Mikuni conversion for Aero NH125

Aero 125, Elite 125, Elite 150, SH150i, Elite 250, Helix, Big Ruckus, Reflex, Silverwing and PCX 125 / 150, Forza
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Johnniespeed
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Mikuni conversion for Aero NH125

Post by Johnniespeed »

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After much reading about the Aero 125 restriction from the Keihin carb, I decided to upgrade to a Mikuni flatslide 24mm. My goals were simple, I wanted to be able to maintain 60 mph while cruising and able to hit 70 mph for short periods. The first challenge was to add a choke cable, so my end result was not some cobbled up , half finished project.
I used a Delorto cable, a Mikuni cable conversion kit and a heavily modified choke piston, that was shortened and reshaped to allow full travel.
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The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
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Johnniespeed
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

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The second challenge was to adapt the carb to the engine. The popular method was to stack a CT manifold intended for the DIO scooter on top of a nice adapter made by Bear. Once I saw the DIO manifold everyone used, I realized the crankcase volume was going to be enlarged greatly. Knowing that enlarging crankcase volume moves the power to a lower RPM from experimenting with reed block spacers , I quickly realized this was not going to provide the results I wanted. So I grabbed up a chunk of aluminum and hacked out a crude adapter. This reduced my crankcase volume and moved the reeds closer to where Honda intended them to be.
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
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Johnniespeed
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

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Then I read the negative reviews of the DIO adapter manifold reed block, it has been reported to crack and break by more than one person. If it breaks for others after some use, it will for sure break and lean out my engine, as I run these scooters pretty hard. So after a little reading I found the CT adapter manifold intended for the DIO scooter, uses a copy of the KX65 reed block. So I just purchased the V-force 3, reed block for a KX65 and fit it to the DIO manifold.
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
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Johnniespeed
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

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Thanks to Toddlamp who hunted down the vacuum fitting and curved hose, that made the install easier. I placed an o-ring on the carb groove before sliding the hose on, that made the hose fit tighter and less chance of leakage. Also thanks to others who told me to begin with the 155 main, according to how it drives, plug color and current very cold fall temps, the mix is extremely close.
The last challenge was the air box, I shortened it a little and was able to use a UNI two stage filter within my air box.
The results were a little disappointing, but it is also very cold here now. I will dial in the jetting and lean it down in the spring.
It starts much quicker since it has a manual choke, idles perfect, no hesitations, seems to run the same to about 4000 RPM, then the throttle response is quicker above that, the intake noise is louder since there were air box mods. The engine used to run out of power about 9000 RPM, now it pulls to 10,000 RPM.
I have always believed that adding an expansion chamber was going to be the trick that woke this scooter up, and I still believe it.
Overall the carb and reeds did add a little performance, but not a lot. My next project will be an expansion chamber.
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
Aero125
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Re: Mikuni conversion for Aero NH125

Post by Aero125 »

nice looking work !
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

An update on the Mikuni swap, I am currently using both the stock CDI and the 84 Aero 50 CDI with a switch. I just swapped out the 21 gram rollers for 15 gram sliders and the combination of the carb, reeds, CDI, and sliders really seem to compliment each other.
With those upgrades I can maintain 55 MPH even with my large windshield, 60 is always attainable if there is no grade or heavy wind. Speeds are GPS verified, as the NH125 Speedometer reads 5.5 MPH slower than actual at 55 mph.
Just so others will know, the windshield takes away about 2 MPH.
Does anyone here use a speedometer cable correction box ? I would like a 10% overdrive correction box so the speedo will be accurate.
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
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Johnniespeed
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

Bump
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
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Johnniespeed
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

Just a little progress report, I have removed the exhaust venturi restriction from the cylinder with some heavy porting ( polishing too) . I am in the process of upgrading to a 56 mm bore, I have an expansion chamber ( tuned pipe) in place and plan on fattening up the main. ( currently a 155 in the Mikuni) The pipe is a modded 125cc DIO pipe, not perfect in theory per exhausting research, but close.
I still plan on building a pipe closer to the "ideal" blueprint.
Why is 70mph so far away ? Currently still at 62 mph, but gets there much quicker. The Aero 125 is very stable and comfortable at 62.
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
Mileslord
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Re: Mikuni conversion for Aero NH125

Post by Mileslord »

Any pics of the "heavily modified choke piston"?
'84 Aero 125 in Grabber Green
'84 Aero 125 in Hugger Orange
'84 Aero 125 -current build
'02 Metropolitan
'06 Metropolitan
'02 Metropolitan GY6 swap - build in progress
'06 Stella 2T - daily ride
'08 Buddy 125
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Johnniespeed
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

No pics, but if you buy the Mikuni cable conversion kit and compare it to the choke piston that comes in the carb, you can see the conversion piston is too long, simply shorten it to match the original piston and reshape the top to fit on the cable. It really is quite simple if you look at the two pistons.
I have converted many carbs to cable choke, the process is similar on every carb I have done.
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
Mileslord
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Re: Mikuni conversion for Aero NH125

Post by Mileslord »

Johnniespeed wrote:No pics, but if you buy the Mikuni cable conversion kit and compare it to the choke piston that comes in the carb, you can see the conversion piston is too long, simply shorten it to match the original piston and reshape the top to fit on the cable. It really is quite simple if you look at the two pistons.
I have converted many carbs to cable choke, the process is similar on every carb I have done.
Thanks for the Info.
'84 Aero 125 in Grabber Green
'84 Aero 125 in Hugger Orange
'84 Aero 125 -current build
'02 Metropolitan
'06 Metropolitan
'02 Metropolitan GY6 swap - build in progress
'06 Stella 2T - daily ride
'08 Buddy 125
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Johnniespeed
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

Broke a piston ring today, caused much damage.
Once I calm down, I will probably not sell it, but for now, I want out.
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
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Johnniespeed
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

Okay, I have calmed down a little and reinspected everything, indeed the top ring broke first causing damage to most everything, the piston was lubricated well, with no hot spots and no seizing. It appears the Suzuki aftermarket piston ring simply broke first.
I plan to ride my Jet Ski's for a couple of weeks, ( still angry about the scooter letting me down ) then I will go through the engine, luckily I have an extra crank, several extra pistons and cylinders, and a spare head , along with a complete gasket set. I am returning to using only OEM Honda rings from now on. This catastrophic failure can be repaired without spending a dime, due to my hoard of parts. I am still ticked off and still plan on selling it.
My Jet Ski has three Mikuni carbs and is a lot faster than this scooter will ever be.
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
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drtch1
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Re: Mikuni conversion for Aero NH125

Post by drtch1 »

I am SUPER glad I didn't use that aftermarket piston. The piston looked ok, But the rings were too soft for me. Sorry about your problems. Been there.
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Re: Mikuni conversion for Aero NH125

Post by Johnniespeed »

No matter how many times I look at the damage, the piston is well oiled, there are no hot spots, the fuel mixture appears to be spot on. The top ring appears to have broken first, then jammed into the port. I should never have used that Suzuki piston and rings.
I have been having too much fun on the Jetski's to wrench on the Aero, but I will get it up and running soon. Luckily I have lots of parts stashed away.
The Mikuni works great and I am happy with the small performance increase.
I will only use Honda rings from now on, in this scooter.
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.
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