Keeping Your Two-Stroke Alive

Are two-stroke engines really easier to work on than four-strokes? Every two-stroke lover will tell you his bike is easier to maintain because it is simple and has fewer moving parts. Yet two-stroke engines have some unique mechanised problems and can be difficult to diagnose and work on unless you know what to consider. Here are some basics to keep your two-stroke—and the argument—alive.

Compression Test

A simple way to determine the mechanical condition of your motor is to do a compression test. Possess Freight (part No . 95187, $29. 99) and Motion Pro (part No . 08-188, $119. 99) sell compression testers with various size spark plug fittings. The specialist works by installing a hose and adaptor into your spark plug hole then throwing the bike over five in order to 10 times with the throttle open and reading the gauge when it reaches maximum pressure. A fresh 250cc engine will usually test between 175 and 200-plus psi. Minis and 125ccs usually test from a hundred and fifty to 200 psi. To get a baseline reading, test a new bike or even after a fresh top end. If the compression is 20 percent lower than the particular baseline, replace the piston and rings.

Worn-Out Piston/Rings

When the piston and rings become worn, the particular bike will lose power, produce more smoke, and the jetting will appear to be rich. If you don’t have an hourmeter on your own bike, install one. Average cyclists should replace their piston plus rings every 20 hours on an 85/125 and every 40 hours on a 250. You can replace just the bands between these intervals if you look into the piston ring groove for distance and wear. If there is any visible wear on the piston, replace this. Measure the cylinder using a dial bore gauge to determine cylinder wear and replacement piston size. Pistons are available in different sizes to account for canister wear. Using the specs listed in your owner’s manual, replace or replate the cylinder (Millennium Technology is an excellent resource for this, mt-llc. com) if this has excessive wear. Improper piston clearance can result in catastrophic failure just like a cold seizure from too limited of a piston-to-cylinder clearance or a damaged piston skirt from rocking when the clearance is too large.

Main Seal Leaks

A main seal leak on the magneto (left) side of the bike will draw air into the crankcase and make the bike run lean. Generally a visual inspection will discover essential oil residue around the seal. Check the turn bearings for play (any motion is a sign of a problem) to determine the cause of the leak. A main close off leak on the transmission (right) part will cause oil to leak into the crankcase. Usually the bike may smoke excessively, appear to run rich, foul spark plugs, and the tranny oil will often smell foul. An easy test, if you use common sense, is to empty the oil and test the bike. The bike will usually operate clean within seconds without transmitting oil in it. Again, check for enjoy in the crank bearings to determine the reason for the leak. A crankcase stress test can be performed by a good repair shop as a more precise method to find a leaking main seal.

Other Leaks

Coolant and air leaks can develop at the head and base gaskets or at the airboot and manifold. Leaks can be recognized by spraying contact cleaner or even spray deodorant at the suspect region while the motor is running. The head gasket leak will cause coolant to leak into the top end. It will usually cause the motor in order to misfire at high rpm or even when it is hot and can produce white-colored smoke out the exhaust along with the sweet smell of coolant. The particular jetting and spark plug will be rich. Head gasket leaks are specifically common on motors that use O-rings for gaskets. The cylinder head should be checked to ensure it is flat plus lapped or milled if it is out of spec. Base gasket and intake air leaks cause the electric motor to run lean and can make it speed up erratically or hold rpm after the throttle is shut off.

Reeds

Reeds should be checked every 10 hours for chips and cracks. Because they reduce tension over time, they should be replaced at least one time a year. A bike with worn or broken reeds will be difficult to start. Jetting will appear rich, and tuning the carburetor will be next to impossible, especially at low rpm.

Exhaust Valves

Carbon can clog a good exhaust valve and cause the particular engine to run poorly. Periodically, remove the valve cover and inspect the way the linkage moves when the bike is revved. Exhaust valves should be disassembled and cleaned whenever a top end is performed. Mild cleaning can be done with solvent, and oven cleaner can be used upon stubborn carbon deposits. Check your owner’s manual to see if your exhaust control device requires adjustment, and check the setting periodically.

Silencer

A carbon-clogged or blown-out silencer may restrict the engine and cause it to run rich. Check that the silencer core hasn’t become broken or even dislodged.

Electrical

Electric problems can range from no spark to misfiring at high rpm when the engine is hot. Stator, coil, and CDI box difficulties are diagnosed with a multimeter utilizing the tests in your owner’s manual.

Fuel

Always use high-quality fuel that is fresh and of the correct octane rating for your motor. Detonation is a common problem when the energy burns too fast in the cylinder and causes knocking. Mixing pump gasoline with higher-octane race fuel, like VP’s T4 or VPR, will help prevent detonation.

What can you do to avoid these problems? Start out with some good basic maintenance.

Air Filter

Keep the air filter clean and thoroughly and evenly coated with air filter oil. Throw out the filter and obtain a new one when it starts to shed its elasticity or has any small tears.

Oil

Don’t be afraid to use oil. If you are a fast, aggressive rider on a high-revving or modified engine, you should be operating your premix 24: 1 . Average riders can use 32: 1, whilst those who don’t twist the accelerator very far can run anywhere from 40: 1 to 60: one An oily tailpipe isn’t usually the sign of too much essential oil. More oil will prevent underside end failures and give longer lifetime to high-revving engines. Dyno screening shows that a properly jetted bike makes the most power when it is run on 24: 1 .

Jetting

Jetting a two-stroke is not the set-it-and-forget-it adjustment. To get the most out of your bike, learn the basics of jetting (see Dr . Grime , Dec. 2013). If your bike accelerates poorly, smokes, fouls plugs, or has a deep exhaust notice, your jetting could be too rich. If your bike surges, runs hot, or has a pinging exhaust take note, your jetting could be lean. Incorrect jetting can cause premature engine use. Before you try and jet your bike, make sure the carburetor is clean and the motor is in good condition.

Spark Plug

Check your spark plug periodically to look for the running condition of your engine. Use the stock heat range plug like a starting point if you are having problems with fouling. Colder plugs have high figures (B10EG) and are used on hot-running, high-rpm engines, and hot plugs have got lower numbers (B6EG) and are utilized on colder, low-rpm engines. Often , novice riders can switch to a plug one range hotter to prevent fouling. Do not replace your plug beyond the boundary outside the recommended heat range.

Finally, stop riding your bike if you suspect it has a problem or if the bike has ever stopped running or momentarily seized. Diagnose the problem and fix it before it becomes a bigger issue.