Announcement

Collapse
No announcement yet.

Possible Valve problem?

Collapse
X
Collapse
 
  • Page of 3
  • Filter
  • Time
  • Show
Clear All
new posts
Previous 1 2 3 template Next
    #1

    Possible Valve problem?

    I'm having some trouble with my '79 425EN. I can't seem to get it to rev above 4500RPM. The bike sat untouched in a barn for 17 years before I got it. I was having some rich running problems so I talked with a friend and he told me to remove the airbox and watch the venturi slides in the carbs. I did this and found them both to be working. But I took the carbs apart thourougly cleaned them and put them back together again and balanced them. Same thing everything works. The odd thing that I noticed is that both times I watched the slides I noticed that the carbs blew Air/Fuel mix back out the airbox side of the carbs. Right side was slightly worse than the left but both had the same problem. I have yet to tear the top off the engine and check the valve shims or do a compression test. Has anyone ever seen this problem before, or have any ideas what could be done to try and solve this.

    I have never done a valve shiming job or valve replacement on anything before, I've read the procedure in my repair manual but still am a little afraid of it. Could it also be that the cam timming is misalined on the intake cam. I have no history of the bike and much of the bike was missing when I received it.
    Tags: None
    #2
    Check the valve clearances first, it's not that hard to do. Then do a compression test

    Comment

      #3
      checked compression

      Sorry for taking so long, It was a crazy week. I picked up a compression tester yesterday and just tested the compression on both cylinders. 140 PSI on both cylinders. I haven't gotten to look at the valve shims yet. It is on my to do list.

      I'm guessing that this 140 PSI means my valve are good becuase it is within the specs called out in the manual.

      Here is how I did the compression test (cold engine).
      1. Remove both spark plugs
      2. insert hose from compression tester into cylinder.
      3. hold throttle wide open
      4. rotate engine until needle on guage discontinued upward movement (about 4-6 compression rotations)
      5. Repeated on other cylinder

      With readings of that good of comprssion I am trying to figure out what could be causing the fuel to be blow out the intake side of the carb. Is it possible I have a sticky valve? What are the other possibilities?

      Comment

        #4
        Planned For tonight

        After scoping around today I found out about doing a leakdown test. Turns out I have all the stuff to build the tester at home in my toolbox . I will slap one together tonight and give it a test. I know that the intake valves have quite a bit of carbon on them and I may be able to just clean them if they are indeed the problem. Hopefully I don't find anything to bad or costly. Otherwise the rebuild is shelved until next summer. (Why do cars have to cost so much to fix? :x )

        Comment

          #5
          Go ahead and check the ignition timing. If it has points go ahead and replace them along with the condensers, should'nt cost to much.

          Also check fuel flow from your petcock to the carbs, and you may want to drop the bowls one more time just to make sure the jets and float needles are still clean. 17 years in a barn make's me think it's a fuel problem.
          1166cc 1/8 ET 6.09@111.88
          1166cc on NOS, 1/8 ET 5.70@122.85
          1395cc 1/8 ET 6.0051@114.39
          1395cc on NOS, 1/8 ET 5.71@113.98 "With a broken wrist pin too"
          01 Sporty 1/8 ET 7.70@92.28, 1/4 ET 12.03@111.82

          Comment

            #6
            Originally posted by RacingJake
            Go ahead and check the ignition timing. If it has points go ahead and replace them along with the condensers, should'nt cost to much.

            Also check fuel flow from your petcock to the carbs, and you may want to drop the bowls one more time just to make sure the jets and float needles are still clean. 17 years in a barn make's me think it's a fuel problem.
            this is not a suggestion but just a comment

            Say jake, i was thinking that the air blowing backthrough the carbs while just cranking the engine may be a normal thing. after all the cam timing is usually quite sloppy on startup even with a stock cam. Yes/No???

            Comment

              #7
              Might be Scotty

              I'm thinking if it's to riched then the fuel may be blown backout, or if it's an ignition problem and the engine won't rev above a certain amount and the throttle is wide open it might be the cause too.

              ???
              1166cc 1/8 ET 6.09@111.88
              1166cc on NOS, 1/8 ET 5.70@122.85
              1395cc 1/8 ET 6.0051@114.39
              1395cc on NOS, 1/8 ET 5.71@113.98 "With a broken wrist pin too"
              01 Sporty 1/8 ET 7.70@92.28, 1/4 ET 12.03@111.82

              Comment

                #8
                Thanks for the info guys. So here is what I found last night. My leakdown test shows me that both cylinders seem to be holding preasure just fine. That is a huge relief.

                As for the breaker boints I just replaced them about 3 weeks ago. I had a hell of a time getting it to time correctly though. It seemed as if the new points didn't fit the advance cam right [can the cam go bad?] and had to fiddle with the breakers and the timming plates until I got the darn thing to time correctly. I may check it again though becuase once again I am back down toward 3500 RPM and it begins to miss and stall after about a mile of ridding full throtle (40 Mph in 6th). But the plugs are as black as they could be, which still leads me to belive that there is something else still wrong.

                Last Time I dropped the bowls I used a peice of wire (about 40 gauge or so) to run through the jets and the passages that I could find. I am getting close to starting to lower the main jet on each carb about a 1/4 to 1/2 turn and see what that does. Hopefully that will lean the mixture slightly.

                Odds are that it is a combination of things.
                1. Mixture from carbs is way to rich
                2. Timming is off or coils are bad
                3. Something with the top end (Valve shims, Cams not put in properly)

                My GF has plans on Thursday with one of her friends so that leaves me the whole night to tear off the cam cover and look at things for the first time. (Watch it be that things are off by a tooth)

                Hopefully it is just a combination of simple things.

                Comment

                  #9
                  Are you trying to ride it without the airbox and airfilter installed? If it's anything like my 1100, it won't rev without it.

                  Comment

                    #10
                    No I do have the air box installed, and Although it is not the factory filter I do have one installed in the cage.

                    Comment

                      #11
                      Last Time I dropped the bowls I used a peice of wire (about 40 gauge or so) to run through the jets and the passages that I could find. I am getting close to starting to lower the main jet on each carb about a 1/4 to 1/2 turn and see what that does. Hopefully that will lean the mixture slightly.
                      If you didn't do it already, take the carbs completely off and disassemble. The best way to clean them is to use a chemical dip, but the spay stuff works pretty good also. It sounds like you have an air compressor - so blow the passages out. I'm not sure how good you cleaned them using the method you described.

                      Comment

                        #12
                        I've had them off three times now for a good cleaning. First two times used the spray carbcleaner and the air compressor. Last time I used an electrical component cleaner on them. It worked really good becuase it pull all the varnish right off everything. Like I said the only thing that I can think of with the carbs now is that the jet height is wrong. I may be wrong but I thought the jets on the GS425 were supposed to be screwed in all the way. I may be worng and that is something I am going to be experimenting with.

                        I spoke with my friend again yesterday who is a suzuki racer. I cannot mention his name he has enimies here. He figures that I have a cam out of timming with what I have been finding. Tommorow will reveil the truth.

                        Comment

                          #13
                          The jets should be screwed all the way in - and tight.

                          You could have a cam that skipped a tooth.

                          Comment

                            #14
                            Originally posted by andycasper

                            I spoke with my friend again yesterday who is a suzuki racer. I cannot mention his name he has enimies here.
                            Sence your friend rides a Suzuki he can't be all that bad, now if he rides a Honda then that's a different story. 8O If he rides a HD then so much the better.:twisted:
                            1166cc 1/8 ET 6.09@111.88
                            1166cc on NOS, 1/8 ET 5.70@122.85
                            1395cc 1/8 ET 6.0051@114.39
                            1395cc on NOS, 1/8 ET 5.71@113.98 "With a broken wrist pin too"
                            01 Sporty 1/8 ET 7.70@92.28, 1/4 ET 12.03@111.82

                            Comment

                              #15
                              Originally posted by RacingJake
                              Sence your friend rides a Suzuki he can't be all that bad, now if he rides a Honda then that's a different story. 8O If he rides a HD then so much the better.:twisted:
                              Well he will only ride his suzuki, He bought his wife a HD and he calls is his girly bike.

                              Comment

                              Previous 1 2 3 template Next
                              Working...
                              X