1994 SL650 bogs at 1/4 throttle up

[imported_jazzman]

About to loose my mind, please help...

1994 SL650 Polaris
On trailer, revs up OK (5 sec test)
In water...
Starts up great every time, idles well
From 1/4 throttle on, bogs down and stalls if throttle not released
1 out of 10 times, if you gently ease the throttle, you can get just enough speed/power to get boat on plane. You can ride like this with 100% throttle for anywhere from 10 to 60 seconds, and then all of a sudden, it bogs and stalls again.

Checks...
Plugs...a little oily and wet
Compression...good
Reed Valves...good
Exhaust System...no obstructions...good
Carbs...
...no debris found upon disassembly
...diaphram condition good
...inlet needle good
...needle arm level with carb surf per manual
...cleaned and rebuilt, condition persists
Fuel System
...new filter no effect
...tank cleaned, pickup looks good
...pump vaccuum line clear/good
...fuel return line pulled from tank (very small but steady stream of fuel returning to tank) "pump OK?"

Carb Adjustments
...set according manual
...If high speed adjuster is moved half turn out (rich) boat less prone to stall at 1/4 throttle, stalls at 1/3 throttle. However, if we do get boat on plane, pulling choke makes it bog more quickly.
...If high speed adjuster is moved 1/2 turn in (lean) boat will stall at 1/4 throttle every time. Can never get to plane.

Moving on to electrical...
...Have conducted all manual resistance checks of coils, stators, etc. All measure OK.

So, I am just about out of tricks...
a) Anything else I can check on the fuel pump short of buying a new one?
b) Could it be the magneto or stator? How do I check it. Working on it means pulling the engine out of the boat.
c) Could the spark plug wires/coils still be at fault. I think they are 1 piece units. Can't wait to see what they cost.
d) Is it possible for the CDI to work at idle but not above?

Help Me!

[Technical Support]

Your fuel pump is shot, and you probably have some minor damage on your top-end from leaning it out all those times and seizing it. You are lucky you still have compression, although I wouldn't be surprised if you have the start of a hole forming on your front piston.

Put a 780 pump on there right away.

[imported_jazzman]

Slow down...

Why do you think the fuel pump is shot? Do you have a prefered test?

The heads were just off 2 days ago, the pistons looked great, little bit of carbon on them. There has never been a compression problem. The carb screws were only adjusted to the lean side for a total of about 45 seconds (to understand the fuel condition better). I checked each carbs setting when I first started working on it, and they were all within an 1/8 turn of the manufacturers specified setup.

[Technical Support]

Because the 650/750 pumps were inadaquate fromthe factory, and Polaris fixed the problem with the 780. It's been a well known problem for years.

[Jazzman]

OK, I purchased a new Mikuni Fuel Pump with dual outlets. Each outlet runs to a T connector between each pair of carbs. I connected the reserve fuel line direct to the fuel inlet on the fuel pump (bypassed the on/off, filter, and water separator). Problem still exists just as it did before.

Then I disconnected the return fuel line (to tank) and plugged it (no fuel going through orifice or back to tank). When I did this I can get the boat on to plane if I ease the throttle. Holding the throttle at 3/4, I can putz around all day just going fast enough to keep it on plane. If I go to full throttle, there will be no speed increase, but I will get a sudden bog/stall after 15 to 30 seconds. [img]graemlins/crying.gif[/img]

[Technical Support]

Is your restrictor still in your return line? Has any work been done to it recently?

[imported_jazzman]

The restrictor was still in the line, and a blow test indicated no obstruction. No work was done other than to check it.

In my example, effectively blocking the restrictor improved my ability to get the boat on plane and keep it there (3/4) throttle. You still have to baby it up there. If you mash the throttle from idle, you get immediate bog and stall (no attempt to cough and get going-i.e. rich)

My assumption is more fuel getting to the carbs is improving things. I can go back through all the fuel lines to check for blockage, but both the reserve and main lines result in same condition. I really don't believe they are both blocked, and the pickup screen on both is clean.

Venting the gas cap does not help, and the tank check valve seems to be working (get an outward puff of air when cap is removed)

[polarisguru]

Rebuild your carbs and replace the needle and seats(they are not opening). The needle/seats are most likely sticking and not letting fuel into the carbs, thus the bog. Check your pop off pressure. It should be around 16lbs. Are you sure that you have the fuel lines hooked up correctly into the end of the rack or thru your T's? Looking down @ the carbs the bottom fittings are the inlets and the top fittings are the return. Also what size hole is in your T's. I see so many people that put T's in the line that have a 1/8"-3/16" hole going thru them. IT NEEDS TO be 1/4" inside as to not restrict the fuel flow to the carbs. You should also be using 1/4" id fuel line not 3/16. When you can plug off the return and the boat runs it is a fuel delivery issue. Also have you checked the ends of the lines going into the gas tank? If you suspect them, then do a temp line into the tank directly to the fuel pump inlet, this will eliminate a problem with your fuel intake into the tank [img]graemlins/buck.gif[/img]

[Jazzman]

OK, I ran a fuel line directly from the tank to the fuel pump. No change. All the routing to the carbs is correct. I respect the thought about the sticking needle, but I inspected and cleaned them. They look great (perfect tringle shape). The way this thing bogs, I can't believe only 1 carb is sticking. And two or more seems impossible.

I ran for 5 minutes at 3/4 throttle (barely on plane), did the instant kill switch and off the throttle trick. All three plugs look identical. Tan tip with black extending down the ceramic (not wet, not powdery).

Is it possible I have some safety cutoff activated? I have a water temp sensor, fuel level sender, and oil level sensor. My wiring diagram says the oil and water are on a buzzer. Does the 94 SL650 also have a spark cutoff or something?

[polarisguru]

What RPM is the motor turning?

[imported_jazzman]

My model does not have a built in tach. If I had to guess, I would say around 3000. What RPM do you need on yours to just get it to plane?

[polarisguru]

I sell a "Tiny Tach" for $59.00 that you should really consider. it is waterproof and gives rpm readings and hours of use and very easy to install. This will tell you more exact where your problem maybe. Your engine should be turning 6200-6250 rpms. If it is not then that will help tell you what is going on. If the motor is running the correct rpm, then it most likely is in the pump or electronics itself(cdi) :D