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Engine surging and popping on part throttle

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    Engine surging and popping on part throttle

    Bike has been a bit slow to start at first I blamed the fuel pump then the battery but they are fine. This morning it was really hard to start and when it finally fired it backfired.

    Got on the road and it was not pulling then it suddenly surged pulling like a train. Shut throttle and the exhaust was popping and banging. Tried to ride through it thinking it would settle when it warmed but after five miles it was getting dangerous surging in the bends I gave up and trundled back home very steadily.

    Took tank and airbox off to check everything fired it up and I noticed the rear cylinder carb the slide was bobbing up and down on tickover, blipped the throttle and it became a blur. Front pot the slide is steady.

    Have I got the dreaded diaphragm problem. I am going to check the carbs over blow through all the jets just to check nothing is clogged.

    #2
    Originally Posted by Fastmongrel View Post
    Bike has been a bit slow to start at first I blamed the fuel pump then the battery but they are fine. This morning it was really hard to start and when it finally fired it backfired.

    Got on the road and it was not pulling then it suddenly surged pulling like a train. Shut throttle and the exhaust was popping and banging. Tried to ride through it thinking it would settle when it warmed but after five miles it was getting dangerous surging in the bends I gave up and trundled back home very steadily.

    Took tank and airbox off to check everything fired it up and I noticed the rear cylinder carb the slide was bobbing up and down on tickover, blipped the throttle and it became a blur. Front pot the slide is steady.

    Have I got the dreaded diaphragm problem. I am going to check the carbs over blow through all the jets just to check nothing is clogged.
    I’m not experienced enough with the Hawk yet to say one way or another but if it is the diaphragm, NRP do them and it only takes 15 mins to swop the old one out with no cutting involved

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      #3
      Originally Posted by Fastmongrel View Post
      Bike has been a bit slow to start at first I blamed the fuel pump then the battery but they are fine. This morning it was really hard to start and when it finally fired it backfired.

      Got on the road and it was not pulling then it suddenly surged pulling like a train. Shut throttle and the exhaust was popping and banging. Tried to ride through it thinking it would settle when it warmed but after five miles it was getting dangerous surging in the bends I gave up and trundled back home very steadily.

      Took tank and airbox off to check everything fired it up and I noticed the rear cylinder carb the slide was bobbing up and down on tickover, blipped the throttle and it became a blur. Front pot the slide is steady.

      Have I got the dreaded diaphragm problem. I am going to check the carbs over blow through all the jets just to check nothing is clogged.
      Not cheap but available
      Attached Files

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        #4
        Popped slide out and diaphragm looking okay
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          #5
          Slide function is best checked while it's installed. Blow and suck on each slide chamber's vent tube as see if they behave the same on both.

          And use your finger to feel the smoothness of the travel against the spring.

          Slides can be sticky in the bore or can have leaks in the diaphragm (from tears or seating problems) or can have weak springs... or a combination of these.


          If you were looking for a support group you're barking up the wrong tree. This place is fulla enablers dude. - Shooter77us

          The bitterness of low quality lingers long after the thrill of a low price has gone. - RacerX450

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            #6
            Are your intake boots new and your bands right and carbs seater fully?
            Don't spend money and buy, spend time and learn.

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              #7
              I did the blow test down the black 90 connection and both sides seem okay. Pushed slides up with fingers and they seem okay there's a bit of the black coating on slide is beginning to wear away.

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                #8
                Originally Posted by 6 View Post
                Are your intake boots new and your bands right and carbs seater fully?
                The rubber connectors from carbs to the cylinders are new but the connectors to the carbs from the box are original.

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                  #9
                  Did you check your valve clearances by chance?

                  Most likely this is somehow carb related, but there are other things.

                  If that where my bike first thing I would think is air leak. Get it running spray some brake clean under the tank around the carb boots and see if it revs.
                  Don't spend money and buy, spend time and learn.

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                    #10
                    i'd guess the big power surge is that one cylinder that's not working is coming to life suddenly, so i suspect a spark problem. check the gaps @ about .030". try to locate which cylinder isn't firing by touching header pipes after starting, then replace the plugs in that cylinder or switch plugs from one cylinder to the other. another guess is that if there is spark problem go in and replace the left front plug since it's usually neglected.
                    "It's only getting worse."


                    MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

                    Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.

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                      #11
                      I have had a go at cleaning the carbs and everything seems okay. Ignition next though I have limited experience with electronic ignition. I can't even find the Magneto

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                        #12
                        I am getting a weedy spark on front and back pots. Possibly spark generator

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                          #13
                          I think I have found the problem. A previous Bubba had sealed the float bowl gasket with black silicone. Pilot jet was clogged with black crap.
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                            #14
                            Originally Posted by Fastmongrel View Post
                            I think I have found the problem. A previous Bubba had sealed the float bowl gasket with black silicone. Pilot jet was clogged with black crap.
                            Glad you found it!

                            Not going to lie.. I have definitely been that guy who tries to gasket make my way out of needing a float bowl gasket, then not used fuel proof products.. and thus gummed up a set of carbs.

                            I believe I only did that once, but I did it..

                            So whomever made that mistake cut him a break for me haha
                            how's it running now?
                            Don't spend money and buy, spend time and learn.

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                              #15
                              It's not back together yet, hopefully get the carbs back in place tonight. The weather forecast is sunshine for the weekend so I will pack a small toolkit just in case and go for a good blast

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