Question about 1980 Honda CX 500 A

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JUST REPLACED THE BATTERY AND SPARK PLUG WIRES. ONE CYLINDER DEAD AT LOW RPMS BUT OK AT HIGH. DETECT SMALL BACKFIRE AT LOW AND MID RPM LEVEL. POSSIBLE CAUSE? THIS IS A HONDA CX500, 1980.

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Check valve clearances. Also, try a new spark plug in the weak cylinder. Check points setting and condition.

Posted on Jul 04, 2009

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If a full a rpm cost backfire


If what you are saying is that when you reach maximum rpm the car backfires, first be aware that most ignition modules have two sections--one for low rpm and one for high rpm. Could be bad ignition module. Also possible that some tune up item (plug wires, dist. cap) is bad, or that the engine is running too lean at high rpms (bad fuel pump, dirty filter, etc.)

Aug 11, 2015 | Cars & Trucks

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Backfires after running and stops, must shut off to stop the backfireing. I have replaced the fuel filter, and checked the gas cap vent,what else could cause the backfire?


For a more specific answer, you should post the applicable elements of Make/Model/Year/Engine Model/Transmission Model/Deck Size, and hours on meter if you have one. A short description of the events preceding the beginning of the problem is also helpful.

Several possibilities for small engine backfire:
  1. Needs new plugs. Start with new plugs.
  2. Shear pin under flywheel is slightly damaged throwing off the timing. Remove flywheel examine shear pin for any damage. Just go ahead and replace it; if it even looks nicked or sliced.
  3. Coil, or spark plug wire, is going bad. Inside the Coil are two windings of wire and no moving parts. With shorted (melted together inside) windings you can still get a spark, but it will be weak. With open (burnt/broken) windings, you get no spark at all. There are also electronic components like diodes which may be failing. Coils are subjected to heat and vibration and do fail on occasion. Another coil consideration is the spark plug wire. Back in the day, we would replace all our spark plug wires when we gave our car a tune up; because spark plug wires do fail. The only way to replace the spark plug wire on a mower is to replace the Ignition Coil.

    Note: Coils may not fail completely at first. They can be complicit in the situation where a mower starts and runs for a while.They may cause backfire. As it heats up the coil parts expand and cause the engine to shut down. It does not re-start until the machine has cooled enough to allow the coil to cool. This can be 30 minute to several hours; perhaps it starts again the next day only to repeat the failure.

    Short of a well running engine, with no special equipment, the only field-test for a coil and the spark plug wire output is to visually assess the color of the spark at the end of the spark plug. Alternatively, you may use a spark tester. A spark tester gauges the strength of spark by making it jump a bigger gap. This test calls for a gap in the range of 4.2 mm (0.166 in). It's important to note that setting a test gap beyond 5.0 mm (0.200) could damage the ignition components. Briggs and Stratton manuals, for the newer engines, specifically state that you should not test for spark with the spark plug out. I do not know why this is. They specify you should use a spark tester.

    B&S notwithstanding (at your own risk), with a new plug attached to the plug wire hold the threaded part against a ground point or wrap some bare copper wire around the threads and fasten the wire to the engine frame or other good ground. Make your shop or garage dark so you can see the spark easily, then crank the engine. The flywheel must spin rapidly (at least 350 RPM). The strength of the spark is revealed in the color. A red or yellow spark is weak and probably will not spark in the cylinder. A blue or white spark is strong and has enough voltage to fight across the spark plug gap even under pressure within the cylinder.
    Note: a good strong spark also makes a strong snapping noise as it fires.
  4. Needs a valve adjustment or a valve job. This is high on the list of the most common reasons for backfire. Start with adjustment.
  5. The other thing that causes backfire is fuel mixture too lean. On a small engine this is not usually an adjustment problem. It may be the fuel system/carburetor is dirty or partially clogged. It may also be an air leak in the gaskets of the intake manifold. It might be low fuel pressure from a bad pump or clogged fuel lines.The electronic fuel shut off valve may be malfunctioning. If nothing else solves the backfire, check fuel flow through the pump and lines, remove the carburetor and clean or rebuild it. This is the least likely of the options so save it for last.
Here is a link to a great essay on magnetos and spark plugs.
Village Science Magneto Spark Plugs

For Twin Cylinder Engines
A power balance, or cylinder balance, test should be run on a twin cylinder engine. If compression is good and cylinder leakage is minimal (in other words if the engine is not worn out, doesn't have too many hours), but a cylinder is misfiring or shows up weak in a power balance test, it indicates a fuel delivery or ignition problem (fouled spark plug or bad plug wire).

If an engine is hard starting, runs rough, misses or lacks power, a cylinder balance test will determine if both cylinders are operating to their full potential. You will need an engine tachometer, a spark tester, and an insulated screwdriver.
  1. Using the spark tester, with the plugs in, start engine and verify spark is equally good on both cylinders.
  2. Remove spark tester.
  3. Connect engine tachometer
  4. Run engine at top no load speed. Note rpm.
  5. Ground one cylinder spark plug with screwdriver. Note rpm.
  6. Ground other cylinder with screwdriver. Note rpm.
The difference in RPM between the cylinders should be less than 75 rpm. If the difference between the two cylinders is greater than 75 rpm, the cylinder with the least rpm loss is the weakest and is a potential problem.

Mar 26, 2015 | Garden

1 Answer

Bogs down in low rpm when in park, nuetral, and first gear. It does not bog in when idling, in higher rpm or any gear over first, but there is still a little bit of knocking. It seems to act like a...


REPLACE SPARK WIRES THAT COULD BE MISFIRE PROBLEM, ANY TIME OLD SPARK PLUG WIRES IS REMOVED THE WIRES WILL BREAK INSIDE PLUG BOOT CAUSING SPARK PLUG NOT TO FIRE.REPLACE SPARK PLUG WIRES.CLEAN FUEL INJECTORS, CHANGE AIR FILTER,CHECK ALL VACUUM HOSES ON THE INTAKE MANIFOLD LOOKING FOR INTAKE VACUUM LEAKS.

Jul 12, 2011 | Subaru Legacy Cars & Trucks

2 Answers

It runs rough sometimes it dies, I have tuned it up , plugs dist cap, wires rotor the computer , It has very poor gas milage .it has a 2300 with automatic trans,


have the intake gasket checked. spray carb/choke cleaner around intake gasket and if rpms change then you have a bad gasket which causes rough idle bad fuel econ

Apr 09, 2011 | Ford Ranger Cars & Trucks

1 Answer

2004 softail runs ok low rpms mid rpm runs like **** high rpms runs ok I checked the insude fuel lines found a pin hole in the down ward line going to the bottom of the tank and replaced it i thought that...


Hi W_orth, and the usual suspects are:
1. Spark plugs in bad condition or partially fouled.
2. Spark plug cables in bad condition or leaking.
3. Spark plug gap to close or to wide.
4. Faulty ignition coil, module and or sensor.
5. Battery nearly discharged.
6. Damaged wire or loose connections at battery terminals especially the ground cable at BOTH ends, ignition coil, or plug between ignition sensor and module.
7. Intermittent short circuit due to damaged wire insulation.
8. Water or dirt in fuel system, carburetor or filter.
9. Fuel tank vent system plugged or carburetor vent line closed off.
10. Carburetor controls misadjusted.
11. Damaged carburetor or intake seals.
12. Loose or dirty ignition module connector at crankcase.
13. Faulty MAP, CKP, and or CMP sensors.
14. Incorrect valve timing.
15. Weak or broken valve springs.
16. Damage intake or exhaust valve.
For a prime suspect please visit website below and good luck:
Harley Diagnostic Codes 04 to Present

Dec 19, 2010 | 2004 Harley Davidson FLSTC - FLSTCI...

2 Answers

Missing? and fuel problem


You probably have one plug not firing. First, check all your plug wires to make sure the boot is pushed on all the way. If there is no improvement, you can pull one plug wire off at a time (with the engine running). If the engine doesn't die, or change when you pull a plug wire off, that will be your bad plug. It should change drastically when you pull a wire. Be sure to use a spark plug wire puller, or a heavy rubber glove. Check for spark in all your wires with a timing light.
If there aren't any dead plugs or wires, the next thing to check is the timing. Aim a timing light at the timing mark on the crank. If the mark jumps around a lot, the timing belt or chain has jumped, and will need to be replaced.
If that checks out okay, the next thing to do is a compression test. You may have bad valve.

Dec 16, 2009 | 1989 Toyota Corolla 2 Door

1 Answer

Car dies


Your 94 should be a 350 engine,is it?
That would be a timing chain,which means the distributor cap was removed to locate cylinder 1,
Your high rpm in neutral,and low rpm in gear sounds like a vacume leak,The turn signal problem I'm not sure because you didn't say if the battery is going dead or if it starts right back up.

Dec 15, 2009 | 1994 GMC Suburban

2 Answers

Backfires in manifold on motor on acceleration. runs ok low speeds


Spark plug wires. If you take it in a garage or wait till it's dark, and have somebody brake torque it while you watch, you'll see spark jumping. But don't get run over! Do it in reverse. Or just change the wires.

Jun 01, 2009 | 1997 Dodge Caravan

1 Answer

98Eclipse 2.0 nonTurbo 5speed 180,000 miles ,code PO301


The po301 is a misfire code. The backfire can be caused by a excessive amount of fuel, bad valve timing etc.
My guess is you have damage to an exhaust valve that may have occurred when you had the timing belt problem.A compression test will indicate if you have a leaking exhaust valve.The reason for the backfire is the exhaust valve is still partially open when the spark plug fires.

Jan 03, 2009 | 1998 Mitsubishi Eclipse

1 Answer

Honda Misses.


Pin point the dead hole and check that injector.

Dec 23, 2008 | 1995 Honda Accord

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