72 Cb500/4 I've got a few issues

bullitt04 · Posted: Fri Feb 03, 2012 3:58 pm Post subject: 72 Cb500/4 I've got a few issues

Both of these issues are probably related but here it goes.

I just changed the spark plugs today (since it's not snowing or raining) and the old ones were black and a little crusty. (I know it was running rich because the coils were bad and the timing was off) Just before winter I installed another set of coils, ( used but had them tested at a Honda dealer) I also installed a Dyna S ignition system and set the timing with a timing light as per the online manual. Back to today. After I changed the plugs, I started it and started smoking a bit from the pipes. Fine, whatever, its 40 years old and hasn't run since November. The bike idled great for about 5 mins around 1500rpm with no taps or rattles or anything. All of the sudden the idle dropped below 1000 and stalled. I started it again and the idle was really rough and wouldn't stay running unless I gave it throttle. That's when I noticed my second issue. While the engine was struggling to stay running, I noticed fuel was dumping out of the bottom of the bike where all of the vent tubes are. I killed it at once and shut the fuel off.

Can anyone help me out?

Russell · Posted: Fri Feb 03, 2012 4:21 pm Post subject:

Doesn't a Dyna ignition need Dyna compatible coils to run efficiently?Your description seems to imply you have replaced stock coils with similar fresher ones.Bear in mind I'm not a mechanic and some-one who is will be along soon I'm sure...

05c50 · Posted: Fri Feb 03, 2012 4:21 pm Post subject:

Sounds like crud (technical term) in the fuel has made one or more of your floats stick and caused the fuel to overflow into your drain tubes. Does your petcock still have the factory strainer on it or do you have an inline fuel filter to restrict crap (another technical term) from getting into your carbs? Is your fuel tank clean, without any rust in it? The first thing that I would try is to tap lightly on each float bowl to knock the dirt loose and free up the floats. If that doesn't work, you'll have to remove the carbs and clean them. If the bike has been sitting for a while, it might not be a bad idea anyhow. You might want to remove the plugs and spin the engine over to make sure that no excess fuel leaked into the cylinders when the carbs overflowed. Don't feel bad, most everyone that's fooled around with these old bikes has experienced carbs that overflow once or twice. Let us know how it turns out.

............Paul

Rizingson · Posted: Fri Feb 03, 2012 4:25 pm Post subject:

What most likely happend bullitt04, was that a float valve/valves failed to close due to sitting since November (could have been from crud or just being sticky.) It just took a few minutes for the bowls to fill up to way higher level than required stalling the engine and eventually coming out the overflow. When this happens my first response is to shut the gas off and use the handle of a screwdriver to lightly tap on which ever carb bowl is overflowing. Many times thats all it takes to get it to seat properly and begin working again after a long storage time. Then restart the engine and open the valve once the level goes below overflow limits. If that don't do it you'll need to remove the bowls and get the valve sealing and moving freely again.
Also make sure you're using a fuel stabilizer (preferably Sta-Bil to prevent that from occurring).

Edit: Dang it Paul, you were on it fast!!! I wasn't copying you, honest, but you must type faster than me. Embarassed

bullitt04 · Posted: Fri Feb 03, 2012 4:34 pm Post subject:

bullitt04 · Posted: Fri Feb 03, 2012 4:37 pm Post subject:

Thanks to all Smile

I'll give it a shot tomorrow after work as its getting dark now and I have crappy lighting.

05c50 · Posted: Fri Feb 03, 2012 4:55 pm Post subject:

Rizingson · Posted: Fri Feb 03, 2012 5:24 pm Post subject:

Or we could both look like fools in the morning Paul. Embarassed

Lyle