Stumped!

[PGHMAN]

Trying to break-in my 95 XP 720 that I rebuilt over the winter. The past two times out it will run fine (varying throttle 25-30%) and riding 10- 15 minutes and coming a shore to let it cool. After a break 10 minute break it will start and idle but dies immediately if I provide throttle.
Comp is 150 on each, running premix, carbs rebuilt with Mikuni kit - pop off 43. High zero, low 1 3/4.
Pulled plugs which are coca brown and not fouled. For grins I replace with new plugs and let it cool longer and take off and run fine. It sounds like a fuel delivery problem but seeking some guidance. STUMPED!
Thanks.

 

[68ragtop]

I would try pulling the choke some before hitting the throttle to see if that makes the problem worse, or improves it. could be its running too lean or rich on the low speed circuit.

is your idle speed at 1500 in the water?

 

[JJinSC]

Try what ragtop says and let us know. This could be several things, but knowing the results of that test will narrow things down.


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[PGHMAN]

I would try pulling the choke some before hitting the throttle to see if that makes the problem worse, or improves it. could be its running too lean or rich on the low speed circuit.

is your idle speed at 1500 in the water?

Yes, running at 1500 in the water. Meant to add in my original post that I replaced the N/S when I rebuilt the carbs. When I pull the plugs they show wet.

 

[68ragtop]

how long will it idle? Are you saying it will idle for a good length of time, you crack the throttle & it dies? is it at that time that it has wet plugs? Sounds like its loading up at idle. If turning in the low speed screws in doesn't effect anything, is there any chance your needle & seat are leaking? I would imagine you checked this during your popoff test, but its also possible that your diaphragm cover is holding the needle open some? How does it start after its been sitting for a few minutes? sure sound like leaking needles. Both plugs are soaked with fuel? mikuni parts?

 

[PGHMAN]

how long will it idle? Are you saying it will idle for a good length of time, you crack the throttle & it dies? is it at that time that it has wet plugs? Sounds like its loading up at idle. If turning in the low speed screws in doesn't effect anything, is there any chance your needle & seat are leaking? I would imagine you checked this during your popoff test, but its also possible that your diaphragm cover is holding the needle open some? How does it start after its been sitting for a few minutes? sure sound like leaking needles. Both plugs are soaked with fuel? mikuni parts?

It will idle indefinitely and once the throttle is cracked it dies. The plugs seem wet all the time. I have yet to mess with the low speed screw - set at 1 3/4 out. Yes, did multiple tests during pop off to verify the needle an seat did not leak. Does start after sitting for a while and seems to run fine.
I may pull the carbs to triple check the various tests.

 

[PGHMAN]

Yes, I used Mikuni parts.

 

[JJinSC]

I was thinking what ragtop was but wanted to wait and hear the results of the choke test. If when you give it throttle and it starts to die can you pull the choke and see if it tries to come back or not.


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[PGHMAN]

I was thinking what ragtop was but wanted to wait and hear the results of the choke test. If when you give it throttle and it starts to die can you pull the choke and see if it tries to come back or not.


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The issue only appears under load - running for a while. On the hose the throttle response has been very crisp and holds a good idle at 3k. I hope to pull the carbs today after work to take another look. Otherwise I'll try the choke test this weekend when I get out.
Thanks guys for the guidance.

 

[68ragtop]

Any chance the rotary valve timing is off?

Did you buy this as a non-running ski, or was it running good at some point before your rebuild?

 

[PGHMAN]

I was very diligent when I set the rotary timing. It was a non-running ski - needed a project
I had a thought in the past hour......the carbs are replacements that I purchased locally and I did not check the jets as far as size. Again, the N/S are 1.2 and the pop off is 43. What effect will the incorrect jets have....if they are the wrong size?
Pardon my ignorance on carbs. My other and first ski is an RFI.

 

[jimmaki]

I was very diligent when I set the rotary timing. It was a non-running ski - needed a project
I had a thought in the past hour......the carbs are replacements that I purchased locally and I did not check the jets as far as size. Again, the N/S are 1.2 and the pop off is 43. What effect will the incorrect jets have....if they are the wrong size?
Pardon my ignorance on carbs. My other and first ski is an RFI.

If new plugs temporarily fixed the problem, it might be running rich as opposed a lean bog. Try coming in on the low speed adjuster a little at a time. The low speed jet affects the throttle range just above idle so make sure yours are to spec. Mikuni jets have the square brand mark and the size stamped on them.

 

[PGHMAN]

No bog what so ever when is first starts out and runs for a while. I have yet to go WOT but the response is crisp.
When I ran on the hose the other day (runs fine) for 60 - 90 secs I pulled the plugs and they show wet. Also notice the top of each piston is wet when I rotate.
I plan to check the jets size once I get home. So go in with the low speed in small increments?

 

[1983]

1 carbs ( possibly both carbs ) Needles and seats are stuck open causing fuel to dribble into carb throats at idle and an over-rich condition.

Pop off is one measurement to do when rebuilding carbs, but ive seen it a million times. The carb holding psi test also has to be performed. Diaphram and metal plate installed. I did the psi holding test and it passed, then I installed metal plate over diaphram and installed carbs in skis, still wouldnt start well when warm after riding. Took off airbox, started ski and looked down into carb throat with flashlight and mirror, MAG carb was dribbling fuel into throat and it shouldn't be. Took carbs back apart and adjusted needle/seat lever arm then retested. It passed. Carb should hold a pressure below pop off for a certain amount of time without bleeding down. If gauge bleeds down, needle and seat and bleeding psi ( same as bleeding fuel while running )


Rob

 

[jimmaki]

No bog what so ever when is first starts out and runs for a while. I have yet to go WOT but the response is crisp.
When I ran on the hose the other day (runs fine) for 60 - 90 secs I pulled the plugs and they show wet. Also notice the top of each piston is wet when I rotate.
I plan to check the jets size once I get home. So go in with the low speed in small increments?

Yes, in the water try coming in 1/8 turn at a time and ride for a while to purge the crankcase. You won't ever tune it on the hose.

 

[1983]

I read and studied these on my first carb rebuilds note section I pasted from that thread. The second test in red is what im talking about.

http://www.seadooforum.com/showthread.php?40380-Carburetor-Adjustments

WONT START WHEN HOT? A pressure test consists of two tests. One when assembling the carb, by installing the needle valve, the lever and the spring, then soaking the needle with gas or WD40, then pumping up the pressure and watching for bubbles around the needle valve, then more pressure to measure when it pops off.
The second test comes after full assembly. This is the one that gives you an idea if they leak or not. You pump up at least 10 psi and watch the guage to see if it leaks off. It should hod 10 psi for ten minutes.
What is happening if the needle valves are leaking after full assembly, is that the diaphrams that you installed over the lever, is actually holding the levers down enough to allow the otherwise good needle valves to leak. This can be stopped by bending those lever arms down a little bit so the nipples on the diaphram are not resting against the levers that open the needle valves..

 

[PGHMAN]

I read and studied these on my first carb rebuilds note section I pasted from that thread. The second test in red is what im talking about.

http://www.seadooforum.com/showthread.php?40380-Carburetor-Adjustments

WONT START WHEN HOT? A pressure test consists of two tests. One when assembling the carb, by installing the needle valve, the lever and the spring, then soaking the needle with gas or WD40, then pumping up the pressure and watching for bubbles around the needle valve, then more pressure to measure when it pops off.
The second test comes after full assembly. This is the one that gives you an idea if they leak or not. You pump up at least 10 psi and watch the guage to see if it leaks off. It should hod 10 psi for ten minutes.
What is happening if the needle valves are leaking after full assembly, is that the diaphrams that you installed over the lever, is actually holding the levers down enough to allow the otherwise good needle valves to leak. This can be stopped by bending those lever arms down a little bit so the nipples on the diaphram are not resting against the levers that open the needle valves..

Hey Rob, I pulled the carbs to retest and will perform the 2nd test which I failed to do when I rebuilt originally.....rookie mistake.
Thanks guys for the guidance. I'll report back.
Rob

 

[PGHMAN]

I pulled the carbs last evening and discovered the main jet size is 137.5, pilot 67.5. Seadoo Source specs show main at 135. No where on spec sheet do I show any application for a 137.5 main. Should I replace the 137.5 for the 135? I understand the smaller the number the lower restriction on fuel delivery. Can I compensate by turning in the high/low? Current settings at 1 3/4 on low and zero on high. Continue to be Stumped!

 

[68ragtop]

At idle, there is so much vacuum on the low speed side that nothing comes out of the high speed. In fact, thats what that clear check valve (flap) is for in the metering block, keeps the low speed from pulling air instead of fuel. at idle, the low speed has the high speed completely shut off.

I wouldn't think the larger jets on the mains would cause the symptoms your having. Unless there is so much fuel at WOT that its loaded up before you come back to idle? there is one low speed port that is only controlled by the jet & two (on most carbs) that are controlled by the low speed adjuster. In theory, you should be able to turn in the low speed screws until it starves for fuel & dies. at this point it would require the choke to restart. I would run your LS screws in until you can make it go lean. if you can't, somethings still dumping fuel in there. You tested your needle leak test with the diagrams & cover in place, correct?

Diagnosing troubles like this aren't easy sometimes. Too bad you didn't have another set of carbs you could throw on to test with.

 

[Dr Honda]

OK....


are the carbs still off the ski???

Here's a list to start with.

1) Verify that the N/S is OEM Mikuni. Is there a little box, with a corner box stamped on it. (it's their stamp logo) Also, verify it's a 1.2. The 720 can run on a larger N/S,, but then the pop-off should be down around 24-28 psi.

There is a known issue with the aftermarket N/S. Basically, they aren't machined to the proper lengths, and in turn... to get the right pop-off... you put in a stronger, or weaker spring. One thing to keep in mind... the "Pop-Off" test is just a bench test. The carbs DO NOT operate that way. They actually get sucked open from the diaphragm side. So, it's a totally different dynamic. If you find it's not OEM... I'd put the old ones back in. (assuming they aren't destroyed)

2) Lets get that smaller main jet in there !! I know that the jet listed for your engine is a 135 main... but in '96, Seadoo dropped the 720 down to a 130. So, being at a 137.5 is really too big.

As far as the question above... "Can I compensate with the needles?" Yes you can, but unfortunately... your high needle should already be closed. (so you can't go less than that)

Personaly... if this was my ski, and knowing that it's running rich... I'd jet to the newer spec. (130) Then... if needed, you can open the high needle a little if you want. (I'd start with a 1/4 turn open)

3) Reflecting on #2... how do the needles look? Are they beat up? are they bent? are they corroded?? If they are leaking, then they aren't doing their jobs.



To be honest... when I was rebuilding carbs at my shop... I almost never replaced hard parts. I know there is a trend to "Rebuild" carbs... and people buy a "Rebuild Kit", and basically install it, and think that's good. BUT... what should be done, is to take them apart... evaluate what needs done... and only replace what needs replaced. A normal rebuild in my shop would be a simple cleaning. sometimes I would replace the diaphragms, pump valves, check valve, and gaskets. MOST of the time, I would replace O-rings, and similar rubber parts.

 

[Dr Honda]

Part 2.


So... it seems like it runs well, until the plugs foul. Right?

IF that's the case... then I'd say the RV is probably in the right spot. If you were out, even half a tooth... it would have some running issues. (bad idle, back fire, etc)


You made mention that you are running pre-mix. Is that just for the break-in, or did you not put the injection pump back on?


This is a rebuild... so, did you do the work? Did a shop do the work? (The actual rebuild, not the install)

 

[PGHMAN]

Good info Dr and Ragtop! The N/S are Mikuni 1.2, needles look very good - straight w. good tips. Pop off is 43 - is this too high? I got the spec from Seadoo Source.
Yes seems to run well for a while but after coming ashore and sitting for few minutes it will start but when throttle is applied it dies. The plugs are a coca brown not really fouled w. carbon but wet. The top of the pistons are also saturated.
I am running premix for break-in along with the oil injector. I did the rebuild using rebuilt OEM crank and FullBore did the top end WSM pistons .5 over. Performed leak test on motor prior to install. I was very diligent on setting the RV timing. I have yet to go WOT but to half throttle runs crisp with no bog or hesitation. In water idle steady at 1500.
One thing I do notice that the motor seems to run hotter than my 98 GTX RFI. All the cooling line/ports have been doubled checked and I have stream out the pisser. The pisser stream is not a strong the RFI.

 

[1983]

Did you do this test before disassembling carbs? If not you are chasing your tail. This needs to be done before disassembling carbs or you will never know if it is the culprit to your issue.

The second test comes after full assembly. This is the one that gives you an idea if they leak or not. You pump up at least 10 psi and watch the guage to see if it leaks off. It should hod 10 psi for ten minutes.
What is happening if the needle valves are leaking after full assembly, is that the diaphrams that you installed over the lever, is actually holding the levers down enough to allow the otherwise good needle valves to leak. This can be stopped by bending those lever arms down a little bit so the nipples on the diaphram are not resting against the levers that open the needle valves..

I pulled the carbs last evening and discovered the main jet size is 137.5, pilot 67.5. Seadoo Source specs show main at 135. No where on spec sheet do I show any application for a 137.5 main. Should I replace the 137.5 for the 135? I understand the smaller the number the lower restriction on fuel delivery. Can I compensate by turning in the high/low? Current settings at 1 3/4 on low and zero on high. Continue to be Stumped!

 

[Dr Honda]

The output stream isn't a huge factor. As long as it's coming out... it should be OK. So... why do you think it's hotter? Did you verify temps?

Regardless... a new, tight engine will run hotter, until the rings fully seat, and the pistons wear in.


The pop-off of 43 is fine, assuming OEM, and correct size parts.

What are the plugs wet with? Is it oil or fuel?? Knowing it's unburnt oil... it will be the color of your oil. Take a plug, and lightly touch it to a white towel, and let the "Wet" wick onto the towel. DO NOT wipe, because we don't want to put the burnt stuff on the towel.

How much oil is in the fuel? AND, did you verify the pump arm is on the right way, and adjusted properly?



Now... to 1983:

Why do it before taking the carbs apart? (or do you mean after the second time removing them?)


But he's basically right. After you verify the pop-off... then you put the diaphragm and cover on... then put 10 psi on the carb, and see if it holds. If it leaks down after a couple seconds... there's an issue. If it holds for a minute or more... it's probably OK, since the fuel pressure will drop faster than that, after the engine is off. But realistically... it should hold the pressure for a long time. (More than 5 min)

 

[1983]

I am saying after taking carbs off this most recent time to delve into the issue at hand with ski operation. Before disassembling diaphragms and all that to pump the carb up and see if it holds psi, or bleeds down to either verify this is the problem with ski, or rule it out. Happened on my ski where everything passed with diaphragm cover/plate not installed, but once installed it was touching diaphragm ever so slightly which pushed needle and seat lever arm and caused it to bleed down.

Rob

The output stream isn't a huge factor. As long as it's coming out... it should be OK. So... why do you think it's hotter? Did you verify temps?

Regardless... a new, tight engine will run hotter, until the rings fully seat, and the pistons wear in.


The pop-off of 43 is fine, assuming OEM, and correct size parts.

What are the plugs wet with? Is it oil or fuel?? Knowing it's unburnt oil... it will be the color of your oil. Take a plug, and lightly touch it to a white towel, and let the "Wet" wick onto the towel. DO NOT wipe, because we don't want to put the burnt stuff on the towel.

How much oil is in the fuel? AND, did you verify the pump arm is on the right way, and adjusted properly?



Now... to 1983:

Why do it before taking the carbs apart? (or do you mean after the second time removing them?)


But he's basically right. After you verify the pop-off... then you put the diaphragm and cover on... then put 10 psi on the carb, and see if it holds. If it leaks down after a couple seconds... there's an issue. If it holds for a minute or more... it's probably OK, since the fuel pressure will drop faster than that, after the engine is off. But realistically... it should hold the pressure for a long time. (More than 5 min)