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Thread: Pop Up Forks

  1. #1

    Pop Up Forks

    Hi everyone
    I have just been doing some research on suspension setups and have found that the forks on my popup are under sprung and underdamped. My question is what springs have have other people had good results with and how much heavier weight oil than 15 weight will still work . I have read in other post about revalving and was wondering what this involved. Also I am thinking that with the forks being so soft and underdamped could be a contributing factor to the bike getting handlebar shake if I take my hands of the bars when I am off the power.
    Cheers
    Buddha

  2. #2
    Senior Member QLD darkside's Avatar
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    Budda,
    Cant really answer the revalve question, I run a 20mm spacer in each fork to take up some of the soft first travel and restore ride height and 15 wieght oil.
    While not brilliant I find it adequate with no desire to modify...

    But then I dont have a wobble,and often take hands off bars on over run. What sort of front tire do you run and have you experimented with pressures and how are you stem and wheel bearings?

    Cheers John
    HKSI


    "But what would I know, I cant even diagnose a vacuum leak"

  3. #3
    I running a Bridgestone BT45 which is getting fairly worn. The wobble has been getting worse as the tyre has worn.Also it has worn in a sawtooth pattern. Just a side note I have checked the steering head bearings and they are OK.I recently got a MV Agusta F4 750 and realized how good suspension should be and feel the old Popup deserves more.

  4. #4
    Senior Member NSW Nick Kakasiouris's Avatar
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    Hi Buddha, on all my Katana's i have taken them to Shock Treatment and had bigger front Springs and Gold Valve emulators installed. Putting spacers in and bigger fork oil is not the answer as you need to look at the fork tubes as they may need to be re-chromed also the inner bushes will be worn and will need replacement. I will take my '84 pop up and have the suspension overhauled soon and the rear sag will be measured and correct rear spring will be installed that includes me on the bike. It does cost a bit and the pay off is a good handling motorcycle and you need to check your tyre pressure and if the front is worn then replace it.
    Nick
    You always meet a better class of people who ride and enjoy Motorcycling

  5. #5
    Moderator QLD Shin-Ken 1074's Avatar
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    Hi Buddha, before you spend money on the forks have you checked the fork internals and fork oil? The original fork springs are a bit soft and depending on the riders weight the front can dive a bit under load if the anti-dives are on the Fritz. Replacement fork springs designed for the combined weight of the bike and rider will improve the ride. Is the frame straight?

    Before spending up on springs and other mods check the fork oil. Recently a mate had issues with the forks feeling soft, some vibration from the front and handling being less then desirable on his Kat so we dropped the forks off to check them out. First thing we found, or should say didn't find was fork oil. We measured the amount of oil from each fork - 45ml and 30ml. Yep only 45ml and 30ml from each fork and it was the usual grey sludge and hadn't been oil for a long time. Cleaned out the forks, took off the anti-dive units, forks back together with 230ml 10 weight fork oil in each fork, (1100S Kat). The Kat manual has 15 weight fork oil however, 10 weight does a better job with the correct fork springs and no anti-dive units fitted.

    Springs control fork compression, oil controls fork rebound. Stiffer springs and heavy oil is not always the answer. Correct springs and lighter oil is a better solution, heavy oil slows the fork reaction and impacts on the time taken to put the wheel back on the road. The Kat had brand new good quality adjustable shocks fitted with the correct springs for the combined rider/Kat weight.

    Suspension problems are usually not isolated to front or rear on their own. In most cases the solution is found by sorting out the rear and front suspension as a total package.

    First ride after the work was like riding a totally different Kat, no excessive diving, smooth cornering, headshake gone and now is a much better Kat to ride.

    If your fork oil is fine and has the correct amount then maybe its time to look at springs and valve mods however, don't ignore the rear end. If you are lucky the anti-dives on your bike may work as advertised however, most anti-dive units don't work and if the valves are not operating in sync then problems with handling can appear. A very effective way to help improve handling is to remove the anti-dives. If you want to keep the bike looking original and retain the anti-dives maybe talk with Darkside, he is our Pop-up Guru.

    The F4 is one sexy machine and I should have bought the 2004 model when I had the chance, sex on wheels! Anyway back to the real world. Comparing the industrial qualities of the Pop-up suspension to the wizardry of the F4 is a pretty uneven match. Unless big money is spent converting it to cartridge forks or spending huge money grafting a later front end to it a Pop-up will never be as sweet as the F4 in the suspension department.


    Quote: "The wobble has been getting worse as the tyre has worn." End Quote. It's a Catch 22: the wobble has created the uneven wear and now the uneven wear is making the wobble worse.

    Yes, first thing is to replace the front tyre and check/replace the fork oil.



    Headshake on a bike can also be initiated from problems with the rear suspension. Some things to look at:

    Swingarm bearing condition and pivot bolt torque setting.

    Rear wheel aligned correctly.

    Tyre balanced - front and rear tyres.

    Are the shocks in good condition.

    Any oil leaks.

    Correct shock length.

    Correct shock spring rate, soft springs will induce headshake at the front end when under acceleration and in high speed corners as the rear squats under load and lifts the front end.

    Suspension sag set-up for front and rear correct.

    Just a few things to consider before you crack open the wallet.

    Cheers.
    Last edited by Shin-Ken 1074; 17-06-16 at 10:10 PM.
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  6. #6
    Senior Member WA patrick's Avatar
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    Quote Originally Posted by buddha View Post
    I running a Bridgestone BT45 which is getting fairly worn. The wobble has been getting worse as the tyre has worn.Also it has worn in a sawtooth pattern. Just a side note I have checked the steering head bearings and they are OK.I recently got a MV Agusta F4 750 and realized how good suspension should be and feel the old Popup deserves more.
    Check the beading on the tyre is even round the rim ,have had a time when this was the case when the boss at Bunbury yamaha fitted a tyre for me one Saturday morning and I didnt check the fit till after going for a test ride ,in another time I believe the tyre was out of round and balance ,couldn't take my hands off the bars ,that tyre supplied by motorcycle warehouse Balmain.cheers Pat.

  7. #7
    Gave the guys at ProMechA a call and they seemed very helpful and knowledgeable. For around $550 plus any additional parts such as bushes and bearings they will rebuild the forks with springs and damping valves to suit my weight and riding which seems to be pretty reasonable. He also said as Shin-Ken did the rear shock will need attention as well. I will try and check the items recommended this week end. I have done the sag for the front and it is 55 mm static and 65 rider sag. When the front end is bounced it will do 2 up and down oscillations. I don't expect the Suzuki to be anything like the F4 but I think it can be lot better than what it is at the moment without a huge amount of effort.. Has anyone tried fitting a different rear shock like GSXR to a pop up

  8. #8
    Senior Member NSW Nick Kakasiouris's Avatar
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    No need to do that as all suspension dealers work with your original unit and install a bigger spring, spaces and re-valve.
    You always meet a better class of people who ride and enjoy Motorcycling

  9. #9
    Senior Member QLD darkside's Avatar
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    Re rear popup shock...
    You wont find much in different rate springs for the OEM Shock, has wierd diameter.. plus its not a rebuildable type (welded together) some places can still do it but it was mediocre by todays standards even when new. better off replaced,
    link to my effort...
    http://www.suzuki-katana.net/member/...hlight=wilbers
    HKSI


    "But what would I know, I cant even diagnose a vacuum leak"

  10. #10
    Moderator QLD Shin-Ken 1074's Avatar
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    Sounds like you are on the right track and speaking with a suspension specialist you have trust in is a good start. The prices will quickly add up:

    $550 for their time.

    A good set of fork springs can be from $250 - $500 a pair depending on spec and brand name.

    Valves/emulators $190 - $300 depending on supplier.

    Fork internal friction bushes depends if they are O.E.M. or aftermarket where available.

    Bearings - use aftermarket quality brands.

    When suspension is set up correctly you will forget what it cost because you'll be to busy smiling and enjoying riding the bike everytime you throw ya leg over the seat and take off for a blat.

    Let us know what you decide to do and have done to the bike, it could help other Pop-up owners with similar issues.

    Darkside is right about the O.E.M. Pop-up shock. There are much better shocks to use than the very average when new and now over 30 years later very tired original shock. The link Darkside has provided shows what can be done with some lateral thinking, he's very good at that stuff! The link comes up on page two so you'll have to click back to page one to see how Darkside transformed the Wilbers BMW shock to fit the Pop-up.


    Cheers.
    Last edited by Shin-Ken 1074; 18-06-16 at 01:00 PM.
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