1982 Maico 490GS Carb Jetting
I have been rebuilding a 1982 GS 490 and need help with a starting point for jets on the new carb.
I put a Mikuni 38mm round-slide carb on the bike and I am running at 4000-5000 ft above sea level. I have tried a few setups but nothing gives me much although the bike starts fairly easily.
Idle is non-existant until I turn the idle adjust screw all the way in with every jet setup I have tried.
I do know how to do plug checks for lean/rich but have not found a sufficient starting point to even try a full-on plug test.
Thanks in advance for any help you can give me.
First off welcome to !
If you had the Bing Carb on your 490, I could give you the baseline jetting off the top of my head!
But Since you have a Mikuni you will need to join the Yahoo Maico group & ask the gang over there.
MAICOMOTORCYCLES : Maico Off-Road Motorcycles and Registry
Or Call Mark @ Northwest Maico-CZ
Here is what I found searching through the Maico Yahoo Group:
Jetting for 38mm Mikuni on a 81 490.
Q-0 Needle jet
6DH3 Needle (clip positioned as required)
Air screw 3/4 to 1.5 turns off seat.
Mine is an 82 GS 490 but I would think it is close enough.
I will probably jet my carb to these settings this weekend and try it out. I will let you know how well this works.
I also assume this is for sea level, but I will do a few plug checks to make sure it is correct for my altitude.
Last edited by DuoDS; 03-25-2010 at 05:17 PM.
I rejetted the bike this weekend with promising results.
I went with:
stuck with the original needle and needle jet, the one that came with my Mikuni VM38. the needle has a more gradual taper as opposed to the 6DH3 listed below which has almost no taper before the needle just ends.
Started on the first serious kick - with the choke on. Pulled the wheel up in 1st 2nd and 3rd gear.
Did not have the time or space to do plug checks, but this is the first time it has run well enough to even do plug tests
I was at the races yesterday & a new guy came out with a stunning 82'490 GS setup for MX.
It has the reed motor & it sounded great, I think that my friend got a picture of it, I'll have to check.
I have some pics of my bike in action - but I "may not post attachments", so I guess they are not getting uploaded.
The jetting mentioned earlier in the thread is pretty good at around 4,000 ft in altitude, not so good at 6,000 where the bike would cough at WOT and then have to catch up with itself.
At 4,000 ft. it runs strong and does not sputter at WOT - the plug, however, is black (but dry) so I think it is still a little rich. Next time out, I will try it with a one step smaller main. That should do it.
Also, when the bike is warm, it is hard to start - don't know if that is related, but I need to look into that as well.
If the Maico gets harder to start when warm, I'd be looking at the ignition system to see if it still has a good spark. you might want to clean all the grounding points of the ignition system.
I know on the MX versions if that where to happen, I would be checking the Motoplat, but your GS has a Bosh system & I don't know about them.
My Maico has a new PVL ignition that throws a fat blue spark every time it fires. A great upgrade from the original.
The reason why I think it could help on a warm start to go a little leaner is that trying to start the bike when it is warm, it often needs the compression release pulled in order to kick it hard enough to get the PVL to fire (PVL must spin fairly fast to work). When it doesn't start the first few kicks, there is always a serious amount of wetness around the compression release.
I guess this could be normal, but I just figured the warm engine was getting bogged down with too much fuel, perhaps fouling the plug.
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