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needles all the way up, still getting white plugs...

  • Thread starter Thread starter gsBert
  • Start date Start date
OK. I know about the carbs not being stock. I also know the flow characteristics of this motor may not work well with these carbs but I'm no expert on these carbs for sure.
As for the motor, you started this topic by saying the motor is stock. I always take that as meaning the intake and exhaust are stock, being that those two areas have the most effect if changed.
And I wasn't talking about air screws or pilot fuel screws, I meant the air jets. Again, I don't know about these carbs you're using and their design, but typical carbs run primary air jets and sometimes pilot air jets too.
It's also a little hard to follow your test procedures because, such as right now you're changing the main jets in an attempt to get a good 1/2 throttle read. Then you say it should be obvious you're testing for the jet needles.(?) Very confusing, though I'm trying to follow and give help. After re-reading a couple of times, I see what you're trying to do.
Since the air jet/jet needle/needle jet set up in these carbs may cause major tuning problems if used in this motor, I can understand what you're up against.
I also thought it may help to check and compare the factory spec's of the stock Mikuni/1150 carbs against your GSXR(?)carbs and see if a "compromise" could be figured out, but because of any (very likely) flow differences in the two motors that would probably be useless to try.
 
keith: you just confused the hell out of me... what are air jets? do you mean the needles and emulsion tubes?

i have the following changeable/adjustable parts in my carbs:
- needles
- needle jets
- pilot jets
- main jets
- idle fuel mixture screw
- needle clip

to recapitulate:

if i put my needles back in the middle position and use a 140 main jet, everything runs perfectly except it's a tad too lean after 1/3 throttle and very lean on the main jet (3/4 throttle and up)

i raised the needles to see if that would fix it but it didnt so i removed the main jet to provide maximum fuel to the needles, and that got me running rich. i concluded that my main jets were restricting fuel flow to the needle jets.
i'm now going to increase my main jet size until i run rich on the needle circuit (1/2 throttle). at that point, ill lower the needles to the middle position again to see if it gives me clean plugs.
then ill try full throttle to see if the main is rich enough.

i could just bring the needles back down right away, and might do that if you think its the way to go, but i'd rather find my way to too rich and come down from there. on second thought, forget it that idea sucks, ill lower the needles, it'll be easier to see the plug colors that way...
i'll richen my mains till i get dark brown plugs... one size at a time...
thanks for making me think...
 
man, here's why i am confusing everybody, i post to 2 threads on teh same topic...
"plugchop comes out lean opinions please..." is the other one, sorry dor decentralising but please if you get a chance go check the other one out too...

HELP! is there a way of merging both threads?
 
I think Keith is referring to the Air jet on the intake side of the carbs. Pull a filter off and you'll see a jet with horizontal alignment. Jet kits have replacement air jets to use optionally. Bike bandit has the part listed as #52 on the carb schematic..

The air/fuel mixture screws do exist on these carbs and are located on the bottom front of the carbs, behind the support rail. Have you messed around with these?

Keith I hope I'm not butting in here, I knew what you were talking about, at least I think I did, so I spoke.
 
yeah, my mixture screws are 2 turns out.
ill adjust for the fastest idle method as soon as i can manufacture some extension for teh screw. as it is i can't get a screwdiver in there accurately with the engine running. but the bike idles fine and that screw really only affects idle...

air jets.... hmmm... i dont think my slingshots have those... ill have a look as im going down to the basement right after this post...

i seem to remember seeing a bunch (3?) of horizontal brass tubes in the intake tract on the stock 1150 carbs, i just never knew they were replaceable...

ill post again when i get back upstairs...
 
ok, you have my complete attention:

i do have 2 horizontal brass tubes in my intake tract....

what the hell are they?
what do they do?
(just when i thought i knew everything about my carbs one of you wisegusy hits me from nowhere with a ton of bricks)

seriously, what the quack is that 2 brass tube thing about (2 air intakes under my venturi)
do they just provide athmospheric pressure to the bowls?
or is it more sophistimacated?

on a positive note:
i jetted with 155 mains and moved my needles back to the middle clip position. bike starts fien on the choke, revs to 3000 and settles to a nice 1000 idle when its warm and i turn the choke off... NO MORE SMOKE.
ah, i forgot to mention, i also lowered my float height on all 4 carbs...
oops, i have to run back down, i left teh petcock on prime....
there put it back where it belongs....
reason i lowered my float heights is #3 was seeping. good news, its not doing it anymore...
 
From your location description, you've found the air jets. VM and CV carbs typically found on Suzuki's have air jets. Some have separate pilot and primary air jets. Some have only one air jet. They are usually removable.
You should be able to blow into them and feel where it exits, if the carbs were apart.
The pilot air jet supplies air to the pilot circuit, throttle valves closed or nearly closed.
The primary air jet supplies air to the jet needle and main circuits.
In both cases the air jet allows correct atomization of the fuel.
The primary air jet passage leads to and mixes air with the fuel coming up in the space between the needle jet and jet needle. If the air jet is too small, you'll be rich obviously. Many jet kits supply different air jets for use with pods/pipe.
I'm not saying this is your problem, just another possibility. There are lots of unknowns when trying to make carbs work that were meant for another engine.
 
carbs

carbs

Dont forget that the slide cut away has a big effect on the negative vacuum behind the slide, witch is a factor in the mid range fuel draw from the needle jet, buy removing the main jet you have made it so that less vacuum is needed to draw fuel up the needle jet the slide cut away starts to take effect at about 1/4 throttle opening and starts to lose effect at 3/4 throttle, below 1/4 there is not enought negative pressure to do much and above 3/4 your going on the mains (neg pres. is relative to the velocity of in coming air, as keith said you may be able to doctor it in to tune with various jet (ie fuel and air) but it may never be what you hope for, I used to build Amals for racing and many times when cam shafts affected the intake vacuum we would have to cut our own slides from blanks, just my thoughts Iam not really familiar with these carbs, but carbs are basicely the same in funtion
 
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