Carb settings

Ok, I've got a 2000 Tomos Sprint, and I've put on the 70cc kit

( I know, I know .... lots of you hate it )

The thing runs and sounds awesome. I got it because the ped is my new

toy and I wanted to get the most possible out of the smallest motor and

watch the reactions from the local traffic.

Carb adjustments are not my strong point though. The kit came with the

amal carb, and I've tuned it by ear and gotten pretty good results out of

it, but I'm not sure how well I've done. Does anyone have a page or guidelines

on how to set the mixture and idle screws for best performance.

Also, I've seen a lot of mention of getting a hotter spark plug than standard.

Anyone know a plug number or what I should look for at the local hardware

store ?

Re: Carb settings

what is your top speed now?

Re: Carb settings

I don't know my top speed yet, still breaking it in.

Before the kit, 32 mph was about as high as the speedo would go,

maybe 35 down a slight hill, but that's it. On the small street I live

on, I could get it up to about 25 before running out of pavement.

Now I can get up to 30 about 2/3 of the way down the street.

I have had it up to about 40-45, and there is still some room to

go on the throttle. It feels like I should be able to hit the low to

mid 50's, a small twist of gas at 40+ tells me that it's willing

to give me a little more effort. I'm babying it for now till I get at

least 100 miles on the new motor. The bike only has 110 miles

on it.

I put in the 70cc kit, Amal carb, BiTurbo, and 27 tooth sprocket.

Lucky for me I live just a short ride from themopedjunkyard

I've mixed a little extra oil in the gas, so I know that's knocking

my power down a little. I adjusted the carb by turning out the

idle screw while turning in the mixture, till I got a smooth run

while sipping the gas. I have no idea if this is a good or bad way

to do it. The spark plug was still to new to tell if it is burning hot

enough, but I would rather burn out hot burning plugs every month

than have a cold one that lasts forever. :-)

Any hints would be very appreciated.

Re: Carb settings

Ataristyle /

Only 110 miles on your bike and you are already putting that kit on there!? For the first 300 miles on my Tomos Targa LX I ran it stock and did not attempt to open up the throttle all the way when driving it. I did this to give the engine a good break in and so that the bike would last for a while. After the first 300 miles I drove it with the throttle wide open but could hit 35mph maximum if the wind was blowing against my back and I was on a smooth road. I put a BiTurbo muffler, #56 jet and a 27 tooth sprocket on my bike during the winter. My bike now accelerates alot faster with the muffler on and gets top speed of 40mph but likes to be at 38mph most of the time. I did not notice any difference from the 27 tooth sprocket. I also was hitting the same speeds w/ just the BiTurbo muffler and the larger jet in the carb. Good luck with the 70cc engine kit on your 'ped. I really wanted that kit also but I did read up on it and it wasnt too good. One of the guys here, Tim, had the kit and said it was so good until it ruined his bike. He now doesnt like the kit on his Tomos. I'm happy w/ my speed as long as I dont get hit by anyone on the road I'll be fine.

Swarm and Destroy!

Re: Carb settings & Plugs

Like I said, the ped is my new toy, I got it specifically so that I can play with it and the 70cc kit. I've always wanted to get a ped or a scooter (ped prefferably).

Knowing that I was going to put the kit on and that it might ruin the engine ( you see I do pay attention to the posts here ), it seemed silly to go through the time

to break the original engine in, only to have to do the same with the upgrade.

Plus, I would rather break the whole thing in at once, rather than having the trans "used" to the smaller engine, and then adding the newer one.

After riding the ped for a little while, I decided that I really wanted to get more into this, and got out of my last project (anybody want to buy a 54 Chrysler). I can buy

a new motor for the Tomos for what some "parts" cost on the car.

The ped isn't going to see a whole lot of use either, mostly my wife using it to drive a couple of miles to and from work on nice days, and then whatever abuse I can squeeze in on the weekends. Now that she has gotten used to the bike though, I probably will be buying another soon, and just changing the carb and adding a biturbo.

I tried the 27 tooth before I put the kit in and it gave me about 4mph on the top end, letting me get comfortably to 35, but no faster. It's worth the 27 bucks and 15 minutes it took to put in place.

Carefull on the plug

A hotter plug is not a performance enhancer.

The heat range of the plug is based on how the engine is tuned... and it is very unlikely that you need a hotter plug once you start to modify a motor.

Modified motors usually need COOLER plugs... because the increased performance makes them run hotter... add a hot plug to that and you will have a hole in the top of your piston... (maybe).

Base the plug heat range strictly on what color your plug is while running wide open.

In other words... finish your break in... settle on your oil mix... run it good and hard for a half mile... stop on the spot.... and pull the spark plug... If it is a light brown (tan).... leave that plug in.

I would recommend leaving the stock plug heat range in and altering the main jet to suit... not the other way around.

Re: Carefull on the plug

Ron Brown /


You have me going on this one. What color plug would tell me to go hotter/colder?


Re: Carefull on the plug

That makes a lot of sense now that I think about it, Thanx.

I'll make sure to check the plug once I've got it broken in.

Any tips on setting up the carb ?

Re: Careful on the plug

Well like I said... I almost certainly would not go to a hotter plug after modifying it.

And if it was modified radically it would get a cooler plug for sure.

But it's like jetting... If it was white I would go with richer jetting or cooler plug.

Or dark brown...leaner jetting or hotter plug.

I would stick with the stock heat range plug and jet it to suit.

I thought you were going to Daytona Ron?

Re: Carefull on the plug

Well if its like most... those adjustments are for idle speed and idle mixture and don't have much (or any) effect after quarter throttle or so.

So if it idles high enough then I don't worry about it much.

Fiddle with them all you want, you might get it to do something you like...can't hurt.

Re: Carefull on the plug

Thanx, that's about what I've seen in playing with the screws.

I think I've probably got it right, now if I could just get this BiTurbo hooked up

right, I'd be all set. It sat a little low, so I tried to pursuade the pipe into place

and hope that when it heated up it might take on the appropriate shape.

But then my pipe didn't meet the engine right, and I was spewing a fine oily mist

out the engine. No problem, just need to make sure I have the bolts down

tight... oops, there goes the stud, snapped in half.

Has anyone else had problems with the 2 piece biturbo where you can not get the

nut on the stud because it's too close to the pipe. I had to cut the edge off a

deep 10cm socket to get it on the nut, and have room to turn.

Re: Carb settings

have you ever ajusted the needle valve? 2qt or 1/4?

Re: Carb settings

I'm unfamiliar with what you are talking about ( see, I told you carb settings were new to me :-) so I would have to say no.

The only settings I have touched are the set back screw where the cable comes

into the carb (to make sure it was not too loose or too tight), and the idle and mixture screws. I've set the idle down to where the bike is running nice and quiet, even with the BiTurbo. Next I turned the mixture screw one way till it started idling worse, then I turned it back the other way till it started idling worse. Then I twisted it back to the middle position where it was running the best, and re-adjusted the idle to get it back to quiet.

Re: Careful on the plug

Ron Brown /


Thanks, I went back to for a refresher on heat range selection. Like you, it is not something I do very often.

I wimped out of riding to Daytona last week. Excuses like customer pressure, snow, biggest storm in 20 years, etc.

I do still have a place to stay and am going to try to leave early this week. I may have missed the bikes but I hear the sun is still shining and I really need the ride.


Re: Carb settings

Ron Brown /


It sounds like you did it exactly right.

For a good explaination of how to read spark plugs and heat range selection, go to

you should find everything you need here,


zoom zoom

After letting the engine get 100 miles on it, I took it up to 50 yesterday.

I chickened out there because the wind was blowing me around the

highway, but I think I only had another 5 mph in it max.

And boy was that engine whining.

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