Jetting Query

[seacoastzuma]

04 Zuma with 72cc malossi cast, 17.5 PHBN, silent pro, 14/43 gears, 4.5g rollers, snorkel removed.

I have been chasing a bog for a while now. When I dump it from idle, the motor picks up some RPM and generally seems to pull well. When rolling around at below variator speed, the throttle response is awful, big bog and eventually it picks up and pulls away. There’s also this weird transient loss in power/half second bog that happens as the bike accelerates. I’ve been running jets in the 88-95 range trying to figure it out. Today I started at an 80 main, moved the needle through its range, and was suprised the scoot felt ok. I tossed in an 85 and the bike was awful, no power, couldn’t break 20mph, felt dead. How does this work. How could the scoot do ok with larger mains, run mediocre on a 80, and not run on an 85? I’ve been chasing this jetting issue for months and don’t have a clue on how to proceed.

[sinfull]

Start at one circuit at a time after you leak test engine, check everything over again and everything is tight then start at one circuit and work either up or down.

Idle jet
Needle
Main jet

Doesn't matter where you start really, some go from main to Idle, other go from Idle to main

Idle to say 1/4 throttle no bogs and goes clean to Needle no bog and then goes into main jet.

[seacoastzuma]

That's what I did. I started at 80, tried every needle at 80, wasn't satisfied, and then repeated every needle position at each larger jet. I was asking about the mechanism behind the fact the 80 main jet rides, the 85 is terrible. Also as mentioned above the bog is present when I'm already moving and my clutch is engaged/engaging. At a stop, off idle, the bike launches well and pulls well. I've always thought I was bogging due to the bike running lean, but now I have no clue. I'm just really skeptical that an 80 main with the needle all the in is too rich. Currently on a 34 pilot.

[dwint]

Are you using stock clutch springs with that pipe?If so there's your bog.I've had over 40 motorcycles and never moved the needle on a carb.I've always find most like second from the top.If you keep moving both your chasing your tail.Try the second slot but i don't know what clutch springs you have that makes all the difference in the world.

[seacoastzuma]

Oct 23, 2023 17:27:47 GMT -5 dwint said:

Are you using stock clutch springs with that pipe?If so there's your bog.I've had over 40 motorcycles and never moved the needle on a carb.I've always find most like second from the top.If you keep moving both your chasing your tail.Try the second slot but i don't know what clutch springs you have that makes all the difference in the world.

I have a 105mm Polini sport clutch with the springs that came in the clutch. So there is also a distinct possibility that this bog is partly trans related?

[dwint]

That's the first thing i change when i start a build.Take off is day and night.I always use white contra with yellow clutch springs.I couldn't fix my bog awhile back and it ended up being a fouled plug from so many different tests.Make sure its plenty warm before any carb adjustments too.

[seacoastzuma]

Ok, I have a white (malossi) contra I haven't been able to install. I think part of my issue is a fouled-up TD and stock contra that hates to downshift when it gets hot, a bad combo after slowing down from cruising. I'l try to find an impact soon so I can take apart my transmission.

[geoffh]

Seacoast,you need a torque wrench,a variator locking tool and a good read up in the tech section,the list of goofed up cranks due to impact guns is long and lined with wasted$$$ and tears.

Geoff

[Zino]

here are the holding tools I use .
Buzetti makes them
The clutch one hold the nut when you take it off the clutch bell
and then to take off the the torque driver a few wraps on the concrete like the last picture takes it off and taps it back on

[Zino]

I mark every nut before I take it off so I know how far to twist it back to without a torque wrench.

At a glance I can see the wheel nuts exhaust nuts variator and clutch nuts are snugged to the right torque .

[Zino]

I think your chasing a cvt issue masking as a jetting issue

Do your rpms do this when you hit the throttle wide open and keep it there from take off they go way up say for eample to 9000 rpms then drop back to 8500 rpms and then rise to 9000 rpms and above .

If so this is a cvt issue you should have weights that jump to 8500 rpms hold and then rise is what you are looking for .

You can use the rpm gauge to dial in jetting
Start real rich say 90 and track rpms go progressively smaller and see which one gives you the highest rpm on long wide open runs

If you think you are close on the main
Use this race day trick to make sure your jetting is right

With your scoot well warmed up
Run wide open and back off the throttle a 1/8 to a quarter throttle
This will make you temporarily richer 3 things will happen.
Your Rpms will rise This means the main jet is a notch too lean
Rpms will drift down gradually This is right on .
Rpms will drop fast you are rich

[seacoastzuma]

Oct 27, 2023 8:08:09 GMT -5 Zino said:

I think your chasing a cvt issue masking as a jetting issue

Do your rpms do this when you hit the throttle wide open and keep it there from take off they go way up say for eample to 9000 rpms then drop back to 8500 rpms and then rise to 9000 rpms and above .

If so this is a cvt issue you should have weights that jump to 8500 rpms hold and then rise is what you are looking for .

You can use the rpm gauge to dial in jetting
Start real rich say 90 and track rpms go progressively smaller and see which one gives you the highest rpm on long wide open runs

If you think you are close on the main
Use this race day trick to make sure your jetting is right

With your scoot well warmed up
Run wide open and back off the throttle a 1/8 to a quarter throttle
This will make you temporarily richer 3 things will happen.
Your Rpms will rise This means the main jet is a notch too lean
Rpms will drift down gradually This is right on .
Rpms will drop fast you are rich

?
I haven't touched my CVT since I put my pipe on in may. I've just been trying to figure out jetting. When I'm in the range of the Vario (10mph+) the RPMs are pretty much always good when I dump the throttle. Sometimes when I ride for a bit and get it real warm the RPMs might be a bit low/feels maybe a little soft, but runs well. Once I run out of variator range there is a good amount of over rev up to top speed. I changed my needle back to the stock A12 needle, and maybe it helped a little. The only place I cant figure out is the 2-6mph, say rolling up to a stop sign and keeping my feet up, and rolling it back on the throttle. It almost sounds like it leans out before pulling enough fuel to wake back up, but I'm pretty sure it's already pretty rich on idle from me trying to get rid of the bog. The rpm also sounds really low when this happens, like maybe 5k or something really low, which is why I asked about the CVT.

[seacoastzuma]

Sorry Zino I think I misunderstood, are you saying it might be CVT while I think its jetting?

[Zino]

Yes I think you are unbalanced in the cvt
think your weights are way to low for that pipe

I ran closer to stock weight 6 grams plus or minus with thta pipe

When you are to light in weights you spin above the power band and feel sluggish and than it drops down into the power band

Think of a 12 speed bicycle you cruising along at top speed and you down shift gears your legs spin like crazy but you actually go slower not faster because you no longer in a optimal gear ratio

[seacoastzuma]

I put lighter weights in because my issue was too low of rpm down low/poor downshifting, which it still does with the 4.5s. I don’t think they’re too light, as I can feel the bike reach the end up transmission range and it keeps accelerating pretty strong until it really leave the powerband. If anything it feels like it pulls even a little better after the CVT maxes out, as if the transmission is set 400-500rpm low.