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2001 DT225 looses 200-300 RPM's at around 4500

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  • 2001 DT225 looses 200-300 RPM's at around 4500

    Hi all.

    I have a 2001 DT225 that sometimes drops about 200-300 rpm at around 4500 rpms. Sometimes if I shut it down, and restart, I can get the revs back >5.3k on WOT. Sometime not. Doesn't happen all the time. First noticed it about two months ago, then it went away, then noticed it again this past week. Seems to be worse when I have a full boat of passengers. I've checked the fuel (which was good) and replaced the fuel/water separator, with no change in performance. My research has indicated it could be just about anything. Here's the list of potential faults.
    1. Bad gas (Gas is good)
    2. Bad fuel / water filter (replaced)
    3. Clogged inline filters (somewhere?)
    4. Clogged low pressure fuel filter
    5. Clogged fuel injectors (Cleaned with seafoam)
    6. Bad low pressure fuel pump (I think I have two of these?)
    7. Bad Fuel injector pump
    8. Clogged Fuel injector filter
    9. Bad stator
    10. Bad CPI (last replaced in 2014)
    11. Bad fuel regulator
    12. Low batteries? (2 banks reading 12.8V)
    13. Old sparkplugs? (replaced about 100 hours ago)
    14. Other?
    My local suzuki service rep suggested I try a 'hail mary' can of seafoam, which I will do next week. His next guess was a clogged fuel injector filter (8).

    Engine has 800 hours on it and gets run just about every week.

    I don't really have the ability to haul my boat into a service facility and don't want to wait a few months for them to look at it. I'm fairly handy and have the time to self diagnose but am looking for help to understand what to do first, second, etc...

    Any ideas would be greatly appreciated. Thanks all.

  • #2
    Are you always buying fuel at same location?
    Have you tried squeezing fuel bulb when this occurs?
    My best guess, the motor is 19 years old, I would look at plugs to see if any are burning unusually different. Then I would check/ clean/or replace any filters after the VST, to the HP pump, and any going to fuel rail.

    This is a start, try and report back.

    Good luck, post back on what you find out.


    • #3
      Thanks Solarman.

      Went out today and ran a full can of seafoam through the fuel/water separator. Emptied the filter gas into a glass, then added seaform 50/50 to the gas. Ran the engine for 5 minutes, then let it set for 15-20 minutes. Did that 3 times. Thought it did the trick but then on my way back to the dock while tacking 5.2 rpms, suddenly dropped to 4.4 rpms. The change was instant like something bumped the throttle. After that, I could increase the throttle and get a few more RPM's but the engine definitely was sluggish. Got back to the marina and pulled the plugs and they all (12) looked great. The gas looked great, no water at all.

      I have a new fuel filter (15410-87D01) and fuel injector filter (15410-92e02) being delivered on Friday, so thats my next move. Did not try squeezing the bulb this time out but did last week and didn't get any different results.

      Seems odd to me that I would get an immediate change in the RPM's from a clogged fuel line (somewhere). If that were the problem, wouldn't I get performance issues across all RPM ranges?

      Thanks so much.


      • #4
        Honestly, I'm thinking more along the lines of a TPS (throttle positon sensor), or possibly a gear counting coil breaking down at full throttle.

        If you have a Suzuki service manual, you can ohm test the gear counting coil, the TPS requires a special jumper/ patch cord to test.

        I'm thinking the TPS may be breaking down at WOT?

        Also, while testing the gear counting coil, you can test the high condenser charge coil (it is part of the magneto used mostly at higher rpms - you will have to look at wiring schematic for wire colors to test), just to see if it is in the normal range?

        It is always a good idea to run a can of seafoam in each tank of fuel unless you're running marine grade fuel, and know it is clean.

        If you don't have a suzuki service manual, you might need to get one for these tests.

        Good luck, post back on what you find out.


        • #5
          Replaced the fuel filter (15410-87D01) and fuel injector filter (15410-92e02). Ran great at first, then stalled out while idling around chasing a bunch of Cobia (dang). Got it restarted after a few attempts, and then it had the same problem as before on the 10 minute ride back to the marina.

          Ordered a new Fuel regulator as the one on the engine looks pretty bad (see below). Do not have a Suzuki service manual, so i did not test the gear counting coil, nor the TPS , which requires a special jumper/ patch cord to test.

          Was also thinking about cleaning out the Vapor separator?

          Could this be the culprit?



          • #6
            Although many parts may look bad on the outside, the insides may still look new? It only matters if the parts do not work. The service manual usually will tell you how to test these items, including the pressure regulator.

            Good luck, post back on what you find out.


            • #7
              Replaced the Fuel Regulator, problem still exists. It seems as if the engine runs great for the first 20 minutes. I pumped the ball after stalling while idling and the engine restarted but the performance was poor. I headed for home and the RPM's gradually got a bit better but not anywhere near what it was when i started. I also experienced some surging today as the RPM's went from 4 to 4.4 on their own. Still had a drop from 5 to 4.4.

              So maybe my next step is the Throttle Position Sensor?


              • #8
                One other thing, when I pumped the ball, it seemed easy to squeeze (not hard).


                • #9
                  Dan, I believe you could find some Suzuki service manuals online, Google your motor name, year, size, with service repair manual. It is worth the investment if you plan to keep the motor?

                  Cleaning the VST is not a bad idea, but always remove the float needle valve and seat to check and inspect for any debris lodged on the backside of the seat (There have been numerous situations where one or more low-pressure fuel pumps have broken-down, and pieces have lodged/ interfered with fuel entering the VST, causing a surging situation during WOT? As if the motor was running out of fuel type attitude?). When re-installing the float and needle valve assy, you must always reset the float level by the manual. If float level is too high, you may have fuel leaking out of the throat of the VST when running, if the float is set too low, the VST will run out of fuel when running at higher rpms.
                  ALWAYS INSPECT ANY TRASH FOUND WHEN CLEANING. It could identify/ tell you if something else is breaking-down, needs to be inspected/replaced. If you can't identify the trash, take a couple of good, clear pics on white paper towel and post them here. We may be able to help?

                  Good luck, post back on what you find out.


                  • #10
                    Couple of updates.

                    I decided to take another look under the cowling and discovered two things. One, I had a spark plug wire that was disconnected (although this may have come off when I removed the cowling) and two, the fuel filter I installed was leaking (noticed it when I pumped the bulb.) So needless to say, I thought I solved my problem when I replaced a faulty filter or fuel regulator, but caused two more problems in the process of fixing it.

                    Long story short, I got the boat out again, and although it ran great for the first 30 minutes, I experienced the same surging and drop in RPM's again. So, the problem still exists. The mechanic at my marina refuses to work on the old Suzuki 2 strokes but said he believed it was probably an electrical issue (bad ground?) since the problem was intermittent? I guess I can add that to my list of potential problems.

                    So... time to regroup. What do you think I should try next? Thanks so much for your input.


                    • #11
                      I'm still thinking a low pressure fuel pump may be bad (a rebuild kit does NOT include new check-valves, you have to replace the pump to get them.), or the TPS could be acting up at higher rpms, but that was why I suggested cleaning the VST (especially the needle valve seat, to see if any debris is reducing the fuel flow, this could cause the surging). I would start with the VST (identifying any trash found- very important), then go for the low pressure fuel pump(s) closely inspecting each diaphragm and check-valves.

                      Your motor sounds like it is running slightly low on fuel at WOT. This is why i suggest these steps. Your low pressure pump(s) should provide plenty of fuel, surging only at WOT indicates low fuel in VST bowl, a restriction if fuel going into bowl, or a weak LP fuel pump(s) not sending enough fuel.

                      Electrical problems (TPS included) are possible problems, but they are more "on & off", not really a surging action.

                      Good luck, post back on what you find out.


                      • #12
                        I replaced both low pressure fuel pumps and cleaned out the VST. Did not find anything in the VST although if their was something it may have leaked out when I disconnected the hoses.

                        Took it out for a spin, here's the results.

                        Seemed to run a bit rough when idling and then I opened it up for about 1/2 mile at WOT. Ran great. Idled through a no wake zone, then WOT again for about 2 miles. Again ran great.

                        Puttered around at low RPM's for 10-15 minutes scouting some fishing holes when all of a sudden, the engine started running rough and then died. When I tried to start it, it just seemed really dead, like I wasn't getting a good crank. After 2-3 tries, I primed the bulb till hard (which seem flat) and the engine fired back up. Came back to the marina without incident. Tried to replicate the problem but couldn't.

                        Attached a link to a few videos which may help.

                        Download Attachment
                        Available until May 28, 2020


                        I didn't experience any drop in RPM's or surging (which was previously occurring along with the rough idling)

                        So at this stage, I"m not sure if I fixed anything at all. Could it be a vacuum issue or faulty spark plug/wire? Really don't know where to turn right now.


                        • #13
                          Click to Download


                          • #14
                            UPdate. Same problem today as on 4/28. Engine ran good for the first 20 minutes or so. Then I shut it down to catch some bait and couldn't get it restarted (like before). When I initially try to start the engine, I get very little engine turnover, almost like a dead battery. But after waiting 45 minutes or so I"m able to crank the starter quite a bit, but it won't start. I'm convincing myself that this is somehow related to heat as the engine runs good and then once warmed up seems to die.


                            • #15
                              After reading your posts, the primer bulb being flat could indicate a restriction of fuel getting to the bulb from the tank? Is there an anti-siphon check valve that may be giving you problems? A tank vent problem could also cause this, kinked fuel line, dirty water separator filter?

                              The cranking/starter being sluggish, not turning motor over could be heat related, or possibly a wire problem. Check wires from battery to solenoid, and to starter, flex them to see if any seem to crunch (possibly corroding inside insulation, reducing voltage to starter)? Also, All starters, on all motors, should not be used for more than 5 seconds at a time, as the high amperage during starting causes the starter windings to get exceedingly hot. So, too much starting, or holding the starter on too long can damage/short-out the windings, making it turn over slower and slower, until it shoots out completely.

                              Good luck, post back on what you find out.