Tomos A3 - help required please


I've recently acquired a Tomos A3ML 1989, it was a non runner. (UK Member)

I had to sort the electrics and carb out, and generally change the oils and grease/clean/de-gunk everything but I've got it started and running ok, but I need to get its performance up a touch.

I don't want to spend a massive amount on it, but I need to be able to get it up to circa 35mph on the flat.... and for it to climb smallish hills (not mountains).

Looking around on the net I can't seem to find a good supply for cheap 70cc kits here in the UK, so my thoughts go on to keeping the stock 50cc piston/barrel and then changing the gearing and exhausts/carbs etc, perhaps even do a touch of porting work?

Here's my thoughts - if I can drop on to a cheap exhaust and perhaps swap the encarwi carb for a dell'orto 17.5 (fabricate an intake) and get the gearing sorted, what can i expect from it top speed wise.... and hill climbing wise too?

Thanks in advance for any info/support you can'll be greatly appreciated.


Re: Tomos A3 - help required please

I would look into I believe they made a kit for the a3 do you know what mm your wrist pin is? there is a larger wrist pin and a smaller wrist pin and if you have a larger wrist pin you can use any tomos or puch kit pretty much, you can also swap over to a dell and put a pipe on it a nice filter and tune the carb. that's my thought before my a3 wiring and everything whent back on it and need a rebuild I was pulling about 40mph or so with a pipe carb and some other work done to it.

Re: Tomos A3 - help required please

Martin Agronski / is an excellent UK stockist of Tomos parts, and do some big-bore kits.

You're right about the two improvements being carb and pipe.

1 - Definitely get rid of the awful Encarwi and get a Dellorto carb (SHA is fine, but if you're also thinking of a kit, maybe a PHBG instead). Making an intake is easy enough:,3666475,3666644#msg-3666644

2 - Techno Circuit or Bullet exhausts are both cheap and apparently the Circuit is really good for low-end power, which you'll need if you're hill climbing a lot.

A3ML means it's 26x22. I'm just about to put a 24-tooth rear sprocket on my A3ML so it can climb better. Might lose a few mph at top speed, but not crawling up hills at 12mph is better. Also going to open up my exhaust port to 28mm and maybe put some piston ramps in so the blowdown is closer to 17%. Modding the piston rather than the cylinder is a good way to experiment without turning your engine into a boat anchor.

Might be an idea to change your piston rings and re-time your points, too. Get a cheap timing light - A3's are very fussy at what RPM they make power vs. points timing.

Good luck, and keep us informed! ;)


Re: Tomos A3 - help required please

Fabio Dougie /

So, just to confirm.....

If I replace the encarwi with a dellorto sha or phva (your inlet solution looks very interesting!) and buy a new exhaust bullet or circuit, and get the gearing sorted, do you think then that it'll be more useable (35mph and climb small hills better) I on the right track here

What gearing should I go for?

Thanks in advance



Re: Tomos A3 - help required please

Martin Agronski /

You should get 30mph out of your current set up, easily more with the upgrades you're talking about and the 26x22 gearing you're probably running at the moment - the numbers are stamped on Tomos gears - try cleaning some of the old grease off if you can't see 'em. The carb and pipe will be a good start.

There are Tomos riders here that can break 40mph with 50cc cylinders - running custom air filters, higher gear ratios and serious performance. I have my own doubts about how long it takes them to get up to that speed, however ;)

...but don't forget it's a 50cc piston-port engine with fixed gearing - you won't get a top speed of 45mph AND hill-climbing performance. There's always a tradeoff between speed and torque, RPM power-band and take-off acceleration. But it's mopeds - experiment! It's easy and cheap to play around, and quite hard to totally screw up - plus if you search the forums and wiki there's plenty of knowledge hanging around to help you out.


Re: Tomos A3 - help required please

it's a 2 speed!

those kits are great, the airsal with the 10mm wrist pin.

if you want some even funner/cheaper stuff to do, just buy an a35 cylinder on the buy sell forum for cheap. get some reeds and a proper intake as well. you use your a3 piston, in the a35 bore. you will need to cut windows in it like an a35 piston. you get reeds, and cooler fins...

i like just about all the exhausts on treats for these. the tecno circuit rules, but is kinda flimsy. the homoet is awesome, but you gotta wait for it.

airsal kit + circuit + 15 sha = goes up hills fast and does 40+ if you do it right.

Re: Tomos A3 - help required please

Rob GasketFace /

I have the 70cc airsal kit (with 10mm wrist pin), a 15.15 Dellorto SHA, 22T rear sprocket and the techno estoril pipe on my A3 and I get 40+mph (64+ kph) with plenty of hill-climbing ability.

It's a relatively affordable setup through treatland, but I dunno about shipping to UK.

I use a #70 jet and advanced timing. Amsoil at 80:1 will help with cooling given the advanced timing. Probably a good idea to get a temp gauge to keep an eye on things. I also have a needle bearing thing for my wrist pin, can't hurt.

Re: Tomos A3 - help required please

Fabio Dougie /

Its definitely has a 22 sprocket at the rear

Its marked "TOMOS 22"

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