Full tank? No go. Half tank? Let's scoot.

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bwhite

bwhite

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One of my skis (rebuilt carbs, new fuel lines except for vent, and new fuel selector) will run on 3/4 a tank without issue. If I fill the tank up it almost will not crank and when it finally does it bogs something awful.

I checked my intake vent (under the front hood) and could push air through. I took the hose off the baffle and Sucked, no issue. Okay, so the tank is getting air, has to be..

I took the entire fuel vent system, lines and all, replaced the lines and blew carb cleaner through all the splitters and adapters, as well as the check valves. I could Suck air out of the rub-rail (pressure relief) valve afterwards but could barely force air through the other direction (out of the tank direction). I assume this is to allow the fuel system to build enough pressure.

Okay, so all should function well now, right? Could there be something I missed? I didn't bother refilling it because at that point I had burnt off the 1/4 tank of gas and it ran great.
 
The fuel system doesn't need to "Build pressure" to run. The carbs have a fuel pump, and suck fuel from the tank.

I know you said you put carb clean thought the valves, and some of the hoses... but have you physically taken the fuel select valve apart, and checked it?
 
Does it run with a full tank and the fuel filler cap left off? I'd put money on the vent (but I'm basing that on motorbikes rather than PWC / boats which I'm new to).
The only other thing I can think of is float height / float sinking in the carb (if you even have a float in the carb ;)) that could be affected by fuel level.


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Dr. Honda, they're brand new selectors. It did this with the old selectors as well.

I rechecked the baffle labels, as well. They're in the right spot.
 
bwhite said:
Dr. Honda, they're brand new selectors. It did this with the old selectors as well.

I rechecked the baffle labels, as well. They're in the right spot.
Click to expand...

OK....


All I can think of, is that you have a leaking needle valve. If it was Mine.. I would pull the carbs again, and double check them.
 
bwhite said:
One of my skis (rebuilt carbs, new fuel lines except for vent, and new fuel selector) will run on 3/4 a tank without issue. If I fill the tank up it almost will not crank and when it finally does it bogs something awful.
Click to expand...

Sounds like gas is siphoning into the engine and almost liquid locking it and flooding it once it's running. I say siphoning because it only happens when the fuel level in the tank is higher than the carbs. So head height pressure of the gas, not air pressure, is driving fuel past your needle valve(s). Either they are leaking, pop off is too low, or the diaphram cover is touching the lever. Make sure you have Mikuni parts, especially the diaphram, needle/seat and spring.
 
I agree with the previous couple posts. I saw similar when I screwed up and set the lever wrong for the needle valve so it was forcing the needle valve open ... yes, I screwed up #2 by not doing a pop-off check with the assembled carb. Almost all of the carbs (not a large number) I have cleaned up had leakage around the o-ring for the needle valve seat.

Bad terminology by me, it would be a leakage test on the assembled carb.
 
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Hmm, the carbs were just rebuilt and pretty sure we did a Pop off test, which was within spec. Hmm..
 
bwhite said:
Hmm, the carbs were just rebuilt and pretty sure we did a Pop off test, which was within spec. Hmm..
Click to expand...

Do a leak down test when they are fully assembled. Block the return port and pressurize something less than pop off and it should hold for, ideally, 5 minutes.
 
I actually bought SBT Mikuni kits, which I thought were Mikuni parts genuinely. Can I purchase just Mikuni diaphragms, since I literally just rebuilt everything else?

The needle lever should be level with the plate, correct?
 
bwhite said:
I actually bought SBT Mikuni kits, which I thought were Mikuni parts genuinely. Can I purchase just Mikuni diaphragms, since I literally just rebuilt everything else?

The needle lever should be level with the plate, correct?
Click to expand...


Yes... you can get just OEM diaphragms... and I'm guessing those SBT parts are the issue. AND... if you used the springs from those kits... they aren't helping either.


Yes, you start with the arm flat... and then can move a few mm up or down to adjust the pop-off. BUT, since Seadoo specs such a large window... it's normally not needed.
 
Dr Honda said:
Yes... you can get just OEM diaphragms... and I'm guessing those SBT parts are the issue. AND... if you used the springs from those kits... they aren't helping either.


Yes, you start with the arm flat... and then can move a few mm up or down to adjust the pop-off. BUT, since Seadoo specs such a large window... it's normally not needed.
Click to expand...
That's probably the case, from what I've read on SBT kits. Pretty sure we used those Springs as well. Ironically this thing runs great unless it's got a lot of fuel in the tank. The other ski's throttle seems to hang at low speed for 3-5secs/hesitates off idle for a second. Any chance I could get a pointer as to where to purchase OEM parts?

While I'm thinking about it, is it normal for the pressure relief valve to not be able to blow (in 6 inches of fuel line) and get the pressure to release?
 
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So far, every post I have read that have replaced the pop off spring has had an issue. Not saying the spring has to do with your issue, just saying that you will likely have an issue once you get it running.

If you have the spring that came out, put it back in...


What do the spark plugs look like when the tank is full and it won't start? Are the fuel soaked?
 
bwhite said:
While I'm thinking about it, is it normal for the pressure relief valve to not be able to blow (in 6 inches of fuel line) and get the pressure to release?
Click to expand...
If the pressure relief is functioning properly you should be able to blow hard enough to release without any hose. I'm not sure 6" of hose would make this too hard. But here is a way to see if you can get it functioning. Take a bike pump with the little attachment for inflating inflatables and give it a pump. If that doesn't get it loose try air compressor if you have one. Once you see it is releasing, force some soapy water through it, then some alcohol. I try to avoid carb cleaner on these as it is plastic and I am sure probably a rubber seal in there.



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Could the carb pop off issue also cause that sticking throttle in water? When I went to flush them today that same one fired up and consistently got higher rpm until it seemed like it was about to cap. I pulled the key and waited a bit, tried it two more times and it did the same thing in a matter of 3 seconds.

It was.. Honestly kind of scaring me from riding them.
 
Thanks Jimmaki, I'll see if they sell indiv carb parts.

Also, the condition I was speaking of was almost like Engine Runaway, except when I pulled the lanyard it would shut off. Could this be from too high of an idle? It seemed to idle perfect in water. (Tachs are not working on either ski, so not sure what the exact RPM is at in water)
 
You're welcome, they do.

I could be, either from too high an idle stop setting, too lean a ls adjuster setting or too tight a throttle cable ... or an air leak.
 
I'll probably tear down the carbs in the next week or so. If I replace those diaphragms with OEM in both skis, think that should solve majority of the throttle sticking/fuel tank full issue? What should I look for when I break them down?
 
Figured I'd post a short video showing out of water after I put a bit more gas in the tank. I lowered the idle speed screw a half turn and adjusted the low speed screw back to 1-1/2 turn out (factory spec is 1-3/4). Still notice a delayed rev later in the video. Seems to idle very rough, though.

https://youtu.be/G04wkV2NFaA
 
Well, I tore one of the skis apart that had a rough idle issue/slight hesitation. The lever was bent up too high and was not flush on the PTO carb. Readjusted that and will report back when I splash them. Also did not realize you should adjust low-speed adjuster for smooth idle and not idle speed stop. Fixed that issue and will correct in water.

As for the other.. both carbs seemed fine. Only other thing I could think of (aside from aftermarket diaphragms) is that the fuel reading is not showing correct. If it's being overfilled, could it technically block off the vent tube in the baffle? No longer allowing a vacuum to suck air through the vent.
 
The low speed screw should be set to stock on a stock ski. That being said it is set to get the highest idle possible not as much as the smoothest idle but I guess they go hand in hand. When they are set exactly perfectly any turn in or out will cause the rpm's to drop but it is usually only noticeable if you have a fast updating tach like a TinyTach.
 
I followed the "makeshift pop-off tester" guide to make a pop-off running off of an air compressor. My question is, there's not really a way to test a diaphragm leak with that, though is there? I'd need a manual hand pump to assure there is no more pressure coming through, right? Any recommendations on where I can get a decently priced manual pump tester?
 
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Yes, as long as you have the ball valve on the new tester simply close the valve and disconnect the air compressor. Watch for leak down. Carb should hold 10 lbs for 10 minutes.


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