Question about results of pop of pressure test

[MPower]

Ok so results from 2 skis.

Ski 1 - 2.0 N/S with 95 gram spring - pop off is 25 psi as it should be on both carbs.

Ski 2 - 2.0 N/S with 95 gram spring - both carbs pop at 18-20 ish psi. Now for shits I also tested with 65, 80, and 115 gram springs. all readings were also low compared to the chart below. For instance the black 80 gram spring popped off at 16-18 psi instead of 21. And the same holds true for the 65 and 115, all low by about the same margin.

So question is, does this mean the N/S itself is bad and needs to be replaced? It is about 5 years old and the ski hasn't been ridden much.

 

[racerxxx]

Needle and seat should go along with carb rebuild kits. I always go fresh.

 

[1of500]

Look at the arms are they bent to alter the pop?

 

[MPower]

Needle and seat should go along with carb rebuild kits. I always go fresh.

Sooo is that a yes, the N/S are bad and not holding pressure properly?


As for the arms, I rebuilt these I guess 5 years ago when I bought the ski. And damn if I can't remember what the pop off was, should have written it down. Nothing has changed since then so it's either a bad N/S or like you said the arm was bent by previous owner. But why bent arm with a 95 gram spring to get 18 psi, just use 65 gram spring......

Anywho, I got new N/S on order. Think I'm missed the OSD deadline to get shipped out today so likely no riding this ski this weekend, damnt.

 

[wfo speedracer]

If I was to venture a guess I would say that the o-ring around the needle and seat is bad

 

[MPower]

If I was to venture a guess I would say that the o-ring around the needle and seat is bad

I had some new orings laying around so I replaced those and that didn't solve it, but that only seals the N/S body.

 

[racerxxx]

When you put wd-40 in there does it bubble? The needle will get a ridge where it sits in the seat. That's where it will leak from and not let it pop at the right time.

 

[MPower]

When you put wd-40 in there does it bubble? The needle will get a ridge where it sits in the seat. That's where it will leak from and not let it pop at the right time.

One of the carbs would do this, but not every time.

I did have to replace th orings on the body because they were leaking like crazy. Wouldn't even hold 10psi

 

[Matt Braley]

Sounds like everybody above is dead on. The need to go fresh, the leaky seat body o-rings, the bent rockers, the ridge, all of it. Trying to think of something to add here....... nope.

 

[racerxxx]

Question.....why are you using a 2.0 needle? IIRC stock is 1.5, even if your running aftermarket flame arrestors I don't think you need to bump up.

 

[MPower]

Question.....why are you using a 2.0 needle? IIRC stock is 1.5, even if your running aftermarket flame arrestors I don't think you need to bump up.

2.0 N/S and 95 gram spring is what Bill O'Neil and Chris at Watercraft Magic told me to run on my ski with just F/As. Been running this setup on both skis for about 6 years now.

 

[mikidymac]

FYI, Mikuni has switched to an improved Coated Viton needle and recommends that we stop using the standard rubber ones since there is pretty much ethanol in all fuel now. Hot Products doesn't even carry the old ones now.
New Number: 786-35018-size ie. 1.5,2.0,2.5.
Old Number: 786-35015-size

 

[MPower]

Well guys I'm at a loss. I replaced all internals and these things are still popping off 5 psi low no matter what gram spring I have in it, but it's 5 low across the board on each. 18 is 13...21 is 16...25 is 20.....

Unless my pop off gauge decided to go crazy in 2 weeks while sitting in the box, then I have no clue what's going on.

 

[mikidymac]

I would almost think it has to be the gauge. The only factor in pop off is the seat size, spring and arm.

 

[1of500]

Try a different arm

 

[MPower]

Try a different arm

I have. I have tried literally everything, except a different gauge. But like I said this guaged worked perfect 2 weeks ago when it was brand new. It's a mikuni gauge.

 

[MPower]

I would almost think it has to be the gauge. The only factor in pop off is the seat size, spring and arm.

Alright so I tested with another gauge and.........same results. W.....T......F?????

 

[Matt Braley]

The body of the carbs must be cut deeper where the seats sit. That way the seats fit a little lower making that slight difference.

 

[MPower]

The body of the carbs must be cut deeper where the seats sit. That way the seats fit a little lower making that slight difference.

Interesting theory, I like it. Have you ever seen this done? It really the only explanation at this point.

I bolted the carbs back on the ski and it runs great, no lean or rich condition felt off idle, nice and crisp, so moving on!