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Author Topic: CB750A Won't Idle  (Read 2733 times)

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smrshl

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CB750A Won't Idle
« on: July 10, 2006, 06:00:51 PM »
I've got a '78 CB750A that i got from a buddy.  I had the tank lined and the carbs rebuilt about 4 months ago.  They also set the dwell and greased the points.  The thing has been running fine ever since then.  It got rained on a couple of times (no cover) this past week and now it won't idle.  I've pulled the points cover off to see if there's any moisture in there and nothing.  It fires right up with the choke full-on, but when you kick it into gear and start going it dies.  If you can get it up to highway speed it runs just fine, albeit you can hear some popping coming out of the mufflers.  What do you guys think?  Do I need new points or something?
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smrshl

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Re: CB750A Won't Idle
« Reply #1 on: July 10, 2006, 08:39:22 PM »
Put new plugs in the other day.  Didn't fix anything. 

I took the points cover off and fired it up.  It looked like a mini lighting storm around the tips of the points.  They were arcing to the base, not between the contacts.  That's bad right?  Do I need to replace the points and condensers or just the points?  What do you think?
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Offline Bodi

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Re: CB750A Won't Idle
« Reply #2 on: July 10, 2006, 09:19:08 PM »
Actually that sounds more like bad capacitors
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smrshl

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Re: CB750A Won't Idle
« Reply #3 on: July 11, 2006, 05:32:00 AM »
Where are the capacitors?  I'm not much of a mechanic (yet). :-)
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Offline TwoTired

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Re: CB750A Won't Idle
« Reply #4 on: July 11, 2006, 01:30:34 PM »
Capacitors and condensers are different terms for the same thing.

Do you have a fuel tank door over you gas cap?

If so, check that the drain for the well under the door is NOT plugged.  When the well fills with water, the tank cap vent allows water to enter the fuel tank.  Gas floats on top of water.  So, all the low spots in the fuel system collect it.  When it sloshes over to a fuel jet in the carb...Well lets' just say a water air mix doesn't burn as well as a fuel air mix.

Water in the fuel is not a good thing and makes metal corrode.  Corroded metal is bad for carbs and can plug up jet orifices.  The first to plug are usually the slow jets as they are the smallest.  If you suddenly can't idle except with choke, you'll probably be looking at another carb rebuild.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

smrshl

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Re: CB750A Won't Idle
« Reply #5 on: July 11, 2006, 04:54:22 PM »
Got two words for you.  SEA-FOAM. 

Got a can of it at NAPA today, put a few ounces in and presto, runs like new, well almost new anyways.  I must have been getting water in the tank, I noticed that there was a little rust on the chain for the gas cap.  I thought this was odd because it was brand new about 6 months ago.  Anyways, I pulled the tank off and drained about 1/2 gallon of gas out to make sure that I got all the water out.  Then I put some Sea-Foam in and sloshed it around. 

It definitly ran better right after that, but the more that I road it, the better it ran.  I'm sure that once I get some new gas in it it'll help big time.  It actually started with NO choke which it hasn't done since I bought it.  Maybe Sea-Foam is the answer to all of lifes little problems.....

Well maybe not.
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