tab in the small block above the main and pilot jets in case it was weak. I rechecked the high speed air screw as well to see if it was missing the washer, spring, or rubber o-ring and it seemed fine. I don't know what else to check??? I haven't tried using a smaller pilot jet but the way the ski is acting seems like the jetting may be fine and something else is causing it to bog like this.
I would see if the carb holds 10 pounds of pressure, maybe the needle is being held open? You can find the procedure for this test in mikidymacs carb rebuild thread or in the manual, while your at it good idea to check that the fuel pump isn’t leaking with 4 pounds of pressure although I don’t believe this is your problem, sounds to me like it’s getting to much fuel. How do the plugs look after it won’t pick up rpm’s? Where did you get the carb kit from?
I did a leak down test and pop-off test on the carbs when I rebuilt them with a Genuine Mikuni rebuild kit (don't remember who I bought it from...but it was the higher cost genuine Mikuni kit for sure). The pop-off pressure was good and they did hold pressure fine. I checked the fuel pump with pressure as well and it was good.
so
It's so hard to look at the plugs when this happens because I have to ride the ski back to the dock and load it on the trailer so I typically get it running good at higher RPM and keep it at a higher than idle RPM while loading. I am going riding tomorrow so I will be sure to idle it around the dock until it does this bogging thing again and then I'll get it on the trailer immediately so I can check the plugs.
I have a compression tester at home (6 hours away this weekend) but I'll check the cylinders as well when I get home.
As far as a leak down test on the motor...I have done leak down tests on my motorcycles (2 strokes) many times so I have what I need for a 1 cylinder test. I'm guessing it will be something like...remove the carbs and exhaust chamber, block off both carbs and both exhausts outlets in the manifold. Pump it up to 10psi and see if there are leaks. I had a 1980 YZ250 a couple of years ago and it just would NOT start unless I bump started it down a big hill. I did a leak down test on the motor and found a crack in the cylinder base leaking massive air...had to trash it and find a new one! But...this is typically for an air leak and shouldn't cause this rich condition. The ski starts fine. It just goes rich when it idles for a few seconds.
so
It's so hard to look at the plugs when this happens because I have to ride the ski back to the dock and load it on the trailer so I typically get it running good at higher RPM and keep it at a higher than idle RPM while loading. I am going riding tomorrow so I will be sure to idle it around the dock until it does this bogging thing again and then I'll get it on the trailer immediately so I can check the plugs.
I have a compression tester at home (6 hours away this weekend) but I'll check the cylinders as well when I get home.
As far as a leak down test on the motor...I have done leak down tests on my motorcycles (2 strokes) many times so I have what I need for a 1 cylinder test. I'm guessing it will be something like...remove the carbs and exhaust chamber, block off both carbs and both exhausts outlets in the manifold. Pump it up to 10psi and see if there are leaks. I had a 1980 YZ250 a couple of years ago and it just would NOT start unless I bump started it down a big hill. I did a leak down test on the motor and found a crack in the cylinder base leaking massive air...had to trash it and find a new one! But...this is typically for an air leak and shouldn't cause this rich condition. The ski starts fine. It just goes rich when it idles for a few seconds.
Hmmm, seems like you’re doing things right. Do you remember what your pop off was? Also what is your low speed screw set at? Pain in the ass but did you happen to see the size of the pilot jet? You did say it ran correctly before the carb rebuild though if I recall? So jet size must be right. Stock air box? This is going to sound stupid, but my HX did the same thing the first time I took it out, acted like it was loading up on fuel, I didn’t have the spark plugs tightened down
. Other than finding where that fuel leak is from, I’m at a bit of a loss. I’ve just been lucky with the carbs I’ve rebuilt. I just check compression, spark, and if I have both of those, rebuild the carbs according to the rebuild thread on here, pressure/vacuum test the fuel system and fuel filter, change the selector valve.
. Other than finding where that fuel leak is from, I’m at a bit of a loss. I’ve just been lucky with the carbs I’ve rebuilt. I just check compression, spark, and if I have both of those, rebuild the carbs according to the rebuild thread on here, pressure/vacuum test the fuel system and fuel filter, change the selector valve.I don't remember what the pop-off was other than it was within spec. Its been over a year ago. I did watch ever video of the rebuild thread (thanks for that btw!, its extremely helpful). I also don't remember the size of the pilot jet either. I just know I used what was already there and it has everything stock (air box and all). I have been messing with the air screw and it does seem to change the idle speed which is showing me the pilot is OK...but after a few seconds of a higher idle after leaning the mixture, it goes back to the really low idle speed, rough idle, motor shaking thing again like its super rich and it won't build any RPMs until it seemingly randomly perks up again and takes off. I can pull the throttle lever in to give it some air but pulling in the throttle lever doesn't seem to make any difference at all. I did check the spark plugs for tightness and they are good. However, your experience is enlightening...I need to run a compression test and probably a leak down test on the motor to see if there are any air leaks anywhere. I've tried to find the problem with carburation but maybe its not the carbs. I bought the ski a couple of years ago and I have never been out once (in maybe 10 trips in 2 years) where it ran perfectly. I replaced the pick up tube in the gas tank first, then fixed an exhaust leak, then replaced the battery, replaced the starter solenoid, replaced the starter, replaced the ignition box, replaced all the gas lines, replaced the water/fuel separator, replaced the pressure relief valve, etc. It has really been a frustrating experience. Before the carb rebuild it was having issues and I've been chasing it from the beginning. Good news is it runs awesome as long as it's not idling. If I can just find this idling issue then it should be right (I hope).Hmmm, seems like you’re doing things right. Do you remember what your pop off was? Also what is your low speed screw set at? Pain in the ass but did you happen to see the size of the pilot jet? You did say it ran correctly before the carb rebuild though if I recall? So jet size must be right. Stock air box? This is going to sound stupid, but my HX did the same thing the first time I took it out, acted like it was loading up on fuel, I didn’t have the spark plugs tightened down
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Good idea, I would start from the Top. When your checking the pop off, you shouldn’t be bending the lever to obtain a certain pop off, the pop off will be what it is and should only be changed by changing the spring to the correct spring. When you’re done, just put the high and low speed screw to factory specs. Might as well check that it’s holding 10 pounds again after it’s back together. I can’t remember exactly what they do or exactly where they are but the 2 Mylar discs that usually have the blue strip. Make sure the blue stripe is up and that you didn’t punch a hole through the grommets that hold them in place. I found dental floss to pull them through worked best for me. Might as well take the pilot jet out and make sure you have good flow of carb cleaner when spraying in there to the 3 small holes in the carb throat, and just for the hell if it, check what size of pilot and high speed jets are there.
