anyone taken the choke arrangement to pieces on the Mikuni 33BST?
My choke is a bit screwy in that in stutters a bit, you give it some revs, it goes to where it should, you back it off it stutters, you give it revs, it goes to where it should and on and on and on.
I saw this (http://members.ziggo.nl/minara/word%20bestanden%20website/Carburetor%20MIKUNI%20BST33.htm) but the guy seems to have some choke arrangement where you burn your hands then crash instead of a lever by your thumb?
ideas? I assume its all manky in whatever the plunger arrangement is a lot of those bits looks fragile and on the expensive side so before I try and work out how it works, ideas?
also I can turn it off after about 3 minutes but it is about 20 `C ambient at the moment and the bike is running really nice so I dont think its bad mixture (smidge lean if anything according to plugs).
also 125 mains is ace.
Edit: not sure of the copyright but thats a pretty comprehensive carb guide - maybe we could get a copy stuck up here? Its appears to be Eastern European by the brands and hosted on a Dutch site so maybe its already be robbed?
also I couldn't see the diaphragm o-rings.
That's an excellent guide.
Don't fear fixing your choke. Probably clogged. Choke on it should "idle" at like 4-5K rpm. Open the throttle it will rev above this and back down to 4-5K. Other behavior indicates something is broken.
Yeah, I'm hoping its just full of grot and needs a clean up. Not seen much that addresses the choke on a bst33 though.
Will give it a go over the weekend and report back.
Quote from: mr72 on June 19, 2018, 02:52:14 PM
That's an excellent guide.
I agree, needs to be saved here somewhere. I don't think I've seen such a thorough look at these carbs (especially not in a video).
That said, the fact he notes cleaning the carbs up as an hour's work makes me a bit sad about the absolute mess of emissions rubbish on the newer carbs making it take an hour just removing and refitting them.
Cleaned up the choke. the left side was ok, but the right had some grot in and didn't slide particularly easily.
The slide the cable goes to has two black clips, pinch the two endy bits in and push through the retainer to release. The grey plastic clamps have two tangs that are pulled in then release the choke mechanism. The needle bit can be removed from the sealy bit with a little pull. they aren't held in but anything but the seal-brass interface. I could have photoed this but I didn't and I've already reattached the cables :(
Will see how it goes a bit later.
Also moved idle screw up to 3 turns out (from 2.75), the plugs are still reading on the lean side and its been slightly tetchy in slow traffic but runs well after that.
Ignore the plugs. Adjust the idle mixture according to RPM when it's FULLY WARMED not the plugs.
IF you are convinced the plugs are telling you it's lean then that's a mid/main jet or needle issue, not an idle mixture issue.
FYI :)
oh how right you were :) I'll back those off to 2.5 and drop a clip position richer on the needles.
Choke is still off a bit, very slight adjustments towards the off end rev the bike a lot. very hard to get it to idle smoothly at say 2000rpm. from cold, it'll sit for a bit at 2k, if you give it any throttle it revs up to 5krpm or so but always needs some throttle input to get it to go into the right place. choke lever has nicer action now though. so thats something.
That's exactly how mine is. Always has been. Gotta blip it to get it to idle up to 5k from a cold start.
Quote from: mr72 on June 30, 2018, 03:14:28 PM
That's exactly how mine is. Always has been. Gotta blip it to get it to idle up to 5k from a cold start.
Oh thank christ. This is exactly how mine is (cold start, have to blip the throttle for a couple of seconds just at the start and then it'll idle on choke) but I kept seeing "it'll idle up to 4k with choke when cold" and thought you could just turn the choke on and press the starter without even looking at the throttle.
It's never really been a problem, as after that few seconds it behaves as normal, but it's nice to know there isn't anything else going on.
Quote from: TGTwin on June 30, 2018, 08:32:59 PM
Quote from: mr72 on June 30, 2018, 03:14:28 PM
Oh thank christ. This is exactly how mine is (cold start, have to blip the throttle for a couple of seconds just at the start and then it'll idle on choke)
Well let me be more clear. My bike has never required you to touch the throttle for it to start unless it has been sitting for a long time (weeks).
The way mine goes, you turn on the choke then hit the start button and it starts basically immediately but it idles at about 1500-2000 rpm if you just leave it alone. If you leave it like that for like 30 seconds it usually will rev itself up to about 4-5K but on rare occasion it will die if you let it sit without touching it. But if I give the throttle a little push *after it is started and running* then it will idle up to 4-5K and stay that way until I turn off the choke.
I think the reason for this is fuel flow. When you cold start it, the float bowls may be depleted of fuel because when you turn it over there is not enough vacuum to open the petcock. When it starts there may not be enough vacuum again to open the petcock fully when it is first running so the float level is very low but the fuel is not yet flowing into the carbs, thus the low(er) warm-up idle and if you don't touch it, maybe it dies after 30 seconds. By blipping the throttle a little after it starts you kick open the petcock and fuel rushes to fill the float bowls and all is well.
That's my theory anyway. I guess I could test it by going out this morning and cold-starting it on PRI and see if it revs right to 5K on its own.
mine similarly doesn't need the throttle to start, fairly rational idea about the reason though. I think mine is probably ok, I just feel a nob sat at the junction I get to 15 seconds up the road with it idling at 3000rpm. The black widow exhaust is trying very hard to be replaced at the moment, way too loud even with the muffler. I assume the deadener is installed anyway. I should check.
bike a lot happier at 4th clip position and 2.5 turns idle screw. is dangerously keen to not be at 30 in the 30 zones now...
Quote from: tobyd on July 01, 2018, 12:07:19 PMI just feel a nob sat at the junction I get to 15 seconds up the road with it idling at 3000rpm.
Eh, the GS500 is quiet enough I doubt anyone even thinks anything of it. Certainly nothing like the two-strokes you often hear revving up and down the place!