1982 CB900C, getting good compression on all 4 cylinders, getting fuel, and getting spark on all 4 plugs. The bike was running fine and with in a month it was a slow progression to what we are dealing with now.
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Your front cylinder is not running. This could be due to spark or fuel, or lack of compression.
Check for spark first by inserting a good plug in the plug wire and holding it against the cylinder. If it shows bright spark, you may have a fueling or compression issue.
Check for compression, should be around 150psi. If you have spark and compression, you probably have a fueling issue.
Check the carb for the front cylinder for fuel level in the bowl. If the fuel level is correct you have another carb issue which will require removal and cleaning/servicing.
Do a compression test. Check for spark at the plugs BUT best to have new plugs.
on any four stroke engine, you must have three things for the engine to run. You need fuel, spark, and compression. The easy one to check is the fuel. Take your air filter off and make sure you're getting fuel to the engine. Then, check your spark. Pull the spark plug wires off the spark plugs in the head and insert another set of plugs in the wires. Ground the plugs against the engine, turn the ignition switch on and press the start button. Watch the plugs to see if you have spark. The next test is compression. With the engine cold, remove the spark plugs. If you have a compression gauge, connect it to one of the heads and spin the engine over with the starter. If you don't have a gauge, simply put your finger over the spark plug hole. Turn the throttle wide open and press the start button. You should show about a hundred pounds of compression if you have agaugeor the compression should blow your finger off the hole with a good deal of force if you're checking it that way. If you have all three of these and they're timed correctly, the engine should run. If the engine won't run, find out which of the three elements is missing and work from there.
what an awesome bike. You'll to eliminate problems one at a time, spark, fuel, compression. I made a dandy home made tester with a spark plug, hose clamp and a battery charger alligator clamp. With goo clean grounds attach the plug to the alligator clamp with the hose clamp, open the gap to around .040 if your ignition is good it should jump that gap, as if it's under compression. Attach to the wire, turn over the engine and see if you have a nice blue consistent spark. If you do, be sure you have good fuel flow, remove the fuel line to the carb (kinda tricky as it's hard to get to) and be sure you have fuel. What I do is with the engine running I shoot a very meager shot of starting fluid into the suspect carb with the engine running, if it perks up momentarily odds are something's wrong inside the carb. Lastly compression. Test the two running cylinders, average your readings and then test the bad cylinder, if it's 10lbs lower than the other two, internal engine damage trouble. Try these steps and report back, we'll figure it out.
hi i presume you mean inside the cylinders, if so it would be recomended that you remove all fuel from the cylinders as you clearly know the dangers of the exsess fuel , also the spark plugs would be constantly wet and the engine would not fire, remove the spark plugs isollate the ignition coils to avoid ignition of the fuel, and turn over the engine to remove the fuel in a well ventilated area, hope this helps
You didn't say whether the cylinder was misfiring occasionly or not firing at all. The number of things that could cause that are quite high. From an ignition standpoint, you could have a bad coil or a bad ignition unit. From a mechanical standpoint, your compression could be low. From a fuel standpoint, you didn't say whether your engine was fuel injected or carb equipped, you might not be getting fuel to the cylinder or you might have a vacuum leak at the intake.
Check the spark first. Pull the spark plug wires off but leave the spark plugs in the heads. Install another set of plugs in the wires and lay them on the engine where you can see them. Spin the engine with the starter and watch for spark. If you have spark, is it a bright blue spark or is it a yellow looking spark? The bright blue spark is what you want.
If you have good spark, run a compression test on the engine. Screw a compression tester into the spark plug hole and open the throttle wide open. Spin the engine to test for maximum compression. Write down the reading you get. The squirt about an ounce of oil into each cylinder and run the test again. If the compression comes up more than 10%, it may be time for a top end overhaul.
Try this and repost with information and we'll go from there.
Not likely valve timing if it will run, cams are one piece so if one is right all are right. Have you checked compression with a gauge, or just by feel? Try swapping the sparkplug wire with the #1 cylinder and see if the dead cylinder moves with the wire. Also try moving the spark plug to another cylinder and see if the dead cylinder moves with it. If the compression is indeed good, the problem will be with the spark plug/ wire, or in the carb, these are the only things that can kill a single cylinder. The coils run a pair of cylinders so a bad coil would put out 2 cylinders at the same time. Start with the spark plug, I have seen a perfectly good looking plug, that would fire whun held to the head, but would not fire in the cylinder.
Are you saying that 2 & 4 got gas with external tank but not with gas tank? If so something else has happened ,if gas is getting to the carb it cannot by-pass 2 to get to 1. Take the tank back off ,connect to external, again. See what happens.
Try starting it then pull the plug out right after trying if the plug is wet you have to much fuel and the float is stuck or has a hole in it and it is most likely your problem if you have fire. if it is flooded you can pull out the spark plug and clean it and kick the motor over to get excess gas out of the cylinder try installing it again then start it, does it fire up? if it does it's flooded due to the problem listed above. If it does not start pull plugs out again add a cap of motor oil in the cylinders and if the plugs are dry reinstall plugs and see if it runs, If it does it may have stuck rings the capful of oil will make the rings seat once this happens they rings should loosen up if not and it will not run after you shut it off then you have low compression. This is assuming you know you have a blue spark to the plug and have cleaned and gapped the plug or plugs. If you need more help psot here and reply tothe e-mail you recieved with this. Hope this helps.
If all the rest are fine then it's not timing, and if you took care for the carbs it's not fuel
Last two things to check is spark and compression. A quick compression test of all your cylnders will give you a good idea of the condition of the engine and if thats the problem.
The spark could be missing for several reasons. First replace the spark plug, local auto parts shops should have it, should be the same as most honda cars. then test the coils for the proper ohms, a service manual will have the specs for your bike, or google it, and then make sure the coils have juice running to them.