Questionhi, i own a 1986 honda vt250f and i'm having some trouble. it has been hard to start and for the last couple of days it hasn't started at all. it was low on oil but i have topped that up with no effect. it has also been draining the battery while i'm riding it (when it was going). my dad said that it might be flooding but niether of us know that much about bikes to go much further. it turns over when i press the start button but it doesn't fire up. if u could give me any ideas of the problem or where to start and what to do that would be great. also would u know where i could get an owners manual and repair manual for it. thanks heaps.
Matt
AnswerHi Matt,
I suspect the charging system is failing. If the altenernator output is not within service limits, you'll experience the symptoms as described.
I would have returned tech files to help you test the electrical system, but there was no email with question as requested.
The best advice I can give you is to obtain a copy of the service manual and follow testing procedures. Find manuals at "www.bikebandit.com" and at Ebay.
Visit the following website and follow their Troubleshooting Chart: "www.electrexusa.com"
Respectfully,
Mark Shively
(sample tech file)
Electrical Testing
(Basic electrical troubleshooting tools)
Few things can be as frustrating as trying to troubleshoot an electrical problem on a modern street or dual sport bike, with their plethora of unidentifiable electrical components, hard-to-remove electrical connectors, sealed wiring harnesses, etc. Much of the trouble associated with fixing electrical problems can be attributed to a lack of proper tools and technique.
Your best friend when troubleshooting bike electrical systems is an electrical multimeter, sometimes referred to as a VOM (Volt-Ohm Meter) or just plain old multimeter. A multimeter reads current (amps), potential (volts), and resistance (ohms), each over a variety of ranges that the electrical troubleshooter must choose. Cheaper model multimeters can be had at Radio Shack for less than $20--more expensive digital models can cost hundreds of dollars. Nonetheless, no garage should be without one.
If you're buying your first multimeter, a cheaper model is recommended for two reasons. First, the measurements you'll need to make when working on your dirt bike are mostly crude kind of checks which require little real accuracy. Secondly, as a electrical neophyte, the possibility always exists to smoke the meter through a wrong connection or test procedure. While superior meters are better protected by fuses, circuit breakers and the like, the ramifications of frying a $20 multimeter are not all that serious. Bottom line: buy the cheapest meter you can find that offers some sort of fuse protection. And buy extra fuses too! An up-to-date electrical schematic of your project is also nice to have, especially when trying to identify various mystery components. However, it is not essential, and in a pinch can often be overcome by a little patience and common sense.
There are essentially three troubleshooting techniques, facilitated by the use of your trusty multimeter. They are: measuring continuity, measuring potential and measuring current. Continuity means that there is a electrical connection between two points, whether they be via a dedicated wire or through the engine or frame. Measuring continuity is especially useful for locating grounds, intended or unintended, checking switch operation, mapping out wiring harnesses (when a schematic is unavailable), checking fuses or connectors for good electrical contact, and so on. Continuity is checked by using the meter to measure resistance, selecting the R X1 scale and connecting the two leads of the multimeter, in parallel, between the two points for which continuity is in question. The R X1 range is used to limit meter pegging (which could potentially damage the meter), and is certainly sufficiently accurate for this simple test.
The meter essentially sends a low voltage signal between the two points (generated by the meter battery) and indicates whether the circuit is completed or open. Open circuits (no continuity) are read as infinite resistance (no meter needle movement), whereas a completed or closed circuit reads as zero (or near zero) resistance (full sweep of the needle). Caution must be taken when using your multimeter in the resistance mode not to run an outside current through the ohmmeter (i.e. checking for continuity between a hot battery terminal and ground), as this will either blow a protective fuse (on meters so equipped) or fry the meter outright. A good precaution is to disconnect the positive battery lead and allow sufficient time for any system capacitors to discharge (on machines so equipped).
Switch your meter to the voltage measuring mode when you need to find hot leads for connecting accessories, check the health of your battery or lighting coil output, and determine if power is reaching a malfunctioning component. A zero voltage check across two points will also tell you it's safe to do a continuity check without fear of meter damage. Voltage measurements are taken with the meter linked in parallel with the suspected potential. Most multimeters have ranges from a couple of volts to a couple of hundred volts, measuring both AC and DC. Surprisingly, you may need both capabilities as the output (lighting) coils of most bikes produce AC. While nearly all street and dual sport bikes rectify this AC voltage to DC (because it's easier on electrical accessories), enduro or trail bikes often run the AC right to the headlight and tail light.
If you're checking an ignition coil output or an unrectified lighting coil output, start by using the AC scale closest to, but not less than 12 volts. For rectified lighting/accessory voltage checks, again choose the scale closest to, but not less than 12 volts, from the DC choices. If the meter reads DC voltage backwards, simply reverse the polarity of the meter leads. With analog meters, it can sometimes be a little tricky determining what the actual voltage reading is, as there are usually several scales printed on the front of the meter. The trick is to look for the higher number of the range you've selected (i.e., look for a 50 if you've chosen the 0-50 VAC range) at the extreme right of the meter and that's the scale that should be used.
Current flow is measured using the ammeter function of your meter. The presence of current flow indicates that your lighting coil or battery is actually accomplishing some work. This is good if a head lamp, turn signal or the like is in operation, but bad if everything is turned off (dead battery syndrome). The ammeter function of your multimeter is useful for locating shorts or determining the draw of a particular accessory. Current measuring requires a slightly different technique, as the meter has to be in line (in series) with the circuit. Most multimeters are capable of measuring a couple of amps draw, way on down to milli- (1/1,000) and even micro- (1/1,000,000) amperes. When using the current measuring function, choose a high current range and work your way down to lower ranges. This prevents the dreaded meter pegging and associated damage.
Troubleshooting techniques are dependent upon the notion that current flow should be zero with the ignition and all accessories turned off. If you're still reading current at this stage, then you've probably got a problem with a shorted or failed accessory. Start disconnecting things until the current draw goes away, and that'll isolate your problem. Beware, however, of charged capacitors discharging and reading as current flow.
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Charging System
The charging system consists of the alternator (rotor/stator), rectifier, voltage regulator and the battery. Problems with the charging system of these older bikes is rare in bikes of 350cc and less, moderate in bikes from 500-650cc and very common in bikes of 750cc and over. It will require a manual to do a good job in this area and if you don't have one anyway, get one(Clymer is good). Here is a breakdown of what the parts do:
• alternator: produces an alternating current by passing a moving magnetic field (rotor) through a nonmoving or static (stator) winding of wire. Gasoline is thus converted from a chemical energy to a mechanical energy (within the engine) to an electric energy (within the alternator). This energy is then sent to the rectifier.
• rectifier: converts alternating current (AC) to direct current (DC). Early rectifiers simply took half of the energy (single wave), and sent it to the battery. Since alternating current travels in both directions, the early rectifiers simply grabbed the energy going in one direction and set it on. Later rectifiers use a diode group to grab both directions (full wave) of current and combine them into one direction and sent this on. Later rectifiers were much more efficient but more prone to failure.
• voltage regulator: governs the amount of current coming from the alternator and limits it to about 14-15 volt. This is usually combined with the rectifier to make one piece of hardware. If too much current is generated, the regulator sends it to the ground or frame.
• battery: stores energy and is the main place to dispense energy as needed, to plugs and lights.
A sign of a bad charging system is when the headlight blinks or strobes at idle or when there is a marked increase in headlight intensity when you gun the motor. All bikes show some increase in headlight intensity with higher RPMs but if it goes from dim to bright, it is probably the charging system.
I will tell you in advance that finding why your battery does not charge is a hard thing to do! This is the procedure I follow to try and solve this problem.
1. Make sure the battery is good! Use a volt/ohm meter to see if it is providing near 12 volts. If it reads 10 volts or less, replace it. If it can hardly crank over the engine, replace it. Motorcycle batteries are not real good providers. They can go bad even if you take real good care of them. The small thin lead plates within are not as vigorous as a car battery ones and can be damaged easily.
2. Using your manual, read on how to connect your volt/ohm meter up to your bikes alternator. First check if there is an electrical leak in the wiring of your stator. The insulation of the miles of coiled copper wire can deteriorate and cause the wire to short and thus not provide the extended length of wire needed to pick up the energy from the magnetic field. If a short is detected, it must be replaced ($ ouch).
3. Start the bike and using your volt/ohm meter test the output of the alternator. It must be within the specs of your manual. In the 750cc, the alternator portion of the engine is low and sticks out, just waiting to be smacked when the bike goes down. If your bike has been dumped or impact has occurred to this portion of the engine, you may lose your charging power. The rotor is a magnet and can lose power with an impact.
4. Using your manual, read on how to connect your volt/ohm meter to the rectifier. With the bike running, check its voltage output. It should be within specs (14-15 volts). Now here is a problem, the rectifier converts AC into DC and this conversion requires that some of the electrical energy be converted into heat energy. You can locate the rectifier because it has heat dissipating fins located near it. Unfortunately this heat can cause a failure in the unit which can not be detected except under load (blasting down the road) conditions. So..... the rectifier may read good at idle or high RPMs in the garage but it fails on the road! Many shops will swap rectifiers if they are suspect and test ride to see the result. For us home mechanics this is not possible!
5. I have found that the voltage regulator is rarely at fault. But you can still test it by following the method outlined in the manual. The test consists of using two batteries in series and a variable resistor. In effect you try to put over 14 volts across it and see if it stops this too high voltage.
In my experiences with bad charging systems it is the rectifier. The exception is the 750 cc engines where the rotor can easily be bad.
