95 SL 650 fouling plugs/stalling after 50% throttle

[Texan_Riot]

So I've got my 95 SL650 starting up and idling like a champ on the trailer. The first time I went to put it in it would stall as soon as it fired up so I had my mechanic come out and work on it and we've gotten it to a point where it will start and run mildly as far as throttle but as soon as you try to really get on it, it dies out but can be started back out. My mechanic found that the plugs were getting fouled after a few attempts and after an hour or so of pure tuning while on the water we still had no luck as far as getting it run perfectly. Below I listed all the parts and things I've had done to it this far below:

-All new fuel lines and fuel filter
-Brand new battery
-3 new sparkplugs
-New fuel pickup/sender at the tank
-New gasketmaker seal at the base of the intake on the block
-New stainless steel starter switch
-New Jet Logic key
-Venom 3 carb rebuild kit including jets, springs, diaphragam, etc
-New fuel lines between the carbs


I'm really hoping you guys have some suggestions because at this point I really cant figure out whats going on with it. My mechanic had the idea to put the original springs in and possibly some other options but I wanted to check with the pros of Green Hulk first!

[xlint89]

Engines start easily on the trailer as there's no load on it and require little fuel. (like neutral in a car) When you start it in the water, it has a load and generally requires more fuel. So your idle air mixture screws are off, or you just need to simply turn up the in water idle screw to raise the RPM to whatever spec is. (prob around 1100 RPM) Normally the engine will run around 3600 RPM when on the trailer and about 1100 RPM in the water when tuned in correctly.

An abrupt shut down at speed is normally a lack of fuel or cold piston seizure.

When you say the spark plugs got fouled out after a couple attempts, how were they fouled? wet and oily? or just a dry black carbon look?


Is this boat running premix fuel, or are you using the oil pump?

What fuel/oil ratio are you using if premix? Did you mix it well before putting it in the boat if premix?

We had a guy dump oil into his gas tank before adding fuel once and it never mixed well. He kept (oil) fouling out spark plugs.

What spark plugs did you install? NGK BPR8ES gapped at .028" is what you should have.

When you attempt to accelerate, try closing the choke a little bit and see if that helps. This will richen the mixture and help identify a lean air fuel. (needing more gas)

NOTE: do not ride around with the engine in this condition, you will cause engine damage if you are not getting sufficient fuel.

Let's address your list:

What fuel filter did you replace? Does your ski have the fuel filter water separator? Or is it just the water separator? (the filter separator has an orange ring and SS mesh cylinder in it. The separator only is just the clear bowl)

What spark plugs did you install and what were they gapped at?

New gasket maker seal at the base of the engine block? I'm confused on this one. You should have a gasket, the reed block, gasket, then intake manifold.

Venom 3 carb rebuild kit? How about a link to this? I've never heard of these. They include jets? What size, and did you install them? We recommend only genuine Mikuni carb rebuild kits.

1. Make sure your throttle cable is not hanging up and have about 1/8" of play on your throttle lever.

2. Make sure your carbs are sync'd. Meaning all 3 throttle plates are working in unison and opening at exactly the same time and the exact same amount. There are adjustment screws to do this. The instructions are in the Mikuni manual of post #7. Fuel Fuji Carbureted (greenhulk.net)

3. What jets were installed?

4. Was pop off pressure checked?

5. Are the low idle speed adjustment screws good? Best way to achieve this is to leave the ski strapped to the trailer and back it in. Start the engine and get it up to normal temp. Adjust the idle speed screw to get 1100 RPM. Now turn the idle mixture screw (mounted low on the carb) in and out of the MAG cylinder to achieve highest RPM. Make 1/8 turn at a time and wait for the engine speed to correct itself. Adjust the idle speed screw to get back to 1100 RPM. Then do the same for the CEN cyl. Adjust the idle speed screw again to maintain 1100 RPM. Now do it for the PTO cyl. Doing this should get you the best/smoothest idle and take off.

If you find turning the low idle mixture screws all the way in get best results, you have too big of low speed jets installed.

If turning the screws out more than 2 full turns from a LIGHTLY seated position gets you the best results, you need a larger low speed jet installed.

The hi speed adjustment screw (mounted high on the carbs) is for WOT tuning. When it comes to this, it's best to start out with too much fuel and take it away to achieve proper supply. So I'd suggesting starting at 2 full turns out from a lightly seated position and watch your RPMs and/or piston wash for proper fuel supply.

[randys]

does it "load up" before it dies?

[Texan_Riot]

Load up meaning increase the RPM as I give it more throttle?

[Texan_Riot]

What fuel filter did you replace? Does your ski have the fuel filter water separator? Or is it just the water separator? (the filter separator has an orange ring and SS mesh cylinder in it. The separator only is just the clear bowl)
-The filter I replaced was the bucket style that was the factory one for an in-line fuel filter. I believe the kind I'd replaced was the separator style. I didn't think that would have an effect on fuel flow

What spark plugs did you install and what were they gapped at?
-Not sure to be honest. My Mechanic grabbed them. They could be anything but I asked him.

New gasket maker seal at the base of the engine block? I'm confused on this one. You should have a gasket, the reed block, gasket, then intake manifold.
-The gasket at the intake manifold between it and the reed block. It disintegrated when he checked it.

Venom 3 carb rebuild kit? How about a link to this? I've never heard of these. They include jets? What size, and did you install them? We recommend only genuine Mikuni carb rebuild kits.
-It was a kit I'd found on Amazon that was cheaper but still had good reviews as far as use. Now I'm starting to think it's the problem.

1. Make sure your throttle cable is not hanging up and have about 1/8" of play on your throttle lever.
-Good idea. I want to say it has a bit of play on it but I could be wrong as well

2. Make sure your carbs are sync'd. Meaning all 3 throttle plates are working in unison and opening at exactly the same time and the exact same amount. There are adjustment screws to do this. The instructions are in the Mikuni manual of post #7. Fuel Fuji Carbureted (greenhulk.net)
-My mechanic sync'd up all 3 carbs and even installed 3 extended hoses now mounted to the side and capped off in case it needed to be sync'd again

3. What jets were installed?
-I believe the ones that came with the Venom kit although I did keep all original parts that were replaced for a situation like this

4. Was pop off pressure checked?
-I believe so but I'm not sure how that's done

5. Are the low idle speed adjustment screws good? Best way to achieve this is to leave the ski strapped to the trailer and back it in. Start the engine and get it up to normal temp. Adjust the idle speed screw to get 1100 RPM. Now turn the idle mixture screw (mounted low on the carb) in and out of the MAG cylinder to achieve highest RPM. Make 1/8 turn at a time and wait for the engine speed to correct itself. Adjust the idle speed screw to get back to 1100 RPM. Then do the same for the CEN cyl. Adjust the idle speed screw again to maintain 1100 RPM. Now do it for the PTO cyl. Doing this should get you the best/smoothest idle and take off.
-Are the cylinders you listed in order from front to back or the other way around? Also how would I be able to check the RPM's of the motor without a gauge? Still pretty new to a lot of this so I'm learning as much as I can

If you find turning the low idle mixture screws all the way in get best results, you have too big of low speed jets installed.

If turning the screws out more than 2 full turns from a LIGHTLY seated position gets you the best results, you need a larger low speed jet installed.
-I think he had mentioned something about them being around 2 turns from the lightly seated position. I sent him your entire response to get the precise answers for you tomorrow

The hi speed adjustment screw (mounted high on the carbs) is for WOT tuning. When it comes to this, it's best to start out with too much fuel and take it away to achieve proper supply. So I'd suggesting starting at 2 full turns out from a lightly seated position and watch your RPMs and/or piston wash for proper fuel supply.
-WOT tuning?

[Texan_Riot]

https://www.amazon.com/dp/B079TD3HFP?psc=1&ref=ppx_yo2_dt_b_product_details

This is the kit I used to have all 3 carbs rebuilt

[Texan_Riot]

Also I've been looking online and cant seem to find any genuine Mikuni rebuild kits. SBT has this one https://www.shopsbt.com/jetski/mikun...ki-yamaha.html but I can't tell if it would be compatible

[K447]

- genuine Mikuni rebuild kits.

www.Watcon.com has Polaris specific carburetor rebuilt kits using genuine Mikuni parts, and just the parts you need for a Polaris carb.

Fuel pump kit is sold separately

[Texan_Riot]

Thank you! I'll order them today

[Texan_Riot]

www.Watcon.com has Polaris specific carburetor rebuilt kits using genuine Mikuni parts, and just the parts you need for a Polaris carb.

Fuel pump kit is sold separately

I pulled up the 3 carb kit for Polaris skis but it looks like its just the diaphragm, jets, filters and springs. Although I guess I wouldn't need the gaskets replaced since they came in the Venom kit I already got

[xlint89]

When Randys asks if it's loading up? That's a common term for the engine getting too much fuel at idle and takes a few moments for the engine to accelerate. When you hit the throttle the ski fails to go, but "blubbers" for a moment or 2 and then takes off like a bat out of Hell. "blubbering is when the engine is still running but is flooded with fuel. Another Randy once put it as a schoolgirl trying to guzzle a quart of beer.

Generally when an engine is lean, and you stab the throttle it will just die.

I hope you understand what I'm saying.

Depending on what fuel filter was installed, some do restrict flow.

It's a lot of work for the fuel pump to draw fuel all the way from the fuel tank to the carbs. That is why the fuel tank vent valves are needed to create pressure inside the fuel tank. The fuel pressure inside the tank helps to "push" fuel to the pump. Hopefully your vents are in place and working.

Side note: were your fuel hoses replaced at all? If so, were they clear? Clear fuel hoses are a bad choice for this application. Have you inspected the fuel hoses inside your gas tank? Those often fail and cause fuel supply issues. Those are a special hose required since they are immersed in fuel. PLEASE INSPECT THESE AND GET BACK TO US ABOUT IT.

The manual calls for a NGK BPR7ES spark plug, but were recommend the 8 because it's a little "cooler" running and helps prevent possible piston issues. You can look at the sparkplug and see the numbers stamped on them.

I'd suggest getting new gaskets for the reeds. RTV is not good. And some may not be compatible with fuel. If you're going to be removing your carbs for a possible rebuild again, it would be a good time to remove the reeds for inspection and replace the gasket maker with the correct gaskets.

The venom 3 carb rebuild kits I have never heard of, but we tend to find the aftermarket kits are part of many people's problems. It appears to be a nice kit, I just don't know if they are equal to Mikuni parts. John at Watcon sells just the parts you need, nothing more, nothing less. I believe his kit also includes the needles and seats (which you keep referring to jets) which the Mikuni rebuild kit does not. John's a great guy and the kit is what we KNOW works.

Your mechanic must have used a vacuum gauge carb sync tool. I have not used one, but hopefully we has them balanced well. If you look down the top of the carb throats, do the bottom throttle plates all move at the EXACT same time, and the EXACT same distance? This is what I refer to being sync'd. There are adjustments that can be made in order for them to be.

There are no jets with that kit. Those are the needle and seats. Pretty sure they should be a 2.0 size

So we still need to know what size jets are being used. Most likely the stock size from the factory, but we're chasing our tails if we do not know for sure what size are actually installed.

Pop off pressure is used to measure when the needles raise off the seat and allow fuel to flow through the carb's main circuits. It requires a low pressure gauge for reading. Hopefully your mechanic has one and took the measurements. Too low of pop off and you get fuel flow too soon causing a rich condition and possibly fuel leaking past the seats at idle . Too high of pop off pressure and you get a lean hesitation because it's starving for fuel. All 3 carbs need to be the same or you will get cylinders reacting differently from throttle position during acceleration.

MAG refers to the magneto cylinder or front of the engine. (that's where your flywheel and magneto are bolted to)

CEN is center

PTO or Power Take Off is the rear cylinder

If you don't have a tachometer, you can buy a cheap aftermarket one that reads 2 stroke engines and use it. Something like this.
Amazon.com: Timorn Tachometer for Small Engine,Inductive Hour Meter for 2 Stroke & 4 Stroke Small Engine, Replaceable Battery Waterproof Tachometer for Chainsaw Marine ATV Motorcycle UTV Engine (Black): Automotive

Or you can just tune by ear. With the ski in the water and the engine up to normal operating temperature, idle the engine just about as low as it will go without stalling. Then turn the MAG low speed mixture screw until you get the fastest idle speed possible. (you're going to make about 1/8 turn adjustments and allow the engine to react. Then adjust 1/8 turn again, wait for it to react, etc...)

Reset the idle speed to as low as possible using the idle speed adjustment screw

Then start adjusting the CEN low speed mixture screw.

Reset the idle speed to as low as possible using the idle speed adjustment screw

Then start adjusting the PTO low speed mixture screw

Once that is done, set your idle speed adjustment screw to the preferred idle speed for a no wake zone. This is normally around 1100-1200 RPM or about 3-5 MPH. You should now have a nice idle and pretty smooth acceleration.

WOT tuning is done with the hi speed (mounted hi on the carb) adjustment screw. It's for fine tuning fuel flow to achieve maximum RPM and performance. You are not here yet, but hopefully we will be addressing this soon.

Now let's get this tuff squared away and get you going on the water ASAP.

[xlint89]

How about posting up some pictures of your engine so we can get a better feel for what we're dealing with please?

Fuel filter and hoses.

silicone at base of engine

Spark plug numbers

[Texan_Riot]

I'll be heading out there this week and can get you more pics! As always you're the man!!