QuestionHello,
Long post, sorry. I figure the more information the better, for this kind of question. I have been having trouble with a 1972 CL350E. I have had the bike for a few months and have replaced the condenser, points, rectifier, carbs (more on this later), carb boots, spark plugs, plug caps, and a few other things assuredly not related to the problem at hand (like brake pads). I have adjusted valve clearances, ignition timing, cam chain (more on this later), and point gap. Both sides have ok compression - about 155 for both. The problem is that one side runs very hot and the other side barely runs and is much colder. Both sides can start up independently of the other one but on the side that barely runs you have to twist the throttle like halfway for it to fire up. When it does fire up it sounds very muggy, sort of like it is too rich, but I'm not sure. No amount of adjusting the idle air screw or throttle stop screw makes the cylinder sound any better (actually, you can get it to sound a wee bit better but not much). If I turn the throttle stop very far in then it will idle on that side but the bike will run very badly and the carbs will be out of sync. I don't think syncing them that way would help; it seems the idle would be way too high. When I am adjusting the carbs the air screw is at factory setting - 3/4 to 1 turn out (they mean 360 degrees is one turn, right?). I have cleaned the carbs many times with carb cleaner and blowing through the passages with compressed air. I had a very dingy pair of carbs on the bike so I bought another used pair off a running bike, thinking that maybe something was still clogged (I couldn't get the idle jet out to clean it). The newly bought carbs made both sides run a little bit better but the problem persists. One side runs rather hot (you can't touch the exhaust pipe after about 15 seconds of it starting up, and after a minute or two it starts smoking a bit) and the other side barely runs and runs cold. What seems like an indicator is that the left side exhaust (badly running side) seems to be sucking air in a bit out the end when it's running. It is not full on sucking but it is not blowing out as cleanly as the other side. I was thinking this would indicate a weak spark, bad compression, an air leak, or bad timing. I just realized - it might also just be because there is a small hole at the bottom of the exhaust on that side. I can't check it right now to make sure.
If I set the timing way off on the problem cylinder (far from TDC) then that side will fire up and heat up but still sound muggy. I have checked for air leaks, to no avail. I was suspecting the cam chain was so loose that the timing would be off even if it was set to the correct marks. When I adjusted the cam chain tension I followed instructions from a shop manual - move the rotor counterclockwise until the left exhaust valve just begins to open, then move it clockwise until 90 degress past TDC. I have heard that this is not a good idea and that to set the cam chain tension you need to be always moving the rotor counterclockwise or else the chain will be too loose. I was going to try it this way when I stripped the already halfway stripped sparkplug hole threads on the cylinder that isn't running right. I have ordered a helicoil kit to fix it. I figured that the half-threads wasn't the cause of the bad runnings because the screw-in compression tester gave a good reading. However, I was wondering if this could cause the spark plug to not fire as good because it might not be getting enough of a ground. Doesn't seem likely but maybe.
I have checked the coils and they seem fine (blueish spark on both sides) but maybe it is not firing under compression? I have ordered a helicoil kit and I was thinking of doing an engine rebuild to replace the cam chain, head gaskets, and possibly other parts if they are worn. I was wondering your thoughts on the problem before I dive into it. My theory on it is that the cam chain is loose, making it impossible to set the timing right, and that maybe the oil filter needs to be cleaned to prevent the right side from overheating. However, I am confused as to why the bad cylinder sounds bad even when the ignition timing is set way off to (apparently) compensate for the loose cam chain. I have oiled the spark advancer and it seems to be running right although I am not sure how to check. The battery is fully charged and the alternator seems fine (was charging the battery). Running it with the air filter off doesn't change it much. The bike has 30,000 miles. Thanks for reading and thanks for helping. This is my first bike. That's an even longer story.
P.S. I sent this to another allexpert expert already but due to the nature of the problem (doesn't seem to be anything obvious) I felt a second opinion would be helpful.
AnswerYeah. It sounds like you have done all the right things to get it running. Without actually seeing & hearing it I don't know how much I can help.
I would start by eliminating a couple of possibilities:
You don't mention balancing the carbs. If you haven't already you should. Balancing carbs consists basically of connecting vacuum gauges to the carbs and adjusting the carbs so that they both draw the same amount of vacuum. The proper procedure for your bike should be in the shop manual.
Try swapping the spark plugs from one cylinder to the other and see if the problem moves. Next, try swapping the coils (you will need to switch the plug wires and the wires to the points). I don't think this will solve the problem but you will know for sure it is not spark related.
While looking for info about the CL350 I came across this page http://www.tholt.com/cbtip.html He mentions that the diaphragms in these carbs are prone to tearing. I would take them out and look theem over carefully. Since changing the carbs didn't fix it they probably aren't your problem, but you never know.
It is barely possible that your problem is related to the stripped threads if they were loose enough to leak. The only thing you can do to find out is wait for the helicoil and see if it makes any difference (it has to be done anyway).
Another not so likely cause is a mis-timed camshaft. Double check the cam timing (you will have to take the cylinder head cover off and see if the camshaft is in the correct place compared to the timing marks - look in your shop manual under camshaft installation). It is possible that the previous owner had it apart and put it back one or two teeth from where it should be. It wouldn't hurt to re-check the valve clearances afterward too.
If none of that does any good I have a funny feeling that the problem could be in the exhaust system. Maybe a blocked exhaust pipe or muffler. Try it with the exhaust removed and see what happens. Don't run it too long without the exhaust pipe & muffler because you could burn the exhaust valve.
