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  1. #1

    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 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!


  2. #2
    Mpeavler's Avatar
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    1.5-2.0 PSI at idle and around 6 psi at WOT


    M

  3. #3
    Quote Originally Posted by Mpeavler View Post
    1.5-2.0 PSI at idle and around 6 psi at WOT
    So my existing BN carb, which I rebuilt, is making sufficient fuel pressure at 3.5PSI during cranking?

  4. #4
    Mpeavler's Avatar
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    Just seen you have a "BN" and not a Super "BN"....not sure on that carb =0(

  5. #5
    Old Ski Insanity w/rpm500's Avatar
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    first thing how is the pulse hose from the engine? if bad or loose replace it..., it will create low fuel pressure..also check the oil scavange hoses that suck the oil residue out of the crank case when running......these hoses are 20+ years old now..

    if you rebuilt this ,please make sure you stacked all the rubbers and mylars in the right sequence .. the bn is lots more confusing because of the abundance of gasket that come in its kit... thay cover a bunch of that model carb..

    the original bn is an ok carb for the 500... not as good as the sbn but it works. if you buy one make sure you get it for the wr/wj series as it should then be jetted properly...if you dont mind spending the green for it its a great carb to update with.. you will like it!!!

  6. #6
    Quote Originally Posted by w/rpm500 View Post
    also check the oil scavange hoses that suck the oil residue out of the crank case when running......these hoses are 20+ years old now..
    How do I check these? (I'm not sure where they are located)

    Thanks for your help!

  7. #7
    Quote Originally Posted by w/rpm500 View Post
    if you dont mind spending the green for it its a great carb to update with.. you will like it!!!
    If I was certain it would fix the problem, I would order one right away. However, I'm concerned there may be something else I've overlooked that a new carburetor won't fix.

    I hate throwing parts ($) at a problem without understanding the problem. Unfortunately, I still don't understand what is causing this fuel supply issue. I've searched a few other posts that imply 3.5PSI (measured at the fuel return outlet) is sufficient?

  8. #8
    Old Ski Insanity w/rpm500's Avatar
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    the pulse line is short one of the three that you take off when you rebuilt the carb.. its the only one that doesnt RETURN to the tank or FEED from gate valve... its whats pulses the carbs fuel diaphrams that pump/suck the fuel out of the feed/gate line...

    what i would do is verify fuel is getting up to the carb first. take off the feed line at the carb , (feed is the line from the gate to the carb,that is mounted on the plastic (generally)nipple , at the very end of your diaphram stack of the carb , pulse is the one that comes out at 4 oclock and feeds off that small 8 inch hose to the manifold, return is the hose nipple thats left... it come out of the side of the carb..)

    this test would verify your gate valve is working at the same time ( swing it to both extreems from center,to verify flow).. hold a rag over open fuel neck and pressureize the system enough to get fuel up and thru the lines (this will verify everything is working to that point)..

    next if your sure your diphrams are in correctly, reattach all hoses except the fuel feed at the carb...get a short length of hose( 1 ft or so) and seafoam arrisol spray oil... spray this down the hose holding the end and can higher than the carb assembly ( i do this as the bn dry, will not pump fuel until it is primed well) ... reattach your feed hose and the see what the ski does while starting ..

    the scavange lines , are two small diam lines off the side of the block.. they attach via tiny nipples to the side and feed to the bottom ...they can crack or leak,causeing a lean condition and burn your motor up...

    SEA FOAM SPRAY HAS GASOLINE AND OIL IN IT.. LOTS OF PEOPLE USE IT AS A SPRAY FOGGER.. YOU CAN DIRECTLY SPRAY IT DOWN THE CARB AND MAKE THE MOTOR RUN WITH OUT ANY HARM .. SPRAY IT LIGHTLY UNTIL THE MOTOR RUNS BY IT SELF ( DONT USE TO MUCH WHILE RUNNING OR IT WILL FLOOD YOUR PLUGS...)

  9. #9
    Well, here’s an update…

    I ended up pulling the motor out, in order to inspect the oil scavenger hoses. (It’s really cool how easy it is to pull the motor!) The hoses are good (I pulled them off and checked each with a vacuum pump). I’ll probably replace them anyway, to be safe.

    I pulled the intake manifold to look at the reeds. At least one of the petals was slightly “lifting” away from the valve body (or whatever it’s called J).

    I tried to pressure test the case, but was unsuccessful. I should have done this before I removed the intake manifold. I put it back on for the pressure test with the old gasket, hoping it would be adequate for the test, but it leaked. I couldn’t even draw as much as 1 in. Hg of vacuum. I was able to momentarily pressurize to 3 PSI, but the pressure bled off almost immediately. I’m not sure if it was all leaking out the intake manifold gasket, or if there was another leak, or if I just didn’t get everything blocked off correctly.

    At this point, for peace of mind, I’m thinking I will replace the crankcase end seals, (maybe even replace the piston rings, and hone the cylinders, since it will be open that far), replace the reeds, and buy a new SBN carb. As I mentioned earlier, I don’t usually like to throw parts at a problem, but I think I would end up with a solid running machine.

    Any thoughts?

  10. #10
    Old Ski Insanity w/rpm500's Avatar
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    Quote Originally Posted by butter View Post
    Well, here’s an update…

    I ended up pulling the motor out, in order to inspect the oil scavenger hoses. (It’s really cool how easy it is to pull the motor!) The hoses are good (I pulled them off and checked each with a vacuum pump). I’ll probably replace them anyway, to be safe.

    I pulled the intake manifold to look at the reeds. At least one of the petals was slightly “lifting” away from the valve body (or whatever it’s called J).this is normal , take it off turn it over ...,reinstall it ( boysens or tdr reeds will help this if you wish to buy em anyway

    I tried to pressure test the case, but was unsuccessful. I should have done this before I removed the intake manifold. I put it back on for the pressure test with the old gasket, hoping it would be adequate for the test, but it leaked. I couldn’t even draw as much as 1 in. Hg of vacuum. I was able to momentarily pressurize to 3 PSI, but the pressure bled off almost immediately. I’m not sure if it was all leaking out the intake manifold gasket, or if there was another leak, or if I just didn’t get everything blocked off correctly.cut a thick rubber gasket for the carb mount then reinstal the carb ( one block off done) plug the exhaust wit a hose and a freeze plug ( exhaust done) put a hose betwwen your water intake nipple and the flush nipple (# 3 done) ....make sure those little scavange hoses are tight(4)... on the manifold you will see 1 pulse line nipple .. this is where you can pressureize with a tire valve that had the rubber cut away ,retained with a clamp in the hose...( all exits must be capped for this to work properly ...)if it hols steady for about 10 min.s your good...

    At this point, for peace of mind, I’m thinking I will replace the crankcase end seals, (maybe even replace the piston rings, and hone the cylinders, since it will be open that far), replace the reeds, and buy a new SBN carb. As I mentioned earlier, I don’t usually like to throw parts at a problem, but I think I would end up with a solid running machine.you will liek what the sbn will do for you .. as you dont know how the bn feels .. take my word for it... buy a o/e manual if you can find one on line or the seloc ( chiltons as a last resort) the seals are pretty much all youll need .. the rings if the cylinders are not scored are chrome and hard surfaced .. if the block is good give it a light scuff with 400 grit wet or dry sprayed with cutting oil ( penatrant oil will work) ... them reassemble with 2 stoke oil on the cylinder wals and some light grease on the piston needles to hold them...word of caution: this engine is the only pwc motor yami built with uncaged bearings ( that i know of) .. keep trak of those needles as the can easyly be lost..... note where all your different bolts come from.. they are easy to install wrong and do damage ( zip locks with sharpies work great)... third.. tap all of your holes to clean them up and to remove prior thread locker ( you'll basicly need a 6mm tap and an 8mm tap,then use blue locker on everything) ... and lastly take a few pictures of your build to use as reference in case ...... ( pm me if you need any help...)

    yes this is as simple as they come... (thats why i like em!!!) oh, and lastly use 1211 on the case halfs spairingly( this is a close machied surface already so that sealer is just a glaze to fill imperfections in the mill process..
    Any thoughts?

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