Boggy midrange - needle questions

[MOC]

GS450L
Stock exhaust
Pods
floats are at 26mm

Carbs have been completely torn down, dipped, and rebuilt using new rubber (thanks cycle-orings.com) including manifold boot gaskets. they are clean as a whistle.

I obviously needed a rejet after the pods. the bike would bog at anything above around 1/4 throttle.

I upped the mains to 130 from 115 and then raised the needle by about 1.5mm

now the bike pulls nicely through 1/4, then stumbles through the midrange, then transitions onto 100% and pulls fine.

I would continue to raise the needle but it's the kind that only has one groove, and it's not set up where i can just add shims beneath it, it's got shims above that have to be removed to raise the needle.

i'm out of shims to remove.

what do i do to richen it up in the midrange in this situation? I really don't want to play games with new needles if i can avoid it. anybody have experience with this problem?

 

[Agemax]

you need to do some mid range plug chops to see if it is actually running too lean or too rich before you go any further.
a stock exhaust may be too restrictive with the pod filters to get them to run right throughout the rev range

 

[MOC]

that's an excellent point. i hadn't thought about that.

 

[BassCliff]

Hi,

Sometimes it's worth it to buy the jet kit just for the slotted needles.



Thank you for your indulgence,

BassCliff

 

[MOC]

i've looked for jetkits for my bike, but alas, they make none. if i knew the taper on the existing needle i'd just buy replacements with slots, but again, i'd like to avoid that.

ive also discovered a slow leak in my petcock which has hampered any tuning attempts. parts in the mail currently.

once that's sorted, it's off to the stadium parking lot to blast around doing chops and hopefully that will sort things out.

 

[Guest]

Stumbling in the mid range could also be too rich. You might try dropping the needles slightly to see if it smooths the mid range stumble out, and then do plug chops to insure it's not too lean.

 

[MOC]

Preliminary plug chops indicate a lean condition. I rode at half throttle up a long hill in fourth and chopped twice just to be sure. Plugs were not white but definitely light gray and ashy.

My petcock parts arrive tomorrow. After I install that I'm thinking maybe increase the float heights slightly? I would like to avoid modifying the plastic retaining clip that holds the needle down but I can't think of many other options besides playing musical needless.

Thoughts? As always your expertise is greatly appreciated.

 

[Guest]

You are not going to gain anything except ease of accessibility from pods. Going back to the stock air box would make your life a lot easier.

 

[Agemax]

send a PM to Pete, he is the resident expert on the 450's on here. he has modified his carbs for pods and an exhaust with good results. he will help you out

 

[Steve]

My petcock parts arrive tomorrow. After I install that I'm thinking maybe increase the float heights slightly?

If you adjust the float height, you will affect all the circuits. Yes, you will richen up the mid-range, but you will also richen up the pilot and main circuits, and you will likely be chasing your tail trying to get them all in sync. Just keep the float height at the proper level and tune each circuit as needed.

I would like to avoid modifying the plastic retaining clip that holds the needle down but I can't think of many other options besides playing musical needless.

One option would be the one that most of us choose. Don't modify your retaining clip. In normal assembly, there is a nylon spacer above the clip. Its thickness determines the position of the needle. If you replace that spacer with a short stack of washers that is about half the thickness of the spacer, you will effectively raise the needle about one notch. If you were to swap the positions of the nylon spacer and the metal washer on the other side of the clip, you will raise the needle the equivalent of two notches.

.

 

[MOC]

that nylon spacer is already gone. i'm down to only the clip. as for going back to the stock airbox, it was cut in half by the PO and is a nice oily paperweight now.

 

[jeffasaurus2]

So I've just gone to K&N pods and a much free-er set of mufflers on my 450. I've got a 140 main and had to up the pilot jet one size, haven't touched the needle. It seems to be pretty close to where it should be, I have no stumbles in any range.

Without proper chops the plugs look a little grey, I plan on going through the carbs properly Friday if the weather stays nice. We'll see where they are really at.

 

[MOC]

thats surprising to me, given your altitude in denver. do you just have slip on mufflers? or did you ream out the stock units?

 

[jeffasaurus2]

They're the shorty reverse cones from Dime City Cycles. Slip-ons. They seem to be only slightly more restrictive than running open headers.

 

[MOC]

petcock parts have just walked through the door. thanks to daylight saving time i have the chance to fiddle with the carbs for an hour or so after work too. i will try to get a test run in this evening and report back.

cheers

 

[jeffasaurus2]

best of luck!

 

[MOC]

I fixed the petcock today and then reset the floats from 26 to about 24.5. Didn't get a chance to do any chops before dark but I took it for a spin and it pulls MUCH harder through the midrange. I'm going to need to fiddle with the idle mix a bit but it's much better. I'm not freaking about it burning up from lean condition as much anyway. Thanks fellas

 

[Guest]

Hey mate, sorry I've been away on holidays and didn't see this or your PM until now.

My 450 has K&N pods and a quality custom 2 into 1 pipe that is very free flowing.

I'm still working out my tuning slowly and haven't done any plug chops yet to confirm, but so far this is what I have:

Float height is stock (26.6mm - the Clymer is wrong for these).
Stock pilots, still getting mixture screws set right.
Stock needles raised as high (rich) as they will go.
132.5 main jets but about to try 137.5 mains tomorrow.

Essentially from the rebuild my bike felt "boggy" just off idle up until about 1/4 to 1/2 throttle and had what I thought was surging when holding steady around the 1/4 throttle mark and I thought I had jetted it too rich.

When I finally started trying things, I discovered the opposite and that I had been running lean, so I had hesitation at part throttle and the surging was actually stumbling.

I probably need to go for a richer needle, but the length of the stock needles (4C3) is 48.3mm whereas all the Mikuni replacements I can get are just over 50mm, so doing a comparison to determine an appropriate needle will be a little difficult. I have measured the various diameters to make a comparison though.

I'm still slightly too rich on my mixture screws as I occasionally still get pops on decel and it has been improving as I lean them out.

It sounds like you're on the right track with richening things up, but with your needle, you will definitely be able to add more shims.

The way to add the shims is between the washer (8) and the C clip (7):

This is not the greatest photo in the world but you can just make out the shim here that I was trying:

I have also gone one step further in increasing throttle responsiveness and have trimmed just under 20mm from the slide springs as well, but don't do this unless you're really keen and have got them running right first...

You can also drill out the vacuum hole in the slide to get even more response but I haven't gone down that path yet, that's a little more drastic...

 

[MOC]

Pete, this is awesome. i'm glad you can identify with my trials and tribulations...

Regarding the shims. the problem i face is this:

Adding a washer beneath the clip won't raise the needle any more than it is already because it's already pushed firm against the base of the jet needle stem. (4) it took me about 3 teardowns with different washers to realize this. Raising the needles has meant removing the spacer (5) so that the needle can travel farther up towards the stem, but i've already pulled that spacer out. in other words, i'm at a dead end. The needle is pressed up against the stem as high as it will go and i've got nothing i can remove to free up its travel any further.

one of the consequences of raising the floats has been an idle mix that's too rich, so i've been trying to iron that out which i can't really sort out until i've got my midrange mix dialed in.

i think i could probably also use a bit more fuel in the 1/4 to 1/2 range, but again, i've run out of options in that department which is why i've resorted to gaming the floats


this leaves me with two options:

1 - play musical needles (nightmare scenario)
2 - risk modifying the needle stem (also a nightmare, and one i can't undo)

i'm hoping i can game the floats a bit more and be on target. the 130 main has proved to be enough at full throttle, although i haven't done any chops to confirm the mix is perfect. it pulls like a brute at WOT, so it's definitely not starving for fuel. it's just a tad bit lean from 1/4 - 1/2, which sucks because thats the band i'm in the most when i ride around baltimore.

fiddling will continue. I'll let you all know what i learn, and hopefully you might be able to figure yours out as well Pete.

cheers

 

[Guest]

Wow ok, you really are quite a lot richer than stock!

One thing I'll add though is the US needles and mains are different to the Aus needles and mains. The stock needle for you guys is a 4C2 whereas in Aus it's a 4C3 and this is a slightly richer needle. The stock mains in the US are 115's whereas in Aus they're 117.5's, again slightly richer.

At this point if I were you I would try one of two things... see if you can get a hold of the Euro version Dynojet E3305 stage 3 kit or start playing with richer needles.

This page may help you somewhat with your needle selection:

http://www.mikunioz.com/needles_numerical_list.htm

I've measure my 4C3 needles but that won't help you with the 4C2, you will need to measure and compare.

You will see the stock needles are shorter than the genuine Mikuni replacements also to make it that much more difficult:

After a good ride in the sun (finally) yesterday, I reckon my needles are pretty good now but I think I still need bigger mains. Next size to try will be 142.5.