'99 Prebug Zuma Build

[billwill]

Dec 19, 2023 9:57:43 GMT -5 Lucass2T said:

Maybe it's just me but it sounds like you are lean on the main jet?
It sounds like it's grasping for fuel when you go from cruise to WOT.
Please check if it feels stronger/happier at 9/10 throttle. If thats the case, you're lean on the main jet.

This could very well be the case... I dropped all the way down to a 105 main. Forgot to mention on that ride above, the CHT's didn't go over 320º. 

I'm not sure if the cooler weather was keeping it cool (it's was about 40º F here) or what. I imagine on a hot, Summer day that I would be seeing higher temps. 

ALSO... found a guy on facebook who had imported one of these bad boys from Italy, and I've been thinking of bumping up to a C16...

www.st-racingparts.it/shop/marmitta-st-70s-verticale-70cc/

So... more updates to come but I pulled the trigger and cannot wait to check this pipe out. Word on the street is that it's the only one in the U.S. right now.

[Lucass2T]

Dec 19, 2023 10:55:10 GMT -5 billwill said:

Dec 19, 2023 9:57:43 GMT -5 Lucass2T said:

Maybe it's just me but it sounds like you are lean on the main jet?
It sounds like it's grasping for fuel when you go from cruise to WOT.
Please check if it feels stronger/happier at 9/10 throttle. If thats the case, you're lean on the main jet.

This could very well be the case... I dropped all the way down to a 105 main. Forgot to mention on that ride above, the CHT's didn't go over 320º. 

I'm not sure if the cooler weather was keeping it cool (it's was about 40º F here) or what. I imagine on a hot, Summer day that I would be seeing higher temps. 

ALSO... found a guy on facebook who had imported one of these bad boys from Italy, and I've been thinking of bumping up to a C16...

www.st-racingparts.it/shop/marmitta-st-70s-verticale-70cc/

So... more updates to come but I pulled the trigger and cannot wait to check this pipe out. Word on the street is that it's the only one in the U.S. right now.

Nice unit!! And very special. I have not heard of this brand before but it looks like a real quality product👌

[billwill]

Dec 19, 2023 11:42:01 GMT -5 Lucass2T said:

Dec 19, 2023 10:55:10 GMT -5 billwill said:

This could very well be the case... I dropped all the way down to a 105 main. Forgot to mention on that ride above, the CHT's didn't go over 320º. 

I'm not sure if the cooler weather was keeping it cool (it's was about 40º F here) or what. I imagine on a hot, Summer day that I would be seeing higher temps. 

ALSO... found a guy on facebook who had imported one of these bad boys from Italy, and I've been thinking of bumping up to a C16...

www.st-racingparts.it/shop/marmitta-st-70s-verticale-70cc/

So... more updates to come but I pulled the trigger and cannot wait to check this pipe out. Word on the street is that it's the only one in the U.S. right now.

Nice unit!! And very special. I have not heard of this brand before but it looks like a real quality product👌

Really excited... I messaged the guy on Facebook who makes these by hand and confirmed that it would be a good fit for my kit. Was concerned it might be too much pipe but it should sing with it. The 4 race definitely felt like it lacked a bit on the top end.

Some of these videos are pretty wild on Scooter Tube's channel. They even have one with the Team Cristofolini water cooled vertical kit:

[billwill]

Took it out for another run at lunch today with the MHR overrange this time. I mixed the rollers I had for a total of 4.6g per roller and I can't say it felt much different. I will probably keep the MHR overrange on since the stage6 kit is definitely more for racing. I can tell the stage6 overrange grips harder when downshifting.

I did confirm though, that more carb (and trans obviously) tuning needs to be done - there is definitely a womp womp sound at 3/4-full throttle where there is no noticeable change in power and the bike sounds different. Temperatures were around 280 or 290 tops but I never had it pinned for more than a few seconds.

If anyone has feedback on this noise, I'm stumped, other than to try upping the main and playing with the needle. Right now I'm at a 105 main.

What's crazy is it didn't run that much differently with a 138 main.

I was getting good at tuning dellortos but this PWK is something else.

[190mech]

Might want to try a different profile jet needle and see if that makes it more tuneable..

[billwill]

Dec 19, 2023 19:14:21 GMT -5 190mech said:

Might want to try a different profile jet needle and see if that makes it more tuneable..

I have a whole pack coming that I found on Treatland. Just realizing now that I got some generic or OKO set when they actually do have a legit Polini set... DOH. Oh well, should be good enough to try a few and make some changes.

What I have coming: www.treatland.tv/OKO-carburetor-NEEDLE-set-PWK-p/oko-10-pack-needles.htm
What I probably should have bought: www.treatland.tv/polini-PWK-carburetor-needle-SET-p/polini-pwk-needles-342.0129.htm

If you have any idea or suggestion on which one to start with, I'm all ears.

Found this review on the Polini set from Treatland, so will probably start with one that's closest to JJN as I can.

Made in Italy. Precision and consistency are a given. This pack provides sizes that are actually "moped friendly", with tapers and thicknesses welcomed by our automatic 1/2/vario speed two strokes.

Perhaps the single-most important part of my whole carb. Your nice Polini main jet is no good if you can't cleanly get the revs up there...and forget it if you have a power jetted variant. If you buy a PWK and don't get these with it you're wasting your time and money.

I went from the cheapies to these and gained an easy 5mph! I still can't believe there was that much more left in my set up. New RPMs will be reached - get these.

PS: the JJN is amazing

From looking at this chart, it looks like I could try the JJK since it's close to the JJN.

[billwill]

Definitely some opportunity for better belt travel on the variator. 

[billwill]

Been thinking a bit about my 3/4-full throttle issue and reading a few things in Facebook groups and I'm wondering if the bowl is running dry.

Would it be worth switching to a manual fuel petcock just to eliminate this as a factor?

Does anyone have one they might recommend?

I'd rather not run one if I don't need to for sheer convenience. Also, there seem to be quite a few generic ones listed on Scootertuning so not sure which would work or be best.

[aeroxbud]

You can check the flow by sucking on the vacuum pipe while running the fuel line into a clear container.
If it's a strong stream of fuel. You won't gain much from deleting the petcock.

[billwill]

Dec 24, 2023 10:37:53 GMT -5 aeroxbud said:

You can check the flow by sucking on the vacuum pipe while running the fuel line into a clear container.
If it's a strong stream of fuel. You won't gain much from deleting the petcock.

Certainly seems like more fuel than this thing could consume, so I guess I'm good there. Maybe I should replace the clip on the vacuum hose to carb connection because when I was checking, it wasn't super tight. 

Also, ST exhaust arrived the other day and I have to say WOW, this thing is an absolute work of art. Fit and finish is what you would expect. Got it mounted up and started it but haven't taken it for a spin yet. I can already tell it has somewhat lower torque at low RPMs than the Polini 4 Race. 

Might adjust the clutch engagement because its catching around 6k and this pipe probably wants something more around 8k.

I'll get some running clips this weekend.

[190mech]

COOL! Looks like it has the replaceable (Fath)nozzle feature for fine tuning..

[aeroxbud]

Looks beautifully crafted

[billwill]

With Christmas, New Years, some family colds spreading around and buying a new car (in the background of the vid lol), I didn't get to do the following work as quickly as I had wanted but it was a great break from work and time with the family. Hope everyone else had the same!

Did quite a bit of tuning to the bike since my last post and here is what I've done:

1. Added manual fuel petcock (I don't think I needed this but I wanted to remove it as a point of failure and/or possible issue).

2. Tried another needle from my kit from treatland, ended up going back to what came with the polini PWK. maybe i'll switch to another in the future or play with clip position again.

3. Lots of transmission tuning. I tried all types of contras and where I landed was a Malossi red contra with the 3.8g rollers that came with it. It also came with 3.5g rollers but I'm not even going that low - I think I need just slightly heavier ones. 4-4.2g is what I'd like to try next.

4. I swapped in a new polini atomizer with some mangus holes - a lot of material from polini and other carb manufacturers says this is more applicable to 4 strokes but people on multiple facebook groups had said it was a good improvement. Pics below of the differences.

5. Of course you guys have seen it but I threw on the ST exhaust. My god what a beauty and this thing screams compared to the polini 4 race. Right now it sits around 11.8-12k rpms and feels like it wants more. Maybe lighter rollers could be had.

6. The pipe doesn't even come alive and bogs up until 8k. I had trouble getting the clutch to engage higher than 7k so I removed the stage6 orange springs and threw in a set of (I think? I've had them so long I forget) Malossi black springs. They are firmer and larger gauge metal than the other springs, so I'm not too sure. Interestingly enough, all I could get out of them was an engagement of 7.5k and the pipe picks up at 8k so there is still a bog and more tuning here to be done. I have just a slight bit of adjustment to make them tighter on the stage6 clutch, so that will be my next move before getting even stiffer springs. 

I took the scoot out over the course of multiple days here doing this stuff - not so fun in the 30-40º weather we've had here but I'm loving tuning this thing. 

Unlike you're supposed to, in making incremental changes while tuning, I did NOT, lol. So its hard to say what took care of that dead spot in the carb but between all of the above, its much improved and 10% of what it was before. 

I still need to do some plug chops and take a look at the plug at all, but I'm guessing the main isn't where it should be. The needle either but it runs good enough for now while this weather continues to only allow for 5-15 min rides before my hands turn numb.

Top speed though, is still depressing lol. A whopping 61mph was the best I could get. I'm really stumped at this and thinking:
- there is just way more transmission and carb tuning to be done
- the gears I threw in were too much for this kit
- I'm fat as hell (really only above average I guess at 220lbs)
- the cold weather and 32:1 break-in premix I'm running is throwing things off

Oh well, having fun and open to suggestions. I'm chasing 70mph on this bad boy and won't be happy until I get it.

Oh and, on my last ride I noticed my front break felt spongey... it seemed to clear up with a few pumps so didn't think anything of it. Got back home and thought I had ridden threw a puddle or something and nope, front brake line was loose. Sheesh.

Here is a link to the manual petcock on Amazon in case anyone needs one. Super cheap and should fit prebug zumas and I'm assuming buyeyes too: www.amazon.com/dp/B08Z34VRBJ?psc=1&ref=ppx_yo2ov_dt_b_product_details

Some pics and a vid of the stuff I did. Sorry no riding/revving video - want to get one soon but time hasn't been on my side lately.

[billwill]

Oh and, as can be seen, got rid of the stock handlebar setup finally. I did NOT like that and missed the naked bars. Being able to see the speed (albeit KM/h and I'm stateside) and if high beams are on is nice I guess, but glad to have the naked bars back lol.

I was curious just now about variator travel so I hopped in the garage and took a peek. Sure enough there is significant unused area here. Maybe the red contra is just a tad too strong but the yellow didn't feel great either - to be fair I didn't try this light of rollers with the yellow.

I also threw on some new rear brake pads since the rear brakes have been so weak. Still weak and tried several adjustments with the nut in the rear, the angle of the brake pivot arm thing. It will grab but not lock it up and I can quite easily pull the lever all the way into the bars. Maybe a rear disc setup is calling my name but this setup is trash right now for what it is and I know it can be better.

[aeroxbud]

You should be able to lock the rest wheel with a drum brake setup. Good quality brake pads. Plus a good cable with very little drag should make it easy to apply pressure.
I did find once trying a cheap cable. It would just stretch as I pulled it. 😞