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Thread: 951 Carb issues

  1. #1

    951 Carb issues

    After many trials and tribulations, I've figured out what my RX 951 problems are. Symptoms were that the ski would run up to 3700 rpms and then the PTO cylinder would shut down. Well after adding a long fuel line from the Mag pump nipple that feeds the PTO carb, it is losing pressure at that point. Running on one cylinder, it will pump a good stream up to 3700 and then it stops pumping to almost nothing. Do I just need to order another pump or is there something I might check? Are there any check valves built into any inlet/outlets of the pump? I've checked the clear values and those are in the correct position and on the correct side. I've rebuilt the carbs twice with OEM replacement parts. Should mention that I'm not using the accelerator pump and I'm jetted 95 low - 165 high.

    Thanks
    Mark
    Last edited by marshef31; 09-15-2019 at 07:11 AM.

  2. #2

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    Maybe check pulse line connections on both ends. Maybe splice in a short clear line between the return line & the return nipple to see if there are bubbles which indicate an upstream leak allowing air in. You can observe flow too.
    Was the fuel line you added clear or transparent?
    The restrictor orifice is built in inside the MAG fuel pump block and should be built in to the PTO carb front cover. No service to them is necessary except to make sure they aren't clogged.
    Also, maybe try to run it with the gas cap off to see if it improves which would indicate the inlet check valve for the fuel tank is stuck closed.

  3. #3
    FL_Rider, Thanks for your reply.

    I did not use clear hose when I did the test from the Mag pump nipple to check for air bubbles. I will definitely try clear hose and look for bubbles. Am I correct in that the restrictor orifice is just a smaller restriction and not a one-way value? There is a good stream coming out the MAG pump block nipple that goes to the PTO Carb. until it reaches the 3700 and then it goes to almost nothing. I have had the pulse lines (replaced hose) off and on several times with the same results. I have connected a separate hose bypassing the fuel selector valve and bypassed the inlet check value form the tank. I have the 4 tank hoses as follows,ON going to the fuel inlet on the carb, RES going to a hose that I have capped off (assuming it should be this way when the selector would be set to ON), RET going to the return nipple of the MAG carb, VENT going to an hose open to the atmosphere. Going back to the pulse lines. I did see some dark fuel in the MAG pulse inlet cover between the clear diaphragm and the metal cover. I assume that would have to come from the crankcase. I did put some fuel/oil mixture into the dead cylinder for lubrication when test running on 1 cylinder (very short time). Would that indicate anything?
    Thanks for your help.

  4. #4
    Tool Bag water worx's Avatar
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    My head hurts trying to read that.


  5. #5
    So after replacing fuel lines with clear hose. Installed a new pump and checked diaphragms. No bubbles at all from the tank to the carb. No bubbles from pump to PTO carb outlet. Very little fuel coming out of the return line. Here's a clip running on 1 cylinder showing the fuel dropping when the engine revs. I don't know what normal is as for as flow, but this seems to be my problem in that flow stops or is very little to the PTO carb once reved a bit. Does this look normal?

    https://drive.google.com/open?id=1ro...h1MExoF1vnZJHd

  6. #6
    I'm not an expert here but that looks normal to me. Hope more experts would chime in.

  7. #7
    I hope someone who knows more will chime in also. The thing that makes me think it's not is that this is only reving up to maybe half throttle and if the stream is say 100% at say idle, it's only like 20% at half throttle. 80% being used by the MAG carb leaving 20% for the PTO and this us not under load, whether that matters or not. It just seems that little dribble is not near enough fuel for the PTO carb and the fact that it completely shuts off on the ski under load at 3700 RPMs. I'm about to test with an external pump split to both carbs producing even flow. I'll report back.

  8. #8
    After tons of different test, a low pressure electric fuel pump has fixed the issue for now. For some reason, maybe residual fuel in the crankcase(was seeing a small amount thru the clear diaphragm in the pump) or whatever, the Mikuni pump would not supply enough fuel for the PTO carbs demands. I removed the 2 small check valve disc from the pump and added the low pressure electric pump ahead of the fuel line filter and the ski runs great. Fine tuned the TPS and have run it for over an hour now and plugs look good. No signs of a lean condition due to low fuel pressure. I'm wiring it into the power side of the Coil so it's only on when you plug the lanyard in. I suspect this has been the cause of many of the PTO failure reports.

  9. #9
    Tool Bag water worx's Avatar
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    Not sure where you are getting "many PTO failures" from ???

  10. #10
    Not sure what you mean by "Not sure where you are getting "many PTO failures" from?...Does it not make sense that the PTO cylinder would have more failures from a fuel delivery standpoint. The MAG is always going to get what it calls for first and the PTO gets what's left. It's not an even distribution like a external Mikuni Pump. I may be way off, just my observation. Also, do you know at exactly what point cylinder pressure drops to a level that you don't have enough pulse pressure (exp. 2lbs to 1lbs) to make the fuel pump fully work. I'm sure there is a point that some are running with too low compression to fully work the pump, which would in turn be a death cycle for the system. There are post where some suspect a lean range from the factory when everything is perfect. Just a lot of variables with the many things that could cause fuel flow issues. Leaks from god knows where, filters, relief valves and on and on. From an engineering standpoint it just seems and external pump like the DF62 would have been more practical and easier to diagnose issues. The 951 is a gas hog at 14-15 gallons an hour on 2 cylinders.
    Last edited by marshef31; 10-03-2019 at 09:02 PM.

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