Boom Vader Carb Upgrade Kit Came in, for Grom Clone 125’s.

I finally received my Boom Vader Carburetor Upgrade Kit, with a Mikuni VM22 designed for 125cc motorcycles. One of the best upgrades I heard to be done to a Grom Clone motorcycle is to get rid of the stock carburetor.

Not only do you open up the engine’s potential, but the Grom Clone carburetors tend to fail badly. Not only limiting the motorcycle’s performance but also leaking gasoline all over the place(speaking of leaking: Why Is My Motorcycle Leaking Gas?).

FYI, a quick web search will result in several videos of gasoline pouring from the bottom of Grom Clone motorcycles. :/

If you are wondering what 125cc carburetor upgrade kit I got for my Boom Vader Gen 2 125cc (BD125-10) Motorcycle, here it is:

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Click for Current 125cc Carburetor Upgrade Kit Prices.

Check out the kit, and looking for feedback, I went in the right direction for this upgrade. I don’t want to limit the performance gains from upgrading the carburetor, but then I don’t want to toss a bunch of money at the solution. This is the Chonda-Way. 😀

What Is Wrong With The Boom Vader Stock Carb?

Address this real quick in two parts:

The first problem, the stock carburetor runs lean(see initially tuned to a higher altitude than I run at) and limits the motorcycle’s performance. When I was doing top-speed run tests (My Stock Boom Vader’s Top Speed Test and 17t Upgraded Front Sprocket Boom Vader Top Speed Test) for my Boom Vader, if I went over 95% open on the twist throttle, I felt no increase in speed, and in my head, I thought I was losing engine power.  

I blew off the power loss, figuring I was pushing the little Boom Vader too hard carrying my big body and accepted I was planning on doing several performance upgrades ( Boom Vader 125 (Grom Clone) Upgrades To-Do List ).

The second problem is the carb fuel bowl design(In my humble opinion). The stock carburetor’s fuel bowl is held on by two screws that are not designed to be adjustable by the end-user. There are no slots in the heads, and there are no flats for a wrench.  

Only having two screws, you are one screw from failure, and Boom Vader’s, like their Grom Clone brothers, are notorious for heavy vibrations. So I figure this is why the bottom gasket seal breaks, and gasoline pours out of the fuel bowl.  Why Is Gas Leaking From The Carburetor (Boom Vader Motorcycle)?

Nonetheless, I want not just a reliability increase but a performance increase in my motorcycle. This carb upgrade is highly recommended for the Boom Vader 125cc motorcycle. Being a Mikuni designer, it was a slam-dunk decision for me.

Wanted To Stay Stock, But Idea Of Upgrading Is Too Much Fun.

Yes, I planned to keep the new Boom Vader Gen 2 125cc motorcycle as stock as possible, minus the immediate oil change ( My Boom Vader Gen 2 Will Stay Stock, For Now, Except? ), till the engine was properly broken in. Now I figured the break-in period was about 1,000 miles(Really a guess due to Grom Clone quality issues), but as I rode the bike, it felt it needed some performance upgrades and parts failure was almost none( Boom Vader (Chinese Grom Clone) Review (First Ride) ).

My first performance upgrade was a larger front sprocket ( Boom Vader (Grom Clone) 17t Front Sprocket Upgrade Steps ). Now, this wasn’t a performance upgrade to the engine but one to the readability of the motorcycle.  

The Boom Vader’s gearing was very low, and limiting my RPMs during the break-in period gave me a minimal top speed out of the box ( Stock Boom Vader’s Top Speed Test ). 

Going to a larger front sprocket increased the range of the lower gears and allowed my motorcycle to increase its top speed ( 17t Upgraded Front Sprocket Boom Vader Top Speed Test ) for the same RPM limits I was riding it at. I was happy(er).

A larger front sprocket upgrade had one drawback, I was increasing the speed of the rear tire but losing torque delivery to the rear tired. I could go higher speeds for the same RPMs’, but now the bike wouldn’t get to those higher RPMs.  

I need more power from the engine.  

My New Quest for Performance Upgrades.

With the larger front sprocket upgrade for ride-ability, the excellent oil change ( My Boom Vader Gen 2 Will Stay Stock, For Now, Except? ), and eliminating the stock chain for safety and reliability ( Grom Clone Motorcycle Chain Replacement Instructions ), my goal is now performance upgrades.

The first recommended performance upgrade was the carburetor. However, just upgrading the carburetor changes a lot on the Boom Vader. The plan is to remove the airbox so that a new air filter would be needed, and all the lines going to the airbox must be eliminated or rerouted.

Several lines are going to the airbox, the crankcase vent, the fuel tank charcoal canister/vent, and the EGR setup has a vent going to the airbox. These need to be fixed and/or rerouted.

Another thing about the stock Boom Vader carb is that the fuel shut-off is built into the carburetor. A separate fuel shut-off means would have to be created; this was an easy fix.

I picked up these valves to be installed in the new carb’s fuel line:

We’ll see how well they work. I haven’t figured yet just to let the new fuel cutoff flow mid-fuel line or mount it somewhere on the engine. Being plastic, they might hand out in the airflow to keep them cool.

Just A 125cc Motorcycle Carburetor Upgrade Kit?

I know a Mikuni VM22 doesn’t sound like a significant upgrade, but it’s the best size/type for these 125 Grom Clone motorcycles. I wonder if this truly is the best carburetor for a 125cc bike.

I thought a larger jump in carburetor size would be a better direction to go, but there is only so much fuel and air this little engine can draw in.

So, for now, as long as my Boom Vader has the stock engine, the VM22 is a good size, I’m told.

The Mikuni VM22 carburetor size concern comes from when I finally decide to tackle the Boom Vader Big Bore Kit (BBK) upgrade. I have the Big Bore Kit upgrade on my list of to-do’s (mentally at least) for my Grom Clone.

The Boom Vader Big Bore Kit is a 141cc engine jug and piston kit made by one manufacturer that increases the engine displacement and should increase the engine power output significantly.

Since dealing with a stock 125cc engine with single-digit horsepower ratings, any power improvement will be significant.

The point is, is this new Mikuni VM22 carburetor a good upgrade for the 125cc and 141cc engines?

I don’t know; I believe the 141cc BBK engine intake is the same size/diameter as the 125cc stock engine, but I won’t know till I try. I will keep you updated on my latest Boom Vader upgrade. You know it. 😀

What Came With The Grom Clone: Boom Vader Carb Upgrade Kit.

I got several parts, and from what I was told, minus a fuel shut-off, it was a complete kit for doing my upgrade.

The Carburetor Upgrade Kit came with:

• New Mikuni VM22 Carburetor.
• New engine intake manifold.
• Gaskets
• Mounting bolts
• A New foam air pod filter.

This kit looks complete(Minus the fuel stop valve, also came with some cheap spark plug I will not use). I am figuring I will have to re-use some mounting bolts from the stock intake, but I am ready for this upgrade.

My Boom Vader 125cc Carburetor Upgrade Kit with the fuel stops I picked up myself:

Next Concerns/Challenges: Boom Vader VM22 Carb Tuning

My recent experience tuning carburetors is limited, mainly with my TaoTao TBR7 motorcycle. However, out turning a Mikuni carburetor compared to tuning TBR7’s Nibbi carburetor, the Mikuni was easier. Feel A Mikuni 125cc carburetor tuning process should be the same as my TBR7’s 229cc Mikuni carburetor tuning process.  

I have jets left over from the VM-26 carb installed on the TBR7 motorcycle( My TBR7’s Carburetor Upgrade! (Mikuni) ), and since I removed that carb( My TBR7 Nibbi Carburetor Installation Instructions (With Hawk 250 info) ), I am not robbing from that motorcycle for my new bike. We can all play nice now. 

But back to the point. The Mikuni Carb tuning experience I have has been good. I wish the fuel/air mixture screws were more accessible, but I can live with it.  

One thing I learned, from my TBR7 Mikuni carburetor tuning experience, change only one thing at a time. I first work on the low range, idle to 25% open, and focus on the pilot jet and idle setting(air/fuel mixture and idle speed control).  

Then I move on to the higher range(75%-100% throttle open) settings. Which is easier, just changing out the main jet till I get the best fuel burn for top speed.  

After this, I plan on tweaking the mid-range (25%-50% throttle open) is just moving the needle up and down to adjust rich and lean settings for again best fuel burning and performance outcomes.

Carburetor Upgrade Feedback From You?

Anyone that has done any Grom Clone carb upgrade on the stock 125cc engine, I am asking for feedback on your experiences. My questions:

• Was the VM22 your final carb upgrade, or did you move on to a Nibbi carb, and why?
• Are the Mikuni jets universals for all their carbs?
• If you moved from the stock engine to a larger 141 BBK(Grom Clone Big Bore Kit), did you keep the Mikuni VM22 carburetor, or did you change it, and should I factor that into the cost of the complete upgrade?

Thank you for stopping by, and remember: Ride Safe, Ride Fun!

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Boom Vader Gen 2 Upgrades