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Mikuni Two-Barrel BS30 carburetors

  • Thread starter Thread starter Thomas Kenny
  • Start date Start date
No matter how gummed up they were, a couple of days soaking in carb dip should have cleaned them good as new. You NEVER use anything hard to clean jets. I've always used fishing line or a toothpick with great results. I normally soak the bodies and jets overnight, spray them off with aerosol carb cleaner or an air gun, then go over them with several sharp toothpicks to make sure it's clean. If it's not, back in the dip.

If he used a bit on the carb bodies, they're probably shot. If he had soaked them long enough they wouldn't have had a problem. If he didn't, I agree that you're probably going to have to buy new jets because you'll never get them balanced or calibrated with oversize jet holes. There's a fine science to jets (as I'm becoming painfully aware with my own carbs) and soft brass is easily damaged.
 
are all of the rebuild parts avail for these carbs thru the dealer? including gaskets, o-rings etc... i don't know if jets alone will do the trick. The carb bodies were not damaged, only the jets were touched with the bit. As far as symptoms, hard starting, poor accell, if it ever stops raining, I will try to take it for another spin. I am not afraid to work on them myself, just don't want to screw them up. Stock is fine with me (it's just for buzzin round town) So, as of tight now, save the $150, spend $30-40 and see what happens? sound right? I appreciate all the input.
 
YOu should replace the o-rings that are behind the carb boots. But those are the only o-rings you shoudl "need' to replace. You should pull out the mixture screws so you can clean them. That will require a drill though.

The jets, and the four aforementioned o-rings are available through a dealer.
 
bits

bits

If you used jewels bits or jet bits of the same size and did it right then there shouldn't be a problem. All my jets are measured with the bit's I have never messed one up so far but I now people have. Like I said be carefull if you do drill jets. Always clean with soft something frist, bits are for the jets that are so bad and you don't have the time or money in your back pocket to spend at the moment. Just my 2 cents. I will buy jets 99% time but I still check there size with my bits, start with the next size down and never force them. just set them in if they fall thru go to the next till one doesn't.
 
what about the o-rings on the end of the jets or mixture screws? those avail from the dealer? again, thans for all the help.
 
ok, i am probably gona tackle tghe rebuild/clean myself. There is a link on the home page to a carb cleaning section. It shows a 4 carb set up. Will these 2 bbl carbs be similar in their construction or are they completely different beasts?
 
Erat, I just finished rebuilding a spare set of Mikuni two-barrel carbs for my 1984 GS550ES that I bought off of Ebay. Get a gallon can of carb cleaner from NAPA or another autoparts store. Tear down your carbs and lay aside all rubber and plastic parts. Remove all jets, the float and needle and seat. The pilot jets are along side each other in small deep holes. Be careful that you use a screwdrive that is the right size for these jets and that you do not force them. I bought an aerosol can of penetrating oil and sprayed down all part that needed to be unscrewed and let them sit overnight before removing. One of my carbs did not have the float bowl drain screw in it and it was pretty rusty inside. The carb cleaner did the trick. Let me know if you have any more questions and how your rebuild goes. I am sure that I have forgotten something but this was my first rebuild and these carbs are not really that complicated.

Have Fun, Tom

Put the carbs in the cleaner one at a time for about 3 days each. Pull them out and wash them off in warm water and then blow out all of the orifices well with compressed air.
 
Well I got my spark issue fixed. I bought four new NGK caps and a used coil from Ebay. I'll get the good ones later Distraction :-). Any way after several attempts with an overhead gas bottle and my vacumm line to the tank plugged, it finally started farting and then started to where it would run slowly although with an occasional backfire. I noticed that my boot between the head and carb was loose as I saw some exhaust gases coming out around the boot when I got a backfire. I tightened up the boot strap, and put my K&N filter in and the airbox cover. The engine starts and will idle but labors up to about 2500 RPM and then acts like it is running out of gas. I got quite a bit of water coming out of my airbox drain line and then it stopped. I started messing with the low speed air jets and they seem to be all over the place although when fully closed on one cylinder at idle the engine dies. All exhaust headers are hot. I just installed a Vance and Hines 4 into 1 pipe on the bike and nothing else. I haven't jetter yet but based on your past experience I am going to get a set of 105's and 110's and start with the 105's. I am just confused because I rode the bike for about 5 miles after installing the pipe and it ran well, just lean when I opened the throttle. I am hoping I haven't burned any valves. Speaking of valve I adjusted them all to .004. Any suggestions as to what I should try. My Signal Generator and Igniter unit check OK.??? Thanks all
 
I put on the other coil that came with the set from Ebay and I have good spark at all plugs. However now I am running on three and I hear a tapping in the area of Number 3 cylinder under the cover. I did a compression check on 3 since the header is now cool and I got 50 lbs with a warm engine and I was getting 125 cold after the valve adjustment last week on all four cylinders. Perhaps my valve adjustment that I did last week is way out of whack on 3, or I have a badly burned valve? I will pull the valve cover off next weekend (only today to work on it) and check for a loose adjuster or a broken spring or???? Plug is sooty black. I hope I don't have a holed piston!!!
 
I hate to bring up an old thread but i found this one whan i was searching for jetting specs. i have an 86 gs550ef and everything is stock. i have the carbs apart and i found sizes smaller than the manual states (#95 for 1,4 and #102.5 for 2,3) this thread recommends #105 for all four and 2 shims under the needles. this seems like a big increase from factory settings and even bigger than what was in there. anyone have anything to say about this?
 
The stock jet sizes for the GSX550's with the two barrel carbs are the 95 and 102.5's. 105's provide more power. It does seem like a big increase, but it works. :-)
 
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