Why don’t many small engines run Mikuni carburetors?

[Pullstart 62,905]

As the title says, what advantages do butterfly style carbs have over slide style, or vice versa?

[Pullstart 62,905]

Governor linkages I could see being an issue…

[ri702bill 8,327]

Hmmmm....   me thinks he probably answered his own question...

Was that not a popular carb in the '60's or so for multi-cylinder motorcycles???

Edited April 20, 2023 by ri702bill

[Pullstart 62,905]

12 minutes ago, ri702bill said:

Hmmmm....   me thinks he probably answered his own question...

Was that not a popular carb in the '60's or so for multi-cylinder motorcycles???

Is that the only thought you have, governor related?

[oldlineman 1,481]

Maybe they are more expensive $$$$$$$ 

[RED-Z06 2,221]

Slide carbs offer poor Power response at low throttle inputs, a small engine running at 3600 with no load only uses about 5-10% of the actual throttle throw on the carb, but when load is added, you want immediate response.  A side or down draft butterfly carb offers excellent idle, mid range mixing, and throttle response.  A constant velocity carb helps the response by simulating a smaller carb at lower speeds...however they are finicky.

 

As mentioned, linear governor linkages can be complicated with a cable driven system...as well, the slide would be making hundreds of movements a minute, wear would be a problem.

[ri702bill 8,327]

And there you have it............

[Pullstart 62,905]

Thanks @RED-Z06!  My wife found one today at an Amazon returns kind of store at lunch time.  $4.  I have no idea what size it is, but I’ll find out here in a bit.  I was just thinking, what could it be used on?

[ri702bill 8,327]

19 minutes ago, Pullstart said:

My wife found one today at an Amazon returns kind of store at lunch time.  $4.  I have no idea what size it is, but I’ll find out here in a bit.  I was just thinking, what could it be used on?

A motorcycle that was returned earlier.. !!!!

[kpinnc 12,066]

2 hours ago, oldlineman said:

Maybe they are more expensive $$$$$$

 

Onans and Vanguards use Mikuni carbs. And yes they are much more finicky than a Carter or Kohler or even most Walbro. 

 

They certainly don't run well when dirty or gummed at all. Otherwise they are awesome. The sediment bowl being part of the body is a design flaw in my opinion. The ability to drop the bowl and get rid of sludge is a huge plus. 

[RED-Z06 2,221]

27 minutes ago, kpinnc said:

 

Onans and Vanguards use Mikuni carbs. And yes they are much more finicky than a Carter or Kohler or even most Walbro. 

 

They certainly don't run well when dirty or gummed at all. Otherwise they are awesome. The sediment bowl being part of the body is a design flaw in my opinion. The ability to drop the bowl and get rid of sludge is a huge plus. 

Those (should) use Nikki carbs, I think early ohv Kawasakis used a mikuni, and an aluminum Mikuni pump.  Haven't seen a Mikuni on one factory 

[Skwerl58 704]

I bought a Mikuni for a Suzuki Quad Runner about 5 years ago and it was right at $400. I sold the old carb  on the auction site for $135 so they are a valuable item. Some have the numbers on them so check it and crossover and might get a good return!

[kpinnc 12,066]

4 hours ago, RED-Z06 said:

Those (should) use Nikki carbs,

 

Dangit. Got my names mixed up. 

 

It's the same reason I carry ID. It's so I don't forget my own name...

[RED-Z06 2,221]

9 minutes ago, kpinnc said:

 

Dangit. Got my names mixed up. 

 

It's the same reason I carry ID. It's so I don't forget my own name...

Wait til you get into the chinese carbs that briggs is using now that the fuel solenoid burns up (literally) at 2 years of use...finding parts for them is fun.

[kpinnc 12,066]

1 hour ago, RED-Z06 said:

Wait til you get into the chinese carbs that briggs is using now that the fuel solenoid burns up (literally) at 2 years of use...finding parts for them is fun.

 

I was thinking about that yesterday. I'm running an electric pump (1-2 psi) on my Vanguard 14. I do not have a fuel shut off of any kind after the pump. I've seen solenoids used with Vanguard carbs, but I haven't used one. Not sure if I'm flirting with danger or not...

Edited April 21, 2023 by kpinnc

[ri702bill 8,327]

From my experience with them, there are 3 reasons, by their own design, the Fuel Shutoff Solenoid can be a PITA....

 

The device works when the engine is off by applying spring pressure to "force" the carburetor inlet needle into the seat. At first startup in the spring after a winter's nap, even though the solenoid retracts, it can leave the needle stuck into the seat - no gas flow. The plunger is not attached to the needle and does not pull it OFF the seat ..... carb has to come apart.

 

The solenoid can have a short life because it has a 100% duty cycle - it is energized all the time the ignition is on. (If you run it for an hour - the starter solenoid only had a 1/2% or so duty cycle for comparison).

 

My favorite - you have an external device acting on an internal part swimming in gasoline - a potential fuel leak.... (wasn't that what it was supposed to STOP !!!)

Bill

 

 

 

Edited April 21, 2023 by ri702bill

[RED-Z06 2,221]

2 hours ago, ri702bill said:

From my experience with them, there are 3 reasons, by their own design, the Fuel Shutoff Solenoid can be a PITA....

 

The device works when the engine is off by applying spring pressure to "force" the carburetor inlet needle into the seat. At first startup in the spring after a winter's nap, even though the solenoid retracts, it can leave the needle stuck into the seat - no gas flow. The plunger is not attached to the needle and does not pull it OFF the seat ..... carb has to come apart.

 

The solenoid can have a short life because it has a 100% duty cycle - it is energized all the time the ignition is on. (If you run it for an hour - the starter solenoid only had a 1/2% or so duty cycle for comparison).

 

My favorite - you have an external device acting on an internal part swimming in gasoline - a potential fuel leak.... (wasn't that what it was supposed to STOP !!!)

Bill

 

 

 

Close, the fuel solenoid sits inline with the main jet, at key on the pin is pulled out of the jet and fuel passes into the fuel circuits, at shut down the pin closes off the main jet, the float and inlet needle still let fuel into the carb but the jet prevents fuel from entering the intake. Reason for this is as a running engine slows down it would otherwise keep pulling air/fuel into the engine and muffler.  The muffler would fill with superheated fuel but lack the oxygen to ignite it.  As the engine stops, air enters the muffler and the superheated fuel instantly combusts...and you get a backfire.

[ri702bill 8,327]

2 hours ago, RED-Z06 said:

Close, the fuel solenoid sits inline with the main jet, at key on the pin is pulled out of the jet and fuel passes into the fuel circuits, at shut down the pin closes off the main jet, the float and inlet needle still let fuel into the carb but the jet prevents fuel from entering the intake. Reason for this is as a running engine slows down it would otherwise keep pulling air/fuel into the engine and muffler.  The muffler would fill with superheated fuel but lack the oxygen to ignite it.  As the engine stops, air enters the muffler and the superheated fuel instantly combusts...and you get a backfire.

Two of the older Briggs OHV engines I had to pull the carb, a 12 HP and a 14, had a setup just as I explained - not the main jet. They go back to the mid 1990's.....