One cylinder not running but I have spark.

This is actually for a 1982 cb450 but the concept is the same so I am posting it here. I am only hitting on 1 out of 2 cylinders. I know this becuse the bike lags badly and when I get done riding it one exhaust header is touchable but the other one is untouchable. I pulled the spark plugs out and I can see them sparking when i turn the motor over. I am at a loss as to what the problem is.

 

could be the plug is not firing under compression. I would try a new plug first.
What does the plug look like? Black and sooty, white, tan, wet??

 

black but not super bad. Ive swapped the plugs between the cylinders and it runs the same so I didnt think it was the plugs. I also swapped the plug caps and it worked the same. I was going to try to swap the wires but they seem pretty firmly attached to the coil.

Could it be a float valve or something in the carbs not allowing fuel to get in?

 

by the way the bike will sit and idle forever and other than being slow and having to hold wot to get anywhere with a top speed of about 45 it runs great.

 

This can likely be a lot of things. Off the top of my head I would try the following:

1. Are the spark plugs gapped correctly?
2. Is the timing set correctly?
3. Are the pick ups working correctly? Brushes?
4. Is the resistance in the plug caps/wires too high?
5. Is the fuel/air mixture for that cylinder set correctly?
6. No vacuum leaks for that cylinder?
7. Is the TDI/CDI unit working correctly?

So many things...Try the ones that make sense to you and let us know how you make out.

Good luck.
Rob

 

Oh and check your valve clearances for that cylinder too.

 

Ok, if you switched the plugs and it ran the same are you saying the same cyl. stayed cold or did it move to the other side.
If it moved to the pther side then I would still say bad plug.

 

no the same cylinder stayed cold.

 

All the other stuff included you might check your compression between the two cylinders and make sure they are almost the same. (no compression tester? does it blow your finger off the plug hole when you turn it over?)
Not sure about your type of carbs I'd check for vacuum leak and plugged air filter
Luck

 

Unplug the connectors from the coils to the wiring harness -- SWAP THEM --not the plugs. If you still have the problem of Missing or Misfiring but the other Bank is cold now ... you need a coil. If the coil-swap test indicates you need a coil ... your troubleshooting is over. If not ... you have a whole couple-hours worth of shaking-down to do. If the coil swap shows "Bad-coil" ... and that's all it is ... well, that's the good news. If the coil-swap tells us to look elsewhere ... you'll need a test light and a meter to go after it ... but, we'll find it. In the mean time,, after the coil swap -- see if you can get a compression test done. We'll be needing that info.

Rick Massey

 

I basically agree with what's been said so far. I'd like to add a few things also.

If the valve clearance is really out on that cylinder an easy way to check is to take out the sparkplugs, put the wires aside such that they don't short with anything, put your thumb on the sparkplug hole and crank the engine. If the clearances are way out of spec you won't feel the pressure against your thumb when the piston moves up (this case is very unlikely).

If you do have pressure there (compression), then you should have vacuum as well. And if you have vacuum and spark, then the culprit has to be the carb. You could bypass all the above by spraying a little "Quickstart" into the intake port of that cylinder while idling. If that cylinder takes off all of a sudden, then you know the problem is with the air/gas mixture and therefore the carburetor.

If so, then a carb cleaning might be in order.

Hope you find the problem. I know from my experience how nasty it is to run in one less cylinder, even when you have four in total

 

Ohmega, your post was great. One small issue to add. I was a bit confused about "put the wires aside such that they don't short with anything". I assumed from the post that you were referring to the spark plug wires and I assume (yup, I'm going out on a limb here) that most other folks would read it the same way. I must clearify that one should NEVER turn over the motor or energize the ignition system without also grounding the sparkplug wires, since this runs the very real risk of frying the TCI unit. If you were referring to the wiring harness, I apologize, I just don't want anyone to have to replace a TCI, they don't come cheap. I felt compelled to speak up rather than let someone blunder off and learn the hard way. No offence is intended.

 

Robert, thanks for the clarification! Correct, plug wires should be grounded, as explained in the manual.

 

Sorry about the confusion.

 

2 quickies, first off what am I looking for when I spray quick start into the intake on cylinder 2? Secondly and maybe most stupid but how do you ground spark plug wires? Thanks guys

 

First a warning: some people think that using quick start spray in the long term has a bad effect on the engine. I've used it now and then and had no problem, but it's better to know what other people think.

Let's see if I can explain myself better this time. For the cylinder to work properly, it needs air+gas mixture in a roughly right proportion, this mixture needs to be compressed, and strong enough spark is needed at the right time (when mixture is fully compressed).

The idea of spraying quick start into the intake of the non-working cylinder is that it will provide an acceptable mixture of combustible gas to that cylinder. If that cylinder is working properly for the short duration of you spraying quick start in the intake, then it shows that you have all the other needed elements: spark and correct timing and compression. So, you've eliminated then the other major causes of malfunction for that cylinder. In that case you can concentrate your investigation on the carburetor, which is obviously not providing the right mixture of air and gas.

I hope this makes more sense.

As for grounding the spark plug wires... I admit I never do it, but strongly recommend that everybody else does it by the book ... oops. I assume that one just connects the wire to the bike frame? I'll let people with more experience explain this.

 

All I've ever done is connect the wire to a spark plug and lay the plug on the engine head in an out of the way spot.

 

I disagree with the notion that the plugs need to be grounded while doing a compression test ... and I doubt there is any risk. Take out the plugs and put them on the bench. If you are worried about the Ignitor ... un-plug it. Just remember to conduct the compression test with a fully charged battery and the throttle cranked -- FULL OPEN! My opinion on doing damage to the CDI -TCI is such: "Remove the possibility that the unit will be damaged ... by ... REMOVING THE UNIT. You may all do as you wish. The preferred method of spinning the motor over to conduct a proper compression test is to use a remote start switch across the solenoid. I will advise you to take the precaution of preventing damage to the "Makes-it-Go-Box" ... by ... physically removing it from the motorbike if any type of welding involving electric current is involved. If you are testing to determine if the plug IS firing ... wrap a half-shell of black construction paper around the plug ... and, GROUND the plug to the cylinder head. A jumper wire with heavy-duty "alligator clips" is an ideal way to be able to watch for spark. This test requires that everything remain "hooked-up", the ignition key ON and the START button depressed. Good luck. I hope you get that bike running like a Rolex real soon. /// RickCoMatic

 

Ok, first quicky. Your looking for the "fuel" that Quickstart represents to provide the needed "fuel" in the combustion process. Air+Fuel+Compression+Spark= BANG. Thus, if you introduce fuel to the flow and the cylinder starts firing (I'm guessing the engine would smooth out somewhat, never done this. It is a brilliant idea too), you have effectively demonstrated that your ignition system and compression are good and that the carburetor for that cylinder is not producing the needed air/fuel mixture. This would indicate a good cleaning is in order.
Second quicky. There are a few ways to do this. I let gravity pull the re-inserted sparkplugs down 'till they touch the valve cover in front of the engine. You want to get that spark as far away from the plug hole if you have any fuel in the system (BOOM, flames, people running around crazily, don't ask). That is the cheapy way. Next is the best way and that involves making/purchasing your own test lead clips. I buy the cheap ones at the discount electronic shop out here. They are simply alligator clips on the ends of wires. I clip the primary lead to a fin on the head, thus no spark. Good for safety but bad for verifying coil and sparkplug operation. I actually made a test board once, can't remember where it got off to. I'll probably make another soon. Pictures will surely follow. Hope this helps you out. Looking forward to hearing of your success.

 

alright today I pulled the plugs and checked for compression. I got it on both cylinders. Next I drained the float bowls in the carbs. As I suspected the float bowl on the dead cylinder had alot more gas in it than the other. So I took off the float bowl but it looked decent inside and the float needle was pointy so I put it back together and took off the boot connecting the intake box and the carb. I cranked it and rode it around for about 5 minutes. It now started to jump about in the power and rpm levels but I think thats because my battery is old. I took some starter fluid and sprayed it in the carb as I gave it some throttle. I got a big jerk forward everytime but I didn't spray it in for very long.

I guess this means i need to go through the carbs right?