About Rich Johnston Expertise I have honda repair experience on all vintage Hondas from 1972 through 1980. I worked in a Honda dealership while going to college and have experience in all types of honda motorcyle repair. I don't have any experience on other brands.
Experience
Education/Credentials BS degree in mechanical engineering, Honda technical school graduate of 1975
Question Hello,
Long post, sorry. I figure the more information the better, for this kind of question. I have been having trouble with a 1972 CL350. 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 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 it 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.
Answer Marc, I appreciate the detail but it's not the cam chain. The camchain only impacts the valve timing and it won't get so loose to cause this problem.
This is a fueling or ignition problem. You need a timing light to diagnose this problem. First, manually set the timing with an ohm meter set on continuity check. THere's two slots in the point backing plate. Line that up with the notch in the cam bearing housing to center things up. Set both point gaps to .014 inch and then adjust the backing plate to the left cylinder opens at the F mark on the flywheel. Then turn the engine 180 deg and set that point with it's adjusting plate to the fire on the F mark. Check the timing with the bike running now using the timing light. Make sure when you rev the bike up the timing advances to the two hash marks on the flywheel. You have to check both cylinder separately. Also make sure there's not a lot of sparking at the points indicating a bad condensor.
If the timing is set correctly, the problem is fuel. Do both cylinders fire when the choke is on? If it doesn't make sure the plug isn't wet with raw fuel. An air fuel mixture that is too rich won't burn either.
