Super Jet Limited Mod SJ stalling during Wide open pull

[Lil Mack]

My background: Experineced engine builder and mechnaic. Experience with any thing from a chain saw to turbo v8's.

Issue: Super Jet sometime stalls during a long run at full throttle on flat water.

Ski: 2013 SJ - Purchased new in 2013, Ride 4-8 hours per week, Use non-ethanol fuel with Yamalube 50:1.
Mods:

-Blowsion S/S Intake Grate
-Impros Hooker impeller (10/16)
-Solas Yamaha 144mm 12 vane pump
-Dual cooling
-Scupper
-Stock rideplate for now(D-cut)
-Blowsion Steering, 0° bars
-TTO tach

-Wamiltons Bpipe - Mod Chamber
-Blowsion Flow control to stinger
-Blowsion Girdled Head, B8ES plugs
-35cc chambers
-V Force 2 reeds
-Blowsion F/A's with outerwears
-MSD Enhancer - Set to max RPM

Carb settings: Carbs cleaned and all new gaskets installed when carbs were jetted. Fuel system is stock including the selector valve and the fuel filter.
Main 135
Low 75
Low speed - 7/8
High speed- 1 1/8

Skit runs great and hits hard. No issues in starting, turning, pulls from idle all the way up with no issues. Twice last weekend (first weekend with engine mods) it stalled during a long wide open run. The first time was with 1/3 tank of fuel. Refilled it and rode with no issues. Later that day it stalled again at WOT, this time was at 2/3 tank.

Thinking I might have some trash in the fuel filter causing this issue.

 

[Vumad]

Lean seizure. I have 140 mains.

How long has it been together with the pipe. Have you always ran it wot. Do you have a tach. If so what is your rpm. Does your rpm decrease at wot from just before wot. Have you adjusted your highs for warmer weather.

 

[Lil Mack]

This was the first run after the pipe install. Tach is mounted under the hood where I can't see it while riding. (Need to extend the wire).
I only made the two long WOT pulls. Put it on the trailer after the second time.
To adjust for warm weather I would normally lean it out some on the needles.

 

[Vumad]

This was the first run after the pipe install. Tach is mounted under the hood where I can't see it while riding. (Need to extend the wire).
I only made the two long WOT pulls. Put it on the trailer after the second time.
To adjust for warm weather I would normally lean it out some on the needles.

I ran my hardline tach wire out the rivet hole that holds the dash cover on and stuck it on next to the hood latch.

FPP does recommend 135 mains but I had the same story you did. No tach, 135 mains, stuck piston WOT. I had 4-point seizure. Did you just put on an o-ring head? If so, it's easy to pop it off to check, or you can try to inspect the cylinder walls through the plug hole. There are inspection cameras that plug into android phones for about $11 on amazon.

I ended up giving it to bad boys racing because I just didnt have the time to deal with it. THey gave it back jetted at 140/75@32. It has ran great. Can load up a little in the surf with such a low popoff but I generally just skip the surf when its that choppy.

Edit: Corrected popoff from 18 to 32. I have 1.5n&s w/ 65g spring. Jets were correct.

 

[Fro Diesel]

Lean seizure. I have 140 mains.

How long has it been together with the pipe. Have you always ran it wot. Do you have a tach. If so what is your rpm. Does your rpm decrease at wot from just before wot. Have you adjusted your highs for warmer weather.

Not if he has 2.3 or 2.0 n/s. What is the popoff of the carbs? Pretty sure i am at 145 main and 2.0 n/s fwiw.

I had a fuel tank one way valve fail on me recently. Had symptoms similar. It should let air into the tank, but not out. The autoparts store one do not hold up, needs to be oem.

Also put new fuel filters inline, and check the ones in the carbs. The little filter screen can get clogged and it will stall at wot bc it cant get the fuel delivery through the carb.

 

[Vumad]

Not if he has 2.3 or 2.0 n/s. What is the popoff of the carbs? Pretty sure i am at 145 main and 2.0 n/s fwiw.

I had a fuel tank one way valve fail on me recently. Had symptoms similar. It should let air into the tank, but not out. The autoparts store one do not hold up, needs to be oem.

Also put new fuel filters inline, and check the ones in the carbs. The little filter screen can get clogged and it will stall at wot bc it cant get the fuel delivery through the carb.

Pretty sure the N&S size doesn't matter at WOT as long as it is 1.5 or bigger. Your 145s are substantially more fuel than has 135s.

 

[Lil Mack]

Oops how did I leave that out. Stock N&S 95g Spring don't remember pop off pressure

 

[Roseand]

Pretty dumb to put a pipe on, rejet, and then just go WOT for long periods of time and hope your tuning was correct without using a tach or thoroughly verifying you're not running lean. Just because it goes from idle to WOT fine doesn't mean it's tuned. Gotta check from idle to wot, 1/4 to wot, etc. Ask me how I know..
Check fuel filter, internal fuel filters, and tank vent. I'd check your compression for peace of mind. But don't be surprised if you lightly squeeked a piston a couple times. It's very easy to do if you're not tuned just right.

Sent from my SM-G920V using Tapatalk

 

[Lil Mack]

More Details:
Compression checked after head installation: 186/187 psi
Set low speed speed jets and set idle strapped to the trailer
Rode and checked wake-zone and mid-range fueling, checked head and pipe for temps multiple time. Checked compression during a plug swap and engine warm 185/185 psi.
Plug chopped the top end three different times, Cut the last set of plugs and had good fuel ring. Pipe never got hot enough to sizzle water 3-4" past the coupler.

Rode buoys for about an hour prior to any extended WOT pull (Long WOT is not something we do often where we ride)
Was tooling around following my wife on her RXT, while trying to catch up to her after some wave jumping it stalled. Before it came to a stop I changed to RES and fired it back up instantly.
Back to the beach cart and checked everything out, discovered about 1/4-1/3 tank fuel. Added a few gal and went back out.

Rode bouys and boat wake a couple different times (5-10) min each, stopping 10-20 min between each ride. We have a private beach on a river so we do more hanging out than riding when the temps are low. The second stall happened after making a long run around the outside of our buoy course, long sweeping turns attempting to hold WOT. Afraid of a lean seizure I held the stop button and hit the start. Motor spun over freely, I did not start it and pushed it on the trailer.

I have not had a chance to pull the head after the last stall.

 

[air blair]

Lean seizure. I have 140 mains.

How long has it been together with the pipe. Have you always ran it wot. Do you have a tach. If so what is your rpm. Does your rpm decrease at wot from just before wot. Have you adjusted your highs for warmer weather.

I'm with vumad here. Up the jet on main for sure

 

[Lil Mack]

Going to check if I have 140's. If not I will get some coming to the house.

 

[Vumad]

Going to check if I have 140's. If not I will get some coming to the house.

Make sure you move your tach too. You need to see if the RPM drops below peak at WOT. WOT should be your peak. If 7/8 is your peak RPM, then WOT is lean.

 

[superjetguy]

Definitely sounds lean. I personally never had luck with those pre filters either try without those .

 

[Lil Mack]

Definitely sounds lean. I personally never had luck with those pre filters either try without those .

What negative experiences have you had with the Outerwear's? I have run them on my K&N filters on ATV's for years without issue. When I pull the hood I can see water droplets on the outside of the Outerwear's and the Flame Arrestors are dry. If it comes to it I will pull them off.

I will be re-positioning the tach to the dash when I pull the head off for inspection. I would rather have the tach on the hand-pole but the wire would have to be extended. I might extend the wire and put it on the hand-pole. I have a Trail Tech TTO.

 

[jetx]

Look up 08+ waterbox issues..,they are different than pre 08 boxes and seem to cause more heat...have seen a couple similar posts like this before.

 

[tomski]

I will be re-positioning the tach to the dash when I pull the head off for inspection. I would rather have the tach on the hand-pole but the wire would have to be extended. I might extend the wire and put it on the hand-pole. I have a Trail Tech TTO.

Buy yourself a real tach.

 

[Lil Mack]

TTO tachs have done well on all of my machines so far. I use them on dirtbikes and ATV's with out issue. They are good enough to provide what is needed to set idle speeds and monitor changes in engine RPM.

Updated original post with impeller information. I had to look that up from last season.

Search is not turning up much about the 08+ Waterbox issues. I have found some threads where others are asking what the issues are. Most repsonses are hear say issues from racers with big engines. I do have access to a complete '99 Super Jet. If I take my pipe off for any reason I will throw in the '99 box.

 

[tomski]

TTO tachs have done well on all of my machines so far. I use them on dirtbikes and ATV's with out issue. They are good enough to provide what is needed to set idle speeds and monitor changes in engine RPM.

Wonderful, but you should still buy yourself a good tach for watercraft tuning.

 

[MTRHEAD]

37cc domes and forget about it. What are the rpms at wot and do they fall? 35cc domes, msd, good prop, and a load (weight or poor octane) is recipe for trouble. Yes lots on this forum run 35's but the combo has to be right for it to last. 37cc is cheap insurance against detonation

 

[Lil Mack]

Haven't had it out on the water again. I'm sure you guys have seen the news of the flooding in south Ms.

Will remount the tach to be visible while riding and up the jet size. If needed I will drop the compression some.