wr500 fuel pressure - PWC Forum: The best hang-out for Personal WaterCraft enthusiasts
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post #1 of 4 (permalink) Old 07-06-2009, 01:00 PM Thread Starter
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wr500 fuel pressure

Hi. I am a PWC newbie, though I have 25+ years of boating experience. I recently purchased a non-running ’89 WR500, thinking I could get it going pretty easily, but it’s got me stumped. Sorry for the long-winded post, but here’s what I’ve done/learned so far…

I’ve narrowed the problem down to a fuel delivery issue. Compression is 125 PSI in both cylinders. I have visually verified there is strong spark, and it will start and run on starting fluid (which I have used very sparingly).

I rebuilt the round body Mikuni BN carburetor (new fuel pump diaphragms, etc…), and the pop-off pressure is about 9.5 PSI. However, even after the carb rebuild, there does not seem to be enough fuel pressure to force fuel past the needle/seat. I put a fuel pressure gauge on the fuel return outlet of the carb, and cranked the engine. I was only measured 3.5PSI. If I understand these carbs correctly, that is not enough fuel pressure to push fuel past the 9.5PSI pop-off pressure of the needle/seat.

There certainly seems to be significant “pulse” in the pulse line, though I’m not sure how to quantify whether it is “good” or not. I have also bypassed the fuel selector switch, and am pulling fuel directly from the reserve outlet on the tank. The tank does not seem to leak and holds pressure. The fuel flows freely (no restrictions) between the tank and carburetor.

I’m about ready to buy an SBN carburetor from atlanticjetsports.com, but wanted to ask if there’s anything I am overlooking? Is there a good way to verify that the “pulse” signal is strong enough? Does anyone know how much fuel pressure a good Mikuni BN carburetor should make? Is the SBN carburetor a direct bolt on swap for the existing BN carburetor?

Thanks in advance for your help!
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post #2 of 4 (permalink) Old 08-02-2009, 09:00 PM
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Will the machine start if you choke the carb manually by hand?
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post #3 of 4 (permalink) Old 08-03-2009, 07:15 PM
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Have you got the main fuel line and the return the wrong way around. Swap them and see what happens. Also, cut 10mm off the bottom of the feed sender in the tank to get the line off the bottom.
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post #4 of 4 (permalink) Old 08-03-2009, 09:47 PM
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Originally Posted by butter View Post
I put a fuel pressure gauge on the fuel return outlet of the carb, and cranked the engine.
I believe the restrictor that gives you the fuel pressure is inside the carb. If I'm right, then measuring the fuel pressure in the return line isn't going to tell you anything since you are measuring after the restrictor.


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