Hi Guys...new to the site! I've just bought a 92 Across to fix up for my 18 year old niece for her first bike. I had one new off the showroom floor back in the early 90's and since then have owned many GS250FW as well....so the Mikuni carbs aren't new to me. When I got the Across last week it was extremely hard to start and when it did, it ran rough, missed and over revved at idle. I've since pulled the carbs, stripped them down bare and cleaned them out thoroughly. I also pulled the plugs and cleaned them up to. Since reinstall, it starts easily and runs smooth without missing.....but its still over revving at about 4g. Even if I push the linkage down it will drop to about 3g Both the accelerator cable and choke cable have been fully slackened off and the idle adjuster has been backed of as well to eliminate them. Any and all help greatfully appreciated! Mark
I know nothing about Across carbs, however over-revving at idle suggests an air leak - check the carb -> cylinder head boots for cracks, or perhaps the ring clamps weren't adequately tight allowing an air leak
Pretty sure the Across carb's are very similar to the FZR250 3LN BDST28 carb's Did you replace the idle mixture screw o'ring's, and the main jet o'ring's ? What do you have the mixture screw's set to atm ? To check the intake manifold's for air leak's, start the bike and let it idle, now spray some wd40, degreaser or carby cleaner onto the intake rubber boot's, if the idle change's in any way then there's a leak there.
Thanks for the replys guys! Ok. Idles screws are set to 1.5 turns from seating, carb boots are supple and rubber grease used on re-install, spraying the carbs, boots and vacumm lines with hot soapy water makes absolutely no difference in idle. No O-rings where replaced as it appears on strip down that the carbs have been rebuilt at some stage in the last year or so. Thoughts?
Try spraying the intakes with degreaser, carby cleaner or wd40, you wont notice it running rich and changing the idle smoothness/rpm's if you you are spraying it with soapy water If you still don't notice any difference try undoing the mixture screw's 1/4 of a turn and see if it still hang's Your airbox is fitted when it's rev hanging isnt it?
Airbox and filter were re-installed with no difference. Mixture screws were altered down to 1 turn up to 2 turns from seating without any difference. I'll try the degreaser.....thanks.
Ok I had a similar issue with my fzx250 zeal. It was the balance screws being way out and holding the throttle open, wasn't hitting the throttle stop at all. To fix I balanced the throttles by eye when the butterflies were fully open. Ran smooth as silk after that. It may not be your problem but it's something to check.
Ok....I've ordered a Carb syncronising kit and a new o-ring gasket set from Litetek....we'll see how that goes. I did notice that the left carb was pulling WAY more air than the right one.
Update.....wound the balance screw back....now I have it idleing at 1k. But its obvious from the rev range that it needs a good tune and correct balance.
Should have set up the balance when you had the carbies off the bike.. then it is only a matter of minor adjustments when it is running... A good source of info on these carbies is... http://teamghettoracing.com/mechanical/carb-efi-work/suzuki-across-gsx250f-carb-overhaul/ Get yourself a gasket kit from litetek as per the link from @GreyImport above and you should be fine. It is easy to check your inlet rubbers while the carbies are off as well.
