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1980 CX500 Backfire & other questions

727 Views 5 Replies 5 Participants Last post by  SketchyRider
My bike is a 1980 model, with Murray's Carbs and Rae-San ignition. I bought it last fall, and have been working on it for the last few weeks.
I haven't really done any major mechanical work though, mostly electrical. The only thing was cleaning the carbs, as the old fuel had been siting for several months.

I took this video to ask if any of you can listen to the engine, and tell me if it sounds healthy or not. But when I played it back I also noticed the backfire at 0:40 and 1:40. Are there any common causes for backfire? I haven't adjusted the valves yet, but am planning to do so soon. Mind you, this was taken when the engine was cold, maybe I should have let it warm up a bit?

The bike has roughly 77 000km on it, so plan is to do a full triple bypass this winter, but I would like to get it running for this season at least. The previous owner said that the mech seal for the water pump was leaking a bit. Should I change this before riding the bike at all, or is it okay to leave it for some time? I've installed a water temp sensor through my Acewell speedo, so I have that under surveillance at least. Speaking of, what is a healthy idle and riding temperature for this bike? And when should I start to be concerned?

Apart from that, are there any other jobs I should do before riding it? There have been 7 previous owners, and I don't know what has / hasn't been done.

Ingvar - Complete amateur rider and mechanic

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You are on the right track. The bike looks good. I believe the idle should be around 1500 rpms, but I am not 100 percent positive. Others may chime in shortly and answer all of your questions.
Welcome to the forum and welcome to the world of antique vehicle ownership (they own us, not the other way around). Your "new" bike is about 4 decades old and may or may not have had all of the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid). And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).
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Factory setup should idle at about 1100rpm. Murray might spec differently for his Mikunis.
you have a plugged pilot from the sound of it i normally just replace them
the slide lift also sounds out of sync
idle should be around 1350 to 1400

if you need any info or pointers just pm me
normally when you are closer we just service and re-calibrate the carbs for free
Thanks for the answers everyone. I'll send you a message when I get the time Murray.
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