Swap SHA for Mikuni?

Keegan Wilhelm /

Hello--

I need some advice on whether this is a terrible idea or not. I've got a 50cc PP hero majestic motor--a weird mix between a laura and a 103 engine-- that uses a clone shaco SHA 12.12. If I could, how bad of an idea would it be to swap to lets say...a vm20 (mainly cause i have one on hand)? I would be putting prolly a shitter circuit pipe on the engine as well. Just didnt know if a vm20 would be too big for an engine that originally ran off a 12.12.

Re: Swap SHA for Mikuni?

Dirty30 Dillon /

The VM20 is going to be a bear to tune, and horribly inefficient for this application. The SHA is more than adequate, even with a circuit pipe.

Re: Swap SHA for Mikuni?

Keegan Wilhelm /

> Dirty30 Dillon wrote:

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

> The VM20 is going to be a bear to tune, and horribly inefficient for

> this application. The SHA is more than adequate, even with a circuit

> pipe.

what makes it horribly inefficient?

Re: Swap SHA for Mikuni?

The size of the vm20 on your 50cc setup. You already have to tune them way down for a 70cc bike.

Get a bigger Sha tho and have some fun. To me, a Sha is so much easier to tune since there are fewer "stages" to it so less tuning options in a sense which makes it a little less daunting to get tuned up.

Grab a 15sha and accompanying intake. Get some jets in the high 50's thru mid 60's range.

Upgrading the pipe will help a lot as well. Ask questions as you have them.

Re: Swap SHA for Mikuni?

Keegan Wilhelm /

> Jay Rivett wrote:

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

> The size of the vm20 on your 50cc setup. You already have to tune them

> way down for a 70cc bike.

>

> Get a bigger Sha tho and have some fun. To me, a Sha is so much easier

> to tune since there are fewer "stages" to it so less tuning options in a

> sense which makes it a little less daunting to get tuned up.

>

> Grab a 15sha and accompanying intake. Get some jets in the high 50's

> thru mid 60's range.

>

> Upgrading the pipe will help a lot as well. Ask questions as you have

> them.

why sha and not something like a bing or a dellorto that has an idle circuit and a main circuit? I've heard tuning a sha is a huge pain due to its...simplistic nature -- one jet and fidling with $10 slides to get it to idle.

I've got a vm20 on a wizard kit and a tm24 on a malossi h2o kit on my nu/nx bikes, and those are super easy to tune imo. Yes, those are kitted, but something like a vm18 may be better suited if I do some minor port work to the engine...

Re: Swap SHA for Mikuni?

Dirty30 Dillon /

Dellorto makes the SHA, and on a setup like this you don't have to muck with slides.

You can attempt to put a VM18 on this, but general rule of thumb is you want venturi size to be at most 50% of bore. So, on a 38mm~ cylinder you wan a ~18mm carb max (and that's theoretical maximum, so including a pipe and porting). Aka, a stock port and intake, and a 12-15mm is more than adequate and youll get better response from the smaller carb.

Re: Swap SHA for Mikuni?

Keegan Wilhelm /

> Dirty30 Dillon wrote:

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

> Dellorto makes the SHA, and on a setup like this you don't have to muck

> with slides.

>

> You can attempt to put a VM18 on this, but general rule of thumb is you

> want venturi size to be at most 50% of bore. So, on a 38mm~ cylinder you

> wan a ~18mm carb max (and that's theoretical maximum, so including a

> pipe and porting). Aka, a stock port and intake, and a 12-15mm is more

> than adequate and youll get better response from the smaller carb.

with the dellorto comment, i meant a phbg or something similar.

makes sense with the size, but id rather have more tuneability over having to dick around with notching slides and having one jet / emulsion tube for the entire rev range. ive got a shit load of mikuni jets, and would rather stick to that if I can.

Re: Swap SHA for Mikuni?

Dirty30 Dillon /

You don't need to dick around with slides. I run plenty of kitted and piped bikes with SHA's with standard slides and they are fine.

And you can have a carb that has swappable parts, but probably will never tune well for your porting/bore size; or a carb that will function just fine for a stock port map and pipe that requires you to buy some jets.

> Keegan Wilhelm wrote:

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

> > Dirty30 Dillon wrote:

>

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

>

> > Dellorto makes the SHA, and on a setup like this you don't have to

> muck

>

> > with slides.

>

> >

>

> > You can attempt to put a VM18 on this, but general rule of thumb is

> you

>

> > want venturi size to be at most 50% of bore. So, on a 38mm~ cylinder

> you

>

> > wan a ~18mm carb max (and that's theoretical maximum, so including a

>

> > pipe and porting). Aka, a stock port and intake, and a 12-15mm is more

>

> > than adequate and youll get better response from the smaller carb.

>

> with the dellorto comment, i meant a phbg or something similar.

>

> makes sense with the size, but id rather have more tuneability over

> having to dick around with notching slides and having one jet / emulsion

> tube for the entire rev range. ive got a shit load of mikuni jets, and

> would rather stick to that if I can.

Re: Swap SHA for Mikuni?

Andy zero must be sleeping off a rally hangover today since this thread has been up for like 3 hours and still no SHA meme.

Srsly don't overthink it, Sha are also the smallest and easiest to mount on stupid dangly engine bikes with no room. Drill 3 holes in a plate and cut it into a flange, weld a handlebar to it, slap an SHA on there, done.

Re: Swap SHA for Mikuni?

I sold a bike once, 50cc with a 15 bing. It came back to me, still 50cc with a nice proper VM20 and intake all done up. It was almost $150 and it was distinctly worse with the VM20 just cuz it didnt really pull enough to be useful. you gotta really scream in the RPMs to need a carb that big on a 50

sha is easy, and sure it's less tunable, but that means it is easier to get to "good enough" with less tuning required...

Re: Swap SHA for Mikuni?

Keegan Wilhelm /

> Born to be WillD wrote:

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

> I sold a bike once, 50cc with a 15 bing. It came back to me, still 50cc

> with a nice proper VM20 and intake all done up. It was almost $150 and

> it was distinctly worse with the VM20 just cuz it didnt really pull

> enough to be useful. you gotta really scream in the RPMs to need a carb

> that big on a 50

>

> sha is easy, and sure it's less tunable, but that means it is easier to

> get to "good enough" with less tuning required...

I dont want it to be "good enough". thats being a lazy ass. i get it, vm20 is too big. i may go vm18 since i already have every single mikuni jet under the sun. i know the vm18 is already "at the max" for a meh 50cc engine...but if i end up with an actual 103 engine, or the 60cc reed valve majestic motor, itll be go for that.

Re: Swap SHA for Mikuni?

You must like the working on way better that the riding on part of this hobby . LOL

Go ahead and squeeze the pulp , but , it'll still be just a moped . ;)

Re: Swap SHA for Mikuni?

Keegan Wilhelm /

> P D wrote:

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

> You must like the working on way better that the riding on part of this

> hobby . LOL

>

> Go ahead and squeeze the pulp , but , it'll still be just a moped . ;)

isnt that half of the fun? getting it to run right, and getting the most out of it vs complaining at every beer stop how its running rich at idle or lean at the top end? just do it right the first time and get it over with

Re: Swap SHA for Mikuni?

Dirty30 Dillon /

> Keegan Wilhelm wrote:

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

> > P D wrote:

>

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

>

> > You must like the working on way better that the riding on part of

> this

>

> > hobby . LOL

>

> >

>

> > Go ahead and squeeze the pulp , but , it'll still be just a moped . ;)

>

> isnt that half of the fun? getting it to run right, and getting the most

> out of it vs complaining at every beer stop how its running rich at idle

> or lean at the top end? just do it right the first time and get it over

> with

I mean, stock (+) mopeds run right with a SHA, without modding slides.

You wanted opinions on whether it was a good idea, everyone seems to think the SHA is going to be fine. If you still want to go Mikuni for your own reasons, roll with it.

Re: Swap SHA for Mikuni?

Keegan Wilhelm /

> Dirty30 Dillon wrote:

> You wanted opinions on whether it was a good idea, everyone seems to

> think the SHA is going to be fine. If you still want to go Mikuni for

> your own reasons, roll with it.

And thats fine. I asked my brother and as soon as I said SHA he looked at me with disgust...then flip flopped to saying that if i want a budget carb that runs "okay" then itd be fine. Really it boils down to me wanting to decide which carb to buy. All I know is, I do not want to use a 12.12 sha lol. Maybe a 16 sha...we'll see. Hell, you could prolly get a lawn mower carb to work, and those have both an adjustable idle circuit and a main circuit lmao

Re: Swap SHA for Mikuni?

You ride one of the bikes I have a Sha on and tell me what it is missing.

But the question didn't sound like it was coming from someone who tunes mikuni already, it sounded like a question about how much carb should I buy for this stock cyl bike.

Go big and tune up that mikuni if you have the chops. I personally would go with a Sha cuz I can tune them really easily and really well.

Re: Swap SHA for Mikuni?

Keegan Wilhelm /

> Jay Rivett wrote:

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

> You ride one of the bikes I have a Sha on and tell me what it is

> missing.

>

> But the question didn't sound like it was coming from someone who tunes

> mikuni already, it sounded like a question about how much carb should I

> buy for this stock cyl bike.

>

> Go big and tune up that mikuni if you have the chops. I personally

> would go with a Sha cuz I can tune them really easily and really well.

yea, true. i like mikunis as thats what i have knowledge with. i was really curious if a vm20 would work, which it prolly wont, at least decently.

i got the replacement motor in from a fellow MA member...while there is "big" gains to be had by opening up the ports (they are stupendously small) , im going to be heavily limited to the itty bitty intake the cylinder has....if im able to get it going. The PO of the motor had the crank "rebuilt"...which it does look nicely done, but the crank had been under water at some point and it heavily pitted the seal surfaces. Its unusable in its current state unless i can sleeve the crank.

Re: Swap SHA for Mikuni?

🇮🇹💦 Of the Loin /

SHA's respond really well to a properly tuned airbox, especially on a stock moped

Re: Swap SHA for Mikuni?

Keegan Wilhelm /

> 🇮🇹💦 Of the Loin wrote:

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

> SHA's respond really well to a properly tuned airbox, especially on a

> stock moped

how does one tune an airbox?

and i if its the box where the air filter goes, i dont have that. its looooong gone and i have no idea where to get parts being an indian made moped.

Re: Swap SHA for Mikuni?

I really like the PHVA's and have had a few real awesome Amal setups in the <18mm on a 50cc range.

If you wanna do it right right tho, make it USE that VM20. port the dicks out of it and get that pulling 5 digit RPMs, cuz on stock, to your original Q, yea it's kinda too big

I think the point most folks are making tho is the SHA is just an easier reliable setup if you're jusst building stock +

And swapping slides is pretty easy, if you're doing it in detail you're swapping needles in the Mik too

But I absolutely feel tuning what you've got. I'd say at least 4/5 builds just wind up with whatever carb I have, or have jets for. my comments are more considering/comparing buying new intake & carb - if I was gonna buy one

I've swapped equal size bings and SHAs and never felt like one was any bit better performing in the end. I like the click action of the choke on the SHA better for starting, and filters are cheaper and more available. SHA idle issues I've only ever had problems with the tiny little idle hole plugging (not the jet, the circuit under tha main bore), and that's easy. The bings maybe have less blowback? but yea just for having a needle vs slide i've got no hard prefs

Re: Swap SHA for Mikuni?

Eric Davenport /

Vm16 is a option

Re: Swap SHA for Mikuni?

So many ways to start making and modding air boxes. You can just use the black cap they come with when bought new. And remove some screens to allow more air flow. Even add some air filter foam in for additional tuning options.

A few boost holes in the slide and some screens out of the filter pack and they really wake up.

> Keegan Wilhelm wrote:

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

> > 🇮🇹💦 Of the Loin wrote:

>

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

>

> > SHA's respond really well to a properly tuned airbox, especially on a

>

> > stock moped

>

> how does one tune an airbox?

>

> and i if its the box where the air filter goes, i dont have that. its

> looooong gone and i have no idea where to get parts being an indian made

> moped.

Re: Swap SHA for Mikuni?

Dirty30 Dillon /

> Keegan Wilhelm wrote:

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

> > 🇮🇹💦 Of the Loin wrote:

>

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

>

> > SHA's respond really well to a properly tuned airbox, especially on a

>

> > stock moped

>

> how does one tune an airbox?

>

> and i if its the box where the air filter goes, i dont have that. its

> looooong gone and i have no idea where to get parts being an indian made

> moped.

A tuned airbox means one with accurate volume for your displacement and properly sized inlet ports. Really, any airbox is better than an open carb.

And you don't need an airbox specific to the moped, just one that mates with the carb being used.

Re: Swap SHA for Mikuni?

And really, 'tuned' is relative, it's mostly just about damping out the pressure fluctuations in the carb so the tuning isn't all fucky. You can go to the next level and actually make it 'tuned' to displacement, rpm, intake porting, but the biggest gains are just from having anything on there at all to give the carb a consistent pressure signal.

Re: Swap SHA for Mikuni?

🇮🇹💦 Of the Loin /

All IC Engines are just basically air pumps

Now think of what kind of conditions a pump likes

Re: Swap SHA for Mikuni?

Graham, it does seem that Sha carbs work better on reed setups for that reason of the reeds making a better consistent and contestant pressure.

Re: Swap SHA for Mikuni?

Dirty30 Dillon /

SHA's don't have a needle, so midrange is only controlled by a) slide position and b) signal pulse, so it definitely likes the staccato, strong pulse of reed or rotary intake WAY over piston port which has lots of return pulse interference and blowback.

Re: Swap SHA for Mikuni?

Yeah exactly, the air in the airbox acts like a spring recovering that energy and smoothing out the reversion wave. If you actually tune it you can recover that pulse like an expansion pipe, but it often makes the packaging difficult on a moped. Even in a full size moto it ends up taking up major real estate in the frame.

Re: Swap SHA for Mikuni?

I am going to find out more about this. I have a big open space on my Magnum that can get filled with stuff for my carb.

> Graham Motzing wrote:

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

> Yeah exactly, the air in the airbox acts like a spring recovering that

> energy and smoothing out the reversion wave. If you actually tune it you

> can recover that pulse like an expansion pipe, but it often makes the

> packaging difficult on a moped. Even in a full size moto it ends up

> taking up major real estate in the frame.

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