Question about 1981 Honda CX 500 B

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Honda cx500 only fires on 1 cylinder

Won,t run on left cylinder ,good spark but lack of fuel,have stripped carbs but i,m new to this ,not sure which screw does what any help welcome,i don,t have a manual so i,m working blind but i will get 1 cheers gary

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Pull the bowl from the left carb and remove and clean the float needle and jet. It sounds to me that this passage is plugged. You might as well clean the whole set since you have it off.
It is a common problem for those carbs on the older bikes for the jets to plug up from old gas, or material such as rust in the tank. Check your fuel filter if you have one. If not I would suggest you install one when you are done.

Posted on Mar 11, 2009


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Posted on Jan 02, 2017


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Cx500 deluxe I have 152psi of compression in both cylinders I went through the carbs, I even replaced the fuel pet **** diaphragm the bike runs great until about 55 mph

Hi, Daniel and the usual suspects are:
1. Severely discharged or a damaged battery, should have 12.5 volts or better and be able to pass a load test if necessary.
2. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
3. Faulty main circuit breaker and or connections.
4. Faulty ignition coil and or connections.
a. Faulty high-speed coil and or stator
5. Faulty spark plug, oil or gas fouled, wrong heat range or service type, wrong gap, loose in the cylinder head, broken electrode or insulator.
6. Faulty spark plug cables, leaking or broken, internal damage.
7. Faulty ignition module, switch, CKP, MAP, CMP, sensor and or any connector in the ignition circuit could have corroded, loose, or broken pins/sockets
8. Burnt exhaust valve or air leak in the exhaust system.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
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2 Answers

1980 CX 500. Why doesn't left cylinder fire until high rpm?

could be a spark plug failing under the higher compression of the increased rpms
start by changing the plug and or HT lead or coil if independent of the other cylinder

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1 Answer

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Just a hunch. Clearly there is a fuel issue on one of the cylinders. Although you cleaned the carb, please confirm that the intake valve is clean and/or reed valves are working properly. It is possible that the 2nd cylinder is only firing occasionally even at the higher RPM but it's less noticeable because of the engine's inertia at that speed makes it "seem" to be running smoother. The clue lies in the fact that the engine runs smoothly at idle when the choke is applied and starts to miss when choke is open ... this is indicative of fuel starvation. And yes, on a 2 cycle, a lack of fuel means a lack of lubrication.

Out of curiosity, take both spark plugs out and crank the engine. Do this outside away from an open flame. Compare the amount of misted fuel that comes out of each cylinder head with the choke closed and then again with the choke open. If it isn't even then the cylinder that is blowing less fuel is being starved. This should identify the problem cylinder and help to narrow down the elements left to troubleshoot and replace/repair/clean. Good luck and hope this helps

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1 Answer

1980 cx500 doesnt want to start

Hi, Darek I would be looking really hard at your starter motor otherwise the usual suspects are:
1. Fuel tank empty.
2. The fuel tank has old dead gas.
3. Fuel tank bottom contaminated with ethanol sludge, dirt, water, rust, etc.
4. Fuel supply valve/petcock turned off.
5. Fouled spark plugs.
6. Engine flooded as a result of overuse of the enrichner.
7. Vacuum hose to the fuel supply valve/petcock disconnected, broken, cracked, or pinched.
8. Fuel valve/petcock or filter clogged.
9. Fuel line to carburetor or throttle body pinched, kinked or blocked.
10. Carburetor float stuck.
11. Fuel injectors clogged.
12. Fuel injectors stuck open.
13. Severely discharged or a damaged battery should have 12.5 volts or more and be able to pass a proper "LOAD" test if necessary, you may have a cursory reading of 12.5 volts or more but little or zero amperage the battery is faulty and must be replaced, AGM batteries fail in this scenario more so than lead acid batteries.
14. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
15. Loose or corroded wire connection at the coil or plug between ignition sensor and ECM module.
16. Spark plug cables in bad condition and shorting check for spark leakage in the dark, cable connections loose, or connected to the wrong cylinders.
17. Ignition timing incorrect due to a faulty ignition coil, ignition module or MAP, CMP, CKP, O2, TPS, ETP, IAC sensors.
18. Faulty neutral, clutch lever, or kickstand safety switch.
19. Faulty fuel pump or fuse or relay.
20. A stuck bent or burnt valve.
21. Tilt sensor needs a reset.
22. Security system not disarming alarm needs a reset.
23. Check for engine trouble codes.
For more information about your issue and valuable "FREE" downloads that you will need for viewing or printing please click on the blue links below. Good luck and have a wonderful day.
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1 Answer

2002 honda vt 750 shadow spirit one cylinder won't fire what's the problems

Pull the plug out and test it on the frame. If no spark you need new plugs. If it does spark look at the plug. If the plug is black and wet it is getting to much fuel and flooding. You will need to adjust your carb's air to gas mixture.

Apr 02, 2013 | 2002 Honda VT 750 CD Shadow A.C.E. Deluxe

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Honda GX 240 engine has spark, new carb; won't fire. what do I do?

remove the muffler and try it there is a screen inside the muffler that get carbon build up if it runs with out the muffler pry it open and clean it

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1 Answer

1979 honda cx500 only runs on one cylinder! I have good spark and feeding it fuel and still wont run !so I'm totally lost on what to do please help???

If you are sure that the idle jet in that carb is clear (spark plug getting wet is a good quick indicator) then I would check the valve clearances as they would be the most likely problem.

If they are o.k. then do a compression test...

Apr 26, 2012 | 1979 Honda CX 500 B

1 Answer

My 650 csr is not running on all fours i determed this mostly by the tempeture of my header pipes three are very hot while 1 is barley warm, i checked for spark and it seems to be ok, this is the left...

Hi there,
You will need to do some diagnosing of the problem. Some things to check
  • compression check across all cylinders. Low compression(less than 100 lbs in a cylinder will prevent it from firing. They should all be with 20 pounds of each other.
  • carby to that cylinder may have a clogged air passage or jet.
  • try a new plug in that cylinder.
  • check for air leaks about the problem cylinder air intake. Use aerosol carb cleaner to spray about the manifold gaskets and carb mount. The revs will change if there is an air leak.
MOst probably you will need to strip and clean down the carbs if you have good compression and spark. Fuel is the only thing left :) Sometimes running some fuel system cleaner additive will also resolve the issue for you without tearing down the carbies. Goodluck regards robotek

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Check for these three necessary elements: spark, fuel, and compression. In order of likelyhood, 1)There's either a plugged up carburetor, 2) defective spark plug, or 3) lack of compression on the non-functioning cylinder.

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