weak right cyclinder, compression ok, swaped ign and carbs

tron · Full Member Joined: Apr 27, 2009 Posts: 63

i get very weak firing with some poping/fireballs out the exhaust on the right cylinder (76') and putting my hand over both exhaust pulses are weaker on the right .. when i pull the right plug wire engine doesnt sound much differnt but dies shortly after, if i pull the left plug wire, the engine sounds way differnt and will die almost right away, basicly the right cyclinder is almost not working

comp test on right cyl was 150psi

i swaped the right coil out with my 77' nothing changed.

i swaped out the whole points disc thing that comes out with 2 screws on the left side with the contacts in it, checked wires 5 times over

thought maybe it was a fuel probem, i swaped the carbs from my 77 to the 76 and new fuel lines. nothing changed

tried plugs out of my other bike, same thing, swaped and ohm'd out the plug wires. nothin funny

any ideas guys ? timing maybe? i want to ride this thing!

skandix

I am having the same problem, have you figured out a solution.

xsjohn

Exhaust..... ?

Retiredgentleman

The voltage has a major overall effect on how the engine runs. Do you have 13 volts or better at idle and 14 volts or better at 3000 RPM?

Check for the quality of the spark using a dummy spark plug. Look at the spark in a darkened area.............should be bluish not yellow.

Is the engine timed correctly using a timing light?

Mofokker · Full Member Joined: Oct 22, 2008 Posts: 46

I had spark plugs that showed spark when testing them, but when I put them in the cylinders the bike would not run. I tried everything, but the last thing I tried was new plugs and it fired right up...Go figure. try some new spark plugs.

skandix

First, Thanks for the responses, My exhaust is clear and no problems there. I just put in new points and have timed it almost perfect according to the manual using a timing light. It has new Plug wires and Caps. Bike fires right up! I have new Iridium Spark Plugs. Voltage @ idle is 13.43V and at 4k rpm it is 14.66V. I swapped the coils, condenser and that made no difference. I cleaned the Carbs with 140psi air and carb cleaner. Compression is stronger on the right piston then on the left piston. I will check the plugs again. Possible bad new plugs.

ghostyder

i had similar problems with a 78 engine im running, after upgrading to the pamco the bike ran great for a day and then started pissing oil out the right pipe. tore it down and was told the right cylinder over heated warping the piston and scoring the cylinder.

ive got the bike back together as of yesterday and am concerned about this happening again.

skandix

I think that is what might have happened to my bike as well ghostyder. I did see some grey smoke coming from the tail pipe before this happened. I will check for oil later today. Thanks

xsjohn

What would I know about the right cylinder.............

xsjohn

ghostyder

reckon xsjohn knows plenty about the right cylinder, but what do i do with my 1979 carbs? arent your kits for the later models?

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

Sounds like you've swapped and tested just about everything -- except the condensers. A bad condenser could cause the problem you describe. Condensers DO go bad over time. Your 1979 motorcycle is now thirty years old. Manufacturers used to recommend that you change condensers every time you change points. But hardly anybody who rides an XS650 does that, cuz the condensers are up under the tank and pulling the tank is a PITA. So the condensers in your bike could easily be thirty years old.

If the condenser fix doesn't work, better get with XSJOHN.

yamaman

Have you got the cam chain & valves correctly adjusted? Must be so to run right........

I think John can help you with the 38's if need be, PM him. Cheers

skandix

Well, put in new plugs right side started to run more consistent, but it is still running rough. If I unplug the left spark plug wire while the bike is running I need to rev tha bike to 2k for the right piston to run on its own. Took it on the highway and opened it up to see if the valves are sticking or anything. Bike ran fine up to 85mph. Checked valves, timing chain and they are perfect. i will swap the condenser as soon as I get it later this week. I did swap the condenser wires and there was no change. If it doesn't change, look like a tear down.

xsleo

you say the compression is stronger on the right than on the left. What are the numbers? Engine warm throttles and slides full open.

skandix

i did the compression test about 6 months ago, but will check again. Slides full open.

skandix

Well, I put in a different condenser and resistor, made no difference. What I did find is that the Right Plug is only getting 11.43volts at the right points, and the Left is getting 12.65volts at the left point. Why the difference? Can this be causing my problem? The right piston gets to about 198F and the left 256F. Before the left never got hotter then 230F.

skandix

Conclusion: Hope this helps someone, After changing Condenser,plugs, wiring harness, plug caps, plug wires and compression test Left 149psi, Right 153psi......etc. I Found the problem. My intake boot has a large crack, that is open. Just glad I don't have to tear it down, with only 11k miles it just seemed odd. But i forget that the bike is 32yrs new. Thanks to everyone who Helped!

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