Announcement

Collapse
No announcement yet.

OK, Who Knows 2 Strokes

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • OK, Who Knows 2 Strokes

    I have an 02 CR250 that is giving me some issue. When I first got it the engine stumbled a lot and didn't seem to make a lot of power, which was fine with me since I was just starting out. I found a broken wire leading from the ECU and repaired that with a huge improvement in engine performance. I cleaned the carb thoroughly and have been able to tune it for a decent idle and lower throttle input performance. It starts with 5 kicks cold, and one kick when warm. At 1/4 to 3/4 throttle it still stumbles some before it get up one the pipe and rips like it should. But my big headache is that oil is coming unburnt out of the exhaust and making a mess of the rear of the bike after just a couple of hours of riding. What's weird is that it does not smoke that bad, does not foul the plug. It does seem to go through a tank of gas pretty quick, but I have no experience in what to expect. I mix the oil at 50:1 with premium 2 stroke oil.

    My research suggests that there may be a bad crankshaft seal allowing transmission oil into the crankcase. Could still be a carb problem. Maybe a broken reed valve.

    Anyone have any ideas before go spending money to get this right?

  • #2
    Weld a fence post to the muffler and put the mess behind you!
    Sorry dude, I was tryin' to save your saddlebags.
    KN, this ride's for You.

    http://i415.photobucket.com/albums/p...ps2ecwj35m.jpg

    Comment


    • #3
      "Back in the Day" we would have to pull the head/cylinder and inspect the reed valves. The head, piston dome and exhaust port
      would become completely carbon'ed up. So much so even the exhaust port would almost be completely closed up and would
      require a good cleaning.

      Two strokes are easy to work on. A good de-carbon/cleaning, spec piston/clyinder, new base and head gasket and you
      will know you are good to go.

      Unless you have already done that?



      Our ability to distribute interesting information is out pacing our ability to create it.

      Comment


      • #4
        Yes, it may be a crank seal as 50:1 premix should burn cleanly. What does the plug look like?

        I've never had to replace a crank seal, but I doubt that it's particularly difficult if you follow the manual and take your time. Obviously, it would be worth having a good look at the piston, rings, etc. while you have it apart.

        "You don't get slower with age, you just get more cautious." Michael Rutter

        06 Ocean Blue ZZR1200, the coolest colour.
        99 Yamaha R1

        Comment


        • #5
          Originally posted by piken View Post
          "Back in the Day" we would have to pull the head/cylinder and inspect the reed valves. The head, piston dome and exhaust port
          would become completely carbon'ed up. So much so even the exhaust port would almost be completely closed up and would
          require a good cleaning.

          Two strokes are easy to work on. A good de-carbon/cleaning, spec piston/clyinder, new base and head gasket and you
          will know you are good to go.

          Unless you have already done that?


          I did take off the exhaust and found a lot of carbon buildup in the head. I scraped out what I could get to, but did not take off the cylinder to inspect the power valve. As I understand, they can get pretty caked up as well. The expansion chamber was cleaned by spinning a frayed piece of cable with a drill in it and then a good soaking in gasoline. The inlet side of the pipe had mucho carbon which was also removed The linkage for the power valve moved easily, so I let it go at that. I was told by the seller that it had a new bottom end and piston not so long ago. The reeds and reed block are aftermarket and apparently no longer in production. Going to need to do a little more research on that, a new block and reeds is about $150, reeds only are $50 if I can find a set. A top end kit is also around $100-$150 and includes piston, rings and a gasket set.

          My gut tells me that the source of spraying oil is a bad crankshaft seal. I have been changing transmission oil about every 10-15 hours, and it always seems to be a little low despite no visible leaks. The trans oil is 80wt and not designed to be burned. What is spraying on the swing is thick black sludgy oil.

          I am gonna start with another thorough carb cleaning and use new gaskets. Pull the reed block and have a look at that. And then resort to removing the clutch and basket to see if the right side seal can be replaced without having to remove the transmission or split the cases.

          Or I could just ride it like it is until the weather gets hot and steamy, and dig into it when the season comes to an end.

          Comment


          • #6
            What does the service manual recommend for "de-carbonizing" if any?

            If there's excessive carbon build up in the cylinder (piston/dome) it will lead to hard starts, degraded performance, inefficient combustion (which would lead to oily exhaust) and even excessive piston wear and cylinder scaring. The flame front needs a smooth surface, once surface has excessive carbon build up the flame front can fire off kilter (so to speak)
            and cause improper piston wear etc.

            Anyway does the service manual have a service interval for "de-carbonizing" just wondering.

            I guess if you had a bore scope maybe you could peak inside cylinder to inspect for carbon build up?

            Also there's a few different procedures using seafoam that can work really well to break up carbon.

            I'd still just pull it apart and clean it all up, doesn't cost much for a couple of gaskets and then you will
            know it's done correctly.


            Our ability to distribute interesting information is out pacing our ability to create it.

            Comment


            • #7
              Mehush, from my experience, when crank seals are blown, you will lose top end compression. Check the compression, if it is low, then vacuum and pressure check the bottom end. That will tell you if the crank seals are blown. But from what you posted, I don't think that is the problem. Seems like it is just running rich. Make sure the right main jet is in it. Good luck
              I AM 62 YEARS YOUNG AND HAVE BEEN RIDING KAWASAKI MOTORCYCLES FOR THE PAST 46 YEARS. I HAVE HAD FOUR 750 TRIPLES, TWO 350 TRIPLES, A 750 TURBO AND A '95 GPZ1100. I CURRENTLY HAVE A '74 400CC TRIPLE and a 2002 ZZR1200. HAVE CROSSED 49 STATES VIA MOTORCYCLE.

              Comment


              • #8
                I don't have the manual for it, so I don't know what the cleaning intervals are. I have probably logged 25-30 hours on it myself. I did a hot plug check on it not long ago and plug looked fine. The guy who sold me the bike assures me that he did the bottom end himself and can all but guarantee that the seals are fine. He agrees with you guys that it just running super rich and suspects the reeds could be the source, or that the carb could still be the issue. I can say that it has the smallest main jet available and the needle is set to one clip shy of most lean setting.

                I appreciate all your input immensely. Gives me hope that crank seal is fine. I'll order up a carb rebuild kit and see what happens. I do agree that a carbon buildup could also be the culprit, but I just don't want to tear the thing down right now since it is prime riding season, and despite the oily mess, it is still a blast to ride.

                Hoping to do my second hare scramble in two weeks if I can get the day off from work, and my back loosens up a little.

                I will try to update this thread when I get the carb kit.

                Comment


                • #9
                  I'd say those jet settings are a definite clue ...
                  "You don't get slower with age, you just get more cautious." Michael Rutter

                  06 Ocean Blue ZZR1200, the coolest colour.
                  99 Yamaha R1

                  Comment


                  • #10
                    I also have a suspicion that the choke seal could be a problem. On this carb, when you pull up the choke knob, it raises a rubber seal that opens up an additional inlet for gas. The spring that holds it closed is very weak.

                    Comment


                    • #11
                      Lower the carb needle one notch (raise clip) and see if mid-throttle stumble clears up.
                      This should clean up exhaust somewhat.
                      What 2.stroke oil are you using?
                      80w sounds too thick for trans...did you check book on that?
                      Finally, remember that it is a 2stroke

                      Comment


                      • #12
                        I have a carb kit coming. It includes a stock main and pilot jet, and new needle. It also comes with a new float needle and seat. I will try and set it all to stock and see what happens.

                        Another thing I did not pay much attention to was the float height. I will take care to set it level this time.

                        And have a look at the reeds while the carb is out.

                        Comment


                        • #13
                          Originally posted by dbsuperbiker View Post
                          Lower the carb needle one notch (raise clip) and see if mid-throttle stumble clears up.
                          This should clean up exhaust somewhat.
                          What 2.stroke oil are you using?
                          80w sounds too thick for trans...did you check book on that?
                          Finally, remember that it is a 2stroke
                          The clip is on the next to the highest setting(needle nearly as low as it can go) already.

                          I'm using Maxima synthetic premix oil. I was using a castor type, it did the same thing. I switched to see if that would help.

                          Yes, 80W gear oil is what is called for.(according to the youtube experts)

                          Comment


                          • #14
                            Carb kit came today, It's apart and soaking. Apparently the stock sizing of the pilot jet is slightly smaller, and the new main is a 420 vs a 370 that was in the bike. Sounds like it is going to go the wrong way. Kit came with a new slide needle so maybe the matched set will work better than what was in there. We will see tomorrow.

                            Comment


                            • #15
                              Put it together with the new parts. Started on the second kick. Still stuttering on the transition from small to large throttle openings. While making an adjustment to the A/F mixture screw, it started dumping fuel out of the carb overflow tube. I had set the float height a good bit higher hoping that a full bowl might cure the stutter. Reset the float height and still dumping fuel. Put the old needle and seat back in and no leak. A couple of more runs and decided to put the old main jet back in. Essentially, it runs about the same as before.

                              The good news is that I took out the reed block to inspect....reeds look fine.
                              Last edited by mehush; 01-17-2018, 08:52 PM.

                              Comment

                              Working...
                              X