Question about 1978 Honda CX 500 A

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Engine turns over but wont start

The engine turns over but wont start. It seem like it wants to start but dont. If it does start it runs like **** and backfires some. I have to pull the choke out and then it runs for abit but then cuts off. I changed the sparkplugs and then it started and idled good but then took for a ride and then when i gave it gas it was like stalling out but then i let off it started to run fine. I took it to a freind to look at and he said it might be the coil. I dont know what coil i need if thats even the problem. I really need to figure this out.

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This is an older motorcycle has it run recently? If it's been sitting for over the winter the carbs may need to be cleaned . But let's say thats not it. The engine needs the three basic things to run. Spark, Fuel, and compression. Unless there's some obvios reason to skip around things should be checked in that order. Sure check to see that there's gas in the tank that's less than a year old and it's clear not fogged with rust or other junk. Make sure the battery is charged up all the way as Hondas require a good and well charged battery to run , and run right. 1 st. Spark, remove a plug wire put another plug in the end or remove the one thats in the engine put it in the end of the wire and crank it with the key on and see the plug fire.it'll need to be laying on the head. If it does'nt check the other one. They fire independatly so check em both. If you have good fire and the plugs have no junk on them ( or clean them off ) and with them out notice does anything blow out of the cyclinders as you crank it. It should make a loud woosing sond as the plug normally holds the compression no antifreeze or water shoul come out and if you block the hole with your finger or a compression gauge if should have goog pressure If you can get a gauge that fits the smaller than common ( cars) size the compression should be ewteen 150 and 175 PSI but certainly over 100 PSI. If not add a little oil to the cyclinder and crank it some and try again as the presssure may build up with oil to an acceptable lavel. I guess you've already checked the oil and coolant in the raditor just like a car it has to have everything. 2 nd. It needs to have fuel. the fuel valve needs to be on and if you remove the fuel hose ( with a rag or a pan under it ) a good steady flow of fuel needs to come out of the tank. If the fuel valve has a small hose going to one of the carbs it may have to have vacume to let the fuel move though the valve. These valves sometimes have a prime position and it'll flow anyway in that position. The valve can be clogged and not enought fuel to go though on main and may have to be switched to reserve. Once the fuel is known to come out of the tank, you should put some in a clear glass just enough to look at it good it should be clear, yellow , pink or blue, but clear not foggy. If not remove the tank dump it in you oil recycleing and put in freash fuel and or if it's nastly clean the tank and the fuel valve. after the tank is free of gas it can be cleaned with soaply water and some driveway stones, after the fuel valve is removed. You'll have the shake it alot, up side down and every other angle keep washing it out till the rinse water is clear, no flakes no nothing. If you can't seem to get into the clean part after alot of tries a nother tank or coating the inside of the tank may have to be done it's alot of work as a new tank can set you back over $400 and used ones are what you can find and the right one is important. once the tank is deliveing clean freash fuel it still may not run as this mess may be in the carbs too. on the very bottom of each carb thers a drain screw the freash cean gas needs to come out of here too. If it does and it still doesn't run your still not done. Honda's and other bikes too won't run with the aircleaners removed or poorly at best. But now that you've checked for good spark with cleaned plugs and you've got good fuel in the carbs ands you saw it puming good when the plugs were out. you still need to verify that the engine can run before you go after the carbs themselves. With the air caleaners connection removed from the carb gas shouldn't be running out and with it all put together except for the air horn put your hand or a reg over the carb end and crank the engine, it should **** on your hand and you should feel a mist of gas. If ti still doesn't start or try too and your hand is dry of gas add some gas the see if it starts for a second. if it does and quits then the carbs need cleaned.. If you get to here and you rebuild the carbs to clean them, Make sure to do the gas tank cleaning step anyway as the clean carbs will go right back to stopped up it the tank is dirty.

Posted on Jul 11, 2010

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