Can anyone provide me with a good carburetor jetting starting point for a 2-stroke Maico 490 with a Mikuni 38mm round-slide carb at 4000 ft above sea level?

Restored bike, with a new carb. I have tried many configurations but have not been able to get the bike to run very strong (it runs, just not well)

There have got to be people around that race vintage bikes at this altitude - thanks in advance for any help you can provide.

 

No idea on jet sizes..

What have you tried and what were the results? Have you tried different jets? (pilot and main?) or just different needle and air screw settings?

On 2 strokes I usually start rich and work my way to a lean setting..

 

So, I had a chance to throw in new jets today - but not enough time (or space) to do any plug-checks, but the initial response is very exciting.

I changed to:

340 main
42.5 pilot
Q-2 Needle jet
6DP1 Needle

The bike started on the first serious kick with the choke on. Ran well enough to pull the front tire up in 1st, 2nd, and 3rd. A little mushy before the power band hit. It idled a little low (need to check the air screw) so I turned in the idle adjustment, now it is fine.

This weekend I will be doing some plug checks and I am taking all my jets with me so I will be able to tune it up and tell everyone what happened next week.

 

Good deal!!

 

So here is the update for jetting my GS490 Maico.

I rode the bike quite a bit last weekend and noticed that the throttle response and power was nice up through 3/4 throttle. When I opened it up to Wide Open Throttle the bike would cough and stutter. Relaxing the throttle a little would let the engine catch up and the bike would take off.

This tells me that my main jet is a little rich but the others are in the ballpark.

I did not change the main jet because I was riding at 6100 ft altitude and the humidity was quite high all weekend. Most of my riding takes place at around 4100 ft altitude in the desert, which is usually pretty dry. The drop in altitude and the drop in humidity allows for increased oxygen which would require the bigger main jet anyway.

Also, running rich is safer than running lean - I would hate the drop in altitude and humidity to cause engine trouble because of a lean condition. So until I get a chance to test in the low desert on a dry day I will run it as is.

All I can say is - DANG that bike has some serious power and with the rebuilt front forks and new rear 'Works Performance' shocks it is smooth too.

Here's to closing up a 2 year mechanical rebuild of this bike. Now it is time to work on the cosmetic issues. New tank, fenders, plastics, and race numbers are next (even though I don't race).

Then maybe if I get really ambitious, I will start power-coating.

 

Id think you could go 1 size smaller on the main jet but its never a bad idea to be safe...

I rode a 490 a few times and was amazed at the power it made with no reed valve or power valve... Those Germans knew Horse Power!!!

I need some pics of this bike even if its not perfect yet..

 

Finally had the Maico out to Knolls this last weekend and it ran better at 4000 ft vs 6000 ft. I agree that it could still go 1 step leaner on the main, the plug was mostly black, with a little dark brown on it. One step ought to do it.

However, it is still a runner. Here are some pics of the bike in action.

No, this is not me, it is a German exchange student who lives with me, he LOVES the Maico, and oddly enough, he had never heard of them before. He rides a bullet bike in Germany, but is restricted to a 125cc machine until he is older.

 

Last Pic - since the upload limit is 5.

By the way, for this rebuild you see many new parts in the picture.

Rebuilt front forks
new front number plate and cable guide
new Performance rear chocks
new tires
PVL ignition - and new Magura kill button
new 38mm Mikuni VM carb (finally jetted correctly)
new K&N filter
All new controls, cables, & grips
New seat (pan, foam, and cover)
Just painted the plastics for now (I have new a tank and front fender waiting to be installed)
Had to get the right pipe for a 490 off eBay (needs to be high-temp painted)
New foot pegs
Aluminum case saver
New chain and chain guide
New shifter lever
I have a new billet rear brake pedal on the way (those OEM ones get stuck)

Wow, that's about all I can remember right now - what a project!

That power-band makes it all worth it

 

Thanks for the pics!!! (and the memories)

 

i was wondering if you could help me figure out the best jeting for my 200 sm it is a chineese suzuki motor i have drilled a 1\2 inch hole in the bafle and drilled four 3\4 inch holes in the air box good power increes but need help geting the jeting just right it has a mikuni 2a 881 carb i have moved thie needle clip down two knoches and incressed the main jet to a 150 from a 122.5 plug is still white on plug chop half thootle an has bit of coulor on wide open plug chop but it hesitates at wide open espesialy if ya let off a bit then hit it it allmost coughs ? please help