Mikuni Vm20 adjustable main jet by Sudco

Chris Carleton /

Just got one off the bay from Sweden came in a week! Anybody got one ?

Re: Mikuni Vm20 adjustable main jet by Sudco

yes, i've had mine for about 2 weeks now.

i come from an automotive tuning background and the level of control over engine parameters (fuel/ign) is something i've sorely missed.

being able to reach down and twist a knob to adjust WOT fueling in real time has been extremely rewarding! i've noticed very subtle shifts in afr as engine & ambient temps change. i can make changes to the main jet of 1/8 turn and immediately note the effect on exhaust note and rpm/speed. last week i made some alterations to the intake tract and it was unbelievably efficient to not have to drain the bowl and fiddle around with jets on the side of the road to tune fuel.

the only downside i can see is that there is no way to communicate my jetting to others. i suppose i could do a flow rate test on various standard jets and then compare to the adjustable, but that's a lot of work.

Re: Mikuni Vm20 adjustable main jet by Sudco

Chris Carleton /

The instructions were sketchy and found little info on the web. Best i could figure was fully in is 200 and each turn out is reduces size by 20? Lmk what you figured.

Re: Mikuni Vm20 adjustable main jet by Sudco

That's a name ive not heard in many years. Sudco

Re: Mikuni Vm20 adjustable main jet by Sudco

> live ɘvil Wrote:

> -------------------------------------------------------

> That's a name ive not heard in many years. Sudco

No surprise . Sudco probably does have much that would apply to mopeds . ;)

Re: Mikuni Vm20 adjustable main jet by Sudco

anyone got actual details or links?

Re: Mikuni Vm20 adjustable main jet by Sudco

Chris Carleton /

Im loving it I can do a reach around at wot and give it a twist and get it jetted spot on!

Re: Mikuni Vm20 adjustable main jet by Sudco

> Born to be WillD Wrote:

> -------------------------------------------------------

> anyone got actual details or links?

will, i will see if i can grab a pic of the single page insert they included. not a lot of info, but iirc two turns out is approx a 250 jet.

the long and short is that it's a needle valve with the machining, tension spring, seals, etc, to replace the main jet in the "external jet" vm20.

ken

Re: Mikuni Vm20 adjustable main jet by Sudco

Why is this item not available me stateside?

Re: Mikuni Vm20 adjustable main jet by Sudco

yeah thats rad

my snowblower has the adjustable jet tecumpseh carb and i have to dick with it every time it goes from -30 to +10, works great, would be super handy on a moped.

Re: Mikuni Vm20 adjustable main jet by Sudco

> Chris Carleton Wrote:

> -------------------------------------------------------

> Im loving it I can do a reach around at wot and give it a twist and get

> it jetted spot on!

Almost like a moped Dutch rudder!

Re: Mikuni Vm20 adjustable main jet by Sudco

Wow cool I want this

Re: Mikuni Vm20 adjustable main jet by Sudco

Ok pics or it never happened.

Re: Mikuni Vm20 adjustable main jet by Sudco

Re: Mikuni Vm20 adjustable main jet by Sudco

> Rebel Moby Wrote:

> -------------------------------------------------------

> Its not new - maybe just to you...

>

> https://www.ebay.com/itm/Adjustable-Main-Jet-Mikuni-VM20-Mikuni-VM22/254217410905

Am I not allowed to see it mounted on the bike? (edited)

Re: Mikuni Vm20 adjustable main jet by Sudco

I ordered one

Re: Mikuni Vm20 adjustable main jet by Sudco

Chris Carleton /

So I contacted Sudco in Sweden to clarify the sketchy instructions and here you go from fully seated 1\2 turn out is equal to 80 jet 1 turn is 135 and 1.5 is 180 .

Re: Mikuni Vm20 adjustable main jet by Sudco

Awesome thanks for that!

Re: Mikuni Vm20 adjustable main jet by Sudco

> Chris Carleton Wrote:

> -------------------------------------------------------

> So I contacted Sudco in Sweden to clarify the sketchy instructions and

> here you go from fully seated 1\2 turn out is equal to 80 jet 1 turn is

> 135 and 1.5 is 180 .

that's 100% consistent with my experience. i've found my sweet spot between 1 and 1.5 turns out, depending on load/operating point/ambient conditions. chappy w/polini, vm20 (obv), mlm intake, modded oem exhaust.

when i'm doing hole shots, putting around town, etc, richer (~180) gives me more torque as i pass through the lower revs. if i'm doing a high speed extended WOT run, leaning out towards 135 will give me 2-3mph more top end. with the long runner mlm intake the knob falls right into my left hand.

fwiw i mix oily (20:1) to contend with the top end "lean" pulls.

Re: Mikuni Vm20 adjustable main jet by Sudco

2386A4F1-90C6-4B48-9FE6-0E7C072B6C6D.jpeg

I like it and so does my eurokitted puch

Re: Mikuni Vm20 adjustable main jet by Sudco

just placed an order for one. will be throwing onto a vm20 on a mb5 down the line. keep you guys posted

Re: Mikuni Vm20 adjustable main jet by Sudco

btw it makes for a great disabler... just dial it closed.

bike will start and idle just peachy until the throttle is cracked, then it immediately stalls on its face.

had a few "wtf is going on" moments this morning after i forgot i reset it last night!

it also provides a handy way to drain the bowl/reprime the fuel line which is why i messed with it.

Re: Mikuni Vm20 adjustable main jet by Sudco

not a Baron Asshole /

yea but all the downsides too: someone can come up and ruin your bike by just turning the knob when you aren't there, could lean it out and seize! also on MOST mikuni's the jet is in a spot where it could just LEAN over onto another bike or rack and mess up your jetting! or while riding! Its good for somethings, just nothing id want to run, and you cant tell where it was/is!

Re: Mikuni Vm20 adjustable main jet by Sudco

Dirty30 Dillon /

> ken gilbert Wrote:

> -------------------------------------------------------

> btw it makes for a great disabler... just dial it closed.

>

> bike will start and idle just peachy until the throttle is cracked, then

> it immediately stalls on its face.

>

> had a few "wtf is going on" moments this morning after i forgot i reset

> it last night!

>

> it also provides a handy way to drain the bowl/reprime the fuel line

> which is why i messed with it.

Yeah... totally convenient

Re: Mikuni Vm20 adjustable main jet by Sudco

having spent about a month now with an adjustable main jet, i can tell you that it's dead simple to remember your proper setting. for example, mine with my current mods is 1 1/2 turns out for summer (~80* ambient).

this morning was more brisk in the lower 60s. i picked up 1mph on a long straight by opening another 1/4 turn.

if i turn down to 1 turn out the engine is noticeably down on torque and will bog hard on a hole shot. if i go up to 2 turns i get a hint of 4 stroking at top rpm. basically anything between 1.25 and 2 is workable, with the two extremes being quite obvious that your fueling is off. i find the idea that a reasonably attentive rider/operator (ie someone who would run one of these) wouldn't notice a catastrophically lean condition within a hundred yards a bit unlikely. (edited)

Re: Mikuni Vm20 adjustable main jet by Sudco

Dirty30 Dillon /

Or just have a single hard jet that doesn't need to be adjusted because you set the bike up right.

The only merit i see would be to tune the bike initially, but that is voided by the fact that there is no way to correlate adjustment setting with a hard jet. I have tuned more than a few VM20's on mopeds and never really had an issue with tuning once in summer and once in cold weather, if needed

Re: Mikuni Vm20 adjustable main jet by Sudco

Brad William /

> Chris Carleton Wrote:

> -------------------------------------------------------

> Im loving it I can do a reach around at wot and give it a twist and get

> it jetted spot on!

...bringing moped love to another level indeed!!

Re: Mikuni Vm20 adjustable main jet by Sudco

> Dirty30 Dillon Wrote:

> -------------------------------------------------------

> Or just have a single hard jet that doesn't need to be adjusted because

> you set the bike up right.

>

> The only merit i see would be to tune the bike initially, but that is

> voided by the fact that there is no way to correlate adjustment setting

> with a hard jet. I have tuned more than a few VM20's on mopeds and never

> really had an issue with tuning once in summer and once in cold weather,

> if needed

how do you know it's tuned to best afr? how many jets did you buy and try that are sitting in a ziplock bag now?

I can tell with a quarter mile of road and a few minutes. ;)

Re: Mikuni Vm20 adjustable main jet by Sudco

Brandon Weiss (Detective brandon to you) /

> ken gilbert Wrote:

>

> how do you know it's tuned to best afr? how many jets did you buy and

> try that are sitting in a ziplock bag now?

Way less than $84 worth, that's for sure lol

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