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Discussion Starter · #1 ·
I am trying to fix a bug or bugs with my 71 cb450. I have not found a symptom similar to mine so excuse me if this has been discussed before. It starts and idles fine with a little help from the choke. Runs good after warming up. And revs good. But as soon as i get up into the gears and putting a load on it the left cylinder drops off. I pull back into the shop for just a few minutes to check the points and carb ect. And will go back to running normal after it cools off for just a few minutes with no load. Same thing over and over again. I get about 10 seconds of good power in the first few gears under load then the left side drops off line. What i have done so fare is clean the carbs and points, new plugs. The left plug is getting fire because it has shocked me by removing the cap and having my hand grounded to the frame. I have also took the air box and filters out to clean. I believe it is the original air filters, and blew them out with a air compressor. There is a bit of rotted rubber seals in for the airbox where they connect together between the boxes but it seems to be good enough for no major air leaks. I did the carb cleaner pray on the intake boot to make sure there is no leak in the boot. The carb float and slide ect is working, i can tell fuel is getting to the left cylinder because when it does fire it blows black smoke out from overloading with fuel when its not firing. Also carbs seems to be sinked. The right side runs good. Just loosing the left side under load. I believe my fuel/air mix supply is good. Im leaning toward ignition. So now i have new points, condenser and plug boot on order. Also new rubber gaskets to replace the rotten ones for the air box on order. Thats all i can think of. Am i on the right track? Any advice or opinions would be greatly appreciated. Thanks
 

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My 71cl does the same thing, the left cylinder cuts in and out occasionally when accelerating. It's obnoxious but i have been living with it for a bit, it used to be a lot worse like yours. Idles fine and starts great otherwise.
What helped me was cleaning the tank, 93 gas, seafoam, filters, new lines, a REAL thorough carb cleaning and new plugs, check the condition of the gas in your bowls, make sure nothing is sneaking in. Wish I could be of more help, I'm sure someone here will chime in with more.
 

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I'm less experienced with the 450 than some others here, but I'd be looking at your coils if it dies when it's hot. Try swapping the leads and see if it gets replicated on the right side (remember, you can't just swap the plug wires, you have to swap the signal wires too). If so, time for new coils.
 

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Yeah, I was thinking coils too... possibly someone left the key on for an extended time before the bike got sold and one of them has gotten hotter than it should have. With the tank off, look to see if one of the coils is "leaking" stuff out around where the plug wire goes into the coil body
 

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Discussion Starter · #5 ·
Ok i think i may have found the problem but i havnt had time to verify it yet. I pulled the tank for a cleaning and was fiddling with the coil wires. The black wire that comes off of the left coil fell off the spade terminal where it ties in with the black wire from the other coil and to the wiring harness. Only the black wire from the left coil came loose, the yellow was good. it had been cold soldered on and was barley connected. So this leaves me to believe this is why the left cylinder would drop off under load and after it warmed up. The week wire connection resistance would increase as heat and current increased and gave bad spark to the left side. But.. what really confused me is i had just enough time befor work and just enough fuel in the bowls with the tank off to try and start it with this wire completely disconected and what the heck, the left cylinder still fired!?? How is this with the black wire on the coil not even getting power? Is there some way there is a loop through the other coil and condenser that gives enough electricity to fire the plug at lower rpms with no load and the engine cold or some voodoo like that? Im in dire need of an explanation to this as i was sure the left would not fire at all with the coil wire off.
 

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you and I seem to have a similar problem. However, if you're running stock coils then it's very possible you have a coil overheating problem. I have aftermarket ones from Z1 Enterprises and never had a problem.
We're similar in the sense that I was experiencing a loud, popping sound as if running too lean but it turned out I needed to do the following: clean carbs and upjetted the mains, reinstalled and rerouted fuel lines, double-checked and adjusted ignition timing, slight throttle cable sync, idle speed adjusted.

Now? Bike idles better, warms up quicker, and under heavier acceleration the bike did not stutter(though I have only tested it under more brief riding conditions). BUT....I have the no start problem once it has been ridden for a little bit. Weird. I was on my block yesterday and let it sit for some time and then, fired right up again as if nothing was wrong. I am going to check this out again today and lube the advance with white lithium grease. Plugs indicated a slight rich condition but I attribute that to the excessive idling during tuning.

If we could pool our resources to solve each other's issue that would be great!
 

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Try swapping the condensers. If you start seeing issues with the R side dropping out then you know you found the problem.

Then do the same with the coils.
 

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To the OP...I re-cleaned my carbs, upjetted mains, readjusted ignition timing and lubed advancer. Then, I sprayed a light coating of electrical contact cleaner on the tips of my plugs where the plug boot fastened and went for a number of brief rides around my neighborhood with varying throttle positions; Issues ceased! swear, these things have minds of their own.
 

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Discussion Starter · #9 ·
Fixed it! First i resoldered a cold solder joint on a wire from the condenser then new points and condenser, reset timing, cleaned plugs. Left cylinder keeps right up. Thank you all for your post and help! Tony
 
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