Monthly mikuni carby thread

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Got a 100 and 20. All he had

Put needle back to middle. Alot lot better !!

Good response, good tick over etc. Just feels a little flat top end !! Needs more playing .... Very happy straight off tho !!

Now main is to big isn't it lol can I lift the needle clip ? Does that effect both jets or just main ?
 
the clip affects the main, allows more fuel through, by moving the clip down or visa versa
also try moving the clip up too, see where it runs best and let us know again.

if it is feeling flat at wide open throttle, i think the main jet may be a touch too big?
this will show up on the bike if it will run better at WOT with the clip on the top notch of the needle.

also, have you checked the joins in the carby to spacer plate, spacer to manifold etc for vacuum leaks?
start it and let it idle, and spray wd40,degreaser or carby cleaner on the joints,
if the idle changes in any way then there is a leak there.
 
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Il give it a go. Il change the position on the needle!

Think the pilot is bang on tho, cause it's pulling hard down low

Shouldn't have a vac leak, I made a nice head-manifold gasket
And mani-carb is sealed with alot of silicone !

Il def try it tho
 
probably not a good idea to use the silicon though, most silicons soften with petrol.

once you sort the pilot jetting on the Mikuni fakes, the rest is pretty easy,
most people just try adjusting them and have all sorts of troubles, but they dont rejet the.
probably why most people chuck them and fit the OKO's etc
but the Mikuni can give you a pretty good all round performance once setup right.


and with the adjusting the fuel mix screw, i use a small flat headed screwdriver bit, by itself.
and adjust it quickly while the carby is on, without burning your hand on the barrel.
there are remote fuel screws available too for the mikuni's, on ebay etc
 
Il try a screwdriver bit and spanner on it

True about sealer , might need rethink that

Doesn't say if locktite 518 is good on the packet itself
 
for the manifold to head gasket i buy some decent thick gasket paper and cut my own.
it compresses when you do it up and helps it seal well.
something like this, but you can usually find it a lot cheaper
http://www.supercheapauto.com.au/on...-Material-305x305x1-6mm.aspx?pid=223650#Cross


and with the sealing faces of the manifold and carby etc,
if you buy some 320 w&d paper and put it on a hard sanding block, or piece of glass,
then gently rub the manifold mounting faces over it, it will cut off any high spots or warped castings, and make it flat again
 
Tried it on the top needle position.

Defo ran better!!

When I first kicked it - it bogged right down on quick WOT. It did get better when I took it a run round the block.

Really need a decent straight and another pitty to compare to up a strip :(

Its definatly better than it ever was tho !!
 
with the clip in the top slot, that is saying a slightly leaner main jet is needed.
 
I swear it feels like it loses bottom end when it's up top position.

I have it back to the middle position and I'm not sure if it feels flatter up top than c clip all way up ... I think it could just be pulling really hard down low then leveling out!?

My plug chops are reading nothing ... I cleaned the plug... Held it flat in 3rd. Switch off, clutch in ... Reads clean ?!

If I get it warm, hold the throttle steady and adjust the mixture in .... The back out until rpm is at it's peak !? That's the mixture screw Set , right ?
 
Maybe I'm expecting to much ??

Im going to re-Do the gaskets. Seal up the bowl.. Try and seal the throttle cable as the grommet has now gone :S

I'm going to get it up against another pitbike as soon as I can.

It's nice and torquey down low. But just wanting more up top.

Quite frustrating trying to set ain't they !? Lol
 
yeah the mixture screw needs to be set like that, but with the rpms at just under mid throttle.
then once you get the highest rpm, drop the idle speed down to normal range.
the idle mixture can still be tweaked a little from there too.

the best position for the clip on the needle is at one of the 3x middle slots
 
I'm going to try a 97.5 main.

Does it makes sense that moving clip up is effecting the low Down throttle ?!?

And plug chops are clean !?

Idle and choke is perfect on middle position ... Not so good when playing with needle ?!?

Just seems random, and not making much sense to me tbh

Does it sound like I need a 97.5? Or that I don't kno what I'm doing ? Or both lol
 
try and find a 22.5 pilot, and see what it does then.

it may also be worth looking at a 97.5 main jet

all the passage ways in the carb are defiantely clear?
and you have double checked for leaks?
 
I'm going to take carb off tomorro, clean everything up and make sure.

I'm confused mate, why would I go 22.5 when up to about 1/3 - 1/2 throttle is good ?

Not doubting you, as u really know ur stuff. But I just want to understand - if possible.

Il try the 95 back in on lowest position ...

Do the needle notches relate to size up/down ? 2 places size up/down or anything like that ?
 
going off this post-
Oznewbie said:
Tried it on the top needle position.
Defo ran better!!
When I first kicked it - it bogged right down on quick WOT. It did get better when I took it a run round the block.
Really need a decent straight and another pitty to compare to up a strip :(
Its definatly better than it ever was tho !!
Click to expand...

with the clip on the top position of the needle it defo runs better,
^^ this is making the slot where the fuel comes out inside the carby smaller, so the main jet is too big.
i'd recommend a 97.5 main as your original 95 main jet was lacking a bit in the top end.


http://tboltusa.com/store/tech.php?pID=61/Simple+Guide+to+Jetting

keep in mind you fuel mix screw has the opposite outcomes of the air screw mentioned here....
 
when you replaced the original pilot jet with a #20, the off idle to 1/4 throttle became better, and revved better.
i'm wondering if it is almost perfect? and a 22.5 pilot jet make make it a bit crisper/cleaner rev off idle?

if the rubber seal on the top cap of the carby is split, then it will allow air into the carby top, and make it run leaner.
if you cant get a new rubber, then some electrical insulation tape will do, wrap it up using a few layers, and zip tie it on so it cant come undone.

another thing, when you pull the needle out, is/was there a thin nylon washer that sits under the clip, or has it been lost?
 
lastly, the needle notches are more like a 1/3 of a jet size,
if you think of a #95 jet with the clip on the 4th notch down on the needle, that would be like a #95.3
 
The washer is there.

Double checked for leaks. When I sprayed misted fuel at the top / cable ... It dropped the revs.

It only runs properly with the choke lever down. Put it up and the revs drop. Down - pick back up.

What way is choke? As long as I set it up properly, I can run with the choke in the on position ?
 
Ok.

On this P-O-S carb. Choke off - down . Choke on - up

26/22mm mikuni fake. Slide style carb.

Seems If it's up ... my choke on (?) - bogs it down/cuts revs ... Running rich already !?

Lever down then revs it's nuts off - obv' needs set up on the mixture and idle screws to bring revs down to right rpm


Where will I get spacer/gaskets for 26mm !! Resonably/cheaply priced !! Before I seal it all up with some heavy silicone we seal gearbox bellhousings on trucks with !! Lol


If I seal it, find choke position and set it to run ok ... I'm done - until I get a coil and ngk in a couple of weeks. Then in few months get an oko
 
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