Starting problems are very common on carbureted engines. This page contains a list of common problems and solutions.
Several conditions must be met for a gasoline to run properly:
- Correct fuel mixture
Identifying the problem will save time and avoid unnecessary parts replacement.
The typical compression ratio is about 9.5:1, which results in a maximum compression of about 140 PSI at sea level. While a pressure gauge is the best way to determine if adequate compression is present, slowly turning the engine over will give an idea if there is a serious problem. With kick start models, leave the decompression lever disengaged and kick slowly. You should feel significant resistance, but the engine will turn over slowly with constant pressure due to acceptable leaks around the piston rings.
Lack of compression can be caused by a failure in the decompression mechanism or improperly adjusted valve clearance. More information on adjusting valve clearance is available here.
Test for ignition by removing the spark plug, grounding the threaded case, and turning the engine over. A spark should be visible, although it will not be fat and blue as mentioned in the Clymer service manual. Lack of spark is most commonly due to a failure in the harness or one or more switches:
- Key switch
- Engine stop switch
- Neutral switch
- Kick stand switch
Some owners choose to defeat the kick stand safety switch with a poor connection that can fail.
A poor connection between the ignition coil high voltage wire and the spark plug boot. To improve this connection, unscrew the spark plug boot and clean the connections with good electrical contact cleaner. A small amount (no more than 1/4") of wire can be cut from the end of the spark plug if needed. Be careful not to cut too much from the spark plug wire as it is integral with the ignition coil and cannot be replaced independently.
The stock spark plug boot contains a resistor which helps to reduce electromagnetic interference. The resistor can fail due to mechanical shock and vibration. The resistor can be replaced, but it's often easier to replace the entire spark plug boot. Refer to the service manual for ohmmeter checks.
Connections from the pickup coil and magneto coils to the CDI should also be checked. In some cases, the stator coils could fail and cause weak spark or no spark at all. Refer to the service manual for ohmmeter checks.
Here is a site that you can buy just the pickup coil for a 91 DR and save a bunch of money by not having to buy the whole stator. http://www.regulatorrectifier.com/catalog/Search-Results?keywords=dr350+pick+up+coil&osCsid=c54f1692cf66df59504660da790ed273 They also have CDI boxes for less than $200
The DR350 ignition timing is maintained by the CDI and cannot be adjusted. The CDI is generally reliable and usually not the source of ignition failure. The connections to the CDI might be a source of problems. Electrical contact cleaner can be used to remove dirt and oxides on the connector contacts.
Fuel mixture Edit
Correct fuel mixture is critical to easy starting and smooth idle. A common, but subtle failure of the stock, dual sport model vacuum petcock is a malfunctioning petcock diaphragm which can cause a continuous dripping of fuel even with the engine off, and an excessively rich mixture making the bike difficult, if not impossible to start. To check, pull off the main fuel line and the vacuum line at the petcock and check for dripping. If the leak is minor it may be necessary to wait a few minutes. With any petcock leak, and/or a carburetor float valve leak, gasoline can contiuously enter the carburetor mixing chamber via the petcock vacuum hose or carburetor float bowl, overflow into the cylinder and seep past the piston rings, filling the crankcase with gasoline. The dirt only models have a manually controlled petcock and generally create problems only when the rider forgets to manually place the valve in the OFF position. Another common manual petcock solution is to buy one for the Yamaha Raptor 660, model years 2001-2005, which is a direct bolt-on replacement. If a non-vacuum type petcock is used it is necessary to cap the orifice at the carburetor with a rubber vacuum cap, available at auto parts stores.
Over time, gasoline in the carburetor float bowl will evaporate and leave deposits that can clog jets and small passages. Follow the CV carburetor cleaning procedure carefully. After cleaning follow the CV carburetor tuning procedure.