Preface: Andrew Brown, one of the Puddle Cutters in Portland, OR (aka, my club) recently put on a carb tuning class at Sabatino’s Moped Shop in St. Johns, Oregon. To prepare he dived in deep and created a handout file for every person at the event. I was so impressed that I asked him to share that handout to the internet and do a little write up about his experience writing it. So please enjoy the research and fun words of Andrew!
If you want to skip the article about how the hotdog was made then please download the hotdog right here. The rest of the article will be by Andrew.
Little bit about me: My day job is to teach medical software to adults that use CAPS LOCK to uppercase the first letter in a password instead of SHIFT. I have to simplify the content into guides and video explanations so that there’s no ambiguity as to what needs to happen and why, always keeping the end goal in perspective. After blowing a handful of kits and being in the moped scene for several years I came up with a plan to figure out how to tune a bike once and for all, then show others how to do that themselves. Sounds simple right?!
To execute a plan like this I needed to do a bit of preparation:
1st, I read every manual I could get my hands on. The two dellorto manuals, a minkuni guide, the polini walkthrough, two stroke tuners handbook, and Performance Tuning by Graham Bell and took notes. After all this and watching too many videos on scooter and dirt bike tuning, I had about 40 pages of notes.
At this stage I was only understanding about 20% of what I’d written and wanted to get closer to 90%. To get to 30%, I needed to organize those 40 pages into something that made sense. In my guide I start with laying the foundation of what a carb is, what the parts are called, and generally the function of that part of the moped.
Have you seen this graph before? It’s not exact for mopeds, but it does the job of explaining that by adding more fuel to an Air/fuel mixture, the burn is richer. And taking away fuel will do the opposite, lean the mixture. I thought, if we can understand how each component of a carb affects that ratio, we can tune!
In addition to knowing that the ratio can be changed, it’s also important to understand that a bike needs different ratios at different intervals of performance. We refer to this as the progression and the rest of my guide breaks down each part of the progression, what components matter when, and how to change the ratio at the various stages. The closer we can get the carb to an ideal A/F ratio at each stage, the closer we get to a serious blaster as well as a more consistent ride.
Getting to that 75% retention level meant I had to actually follow this guide myself and validate it. So I did just that with a ZA50 Maxi and a 19mm PHBG. I bought a large variety of all the internal components and started to compare them.
Another thing about me, I enjoy numbers and comparisons. So it should be no surprise to hear that I also made a chart to track all this info. You can print a copy of if here: Carburetor-Tuning-Chart
Keeping in mind that I initially wanted people to be able to tune their bike more easily on their own, I used all the information and data I’d gathered to draft up a proper tuning steps guide. Starts with sorting out Idle, then full throttle, then worries about the rest of the progression. I’m sure it’s not perfect, but it’s a hell of a lot better than most of the things I’d seen up to this point.
Alright so at this point in the project I’m feeling pretty confident and am definitely ready to bump my understanding up to that 90% retention level, meaning I now need to teach a class. And that’s what I did. In October of 21, with the assistance of The Travis Tutorial, we held a session over at Sabatino’s Vintage Moped shop. Here are a few clips of that day.
Overall this was a positive experience and I feel like a more well informed wrench enthusiast. If you can take my work and do the same ill be happy. I’ll try to make the files more accessible and if you find a mistake I can correct, feel free to email me at musichoard@yahoo.com and I’ll fix it. (Keep in mind if the year is 2030 I am not updating an 8yr old document, get zucced.)