Tuning and Jetting My 1982 450

[jeffasaurus2]

Thanks for putting all this up here Pete! I'm sure I'll be referring to this thread in the next few weeks!

[MOC]

So just out of curiosity, it looks as if you've rerouted your throttle cable to the outside of the left carb. Any particular reason for doing that? also, what is your situation with choke? It doesnt look like you have one anymore...

[jeffasaurus2]

If I'm not mistaken, that is the choke cable you're looking at in that picture. Throttle doesn't seem to be hooked up yet. Essentially converted from a lever on the carb to a choke pull on the dash.

[PPPPPP42]

When you finally get everything sorted out please relist what you have and all your mods and then all the carb part sizes and adjustments. Trying to follow the progress as it happens seems to have broken my brain mainly because you were confused on some of the symptoms indicating too rich or lean and now I am confused on what symptoms actually mean what.

For some others that are confused, I found figure 4 and figure 7 particularly useful here:

http://www.iwt.com.au/mikunicarb.htm

though I believe this is for a slightly different type of carb (ours are not cutaway slide valves right?)

[pete]

Thanks for putting all this up here Pete! I'm sure I'll be referring to this thread in the next few weeks!

No worries mate, I'll be happy if it helps someone else

So just out of curiosity, it looks as if you've rerouted your throttle cable to the outside of the left carb. Any particular reason for doing that? also, what is your situation with choke? It doesnt look like you have one anymore...

If I'm not mistaken, that is the choke cable you're looking at in that picture. Throttle doesn't seem to be hooked up yet. Essentially converted from a lever on the carb to a choke pull on the dash.

Yup, Jeff's got it right. I've always disliked the choke lever on the left carb so I grabbed a later model GSXR left control block off eBay that contained a choke lever.

I made the bracket you see there and the adapter that goes on the end of the choke shaft.

My original throttle cable was the exact right length for it too, so that is actually a throttle cable there

I have no idea why the throttle cable is not installed in that picture...

When you finally get everything sorted out please relist what you have and all your mods and then all the carb part sizes and adjustments. Trying to follow the progress as it happens seems to have broken my brain mainly because you were confused on some of the symptoms indicating too rich or lean and now I am confused on what symptoms actually mean what.

Yup will do that shortly, I'm pretty happy with how she ran today

For some others that are confused, I found figure 4 and figure 7 particularly useful here:

http://www.iwt.com.au/mikunicarb.htm

though I believe this is for a slightly different type of carb (ours are not cutaway slide valves right?)

It is a slightly different carb, but essentially all the principals are the same, and yes this is a very informative page. I have bought jets from this place too and they're good to deal with.

[pete]

Well I still get an occasional little... well... almost crackle on deceleration, but only after holding small throttle openings for a bit and then closing the throttle. If I've had the throttle half or more open and close it, no crackle or pop that I've observed.

I did bump the idle up just a smidge when I got to work this morning as it seemed to be idling a touch too low.

So after all that, I have almost eliminated my jerky throttle closed to open from a standing start and if I need to shut it during a low speed corner. Much smoother transition now.

So, to summarise...

Initial symptoms:
- Hesitation when opening the throttle and accelerating until over 1/2 throttle.
- Stumbling when holding constant throttle around 1/4 throttle.
- Pops and crackling on deceleration with a closed throttle.
- Jerky transition from a closed throttle.

End result:
Pilot Jets: Stock (17.5)
Mixture Screws: 3 3/4 turns out
Needles: Stock needles (4C3-3), raised to the richest position (E clip in lowest position)
Main Jets: Mikuni N102.221 Small Round jets, size 150

Modifications:
Shortened slide springs ~20mm
Drilled slide vacuum holes to 3mm

A couple of other things...

For you US folk, I have no comparison of the stock Aus needle (4C3-3) to the stock US need (4C2) except that the US one is non-adjustable. You will need lots of shims to get it to the same richness as the maximum adjustment on the 4C3. I'm not sure if there is a different taper or not.

If you need to use bigger pilot jets in these particular model of carbs, you will need to get Mikuni VM22/210 type jets, but take note that these have bleed holes down the side that the stock ones don't have. Therefore, I'm not sure if the stock 17.5 is exactly the same fuel flow as a VM22/210 17.5.

Once I get the dyno day done with the Kat guys I will come back to this and update it.

In the meantime I'm going to enjoy the new throttle response and fun

[PPPPPP42]

Most everything here does seem to be fairly screwed up for emissions. Happen to know if the whole slide and diaphragm assembly is different or just the needle? It would be worth while for us here to find stock non US parts to install if they are even available. Or we need to figure out what standard Mikuni adjustable needles are correct for out carbs.
I should also like to find the purpose of those bleed holes.

[jeffasaurus2]

I don't know if the bleed holes make much difference, I've had to raise my pilot jet one size, (I'm at 5200ft+ with pods and a non-stock exhaust), and it doesn't seem to have affected the way in which the idle circuit operates, but then again, maybe I just can't tell the difference.

[pete]

Most everything here does seem to be fairly screwed up for emissions. Happen to know if the whole slide and diaphragm assembly is different or just the needle? It would be worth while for us here to find stock non US parts to install if they are even available. Or we need to figure out what standard Mikuni adjustable needles are correct for out carbs.
I should also like to find the purpose of those bleed holes.

The slides and diaphragms are all the same, same part numbers etc. The online parts fiche shows the differences when I compare the listed jets and needles to what's in my factory manual.

Needles are difficult to work out which is why I'm still running the stock one.

The way to work your needle out is to take measurements along the way then compare it to other needle's measurements as outlined here:

http://mikunioz.com/needles_numerical_list.htm

I don't know if the bleed holes make much difference, I've had to raise my pilot jet one size, (I'm at 5200ft+ with pods and a non-stock exhaust), and it doesn't seem to have affected the way in which the idle circuit operates, but then again, maybe I just can't tell the difference.

The only way I've known anything with the pilot circuit is the pops/crackles on decel with a closed throttle after not having the throttle open that much.

You truly won't know without plug chops or an AFR meter...

[PPPPPP42]

I have trouble understanding exactly which carburetors we have and what series needles fit them, #4 series? Even more so because nothing used stock seems to appear in any charts, so like you say I would have to measure a needle with calipers at various lengths or something to find out what one step richer than a 4C3-3 (which sounds like what we want) with the adjustment notches would be.
Thankfully with the main and pilot jets the numbering system is sane and you just play match that picture to get the right type. Not sure about the needle jet or whatever you call the big tube, probably just as bad as the needle.

Data copied from a chart on that link:
#4 All 18mm Carburetors 22mrn and 24mrnFlange
#5 26mm-32mm Spigot 28mrn-34mm Flange
#6 30mm-38mm Spigot
#7 40mm and 44mm Spigot
#8 HSR 42/45 Carbs
#9 RS and HS Carbs

[wally]

Hi Pete, I meant so e illustrations of the drilling of the vacuum slides.

I am sure I am gonna bug you once I have to dial in mine - when the sparky is eventually done with it.

[pete]

I have trouble understanding exactly which carburetors we have and what series needles fit them, #4 series? Even more so because nothing used stock seems to appear in any charts, so like you say I would have to measure a needle with calipers at various lengths or something to find out what one step richer than a 4C3-3 (which sounds like what we want) with the adjustment notches would be.
Thankfully with the main and pilot jets the numbering system is sane and you just play match that picture to get the right type. Not sure about the needle jet or whatever you call the big tube, probably just as bad as the needle.

Data copied from a chart on that link:
#4 All 18mm Carburetors 22mrn and 24mrnFlange
#5 26mm-32mm Spigot 28mrn-34mm Flange
#6 30mm-38mm Spigot
#7 40mm and 44mm Spigot
#8 HSR 42/45 Carbs
#9 RS and HS Carbs

Yup, the needles are the painful bit! If you look on the parts fiche on Alpha Sports (they have the best fiche but prices are expensive) you will see the jet size and needle type in brackets beside the part number.

Our carbs have the #4 series needles.

If you want to try a different needle, you will have to measure your 4C2 at the intervals outlined and start comparing. It won't be easy which is why I've just richened my stock one as much as possible for the moment.

I'll possibly revise this after the dyno run...

Hi Pete, I meant so e illustrations of the drilling of the vacuum slides.

I am sure I am gonna bug you once I have to dial in mine - when the sparky is eventually done with it.

Aaaah I get ya' Wally! In that case return to post #8 in this thread

Basically, you'll need some very long circlip pliers to get the circlip out of the middle of the slide which will allow you to remove the needle etc.

Once that's done you can safely drill the vacuum hole out. That's the off-centre hole in the bottom of the slide, not the hole the needle seats in.

[wally]

If I open my eyes a bit more I suppose things will go a lot better in life!

[pete]

Hahaha all good Wally

[jeffasaurus2]

Hey Pete, couple questions for you:
- Any info on the snap ring pliers you used for the slide? I'm having a heck of a time finding anything that is remotely close to fitting in there! I've found some Motion Pro ones that look like they'll work but no one carries them in town so I'll have to order them.
- For the modifications to the slide. You shortened the spring by 20mm, correct? The hole in the slide has been upped to 3mm?

Thanks again!