One cylinder firing

[apox]

Ok so it shows how much I know.. I recently posted a video of getting the bike up and running and someone mentioned it sounded like only 1 cylinder was firing, you. Were correct! Did the touch test, left exhaust is cold. Both sides have spark, and great compression. I guess it's the left carb? What to test?

Thanks,
Rob

 

[5twins]

I would check your carb sync 1st. If it's way off, that dead cylinder could be effectively shut off at idle. Play with the sync screw between the carbs. Back it off to slow the right cylinder down then turn the idle speed screw in on the left carb to speed both up. Work back and forth like that until you get both cylinders at the same speed and a 1200 RPM idle.

 

[apox]

Did some more research.. Getting blow back into that carb... Bottom of the diaphragm cylinder is a bit carbon fouled. So im assuming it's an intake valve problem because the compression is great and that doesn't lie!!.. Looks like I've got some work ahead of me. What do you think? And while im in the head what else should I do? I've got the full athena gasket kit so I'll probably do all the valve seals.

Thanks,
Rob

 

[5twins]

Well, I don't know if this calls for a teardown, lol. Black residue in the carb throats is a normal occurrence. That cylinder would have to be pretty bad for it not to run at all and you say it's compression is good. What year and ignition type? If it's points, you may be getting spark but just at the wrong time (check timing on that cylinder).

 

[apox]

Brand new pamco. On a 77 motor in a 1979 special. Previous owner had problems running that cylinder too and thought it was the coil which he replaced with a Boyer on stock tci and fried the tci box.. So I bought the bike and pamco and still cylinder doesn't work. I also switched the carb diaphragms assembly as one had a little pin hole I fixed with gasket cement and it still ran on the right cylinder, left still not running. I got the carburetor from the PO in that discolored and charred bottom state. So whatever the issue is it's been going on for a while as now I assume it was never the bad coil.. That's probably the story I was told to buy the bike weither he knew or not

 

[apox]

My timing gun is dead so I havnt timed the pamco yet, and I havnt screwed with any screws on the carbs. But I put the pamco where it shows In the picture and it seems to do a nice job of firing the one cylinder.

 

[retiredgentleman]

apox;

If you purchase a bike, and you find its not running on one cylinder, its time to remove both carbs to the bench. They need to be taken apart and checked for correct jets, all passage ways clear etc. You may need rebuild kits.

Go to "Tech" at top of page....................go down to "Carbs" and start reading. Make yourself familiar with CV carbs. There is a table there (by 5twins) that lists the corrrect jets etc. for each year carb.

77 motor................but does it have 77 carbs?? Go to mikesxs.com, look under "Tech Tips" for carb identification.

 

[gggGary]

does the dead side plug have spark? Nice fat blue spark? Then it's a carb issue. If it's got compression it will run.

 

[apox]

It's got spark on both sides. Ok question, are the carbs swappable? Like left to right? That should immediately indicate if it's a carb issue. The reason I mentioned tear down before is, my moms friend was here and was a small engines mechanic for 15 years and has worked with many mikuni carbs as soon as he saw that blow back carbon fouled black diaphragm cylinder he said it was rings etc, but then mentioned good compression and he said, valves. Believe me id love it to be the carbs so I will pursue that first.

 

[apox]

Ive done quite a bit of research on the carbs already. Had them apart, havnt checked jet sizes though. They are 1980-84 34s emmission controlled. Canadian needles, new Needle jet 336-Y0 Canadian. New plastic floats set to 22mm on middle of arch of float. I guess I should just go over every thing on the carb, jet sizes and stuff.

 

[tonyc]

You can swap the plug wires to see if it is an electrical problem. If it has spark and air then it must be a fuel problem. Tony C

 

[gggGary]

Not really swappable. I suppose you COULD leave em together and stick the left carb on the right cylinder as an experiment???? It's an air leak or cleaning issue there is nothing else. plugged idle jet (under the rubber plug) not the idle mixture screw, is one common no idle issue.

 

[apox]

Thanks for all the great info. I'll try next weekend, out of town in Saskatoon for work next week I want to work on the bike! Oh well.. Good research week

 

[littlebill31]

As Gary said you could put one carb on the other side, but you can't switch them left for right and run both. The fuel inlet is carb specific. (where the fuel line goes into the carb).

 

[XSLeo]

www.amckayltd.com/carbguide.pdf print it out, read it, read it, read it. Did I mention read the carb guide?

 

[KG808]

IDK if anyone will respond to this one, but I'm having a similar problem. Motor will only run if I keep the throttle open, which is very inconsistent. It will not idle. One spark plug is clean and the other is black. I switched the plugs and the left cylinder is still not firing. Spark plug wires are fine. IDK if its the points that are not firing on that cylinder or the carb on that side is flooding the cylinder with too much gas. I cleaned the carb jets with a file and compressed air. If anyone has any tips greatly appreciated.
Mahalo

 

[Jan_P]

IDK if anyone will respond to this one, but I'm having a similar problem. Motor will only run if I keep the throttle open, which is very inconsistent. It will not idle. One spark plug is clean and the other is black. I switched the plugs and the left cylinder is still not firing. Spark plug wires are fine. IDK if its the points that are not firing on that cylinder or the carb on that side is flooding the cylinder with too much gas. I cleaned the carb jets with a file and compressed air. If anyone has any tips greatly appreciated.
Mahalo

No mention of what ignition system or year model
Perhaps take out the plug hold it against the cylinder se if there is spark please do the readup and be careful. It can hurt the ignition if done wrong
But the first thing to do is check battery and charging voltage since it is important and simple to do
Measure across battery.