HX Carb rebuild done. Now having a problem with gas flowing when I close the butterflys

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bawray

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So...I have two new (old) skis...a 1996 HX and a 1998 XP Limited. I have rebuilt the carbs in both. I *thought* the 1996 HX (tock 717 motor) was good. I ran 3 gallons of gas through it on the first ride and it ran great. Today was the second ride. The first 20-30 minutes the ski ran great again. Then it started having issues. At first it seemed like it was loading up with gas and running super rich. Then it would lean out and run fine. Then as I was going wide open down the waterway the motor would suddenly lose all power then surge and take off again then lose power then surge again. Seemed like it would lose fuel then pick it up again, then lose fuel, then pick it up again, etc. When I slowed down it seemed to load up with gas again. Wouldn't idle either but that may have been the idle screw adjustment. I brought the ski home and removed the air box and "filter" so I could see down into the carb bodies. When the ski is running and I rev it up it seems OK but when I let off the throttle I can see a squirt of gas going into the carb body on top of the closed butterflies on both carbs. When I see the squirt of gas the motor runs super rich and loses power.

Any idea what is going on? When I bought the ski the previous owner had this "bogging" problem but convinced me it was bad gas and the carbs just needed cleaning. Do I have two bad carbs? Did I do something wrong in the rebuild? I used a genuine Mikuni rebuild kit and new Mikuni needle and seat in each carb. I checked the pop-off pressures in both carbs and they were right according to the chart on this site. Those dang little rubber grommets and round thin check values were a pain. Maybe I messed them up??? Everything else seemed to go smooth on the rebuild. Why was it running great then all of a sudden this problem?
 
You need to check the carbs for leak down. You don’t need to remove them but will need to disconnect the supply and return lines from them.
 
I will check for leak down today. Will I need to check each carb separately? Or can I leave the connecting hose on and only block off the return hose from each carb and check both at the same time? If there is a leak then I guess I will have to remove both carbs and check individually then???
 
So, I removed the return line going to the fuel tank and blocked it off. This blocked off both returns from both carbs since they are grouped together at the Y connection. I removed the input line from the fuel filter and attached my pump to the inlet line going to the mag carb. This should create a sealed system of both carbs (right?). I then pumped the system to 10 pounds. Rock solid for over 2 minutes. Just for fun I pumped it to 20 pounds. Rock solid. Even 25 pounds. Rock solid for over 2 minutes. Then I checked the pop off pressure (I know it would be for the carb with the lowest pressure only) and it was about 55 (spec for my ski is 36-60). Seems like doing both like this would be OK as long as the pressure holds it would have to hold for both carbs right? Or, do I need to go back and block off each return line separately and use the separate inlets as well?

Assuming what I did is OK to check leak down...what now?
 
You can't test pop-off with the carb diaphragms installed.

Typically fuel dumping out of the tops of the carbs is a bad check valve. It is the little Mylar check valve on the fuel block that covers the jets in the carbs.
 
On the PTO carb the mylar check valve under the fuel block was probably the culprit. It wasn't centered between the two dots. In fact, it was covering up one of the dots and barely covering the hole. This was the carb with the most fuel being dumped into the top. I really didn't see much (if any really) in the mag carb. I will try to take the ski out later this week and see how it does.

Thanks for all your help mikidymac!!!!
 
As an aside...I now see a great benefit of working on the carbs on the 951 motor...makes the 717 seem SOOOO much easier. Truth be told, even the 717 can be a bit hard to work on too! I am getting better at closing my eyes, contorting my body, reaching into really small spaces, mounting cables, tightening nuts and bolts, loosening nuts and bolts, etc. I am thinking I should maybe become some kind of surgeon after all this. ;)
 
bawray said:
As an aside...I now see a great benefit of working on the carbs on the 951 motor...makes the 717 seem SOOOO much easier. Truth be told, even the 717 can be a bit hard to work on too! I am getting better at closing my eyes, contorting my body, reaching into really small spaces, mounting cables, tightening nuts and bolts, loosening nuts and bolts, etc. I am thinking I should maybe become some kind of surgeon after all this. ;)
Click to expand...
" I am getting better at closing my eyes, contorting my body, reaching into really small spaces, mounting cables, tightening nuts and bolts, loosening nuts and bolts, etc. I am thinking I should maybe become some kind of surgeon after all this." Hysterical! Being triple-jointed dwarf would also help!
 
I finally got a chance to try out the HX today. Still isn't running right. Here is the situation:

1) Rebuilt both carbs on the HX with genuine Mikuni carburetor rebuild kit (including the needle and seats)
2) First ride was about a full tank of gas. It ran great.
3) Second ride it was running great for about 1/4 tank of gas then all of a sudden it seemed like it was loading up with gas and running super rich...or...maybe it was not getting any gas and leaning out? Either way it would barely go fast enough for me to make it back against the current. As I was limping back to the boat ramp it would suddenly speed up and run fine for a few seconds. Then as it got up to speed the motor would suddenly lose all power and stall out, then surge back up with power and take off again, then lose power then surge again. Then it went back to barely making headway. When I got home and was flushing it out after the ride I thought I saw gas dumping in the carb body when I removed the airbox and ran it on the trailer (it was really difficult to see because I had to stand up to blip the throttle with the engine cover open and it was getting dark so I could have misled mikidymac with my previous post).
4) I removed the carbs and reset the mylar check value under the block to be perfectly between the two dots on both carbs. Reinstalled the carbs.
5) Rode it today and it ran great again for about 1/4 tank of gas. We even ventured out in the surf and jumped some waves today. Thank god it ran good in the ocean! Then just after I came back to the ICW it just did the same thing as before. This time I was about 1/2 mile from the dock. The ski would only run fast enough to make headway against the current in the ICW. BUT...this time the ONLY way it would run was at about 1/8 throttle with FULL CHOKE on! As soon as I back the choke off even a little it would lean out and die. I limped it back the 1/2 mile to the boat ramp at maybe 5 mph. So...seems like there is a fuel delivery issue for sure but I don't know exactly what is going on. Maybe it is only running on the idle circuit and the fuel pump isn't pumping any fuel? Maybe the pop off isn't popping? Maybe..maybe??? What is strange to me is how it will run great for a while...then all of a sudden this happens. I don't know if this matters but the fuel filter (maybe it is a fuel/water separator) was torn and I removed it. I need to order a new filter and get a new O-ring too. But that shouldn't be the problem...or is it? BTW...the previous owner bypassed the fuel selector and only used the reserve line to feed into the fuel filter. I replaced the old fuel selector with a new one before the first ride. It seems to be working fine. Could it be a crank seal leaking? How to check that?
6) Posted this plea for help!
 
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Did you bypass the fuel filter or just take out the filtering element and put it back on ?
 
The O ring is there...seems OK...no gas leaks when I replace the plastic assembly for the filter (without a filter inside). But it is hard to know if it is sealing while the ski is running at high rpm and the pump is pumping at a high pressure. I just remember reading something about this o ring needing to be replaced on a thread somewhere and I am wondering if it could be letting air into the system and causing a disruption of the fuel flow.

This is an edit...so I just removed the O ring from the cap...and now I can't get it back in the grove because the circumference is much too big. I wish I could say whether it was in the groove before but I just don't remember...seems like it would have to have been and I am 90% sure it was because I do recall thinking this is O ring is really FAT compared to the O ring I see in another filter in another ski I have. It probably just swoll up and now won't go back in the groove would be my guess. Do I need OEM filter/O ring? Are the filters/O rings on Amazon OK to use? Any of the aftermarket ones to stay away from? Or...better yet just bypass the OEM system and use an in-line filter?
 
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I would get a complete new filter assembly for $30.

It really sounds like either your fuel baffle is cracked and sucking air once the fuel lever gets too low or your fuel vent check valve is bad and not letting air in so as the tank level drops it creates a vacuum in the tank starving it for fuel.

Either way you still have a fuel issue and if pulling the choke helped then it is defiantly lean not rich.
 
I did switch over to reserve and saw no change in the performance of the ski. I also unscrewed the cap and let air into the tank which did not change anything either.
 
Running on the hose is no indication of anything. You will really only see issues in the water under load.
 
mikidymac said:
I would get a complete new filter assembly for $30.

It really sounds like either your fuel baffle is cracked and sucking air once the fuel lever gets too low or your fuel vent check valve is bad and not letting air in so as the tank level drops it creates a vacuum in the tank starving it for fuel.

Either way you still have a fuel issue and if pulling the choke helped then it is defiantly lean not rich.
Click to expand...
Are you saying I should replace the entire OEM assembly or just replace with an new filter and o ring (and the plastic bowl?). Can I just replace all that with an inline filter? If OEM where can I get one for $30?
 
No, do not use a generic inline filter as they can cause fuel starvation.

The OEM one from Seadoo is only $26.99 and includes the housing, top, filter and o-ring which is why I just replace the entire thing.

275500088
Fuel Filter Ass'y | Includes 15 - 17.
MSRP: $26.99
Dealer Price: $26.99
 
mikidymac said:
It really sounds like either your fuel baffle is cracked and sucking air once the fuel lever gets too low or your fuel vent check valve is bad and not letting air in so as the tank level drops it creates a vacuum in the tank starving it for fuel.

Either way you still have a fuel issue and if pulling the choke helped then it is defiantly lean not rich.
Click to expand...
I finally got around to checking the fuel check values on the HX today. As I understand it...there are two. One under the rubber cover under the gas cap (along with a check value for the oil tank). And one in a rubber grommet in the hull (the two vent lines are Y'ed together). I removed both and checked them.

From the parts diagram both of these should be the same check valve (275500398) and therefore function identically. I believe these check values should allow air into the tank as the fuel level drops but not allow air out thus keeping a constant pressure in the system. The check value up top is doing just that (allowing air in but not out). The check value in the hull however is not. It has been damaged (the grommet too). The end is broken off and it is allowing air to flow freely in both directions in and out. So this would allow the pressure to drop in the fuel tank as the fuel level drops. I am thinking this is what is causing the lean issue when the fuel level drops. Is that correct? Does the fuel pump need some pressure in the tank to help it draw the gas into the filter and then into the carbs? I have two new check values on the way and a new fuel filter assembly.

On a side not...the check value for the oil tank is mounting in the opposite direction. Allowing air out but not in. Is that the correct orientation for the oil tank check valve?
 
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If you put that swollen "O" ring in the freezer, it may seal for you in the short run. Almost sounds electrical, in that it runs right, then fails later, could be an ever slightly loose ground wire, it won't cost you anything to go over all your electrical connections,
 
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