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Erratic idle. Loss of diaphragm seal with choke.

Discussion in 'The Garage' started by Prisondawg, Mar 14, 2019.

  1. Prisondawg

    Prisondawg XS650 Enthusiast

    Hello. My bike has been sitting for a bit over the winter and it's starting to get a little warmer out here in the Chicago area, my bike was running pretty decent before I parked it. But when I tried riding it again it just died in the middle of fourth gear and I had to push it home. I thought perhaps I put the slide needle in incorrectly when I moved the clip to the second position. So I took it all apart , cleaned it out with carb cleaner and compressed air. And even added washers to the needles between the spring and clip since I saw them on a diagram of how to assemble them. When I got them back on, the bike was running pretty solid again, then after getting up to speed again it died. And I eventually got it started again in the street. Got it home . Was able to run it again and drove it around the neighborhood, seemed to be working ok. Today, however, when I started it, it would fire and die. I eventually got it to start with choke off but it it had a very erratic idle. Not like a climbing idle you would expect with air leaks. So I pulled the carbs off again and I noticed if I put my thumb over the big intake hole and lifted the slide with my finger it falls slow on both sides, however when I put the choke on they fall fast. I have also seen fuel bubbling from the black boots around the choke plungers, I'm wondering if this could have something to do with it. And if so the best route to take to replace them. I have a TCI ignition. With 78 special BS38 carbs on a 1981 engine. Also when I was kicking it , I was getting a lot of kickback and it backfired at least once. Please help in solving this problem so I can get riding this spring. Thank you.

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  2. grizld1

    grizld1 Grumpy old man Top Contributor

    First time I've heard of fuel moving up past the choke plungers, and I thought I'd seen about everything! First off, the slide will drop fast when the choke is actuated; that's normal. Replacing the boots won't help at all, they're only there to keep out dirt. If I were you the first thing I'd look at is fuel level, with a sight tube. If fuel level checks out, inspect the choke plungers. Make sure that actuators are letting the plungers down all the way, plungers move freely, spring tension is good, plunger chambers are clear, and Viton pad on the bottom of each plunger is in good shape.
    TwoManyXS1Bs likes this.

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