The "exhaust devices" on 2-stroke sports cars are working correctly and authentic.

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March 1, 2026

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The "exhaust devices" on 2-stroke sports cars are working correctly and authentic.

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To compensate for the narrow low-speed torque, Yamaha developed what is commonly known as an "exhaust device" that changed the cross-sectional area of the exhaust port depending on the engine speed range. Yamaha's model 29L and RZ250R were known to have exhaust devices as standard equipment. This device valve was cleaned up for smooth operation.

Table of Contents

1 How long will it be available? ....... We'll stock up ahead of time when repair parts are concerned.
2 Cleaning the exhaust device while disassembling the engine waist. Is it working well?
3 High performance chemicals were used to thoroughly clean the carbon buildup.
4 Device body and cylinder cleaned for improved operation.

How long will it be available? ....... We'll stock up ahead of time when repair parts are concerned.

The overhaul timing on the engine waist up allowed us to have the genuine parts we wanted to replace, but in this day and age, there is no guarantee as to how long old car parts will be delivered or stocked by the manufacturer. It is better to stock them when the manufacturer has them in stock or when they are in circulation, and have them ready to use when the time comes.

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Cleaning the exhaust device while disassembling the engine waist. Is it working well?

While unloading the engine, we checked the condition of the cylinders and pistons. The cylinders are equipped with exhaust devices, so we should remove them and clean them internally.

The device cap was removed and the device valve body was removed with a wrench; it is divided into two parts per cylinder, left and right, and the connection is made with two Dowell pins that serve as locating points.

High performance chemicals were used to thoroughly clean the carbon buildup.

Yamalube brand high-performance chemicals from Wise Gear should be used aggressively regardless of bike make to get the best results. Mix and use at a ratio of 7 gasoline to 3 chemicals.

Mix the chemical with fresh gasoline, but shake the can well and stir before opening. The cleaning ingredients are separated and precipitated, and if you do not shake well, you will not get the maximum effect.

A brass brush was utilized to remove the dirt, but it is easier to dissolve the stuck dirt and wash it off if the dirt is soaked for a while before brushing it off. After cleaning it securely, rinse it off with parts cleaner.

Device body and cylinder cleaned for improved operation.

Once the two-part device valve is connected to the Dowell pin, we should check the joint for burrs or bumps. Burrs should be removed with fine-grit water-resistant paper.

Depending on the engine speed range and throttle opening, the servo motor activates and rotates the valve to achieve the optimum exhaust port area. The valve opening changes the engine characteristics.

The valve holder area on the cylinder side should be sprayed with Super Carburetor Cleaner foam type spray and polished to wash off any dirt. Chamfer the port edges as a final touch.

POINT

Point 1: Work on the parts above the waist of the engine that can be maintained while disassembling the engine as if it were "just for the sake of it.
Point 2: Do not forcefully polish off the dirt, but use chemicals as much as possible to dissolve and clean the dirt.
Point 3 - If you cannot remove stains by any means, use fine waterproof paper to polish them off. If you scrape too much, it will cause the dirt to accumulate.

While disassembling the engine waist, I tried disassembling and cleaning the exhaust device, which is not often cleaned. Since it is troublesome to disassemble the device valves of a parallel two-cylinder engine, I decided to clean them at the same time I was disassembling the upper back of the engine. When I used to own a Yamaha SDR, it was a single cylinder engine, so I removed the device valve from the engine in on-board condition and cleaned the valve and the cylinder side. I assumed that the exhaust device was running smoothly before cleaning. However, when we restored the parts after cleaning and cleanup of all parts and turned on the main key, we noticed that the movement of the servo motor to check the position, "queek, queek," was definitely lighter than before. I knew that dirt around the valve would affect its operability. When we removed the device valve, we found a large amount of unburned carbon that had turned to sludge, as well as a surprisingly dirty cylinder side, which was just as bad. It was because of such a situation that the device valve movement became lighter after cleaning, and this was reflected in the sound of the servo motor. As for the RZ250R this time, the device valve was in good condition with only a thin layer of dirt on it, since it was usually driven mainly on the circuit. Not limited to the Yamaha RZ-R series, owners of 2-stroke sport bikes with exhaust devices are advised to disassemble and clean them periodically.

◆YAMAHA LUBE SUPER CARBURETOR CLEANER◆

◆Yamalube Super Carburetor Cleaner foam type

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The "exhaust devices" on 2-stroke sports cars are working correctly and authentic.

2026.3.1

To compensate for the narrow low-speed torque, Yamaha developed what is commonly known as an "exhaust device" that changed the cross-sectional area of...

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WebikePlus Editorial

Webike+ (Webike Plus) provides daily updates on motorcycle news and information. We cover a wide range of topics, including new models, latest releases, classic bikes, discontinued models, and custom motorcycles. Additionally, we offer detailed information and in-depth reviews of motorcycle gear and custom parts, such as helmets and exhaust systems.