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Discussion Starter · #1 ·
Hello Everybody, New to this forum as I haven't needed help until now.

1981 Honda CX500 Custom

I recently acquired this bike from the first owner. He hadn't driven it in 20 years and thought that the Carbs were just really screwed up. After Cleaning them, and when I say Clean, I MEAN CLEAN. Sodium Hydroxide baby. After figuring out I had a bad stator/CDI box, I pulled the motor and put in a nice used stator and CDI Box. I got it all buttoned up, and it runs beautifully and accelerates like a bolt of lightning.

The problem is, it is so hard to start. It just doesn't make sense. If it runs this awesome, it should start like a champ. Great Compression, Rockers are set perfectly, nice fat spark. Everything is there. If the bike is hot, forget about restarting it. When it is cold, it starts better, but not great.

Any thoughts?

Scott
 

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Hello Everybody, New to this forum as I haven't needed help until now.

1981 Honda CX500 Custom

I recently acquired this bike from the first owner. He hadn't driven it in 20 years and thought that the Carbs were just really screwed up. After Cleaning them, and when I say Clean, I MEAN CLEAN. Sodium Hydroxide baby. After figuring out I had a bad stator/CDI box, I pulled the motor and put in a nice used stator and CDI Box. I got it all buttoned up, and it runs beautifully and accelerates like a bolt of lightning.

The problem is, it is so hard to start. It just doesn't make sense. If it runs this awesome, it should start like a champ. Great Compression, Rockers are set perfectly, nice fat spark. Everything is there. If the bike is hot, forget about restarting it. When it is cold, it starts better, but not great.

Any thoughts?

Scott
If your bike sat for that long a time,,chances are your idle jets are clogged. When you cleaned the carbs, did you remove the idle jets? Did you blow air through them and determine if it was blowing through the idle circuit and out the small holes in the carb throat?

Search "idle circuit" here or on the wiki site.

If it isn't the idle jet(I am guessing it is), is your choke operating properly? You could try removing the airbox to carb boots and pull the choke on and visually confirm that the choke butterflies are closing fully.
 

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Discussion Starter · #3 ·
Thank you for your response. I am leaning away from Carburetion, like I said, it runs dynamite, and Idles wherever I want it to. I currently have it a hair over 1000rpm. I watched the spark while cranking over, it was good. I sprayed the ignition coils with Aerosol freeze, and the spark was grossly better. It doesn't make sense that it would run this excellent, and start so poorly. If indeed it were the idle Jet(s) wouldn't the motor struggle to stay running at low RPM? Would it not also lack power on low end? Because neither of those are an issue. It idled in the driveway for 15 minutes while I was purging the air out of the radiator.
 

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Not wanting to restart hot could also denote an over rich condition.

Here, we call sodium hydroxide caustic soda and use it to clean our drains mostly.

It will attack aluminium depending on length of immersion and strength of concentration.

Maybe the idle drillings have enlarged?
 

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Thank you for your response. I am leaning away from Carburetion, like I said, it runs dynamite, and Idles wherever I want it to. I currently have it a hair over 1000rpm. I watched the spark while cranking over, it was good. I sprayed the ignition coils with Aerosol freeze, and the spark was grossly better. It doesn't make sense that it would run this excellent, and start so poorly. If indeed it were the idle Jet(s) wouldn't the motor struggle to stay running at low RPM? Would it not also lack power on low end? Because neither of those are an issue. It idled in the driveway for 15 minutes while I was purging the air out of the radiator.
Are you sure it is idling on both cylinders?

You could try pulling the plug wires when it is running. Pull one plug wire, see if it makes a difference in the engine. Replace that wire and pull the other side.

I had a plugged idle jet in one carb,,the right side IIRC, the bike idled and ran beautifully, except it idled only on one cylinder. The only way I noticed it was when I first touched the throttle, just coming off idle, there was a bit of a lurch as the other cyl. kicked in. It was barely noticeable, but it turned out to be a clogged idle jet.

Does the bike always start hard, or is it better/worse when it is hot/cold?

These bikes are known to start hard if they sit for a week or so.

edit; I just reread your first post,,I see you say it is worse when it is hot.
 

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Discussion Starter · #6 ·
It idles on both cylinders. I checked for that when the bike was COLD, and waited for the exhaust pipes to get hot. Each one was getting hot.

I've decided that this is a hot start problem. I let the bike cool down for an hour, and it fires right up. Rode it for 15 minutes, shut it down, and immediately tried to restart, and no go. It appears that the spark is weaker when I am trying to restart hot. But, I will repeat how excellent it runs right until you turn it off, and try to restart it.

I am at a loss right now, because this isn't following any rules. Has anyone ever heard of a Stator that only acts strange when trying to restart hot? Or how about a CDI box that acts strange when trying to restart hot, or ignition coils that act strange when trying to restart hot. This is bound to be something rediculous. I can drive it where ever I want, just as long as I don't shut it down and try to restart. It's all about the restart.

And to Mr. CXPhreak from AU, I get sodium hydroxide for my Restaurant. I use it to clean all my nasty parts in the garage, and yes, like you said, it is hard on aluminum, but, as I am sure you know, if you don't over use it, it is the best degreaser/ cleaner money can buy! I learned the hard way a few years ago. I was soaking a big stock pot for the kitchen that we burnt BBQ sauce inside of. I thought it would be a good idea to fill the bottom, and let it sit over night. When I came back the next morning, all of the Caustic Soda was gone. It ate a hole right through the bottom of the pot. That was no cheap pot either, it was only a few months old, and came to the tune of $200!! Hahah, lesson learned my friend.
 

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If your bike is CDI, check the resistance of your plug caps. They should be 5000 ohms resistance between the low and high tension wires. [or 0 if not fitted with resisters].

Test them cold and then hot when the bike isn't starting. See if the reading changes.

Ditto the ignition coils, which should show 7,500 ohms resistance.

Oh, take the caps off the coil leads or your readings will be a combination of the 2 resistances.
 

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Just for grins, before you try to start the next time it is hot, remove the seat and unplug the connector with the 3 yellow wires that comes from the stator, then try starting it.
 
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Discussion Starter · #9 ·
I already removed the the Resistors and put rods in the Plug Boots. I couldn't find the Resistor Value anywhere, so I had nothing to compare my readings to. They were well over 5000 Ohms. Matter of Fact, they were at least 5000k Ohms.

CXPhreak - When you say to check the Ohms on the Coil, are you saying Check the Low tension input wire to ground, or High Tension Lead to Ground?

Allan - What is the potential outcome of disconnecting the Alternator Wires? It is my understanding that although they share the same magnetic field, they are isolated from the rest of the windings? Is there a trick I don't know?

Thanks again, gentlemen.
 

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Allan is right in that defective charging windings can have an affect on the HV windings for the ignition. I don't understand why but it happens.

If you've modded your plug caps they should show 0 ohms. I think you may still have corrosion in the end of your cap if they are still measuring over 5000 ohms.

The test on the coils is to remove the plug cap, unplug the coil from the CDI unit and take your measurements between the plug lead and the CDI wire.
 

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http://cxgl.wikispaces.com/Carb+Theory

This pic if from the above link.

The low speed jet that you're probably having trouble with is in the center here with the red and blue lines. Junk builds up in the small holes in this jet and can cause poor low speed running and hard starting. This jet can be removed by using the instructions in the above link. There is also a great write up in that link.

 

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Allan - What is the potential outcome of disconnecting the Alternator Wires? It is my understanding that although they share the same magnetic field, they are isolated from the rest of the windings? Is there a trick I don't know?
There have been instances where a short in the alternator has caused some bikes to not start. The odd thing is that the bikes will start with a push or the alternator unplugged.

I don't know why this happens, but when I got my first CX, it would not start, it had very weak spark, I was fooling with it and had the alternator wires unplugged one time and checked for spark and I discovered that it had a nice fat blue spark. I plugged the alternator back in and the spark was weak and orange/red.

I wonder if in your case when the bike is hot it could be developing a short which may cause the hard start condition. It is a long shot but it only takes a few seconds to try it. It probably is not the problem but if you try it we can rule it out as a potential source of your problem.
 

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Discussion Starter · #15 ·
Let's say disconnecting the alternator at the harness rectifies the problem (Play on words, I know) Would that show the Alternator windings are bad? Or would it still be the Stator Windings. As we know they share a magnetic field and that's all. I am going to make a video as soon as the neighborhood wakes up, then everyone can see why I am convinced it is not a carb problem.
 

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Both sets of windings are on a common component, if disconnecting the 3 pin plug 'cures' the problem it's the stator either way. Possibly short to earth. May be worth sticking your multimeter on continuity and probing the 3 terminals to ground and to each other.

You want continuity between pins but none between the pins and earth.
 

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Discussion Starter · #17 ·
Are you sure that the Alternator Windings are on a common component? When I had it apart, what appeared to be the alternator was outside the crankcase separate from the Ignition Stator. The device I believed to be the alternator was external, and covered with a small thin steel plate on the very back of the engine, and plugged into a shared harness with a couple of Bullet Connectors. Or is that something entirely different. I have backup one of those, whatever it is.
 

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They're ignition advancer pulsers.

This is a new stator I installed recently. This is a David Silvers replacement, so it's not identical to yours. But, the two larger windings are the ignition windings, the rest are battery charging.



Behind it in the middle you can see the advance pulsers.
 

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Discussion Starter · #19 ·
After sitting all night long, I went out this morning, and it fired on the first revolution. I let it run about 5 minutes, and then started filming. It wouldn't restart. I disconnected the Yellow Wiring harness, tried again, and nothing.

Watch this video, it will confirm that this isn't carburetor troubles
 
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