Custom Motorcycle Mods in California: Rules and Records

Custom motorcycle mods in California stay street legal when each part meets state rules and you can prove it. That means an exhaust with the right federal label, a California Air Resources Board (CARB) Executive Order number on emissions-related parts, and handlebars and lights that fit the Vehicle Code. Keep photos, receipts and a parts list, and you are ready for a traffic stop, a shop visit or a buyer.

Picture a rider in Ontario who spent a winter building out a bike: new pipes, a fuel tuner, taller bars and brighter lights. Each of those parts has its own rule. Here is how to check them and document them.

Exhaust: The Label Rule and the Noise Rules

The EPA label law

Vehicle Code 27202.1 says a person shall not park, use or operate a California-registered motorcycle "that does not bear the required applicable federal Environmental Protection Agency exhaust system label". It applies to motorcycles manufactured on or after January 1, 2013, and to motorcycles with aftermarket exhaust equipment manufactured on or after that date.

It is a mechanical violation. An officer cannot stop a motorcycle only on suspicion of it and must cite it as a secondary infraction. Fines run from $50 to $100 for a first conviction and $100 to $250 for a second or later one. You must show proof of correction, and the court may dismiss the penalty for a first violation once you do.

Mufflers and modifications

Under Vehicle Code 27150, every registered motor vehicle with an internal combustion engine must have an adequate muffler in constant operation, and no exhaust system may have a cutout, bypass or similar device.

Vehicle Code 27151 bars modifying an exhaust so it increases engine noise beyond those rules or the noise limits for that type of vehicle, and bars operating a vehicle modified that way. The 95 dBA test in that section applies to vehicles "other than motorcycles," so it does not clear a bike.

Before you buy pipes, look for the EPA label on the part. If your bike has a catalytic converter, or the pipe changes any emission control, also confirm it has a CARB Executive Order.

Emissions Parts: CARB Executive Order Numbers

California's anti-tampering law, Vehicle Code 27156, bars operating a vehicle required to have a pollution control device unless that device is installed and working. It also bars installing parts that alter or modify the original design or performance of a required emission control system.

CARB's aftermarket motorcycle parts page explains that "VC 27156 only applies to emission-related add-on and modified parts." Its examples include fuel injection systems, re-jetting of carburetors, aftermarket catalytic converters, performance camshafts and gear sprockets.

Parts that pass CARB's engineering review get an exemption called an Executive Order (EO). CARB says the label should show the manufacturer's name, the device name and a valid EO number, and it is either attached to the part or included with instructions to install it in a visible location.

Not every part needs an EO. CARB says direct replacements for stock parts, "like spark plugs, plug wires or air cleaner elements, do not need to be exempted". It also treats headers or mufflers for non-catalyst motorcycles as replacement parts when all emission controls originally connected to the exhaust manifold are reconnected and working.

To check a part, use the parts lookup on CARB's aftermarket parts page. CARB says parts "can be searched by type or by assigned E.O. number". Save a screenshot of the result.

Handlebars and Seats

Tall bars and custom seats are covered by Vehicle Code 27801. You may not drive a two-wheel motorcycle with handlebars positioned so your hands, on the grips, are "more than six inches above his or her shoulder height when sitting astride the seat". The same section bars a seat so high that you cannot reach the ground with your feet.

Measure your bar height while seated in your normal riding position, and keep a dated photo of it.

Lights: Headlamps and Colors

Vehicle Code 25650.5 requires every motorcycle manufactured and first registered on and after January 1, 1978, to have one or two headlamps that turn on automatically when the engine starts and stay lit while it runs. Keep that working if you rewire the front end.

Under Vehicle Code 25950, light visible from the front must be white or yellow, and light visible from the rear must be red, with limited exceptions such as amber turn signals and white backup lamps. Check accent lighting against these rules.

How to Build Your Mod File

Set up one folder, paper or digital, and add to it every time the bike changes:

• Before and after photos of each mod, with close-ups of any EPA or CARB label.
• Receipts for parts and labor, with dates, shop name and part numbers.
• A running parts list with brand, model, EO number if any, and install date.
• Original parts: which stock parts you kept and where they are stored.
• Lookup screenshots from CARB's database.

Keep a cloud copy too. Once the build is done, see our guide to fall motorcycle rides near the Inland Empire.

Keeping Records for Resale

A buyer looking at a custom bike wants to know what is on it and whether it is street legal. Your mod file answers both, so hand over copies of the parts list, receipts and label photos.

According to the California DMV, the seller signs the California Certificate of Title, and "Sellers must also submit a Notice of Transfer and Release of Liability (NRL) within 5 days." Keep a copy of what you submit.

Riding off road too? Our guide to desert riding season and OHV rules covers Green and Red Sticker registration.

Frequently Asked Questions

Is an aftermarket exhaust legal on a motorcycle in California?

It can be. For motorcycles or aftermarket exhausts manufactured on or after January 1, 2013, Vehicle Code 27202.1 requires the federal EPA exhaust system label. Vehicle Code 27150 bans cutouts and bypasses, and Vehicle Code 27151 bars modifying the exhaust to increase noise beyond legal limits.

How do I check whether a part has a CARB Executive Order?

Look for a label with the manufacturer's name, device name and EO number, then search CARB's aftermarket parts lookup by part type or EO number.

How high can motorcycle handlebars be in California?

Vehicle Code 27801 bars driving a two-wheel motorcycle with handlebars that put your hands, on the grips, more than six inches above your shoulder height when you are sitting astride the seat.

What is the fine for a missing EPA exhaust label?

Under Vehicle Code 27202.1, a first conviction carries a fine of $50 to $100, and a second or later conviction carries $100 to $250. The court may dismiss a first penalty once you show proof of correction.

Protecting the Bike You Built

A detailed mod file does more than keep you street legal. If your bike is ever stolen or damaged, those photos and receipts show what was on it and what you paid. Ask how your policy handles custom parts and equipment, because coverage depends on your policy and what you have listed. At Farmers Insurance - Young Douglas, our agents can review how your motorcycle policy treats aftermarket parts, and our advice library has more riding guides. Get a free quote and coverage review with our team.

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Written by LaMonte Douglas, owner of Young Douglas Insurance, a Farmers Insurance agency serving California from Ontario. CA License #4091974.

Sources (all accessed September 23, 2026): Vehicle Code 27202.1; Vehicle Code 27150; Vehicle Code 27151; Vehicle Code 27156; CARB, Aftermarket Motorcycle Parts; CARB, Aftermarket, Performance, and Add-On Parts; Vehicle Code 27801; Vehicle Code 25650.5; Vehicle Code 25950; California DMV, Title Transfers and Changes.

Last updated: September 23, 2026.