Mikuni 18 (vm18) tuning... wtf

Joseph Gummer /

cannot seem to get my 18mm mikuni jetted for my bike.

the current setup is:

Morini M1 (case inducted reed valve)

Gilardoni 60cc kit

Mamba circuit pipe

I've tried 17.5, 15, and 12.5 idle jets and main jets from 140 down to 75. No matter what I do it seems that it is four stroking on the bottom end and the top end... needle is at the leanest setting (top-most setting)

can anyone give me an idea of where I should be with this setup?

Re: Mikuni 18 (vm18) tuning... wtf

#CrazyWayne™ rocks. #CrazyWayne /

Turn the choke off.

Re: Mikuni 18 (vm18) tuning... wtf

Joseph Gummer /

thank you for that wonderful advice... unless the choke is broken in the on position... that is not the problem

Re: Mikuni 18 (vm18) tuning... wtf

im using one on an e50 with the 65cc hero kit and i run a 70 main with no filter and a 60 main with a filter 4 strokes a tiny bit. think i have 12.5 idle in it and its running rich all around. my head temps after 4-5 miles of wot are sitting around 270 with the 60 and filter

Re: Mikuni 18 (vm18) tuning... wtf

vm18's jet really small, for your setup you should be going from 50-75 on the main.

it sucks that mikuni have such coarse numbers in that range, you dont get the fine tuning ability of every-single-number. you can use torch tip cleaners to go to half-sizes or just tune with air filter.

Re: Mikuni 18 (vm18) tuning... wtf

I have a vm16 on my 103 that I'm having trouble with. It idles fine but bogs ou full throttle using jets from 65-105.

Doppler 50cc

Gianelli pipe

Stock head

Rmz cdi 12v

Malossi variotop

Any ideas?

Re: Mikuni 18 (vm18) tuning... wtf

He's giving up, but he bought the carb from me. I had it on an e50 with the Athena reed, and ran a 150 main. When I put it on an MK65 I think I went down to 130.

Re: Mikuni 18 (vm18) tuning... wtf

Joseph Gummer /

You have no idea what you're talking about Mark and that's why YOU gave up. There's no way you should have a jet that big in an 18 Mikuni

Re: Mikuni 18 (vm18) tuning... wtf

Check the float level... The float may be getting stuck and flooding the carb.

Re: Mikuni 18 (vm18) tuning... wtf

turn the fuel mix screw out.....

I only say that because I had been running 4 stroking and boggish on my top end, until I adjusted the screw.... no more worries here.

Re: Mikuni 18 (vm18) tuning... wtf

No, I gave up because it wasn't idling correctly on the metrakit. But it turns out that had nothing to do with the carb. That cylinder had been seized and had some small gouges in it. When it was on the Athena it ran perfectly. Started with half a kick every time, idled like a champ, and got me to mid 40s with stock gearing. That was one of my favorite setups.

Re: Mikuni 18 (vm18) tuning... wtf

Joseph Gummer /

quick retarded question... just to make sure... on the VM18 the choke is in the on position when the little lever is UP or down...?

Re: Mikuni 18 (vm18) tuning... wtf

[Radium City] kyle k $ /

down is "choke" up is not...it's not actually a choke it's a starter circuit that opens and closes that's only used for cold starting which is probably why u have all sorts of problems

Re: Mikuni 18 (vm18) tuning... wtf

Joseph Gummer /

no no I know what the choke does... i get it. The positioning confused me, and then when someone mentioned it I thought I might have the positioning backwards... still having problems

probably need to try playing with the air screw and taking the air filter off. I'm at a 70 main right now, with the needle on the leanest setting

Re: Mikuni 18 (vm18) tuning... wtf

sounds like you're mistaking a misfire for 4 stroking. check your ignition system. bad points perhaps?

Re: Mikuni 18 (vm18) tuning... wtf

kristopher maedke-russell /

holy shit how did you get the plugs out with all that hash on the tip? my 70 reed kit/vm18 combo wants an 85 main and the plugs still are a little dark.

Re: Mikuni 18 (vm18) tuning... wtf

Joseph Gummer /

OK so here is a video I just took. Keep in mind the throttle is in the exact same position for basically the entire video (about 3/4 throttle)... this is just what the bike is doing.

Misfiring or 4-stroking?

It won't do anything else besides this...

(edited)

Re: Mikuni 18 (vm18) tuning... wtf

Beard Road Bruiser (SoB) /

I know this seams weird. Where are you timed, what's the points gap, and when did you last clean the points? Sounds like it could be a spark issue.

Could be leaking reeds too...

Re: Mikuni 18 (vm18) tuning... wtf

Joseph Gummer /

hmm i was worried it might be reeds...

Re: Mikuni 18 (vm18) tuning... wtf

Beard Road Bruiser (SoB) /

In all honesty, I'm not a morini person, but it sounds like its going, not going, going, not going.

It's not constant enough to be a jetting issue. Could be a bad condenser arcing the points. Or dirty points. I would look at a spark issue before jetting if changing jets isn't helping any.

Re: Mikuni 18 (vm18) tuning... wtf

that's(video) not carb , that's spark. Is it points or cdi?

Re: Mikuni 18 (vm18) tuning... wtf

i like waffles /

had a similar issue on a cdi bike, something happened to the trigger. Idles fine but drops spark when ya rev it? if ya have a timing light hook it up and check the spark that way, thats how i figured out what was up.

Re: Mikuni 18 (vm18) tuning... wtf

Joseph Gummer /

It's points, running a external condensor that is only a month old (got it at advanced autoparts) ... could potentially have failed already?

Re: Mikuni 18 (vm18) tuning... wtf

was having the same issue on my maxi II tis mornning i know i need to rejet my carb but i'm willing to bet you're not getting enough air though the filter i know i got pissed off and kicked the maxi knocking off the air filter and in a fit of rage took off down my driveway it kicked on at full power crab walked and threw me off.... try a new air filter simple easy and if i'm wrong no biggie

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