Introduction: How to Polish and Port a Carburetor and Intake
Video tutorial on how to port and polish a small engine butterfly style carburetor. In this tutorial I will also include how to port the intake manifold as well. Doing this procedure will help increase the performance of your engine along with increasing fuel economy, throttle response, optimization the air and fuel mixture, and allowing for increased air flow. This procedure can be applied to lawn tractors, golf carts, go-karts, all terrain vehicles, snowmobiles, dirt bikes, motorcycles, dune buggies, etc.
- 220 wet/dry sandpaper
- 400 wet/dry sandpaper
- 600 wet/dry sandpaper
- 1000 wet/dry sandpaper
- 1500 wet/dry sandpaper
- 2000 wet/dry sandpaper
- bucket of water
- rotary tool (Dremel)
- grinding stone for rotary tool
- 80 grit drum sander for rotary tool
- felt wheel for rotary tool
- penetrating or cutting oil
- metal polish
- soft cloth
- carburetor cleaner (used in the video is Permatex Throttle Body, Carb & Choke Cleaner #80279)
- thread locker (used in the video is Permatex Permatex Medium Strength Threadlocker Blue #24200)
Step 1: Remove, Disassemble, and Clean
The carburetor and intake manifold must be removed from the engine. Clean the carburetor and intake manifold before the porting and polishing process so we won’t have any contaminants. Keep the carburetor disassembled as we will be cleaning it again after it has been modified. Remove both the choke and throttle butterflies by removing the small standard screw for the butterfly plate, then pull the plate out, and slide out the shaft.
Step 2: Port Matching and Sanding
Starting with the choke side, normally this isn’t a critical side as we don’t have to worry about the idle being affected such as the throttle plate area. Start with 220 first, be sure to always pre soak the paper and wet the surface down. Rinse the area off when an access amount of sanding debris builds up and then continue wet sanding. Wet sand until the casting is fairly smooth. Move onto 400 grit and gain the same process, pre soak the paper, then keep the area well lubricated with water. Rinse away any excessive amount of sanding material build up. Once satisfied, move up to 600 grit, then 1000 grit, 1500 grit, and finally 2000 grit using the same process.
The next step doesn’t apply to all carburetors unfortunately as it will depend how your air filter side is designed. I am able to flare out the opening to allow for more air flow, by using a rotary tool and a rotary stone. Apply some penetrating or cutting oil to the aluminum surface and the stone, then flare out the opening, keeping it on a lower speed to reduce any debris splatter. Finish up flaring the opening with the rotary tool and drum sander to smooth out any rough edges. Wet sand the flared opening starting with 220 grit, then 400 grit, 600 grit, 1000 grit, 1500 grit, and 2000 grit sandpaper.
Moving onto the throttle plate side, do not bore out the opening, we only want to smoothen the open. First match the port opening to the intake manifold or engine block by using a gasket and paint market to trace the opening. If they are poorly matched, use the same process as what was used to flare the carburetor opening. Depending how rough the surface is, you can start with 1500 grit wet sanding, as for me I used 2000 grit wet sanding.
Step 3: Polishing Bore
Using a felt pad for the rotary tool, apply your choice of polish (I used Eagle One Original Mag & Aluminum Wheel Polish) and work the product into the surface -apply more product if needed, then wipe away product with a cloth once done
Step 4: Polishing Hardware
For the shafts and butterfly plates, wet sanding them using 2000 grit sandpaper. If the plate is steel, you can start out with 1500 grit wet sanding and finish up with 2000 grit. Polishing the shafts and butterfly plates using polishing compound.
Step 5: Porting the Intake Manifold
Match the ports on the intake manifold if not done already using the gasket method. Start with the grinding stone on the rotary tool, remove the rough casting. Ball hones can be used as well to access the hard to reach areas. Once satisfied, move onto the 80 grit drum on the rotary tool to smoothen the grinder casting.
Step 6: All Done!
Re-clean both the carburetor and intake manifold to remove any access polish or sanding debris and reassemble the carburetor. For the butterfly plate fasteners, I would recommend using a thread locker. The carburetor and intake manifold can then be installed back onto the engine.
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6 years ago
What is the purpose of polishing it?
Reply 6 years ago
Improves performance, increases efficiency, may smoothen rpm, increased fuel economy, and better combustion.
Reply 5 years ago
What type of engine is this for by the way, It looks like a small mower/go kart carb, were you doing this for practice or actually trying to increase power? I'm curious what kind of power gains could be seen in small sub-10hp engines :)
Reply 5 years ago
Toro snowblower actually, has an HS40 Tecumseh. Same engine that was used on Rupp minibikes apparently. I had a bit of spare time on my hands, just did it for giggles lol. I've done quite a few throttle bodies and intakes in the past. This engine was only 4hp, it was a great snowblower before but it's even better now. Now it holds high rpm better under load, will rev slightly higher, and it's certainly helped with torque. Overall, night and day difference. Despite the increased power, fuel consumption has slightly dropped too.
The smoother surface will prevent turbulence and increase air flow. But a polished surface in the intake runner can cause issues such as fuel pooling on the surface. Which is why a smoothed sanded surface is better. That will create a spiral, improving the air/fuel mixture and maximizing the combustion burn.
Reply 5 years ago
To my knowledge like the author stated, it improves efficiency by making the surface the air goes through smoother, creating less turbulence from micro-pits in the metal.