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Low full throttle rpms

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  • Low full throttle rpms

    95 ps 205 lt1 1:1 acme 541 only getting 3800 at full throttle. Don't have a GPS speed. Pushing on the stick seems fine up to 3000 then I have a lot of room with the throttle but ad as you drop it further rpms and speed just seem not to increase. Almost like the trottle cable isn't pulling like it should

  • #2
    Something is wrong, you should be pushing close to ~4800rpm @ wot. What was your rpm's before prop swap?
    Last edited by j.mccreight@hotmail.com; 04-27-2013, 12:37 PM.
    James

    1989 MasterCraft TriStar 190 SE
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    • #3
      Boat was need to me last summer and only pushed it to 4000 with stock 13x13 oj. Could it be trottle cable ?

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      • #4
        Maybe, anything is possibly, can you rev it in neutral past 3800, you can disconnect cable from throttle body and have operate throttle body and see if thats your issue.
        James

        1989 MasterCraft TriStar 190 SE
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        • #5
          Originally posted by skiknox View Post
          Boat was need to me last summer and only pushed it to 4000 with stock 13x13 oj. Could it be trottle cable ?
          Pop off the air cleaner and push the throttle all the way open and you should see the throttle butterflies at perpendicular (90 degrees) or nearly so.



          My first guess on an LT1 not getting full power would be fuel pressure. The pump intake screen on the rear passenger side of the motor
          tends to clog up if you don't have an inline filter installed before the pump. If the intake screen clogs bad enough it wipes out the pump and you get low fuel pressure. Check the throttle opening and the fuel pressure and if they are good you need to start looking at tps,fuel pressure regulator,clogged injector, ignition,compression etc. Fuel pressure is easily checked at the port on top of the motor. There are a bunch of youtube videos on how to check LT-1 fuel pressure and the indmar lt-1 is the same. Depending on load my 97 205 with the LT-1 pushes at least 45 mph and 4500 rpm on a stock 13x13 prop and the 1 to 1 transmission.

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          • #6
            Originally posted by skiknox View Post
            95 ps 205 lt1 1:1 acme 541 only getting 3800 at full throttle. Don't have a GPS speed. Pushing on the stick seems fine up to 3000 then I have a lot of room with the throttle but ad as you drop it further rpms and speed just seem not to increase. Almost like the trottle cable isn't pulling like it should
            You should hit 5000 RPM @ WOT- clean the screen and MEASURE the fuel pressure. Don't guess, don't hope.

            If you have old fuel filter(s), change now. Also, make sure the fuel pickup tube is clear of debris and the anti-siphon is working properly and make sure the shutoff valve is fully open.

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            • #7
              when I winterized I changed both fuel filters, the one that comes right off the tank and the one on the motor. I will look into checking pressure and check throttle body. thanks everyone for the tips.

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              • #8
                hey JimN where is the shutoff valve located?

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                • #9
                  Originally posted by skiknox View Post
                  hey JimN where is the shutoff valve located?
                  JimN is offline, so I will answer that one. The fuel shutoff is on top of the fuel tank between the tank fitting and the hose that goes to the 1st filter. It is an aluminum fitting with a short lever on top and the fuel line is attached to it. Move the lever back and forth a few times. In line with the hose is "open" and perpendicular is "closed". See what it feels like. If it doesn't feel like it is working right, it is easy to remove and inspect.
                  '96 ProStar 205 SD LT-1

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                  • #10
                    Well today I was going to pull the fuel pump and check the screen an figured I would put the fake lake in it first. Well lt1 ran full rpm range with me manually actuating trottle body and with the stick. The only thing I did prior to starting is making sure valve on tank was in on pos and it was but turned it in and off and couple of times. I guess I won't fully know until I get it back on the lake but it should run and diff should it?

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                    • #11
                      Originally posted by skiknox View Post
                      Well today I was going to pull the fuel pump and check the screen an figured I would put the fake lake in it first. Well lt1 ran full rpm range with me manually actuating trottle body and with the stick. The only thing I did prior to starting is making sure valve on tank was in on pos and it was but turned it in and off and couple of times. I guess I won't fully know until I get it back on the lake but it should run and diff should it?
                      I hate to rain on your parade but on the trailer, it can do fine but what's important is how it reacts when it's under load. I used to see the same thing and it was always a fuel delivery problem.

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                      • #12
                        Well sh*t thought I might be in the clear. I guess pull the pump and check pressure is on the list again.

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                        • #13
                          Originally posted by skiknox View Post
                          Well sh*t thought I might be in the clear. I guess pull the pump and check pressure is on the list again.
                          Leave it in place when you test pressure but do it at several RPM- the way we were taught by MC, it should be checked at Key ON/Engine OFF, Idle, 2000 RPM and WOT. You don't need to go too long at those speeds, but you should test it while someone else drives or drive while someone else tests it. Write all results down, so you have a record of it in case something changes.

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                          • #14
                            Some Jim are you saying I have to pressure test on the water under load to get a accurate reading? Or where you just say running it like I did can give you a false range of full rpms

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                            • #15
                              Originally posted by skiknox View Post
                              Some Jim are you saying I have to pressure test on the water under load to get a accurate reading? Or where you just say running it like I did can give you a false range of full rpms
                              It needs to be run on the water, in gear, at the various RPM. In neutral, running it means nothing and I used to try justifying what I found when I would call MC and they (Mark at MC, Monty & Mark at Indmar) finally got me to understand this. It's a PITA to have to take it to the water, but if the weather is good and you have the tools, parts and time, it's not a bad way to spend some time on the water. Take your anchor and a long enough rope, in case you need to replace something away from shore.

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