Super Jet 2005 Superjet problem

[Texan33]

Greeting, fellows. I'm having a problem with my 05' Superjet. It's my first Yamaha jet ski. I tried to use the search tool but no luck so bear with me. The motor, exhaust, carburetors, pump, impeller, and ebox are all stock. The ski is completely stock with no performance parts. It is running like a crap. The ski fires up no problem and idles good in the water. When I get around 1/4 throttle, it would bog down and try to shut down. I had to play with the throttle (bunny hopping it) and then it will run good all the way to WOT. Sometime when I'm riding around, it will bog down and try to die. I had to play with the throttle to get it back to normal. Sometime I couldn't clear it and it shut down. It'll fire up no problem after it died on me. So I made a list of what I did to eliminate as many things that could have been the problem.

*Check-value are good (Fuel tank has good pressure)
*All the fuel filters are good and clean
*Brand new plugs
*Coils are good (getting strong spark in each plug)
*No exhaust leak anywhere
*Compression in each cylinder is good
*Both carburetors are very clean (I just had the carbs rebuilt)
*I cut the stator wires and use deutsch connector for them. (I crimped them really good and soldered them nice. I know how to solder wire properly)
*The ebox is clean and dry.


Basically, I strongly believe it's a fuel related problem. When I took the carburetors apart. I noticed the rubber tip on the needle has some of kind of groove on it (both needles have it). It's very tiny and hard to see. It is like one millimeter or less. I'm thinking that might be the problem unless there is something else I overlooked somewhere. What do y'all think?

 

[swapmeet]

Has it ever run correctly?

 

[Texan33]

Hard to say, I think I'm the third owner of this ski. I bought it from Tom (Superramjet). The ski was in relatively good shape when I bought it. The compression was right on and even. The carburetors was nasty and dirty. I had it rebuild and in the tuning process.


The carburetors had the anti-tamper cap on it.

 

[Vumad]

When you cleaned and rebuilt the carbs, did you replace the fuel filter, the needle and seat, and check the pop off ensuring it is at spec? 53 is stock.

It could be running rich on the bottom. When you hop the pump comes out and the ski is no longer under load. The motor revs past the rich point and starts to balance out on the top. When you let off the throttle, the RPM drops, the ski is rich in low RPM again, and the motor loads up.

Could be a lot of things, but I would double check the carbs.

 

[ProSouth]

Did you use a rebuild "kit"? I've used some kits and none compare to the mikuni carb kits. I would lean towards the carbs at this point with everything you checked. Check pop off pressure. Recheck diaphragms. Good luck

 

[swapmeet]

Yeah, I was curious if you had a functioning baseline to go off of.

Im gonna agree on the carb probability like Vumad said.
On the exhaust leak, did you run with the hood off?

My next guess might be stator/ ignition related maybe?

 

[Vumad]

Did you use a rebuild "kit"? I've used some kits and none compare to the mikuni carb kits. I would lean towards the carbs at this point with everything you checked. Check pop off pressure. Recheck diaphragms. Good luck

My pop off was 23 and leaky (from N&S).
I rebuilt my carbs in march with SBT kits just as a preventative measure while I was cleaning the carbs. Pop off 53.
By the end of may, my ski was boggy and ran bad. Pop off 23 and leaky again (from fuel pump).
I put a brand new SBT kit in my fuel pump. Pop off 23 and leaky, couldn't get them right (from fuel pump).
Put the OEM o-rings back in. Pop off 53. Ski runs like a top.

Just because you put new stuff in them, doesn't mean they are working right. I wish I would have bought a pop-off gauge sooner.

I also bought the JM allen screw kits. Money well spent. Can get the gauge from JM too.

 

[Texan33]

I used the genuine mikuni rebuild kit from Jetmanaic. The filters were clean as whistle. I just checked the pop off pressure on both carburetors. It was a little over 70psi. Bloody hell....... I need to get the needle and seat replaced!!

 

[Vumad]

I used the genuine mikuni rebuild kit from Jetmanaic. The filters were clean as whistle. I just checked the pop off pressure on both carburetors. It was a little over 70psi. Bloody hell....... I need to get the needle and seat replaced!!

So then it is running too lean. The N&S control the fuel to about 1/4 throttle. Once you finally get the needles open, you get the fuel you need. I'm sure when you get the pop-off into the low 50s and tuned right it will be okay.

Did you use the spring in the rebuild kit? There are 4 different springs but the kit only comes with 2. The colors change over time so you may have put in the wrong spring. Put the springs that were in the carbs back into the carbs and recheck the pop off. You can run the old springs w/o any issues if the pop off is right. The target is 53. Close is good enough, you can adjust a point or 3 out with the low speed jet. Most important part is that the 2 carbs have almost the same pressures.

 

[ProSouth]

I run my pressures a tad lower, round 40. But Yamaha recommends what vumad said, around 53. 70's crazy!

 

[swapmeet]

Yup, needles and seats should be ok, just need springs homie... No sweat.

 

[Texan33]

The Mikuni rebuild kit didn't come with new needles/seats. I just cleaned and used the ones that was already in the carburetors. I tested the pop-off pressure with both old spring and new spring, still getting 70psi. The needles/seats are 8 years old. I already ordered a couple of new oem n/s to be safe.



Thanks y'all for the response and help!! I'll let y'all know how it goes when I get the parts.

 

[ProSouth]

Were they 2 different color springs? Shouldn't get 70 out of 2 different springs

 

[Texan33]

I just tried the different springs from the Mikuni rebuild kit. I'm getting 70psi off 115g spring and around 30psi off 65g spring. 115g spring is what the stock superjet uses? According to the Mikuni pop-off chart, 115g spring with 1.5 n/s is supposed to get like 50~55psi.

 

[Vumad]

1.5/115 should give you 55. Maybe your rocker arm is bent. The rebuild kit comes with rocker arms. Try it with both stock and the rebuild rockers. There is a 95gr spring, you could try one of those and see what you get. I'm not sure why your 1.4/115 is reading so high. Make sure your fuel pump is assembled correctly and there are no obstructions anywhere. Also make sure you're not liking up the fuel in/out during your test. Also make sure you didn't somehow get a 1.2 needle and seat in there. 1.2 isnt listed on the chart but The gp1200 comes with a 1.2 stock and makes 70psi.

You don't need to replace your needle and seat if they are not leaking.

Worst case, if you can't get the popoff right, you could change to aftermarket flame arresters, run the lower popoff and a larger low speed jet.

 

[NoviceFlipper]

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