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  1. #1

    95 SL750 stalling when hitting waves-long read

    Hi all, I have a bone stock 95 SL750 that sat parked for over 3 years. I've had it since it was 2 years old but moved out of state and stored it at a buddys house for 8 years. He lives on a lake and ran it every Summer for the first few years, and said that the first tank of gas each season "ran like crap then cleared up". He kept the ski in the lake from May to November. The ski still had all original parts and had not been in the shop since before I bought it. He didn't launch it the last few years and when I picked it up, it had 6" of oak leaves on the cover and lots of ants in the compost it created! It was run in salt water by the original owner in it's first year of life, and it was never properly stored (no fogging). Engine looks like new with virtually no corrosion anywhere. Interestingly enough, the jet pump was completely rotted out and had to be replaced. I assume that the salt started it and sitting in the lake for extended periods finished it.

    Upon moving back to Florida I picked the ski up and researched it on this forum. Before launching it, I drained the gas tank, rebuilt the carbs, replaced fuel lines, added new triple outlet fuel pump, new needle/seats and installed a new battery. Autocock was already removed before I bought it. Compression was around 120 in all 3 cyls and reeds looked new. MFD doesn't work (faded over time to nothing) except blinking red light (what does this mean?). Amazing it survived, considering the annual "sputtering until the carbs clear" event! I do not recall the hours, but they are likely very low (about 4 hours in last 10 years).

    Upon first test run after rebuliding carbs (SBT kits), I partially sank the ski due to forgetting the drain plug . I pulled it from the water, drained it and removed plugs to blow the water out (lots of it). Got ski started on the trailer and then re-launched it a week later, only to discover that the cyls had flooded with gas because I forgot to turn off the fuel switch. Got that cleared up and all seemed well. Luckily I live on a lake so I can yank it in/out without much trouble.

    First ride the ski seemed to lack power even though the RPMs seemed to climb more than they should (almost like when you spin car tires in the rain). After putting around the lake at low throttle and rocking the pump (lean forward back, feathering throttle), it finally planed out and pulled decent. I later found some weeds in the intake grate and suspect that was causing the pump to cavitate. I am not sure it is accellerating as it should; it seems to plow a bit before planing but then pulls well. I do weigh close to 300 lbs so it might just be my fat butt bogging it down.

    After playing around with it, the top speed seemed to be about right. The problem is that every time you jump a boat wake or hit a decent wave, the ski dies. It is almost like yanking the lanyard, it doesn't sputter or miss at all, it's either perfect or it totally shuts off. It also appears to have a stalling issue under very hard turns, although not consistently like with the wave jumps. If you can hit the start button before it comes to a complete stop, 90% of the time it fires up and takes off again without stopping. If you come to a stop, it takes a lot of cranking to re-start. By a lot of cranking, I mean that the battery was going weak and I was thinking I would need to paddle home. The new clear blue fuel lines don't appear to have bubbles in them so it seems to be getting fuel.

    Through trial and error, I learned that it will re-start faster after a stall if you hold the choke and crank it briefly. It will consistently sputter once and die during this brief crank (it won't actually start while choked/warm). After this quick sputter, I can then hold the throttle wide open w/o choke and crank it; it will typically start after a few seconds. When it starts, you will feel it start to fire weakly and then it slowly comes to life (still at WOT) and then vroom it wakes up and takes off. It reminds me of when you catch a fish and keep it out a little too long before releasing it, it just sits there and just when you think it's dead it takes off! If you skip the choke part or don't hold WOT during cranking, it may run the battery dead before it decides to start (this is very consistent). This same symptom applies if you shut it off for a few minutes without shutting off the fuel selector switch, and try to re-start it. If you shut off the fuel switch, it will typically re-start without problems after parking.

    Summary:
    * Rebuilt carb/needle/seat s, fuel pump, lines, good comp., new battery, good reeds.
    * Stalls when hitting waves or porpoising and on some harder turns.
    * Requires a bit of throttle to maintain idle. If you let off it at idle speed, it usually stalls after a few seconds.
    * Re-starting it after a stall or parking with fuel turned on takes a long time and/or finesse. Improved some by choking and brief cranking, then WOT cranking.
    * One concern - SBN carb-rebuild kits each came with 3 separate needle springs. We used the one closest to the original, but my carb guy suspects that the stalling is due to pop off pressure being off, and he said that none of the new springs were the same tension as the originals. He tested it at around 17 PSI IIRC, the valve didn't POP completely open, it just lifted a little and let the air hiss out. I wondered if it should pop all the way open like a valve, or if this leak down was ok?
    * Ski did partially sink at one point, could water have soaked into the CDI box or something else and be splashing to kill spark when bouncing?
    * A search of tech tips indicates stalling under turns can mean lean air/fuel. Would a temporary lean condition cause it to completely shut off?
    * Could bouncing cause the carb needle valve springs to open or dump fuel into the cyls? I believe it is flooding while my carb guy thinks it's lean. The plugs look ok, haven't done a washdown check.

    If you made it this far, thanks! I know it was long, but I wanted to attempt to get all the details in there for the experts to consider.

    Mike


  2. #2
    dont know if you checked this or not but i had my ski out last summer and when i hit waves or spun around it would shut off then start back up. finally i checked the negative and pos battery terminals to find out the neg was loose

  3. #3
    bowsniper's Avatar
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    Wow, that was a lot to read/lol.. Hmmm..where to start.. well number 1 is fogging the engine to keep it clear of rust on the bearings.. that should of been done all the time to keep it good.

    Next is tuning the carbs. go by the factor specs for you ski. do the lows first, get that right, then the highs. then the idle in the water. (1250 rpms)..

    it should take off and not hesitate or blubber(sputtering).

    the lows have tees on them and the highs have blue caps over them. those need to be taken off first to adjust them properly.

    so im assuming you changed the diaphrams in the carbs? (big black round rubber piece behind the covers.) they only go in 1way.

    did you check the pick up tubes in the tank? what did they look like? theres screens on the bottom of them to keep the pick ups on the bottom of the tank. or does your ski have a silver sending unit inside the tank?

    if you do have the tubes, replace them and return the weights back on them. do 1 at a time, they are different lengths. the longer one is your reserve and the shorter one is your main, if you cross them , you wont have a reserve.

    I would pull the heads and water rail off and check the piston wash on the top of the pistons and tell us what ya got there.

    what kind of plugs are you using? BRP-ES8? thats what you should have in there. 9's are cold, 6,7's are hot.

    it may be a little slower than usual if your a big guy, but its the same as 2 people 150lbs.. I had a 94sl and it could carry 2 ok. not super fast but decent for its size. it should still do 45 I would think.

    if its hard to start, you have a problem.. it should start instantly when running right with no choke. maybe a first start may need a little choke but once its warmed up, never. it should shnit n get.

    possible exhaust leak inside the ski? that would make sence if its hard to start and doesnt take off well.(if the carbs are set correctly first) then once it clears the exhaust fumes, it runs ok.

    try this, cut back the spark plugs boots a 1/4 inch, then rescrew them back in and see if your getting bright blue sparks. ground the plug and crank it. see what they look like. is the gap correct? .028?

    you can also check the clearence of the impellor to the wear ring. it should be real close. 20 thous is the limit but thats huge.. should be more like 4 thous.. that can make you cavatate out of the hole.. along with bent blades, broken blades on the stator, pitch is out of whack on the prop, or air leaks from the pump shoe,or the thru hull fitting.

    not sure about the spring thing and the pop off.. another member can guide ya thru that part..

    look for kinks in your new routing of the lines. they should be smooth curves with no binding.

    is the restrictor in the return line? sounds like it is. it was just off the return line with a tie wrap around it, you need to have that in place. that builds fuel pressure.

  4. #4
    thester71's Avatar
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    NGK parts locator and manual says to use bpr7es, I would double check that the motor is secured to the bed plate, and the bed plate is tight on the four motor mounts, check all grounds, and make sure the electrical box is secure including all connections inside.

  5. #5
    Thanks guys, I will check the items you've all mentioned. Here are my replies to Bowsniper's questions:

    Wow, that was a lot to read/lol.. Hmmm.where to start. well number 1 is fogging the engine to keep it clear of rust on the bearings.. that should of been done all the time to keep it good. Oops, if I knew then what I know now!!! Now that I live on a lake, I expect to use it pretty much year round, with the exception of maybe Jan/Feb. Even though it can get chilly here, there are always days where it hits 50 or 60 and sunny, which is fine for a quick ride

    Next is tuning the carbs. go by the factor specs for you ski. do the lows first, get that right, then the highs. then the idle in the water. (1250 rpms)..
    it should take off and not hesitate or blubber(sputtering). We left everything at the factory setting, I will get my buddy who is more experienced with carb tuning to tweek the high/low/idle. We did have it idling at first, but after the first ride that ended. It's also tough to dial it in without the tach/MFD! My buddy suspects that the replacement springs might be dumping too much fuel at idle, but this is just a theory at this point.

    the lows have tees on them and the highs have blue caps over them. those need to be taken off first to adjust them properly.

    so im assuming you changed the diaphrams in the carbs? (big black round rubber piece behind the covers.) they only go in 1way. Yes, we changed the diaphrams, the needle & seat, the pop off spring (probably should have left the stockers in) and the gaskets. The needle was stuck on 1 carb and we got a few little specs of dirt out of the carbs, but overall they were pretty clean for being 15 years old and never serviced before!

    did you check the pick up tubes in the tank? what did they look like? theres screens on the bottom of them to keep the pick ups on the bottom of the tank. or does your ski have a silver sending unit inside the tank? I did not check the pick up or do anything with the tank/sending unit, aside from adding fresh gas. The fuel filters were nice and clean, but good point on checking the pickup in the tank. During the last storage period, the tank was left full and the cap was tight, the gas actually smelled fine and I used it in my lawnmower without issues.

    if you do have the tubes, replace them and return the weights back on them. do 1 at a time, they are different lengths. the longer one is your reserve and the shorter one is your main, if you cross them , you wont have a reserve. Will check this for sure.

    I would pull the heads and water rail off and check the piston wash on the top of the pistons and tell us what ya got there. I think my buddy has a scope, but maybe we'll just pull the heads and take some pics.

    what kind of plugs are you using? BRP-ES8? thats what you should have in there. 9's are cold, 6,7's are hot. I'm embarrassed to admit that I didn't even pay attention to the plugs. They are the same ones it had when I bought it and they look pretty clean, so I didn't bother to check the gap. It has run well with those plugs and it's only had a few hours on it the last decade, but in reading the forums it looks like I need to pony up for some new ones.

    it may be a little slower than usual if your a big guy, but its the same as 2 people 150lbs.. I had a 94sl and it could carry 2 ok. not super fast but decent for its size. it should still do 45 I would think. Top speed feels pretty decent. My other SL750 is a little faster with my 160 lb bro-in-law on it but that's likely just the weight difference.

    if its hard to start, you have a problem.. it should start instantly when running right with no choke. maybe a first start may need a little choke but once its warmed up, never. it should shnit n get. Funny thing is it starts easily the first time after sitting (with fuel off), it's the second-50th warm start that is a hassle!

    possible exhaust leak inside the ski? that would make sence if its hard to start and doesnt take off well.(if the carbs are set correctly first) then once it clears the exhaust fumes, it runs ok. We checked the clamps and rubber and all seems well, don't seem to have any smoke inside the engine area.

    try this, cut back the spark plugs boots a 1/4 inch, then rescrew them back in and see if your getting bright blue sparks. ground the plug and crank it. see what they look like. is the gap correct? .028? Spark looks good.

    you can also check the clearence of the impellor to the wear ring. it should be real close. 20 thous is the limit but thats huge.. should be more like 4 thous.. that can make you cavatate out of the hole.. along with bent blades, broken blades on the stator, pitch is out of whack on the prop, or air leaks from the pump shoe,or the thru hull fitting. I think the cavatation was just a few weeds stuck in the intake grate. I don't recall the tolerance of the wear ring, but my buddy checked it and it was ok. We replaced the whole pump with a good used one from a donor ski.

    not sure about the spring thing and the pop off.. another member can guide ya thru that part.. I think this is going to be a big part of the problem. I still wonder why the rebuild kit came with 3 different springs yet none were the exact OEM spec.

    look for kinks in your new routing of the lines. they should be smooth curves with no binding. We were very careful to route everything to avoid kinks or rough edges that could rub the lines. So far so good here.

    is the restrictor in the return line? sounds like it is. it was just off the return line with a tie wrap around it, you need to have that in place. that builds fuel pressure. Yes, it's there.

    Well thanks again to everyone who answered. Looks like my next steps are to check all the wiring from the battery to the CDI box and harness, and then check the piston wash and fuel tank pick up, then do some carb tweeking. This has definitely been a learning experience for me

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