4th Gen Carb sync / balance without removing the tank

Discussion in 'Mechanics Garage' started by warewolf, Apr 25, 2022.

  1. warewolf

    warewolf New Member

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    Does anyone have a link to the web page that shows how to synchronise / balance the carbs on a 4th gen, wihtout removing the fuel tank?

    I found it a week or so ago, but didn't save it because it wasn't my computer, and now I can't find it. I thought it was a 'sticky' thread or saved in a how-to section of this forum - but I just can't track it down. Google search not finding it either.

    Thanks
     
  2. squirrelman

    squirrelman Member

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    doesn't matter whether the tank is on or off since synch screws are all accessed from below. study the FSM as the exact sequence of screw adjustments is critical, and they interact slightly. if the bike runs well, you'll never need to turn any screw more than about 1/8th turn. if you screw up too badly you'll need to remove carbs and do a bench synch.

    after turning any screw, blip the throttle a couple times so that throttle butterflies settle into their new position.

    (mixture screws and valve clearances should be correctly set first.)
     
    Last edited: Apr 25, 2022
  3. Simon Edwards

    Simon Edwards New Member

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    Actually the top NOTE on page 6-22 and 6-23 says to synch' the throttles first and then see to the mixture screws.

    I ended up doing both as a cycle a few times until I was happy.

    I used a cheap digital rev counter from ebay to measure the 50rpm drop. It did the job.

    Here you go.
    CylinderLayout_4thGen.jpg
    CarbSynch_1_4thGen.jpg CarbSynch_2_PilotScrews_1_of_2_4thGen.jpg CarbSynch_2_PilotScrews_2_of_2_4thGen.jpg
     
  4. squirrelman

    squirrelman Member

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    ok, what differences do you notice after the work ?
     
  5. Simon Edwards

    Simon Edwards New Member

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    Snappier throttle response, smoother acceleration and greatly reduced initial response lag. You know, the usual stuff.

    I don't know if it makes any spectcular difference to do it in this order, as I simply read the manual and did it the way it advised.

    It was pretty easy though - once I got hold of the digital rev counter and wrapped the sensor wire around the plug lead for cyl 1 so that I could see 50rpm changes and change the mixture screws at the same time. Trying to judge the rev change using the main rev counter was impossible. It was too vague and mostly out of sight when kneeling by the bike twidling screws using a 85deg screwdriver on some screws that are positioned mostly out of sight themselves.

    I confirmed the results using an IR thermometer gun to measure the temperature of the exhaust pipes as near as possible to the ports they leave the heads. Using the idle screw to adjust a range of stable RPM for the testing.

    Before the mixture work one or other was always a significant amount lower temp than the three others. Which showed it wasn't getting the same amount of air/fuel mix as the others. The amount of deviation varied by the revs being tested. I couldn't get them all even and also get a smooth response just using the balancing adjusters. After doing the mixture work as well they are always within 5degC across the 1K to 5K rev range, and with a smoother response on the road. Prior to the mixture adjustments they could be 50-100degC out at different rpm.

    I did try to re-balance and re-adjust the mixtures a few times. But always ended up with a very slight temperature imbalance on the same cylinder. I don't claim its 100% perfect, but the process worked well for me and my bike.

    I had scrubbed my gummed-up carbs using sprays and brushes, which we all know is not perfect.

    I've now bought an untrasonic cleaner. So the next time the carbs come off they will get a proper cleaning in it. That may sort out the final cylinder's slight miss-match to the others. But its working really nicely now and I'm in no hurry to take them off again.
     
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  6. warewolf

    warewolf New Member

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    Thanks all, I do have the FSM but the article I saw had some pretty pictures. :D

    The first time I did it on this bike, the tank was off anyway. I did the mixtures first, but the manual says do sync first. I’ve also been told it may take a few iterations if it is way out.

    I would like to track down a digital tachometer for doing the mixtures, too. My search foo was weak because I couldn’t find anything. Could you put up a link to the one you bought, please? That should get me started with the right keywords.

    Ultimately I need to check valve clearances and overhaul the carbs.
     
  7. warewolf

    warewolf New Member

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    I used to balance the carbs on my Triumph Trophy 900 every 7000 km. If I left it to 10,000 km I could feel more vibration at cruising revs, and slightly more sluggish throttle response. It was worth doing.
     
  8. Simon Edwards

    Simon Edwards New Member

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    I simply looked for "digital tachometer" on Amazon and Ebay and chose a small unit. Here is the one I used. It is still available on Amazon and Ebay "Jayron JR-HM032R"

    There are a few variants of it with different mounting and bracketry. All of them seem to have the same fault - there is no "Off" switch that I have found. So you need to keep a spare button cell battery around, or remember to remove the battery when not using it. Each battery lasts many months before the display fades so there is no urgency.
     
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  9. warewolf

    warewolf New Member

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    Thanks. "digital tachometer inductive" did the trick. Previously I was searching for a handheld tool rather than a bolt-on hour-meter type thing, so probably dismissed all those.
     
  10. Simon Edwards

    Simon Edwards New Member

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    You are welcome.

    I wanted one I could tie to someting with a bit of wire. Definitely not hand-held. Both my hands were too busy guiding and turning the around-the-corner-screwdriver-in-a-tube adjusting tool to be holding the tacho as well. If I had a third hand, it would have been holding a small torch. Which would have made the job quite a bit quicker.
     
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