Tuning and Jetting My 1982 450

[pete]

EDIT: Just putting the current jetting setup up here in the first post so it's easy if anyone needs to refer to it... and two changes below after replacing my head gasket and the resulting valve clearance adjustments:

Pilots: Stock (17.5)
Needles: Stock (4C3), raised 1 notch from middle (stock) position
Mains: 142.5
Mixture screws: 3 turns out

I've had a lot of questions recently about jetting and tuning my 450, so even though I'm no guru at this I'll post up here what I've done and how it's going.

I need to be very clear that I'm only familiar with the carbs found on the 1980 - 1982 GS450's as that's what's on my bike, and I am far from any sort of tuning expert and what I have done is all checked by my "seat of the pants" dyno...

So, to start with, I have a 1982 GS450E Australian model with these mods to the intake and exhaust:

- K&N oval pod filters.
- Custom 2 into 1 free breathing (but baffled) pipe.

My engine is stock although I do have a Dynatek DS3-3C kit on there for ignition, but given it retains the stock advance mechanism there should be no performance difference to the stock ignitor.

I have previously published the stock carb spec's in this thread which highlights the incorrect float height setting from the Clymer manual:

http://www.thegsresources.com/_forum...d.php?t=204475

Type: Mikuni BS34SS
Bore Size: 34
ID Number: 44100 (Germany: 44120)
Idle: 1200 +/- 50 RPM
Fuel Level: 6.5 +/- 0.5 (0.26 +/- 0.02)
Float Height: 26.6 +/- 1.0 (1.05 +/- 0.04)
Main Jet: 117.5 (Germany: 112.5)
Jet Needle: 4C3-3 (Germany 4F29-4)
Needle Jet: Y-6 (Germany Y-2)
Pilot Jet: 17.5 (Germany 22.5)
Valve seat: 2.0
Pilot screw: 2.0

As per the other thread, US GS450's seem to have 4C2 needles and 115 mains going by the parts fiche but this is not reflected in the factory manual.

As for my actual tuning and jetting, I started off with my needles one notch richer (raised) and my main jets 8 sizes up from stock (137.5). My mixture screws were something like 3 turns out but I didn't accurately count the turns at the time and have simply adjusted them by feel for the moment.

I ran it like this for about a year but finally got sick of what felt like bogging off a closed throttle and surging at small throttle openings.

So, thinking I was too rich on the needle and mains, I ordered some shims off eBay in the US http://www.ebay.com/itm/TWIN-Carb-Ne...91a9bd&vxp=mtr (I highly recommend them) and set about making some adjustments.

First I went half a notch leaner on the needle and back to the 2 size up mains (122.5). This made the bike almost unrideable and opened my eyes to what was *really* going on with my fueling.

So, the engine was actually stumbling as soon as I opened the throttle due to lack of fuel, and then holding it at low throttle openings was causing it to hesitate as well, so it is very easy to misinterpret these symptoms.

I know plug chops would've shown me this ahead of any jetting changes, but getting the opportunity to perform them is a little difficult around here, especially at WOT!

Anyway, after some trial and error over a few days, I ended up with my 8 size main jets back in (137.5) and my needle on the richest position it would go. At this point it was like riding a whole new bike and it was completely transformed.

This is some video I took when finally getting it somewhere near right:

http://youtu.be/z0kZX5McUzM

I have also discovered my idle circuit was way too rich and so I've leaned that out a quarter of a turn at a time so I'm probably about 1 1/2 turns in from where I started initially. I have yet to figure out exactly where they're at as I've continued to just adjust by feel for the moment.

After a real good ride the other week with some wide open roads and a bit more action with the right wrist, I definitely feel like I'm still missing something at WOT compared to how responsive things are most of the way through the throttle range, so I'm going to try some bigger main jets.

I received 145 and 150 sizes today and have put the 145's in tonight ready to test ride on the commute to work tomorrow.

One other modification I did to the carbs was to trim just under 20mm of length off the slide springs. This has allowed the slides to rise quicker and has definitely made an improvement performance wise.

Ironically enough, my big ride the other day gave me my best fuel economy to date... 252km out of 11.2 litres of fuel (around 52.9mpg). During my commute I typically get about 200km out of the same quanitity of fuel, and I used to get around 230km or a bit more when on a weekend ride. I haven't run to reserve on the commute since making the major changes yet.

Just to clarify what Mikuni jets are used in these...

There is no direct equivalent for the pilot jet, the closest is the VM22/210 which are exactly the same dimensions and fit perfectly, but these have bleed holes down the side whereas the stock pilot jets do not. I have not been able to make a comparison to see if the 17.5 stock pilot is effectively the same as the 17.5 VM22/210.

The main jet is the N102.221 Small Round main jet.

I will report back tomorrow on the 145's and if need be I will go up to the 150's and see how they go.

I'm hoping to participate in a dyno day with a handful of other Katana riders in a few weeks so I can truly see how the fueling is and what (if any) impact it's had on the power delivery. Stock is a bit over 40hp from memory.

One thing I have yet to do is to fully follow Koolaid Kid's guide on tuning the mixture screws:

http://www.thegsresources.com/_forum...d.php?t=199096

I have made a couple of half hearted attempts but will do it properly after getting the mains right.

I hope this is of help to someone...

[wally]

Hectic! I will need to tackle mine once the bike is back and running.

Not looking forward to it. Will also need to it down and study your write up!

Thanx!

[pete]

It's actually not too hard once you get stuck in and start the trial and error process Wally.

I found it very intimidating initially which is why I waited so long to start.

The three key things from my experience is to understand the actual symptoms, know some people who've done it before, and a pair of really long nose circlip pliers for the circlips in the slides.

Actually there's a couple of things I missed...

Do yourself a favour and replace all the carb screws with allen heads.

Once you do this, you can remove the float bowls without removing the carbs using a short allen key.

Also, with a long allen key you can remove the diaphragm covers and lift the slides out being very careful not to catch the diaphragms on anything.

This means all jets can be changed and needles adjusted with the carbs in place so you don't need to fiddle with the throttle cable or get the airbox out for those with the stock intake.

I also have heard that the oval K&N pods (what K&N recommend for our models) work a bit better than the round type pods. I'm not sure why... but they certainly seem to be working well on mine

[pete]

145 main jets today = undecided... not enough WOT action during the commute today and my last chance was ruined by a serious accident that had both lanes of my fun uphill run home blocked.

It did richen my idle circuit up as expected, so it really didn't want to idle for long today, especially in the stop/start traffic around the accident.

Wound the mixture screws in 3/4 of a turn when I got home to make it feel a little better.

Will try again tomorrow but I believe it's supposed to be wet so may be none the wiser yet...

I do have one question... I have been looking into drilling out the vacuum hole in the slides to improve throttle response even more as I have been told that it has a good additional benefit in that regard.

I've been told 3.5mm is the diameter to go to but can't find anything to back this up and I haven't had the slides out since to measure the diameter of the existing vacuum hole.

Any thoughts/input/feedback on this? I'll get the mains right first then think about it...

[pete]

So after a couple of days this week on the 145's I decided to give the 150's a go.

I got a good ride in with the Katana boys today and I reckon she's pretty close to right now. Potentially a little too rich at WOT but I think it's ok.

Before upping the mains, it was like hitting a wall at 130kph, and that was crouching down over the tank trying to get my helmet under the height of the fly screen.

Today, I was easily able to hit 139 at one point and that was sitting up in the breeze, not even trying to get behind the fly screen.

I think the ton is within my grasp at last

[Big Rich]

Pete, do you still have the needle at the richest position? If so, leaning it down a notch might help out any richness with the 150 mains.

As far as the round pods go - you mean K&N round pods? Or the cheap Emgo round pods?

Glad to hear she's running better!

[pete]

Hey Rich, I was thinking today about potentially dropping the needles half a notch again and seeing what that does. Will probably do that first while measuring the vacuum hole before doing any drilling.

The dyno day is on 18th May so I've got a bit of time to do more fiddling.

Did I say round pods? Sorry, I have the oval K&N pods...

And yep, she's running much much better

[pete]

Ok, so this week she's been popping a little on decel which seems to get a little worse as I'm riding... which would seem to indicate she's a little rich as they typically get richer when warmed up...

However, I've chosen to leave everything as is and instead last night I did the drilling...

Measured the existing hole to be 1.79mm:



I had a look at my drill selection and made a hugely scientific decision to go with a 3/32 drill based on what I had available. My smallest bit was smaller than the hole, second smallest bit was only a smidge larger, but 3/32 yields 2.38mm which seemed a more reasonable size increase without going over the top.

Naturally I was careful with a hand drill so as not to do any unexpected drilling or cause damage:





I don't expect to test ride until the commute tomorrow unfortunately but it'll be interesting to see what happens...

[MOC]

i'm VERY eager to see how this goes. i may go up a step on my main jets and shim the needle down a smidge if this works out for you. keep up the good work

[pete]

Cool, will update once I get out for a test ride for sure.

I want everything to "feel" right and good before 18th May so I can get on that dyno day and see how she really is.

[pete]

Ok so it's not a ground breaking improvement but definitely improved throttle response, especially in the 5500RPM and up range.

Right now I reckon my 150 mains are definitely too rich, so will go back to the 145's and see how she goes then.

I think I'm on the right track...

[pete]

Slight change in plans after discussions on the Kat forum over the weekend...

Last night, I found a 3mm drill bit so I now have 3mm vacuum holes in the slides.

The best description of the difference is

The difference between stock and 3/32 was noticeable, but the difference between 3/32 and 3mm is absolutely awesome. Probably not all that much in reality but it feels it. The throttle is much snappier and I like it

I've left the 150 mains as I'm starting to think they might be ok, not enough WOT running on the commute to really tell.

One thing I did tonight though was count my mixture screw turns... seems I lost track somewhere along the way and the left was 3 turns out, right 2 turns out

I've set them both to 2.5 turns again and will go from there tomorrow. She was popping under decel this morning and silly me again thought "too rich" so leaned them out half a turn... of course that was worse for the ride home this avo. I'm hoping it was mainly the right cylinder and with both on 2.5 it should be better.

I have yet to revisit Koolaid Kid's CV mixture screw technique as well, and I probably should revisit carb balancing too.

[pete]

Ok, 2.5 turns out on the mixture screws still had her popping quite a lot on decel, so I pulled into a side street on the way to work and wound them out another half to 3 turns.

Still popping so turned them out to 3.5 turns when I got to work.

It was almost gone on the way home, just a little... well more burble than pop on the way home, so set them to 3.75 turns out and will try again in the morning.

At this rate it's getting close to the next size up pilot jets (20)...

However, I gotta say that I'm still extremely happy with the modified slide action

I do need a good proper run to test it fully though... not sure when I'll get that done at the moment.

[wally]

This is my "huh" moment again... or maybe even "duh".

I don't understand what you have done.

Pics please! I am a graphic designer - I need visuals!

[pete]

Hahaha hmmm... not sure how I can do pic's of this Wally... is it the mixture screws that have you confused? Or more?

This is the best I can find at the moment although I'm sure I have better...



Just above the vacuum port you can just see a little brass slotted screw recessed in. That's the mixture screw, and there's an equivalent on the right side also.

Turning clockwise leans out the mixture, anti-clockwise richens the mixture.

These mainly effect the pilot circuit but on our CV carbs they do influence the other circuits also.

Does that help at all?