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1981 Honda CX500c "Black Widow"
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Discussion Starter · #1 ·
Hey guys,

Finally got my '81 custom all wired up, replaced fluids and filter, cleaned starter and did the grounding mod on it, new solenoid, fresh set of Murray's carbs, new plugs with coil-on-plug mod but can't get it started. It sounds like it's about to go but never makes it. Just kinda sits there chugging. I made sure it wasn't seized by cranking the motor over with the bolt on the front under the fan.

Here's a video of the attempt at starting it: Video

Any thoughts of what's wrong from the sound? Anything is appreciated.
 

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It sounds like healthy cranking sounds to me--but no combustion happens. Are you sure gas is getting to the carbs? Have you checked your plugs for good spark?
 

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Discussion Starter · #3 ·
It sounds like healthy cranking sounds to me--but no combustion happens. Are you sure gas is getting to the carbs? Have you checked your plugs for good spark?
Hey missing linkage, I know the carbs are getting gas since they sucked up all I poured in the via a funnel at the top of the line, but I don't know for sure I'm getting spark, especially with the coil-over-plugs. I will go and bench test them And see what's going on with them. Thanks for the feedback, glad to hear the cranking sounds healthy.
 

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Discussion Starter · #4 ·
Alright I'm not getting any spark from either side. Tested each plug with them inside the spring of the coil overs and grounding the hex of the plugs and firing the starter button.

I've triple checked all the wires and they look good. Might be the CDI?
 

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Discussion Starter · #7 ·
I disconnected the black and white wire and got a good blue spark from both plugs, looks like I need to fix my kill switch, thanks for the help.

Now with spark and good cranking still no firing so it's gotta be the fuel. Larry told me to plug the intakes on the carbs to see if that will draw the fuel in. After a couple of attempts the right side started firing and eventually the left took of and it fired up!

BUT, I started to see flames shooting out of the left carburetor intake! So after about 20 seconds of running I shut the key off but the bike kept cranking and the flame was growing so I unplugged sparkplug connector to kill it. Woah. So the valves need some work right? Especially this left one..
 

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If you don't have a good fire extinguisher near your bike, then I suggest you get one sooner than later!
I would remove the valve covers and turn the motor manually to check that the valves are operating as they should. Good time to check and adjust the gap clearances.
If you have a compression gauge, let us know what it reads for both cylinders.
 

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Discussion Starter · #9 ·
If you don't have a good fire extinguisher near your bike, then I suggest you get one sooner than later!
I would remove the valve covers and turn the motor manually to check that the valves are operating as they should. Good time to check and adjust the gap clearances.
If you have a compression gauge, let us know what it reads for both cylinders.
Hey so I've got one of Murray's valve tools in the mail, should be here tomorrow but I just went and picked up a compression test kit.. have 155psi out if the right side, and a whopping ZERO PSI OUT OF THE LEFT SIDE, the side that was backfiring and shooting flames out of the carburetor.

Will report back with new pressures once I adjust the valves.

But is zero pressure in the left cylinder caused by just an open valve? Guess we'll see. Thanks again for the help, and I will definitely get an extra fire extinguisher for the garage.
 

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Discussion Starter · #10 ·
Okay finally received the valve tools, USPS is real backed up. Got the valves and timing chain adjusted per Murray's video. I had and exhaust valve wide open on the left side which explains the backfiring and lack of compression. Now both sides read 150 psi. Thanks for the help.

So I go to start the bike again and clickidy click click says the solenoid after a half heart attempt to turn the motor over by the stater motor. I've already cleaned it and did the ground mod but I had to find a washer to fit around the shaft in the back of the housing since there was none when I opened it up. There's still a bit of slip in the shaft and a bench test returns spotty and weak power out of the starter motor. Hoping a rebuild kit will give me the correct washers I need.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Charge your battery.
 
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What Randall said. And check the voltage of the battery before you start it and and what the voltage drops to while trying to start it.
 

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Discussion Starter · #13 ·
I've had the battery on a float charger throughout this trouble shooting process and it's new as of a few months ago so I know it's good and full. It read 11.0 dcv standalone and 10.7 dcv when trying to start (on 200 dcv setting).

I really think it's the starter motor since even on a bench test it won't run every time and the shaft slides around still. Here's some pics of the starter guts. Not sure what the amber looking stuff is but I'd guess it's glue. Is it supposed to be everywhere like this?
 

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A good battery should be more like 12.4 volts standalone. Are you sure your charger is working as it should? What voltage do you read when it is being charged?
I would also check the accuracy of your meter.
Can you jump a good car battery and give it a crank? If it cranks normally, your battery is faulty.
Check to find out if anything is draining the battery when the ignition is turned off.
Can you take a photo of the starter mod that you did?
 

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Discussion Starter · #15 ·
A good battery should be more like 12.4 volts standalone. Are you sure your charger is working as it should? What voltage do you read when it is being charged?
I would also check the accuracy of your meter.
Can you jump a good car battery and give it a crank? If it cranks normally, your battery is faulty.
Check to find out if anything is draining the battery when the ignition is turned off.
Can you take a photo of the starter mod that you did?
Okay so I jumped it with my vehicle battery and it started cranking again like normal, so I must has drained my battery past what the float charger could replenish, I will go get a real charge.

Now that I have fixed the compression issue and I was really hoping it would have fired up when I had it jumped but it wouldn't take off. I plugged the carb intakes again to see if it still wasn't sucking in gas and that kind of helped, it made some firing noises but that's it, never actually started. Not sure what to check next. Could it be flooded with gas?

I didn't snap a pick of the starter ground mod but I just drill and tapped a blind 3mm hole for the screw. I do think the starter is fine now that I know the battery is just weak.
 

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Discussion Starter · #16 ·
have you run this test?

View attachment 205013
Sorry I kinda skipped over this, I just ran this test now that I've got my battery back to 12.4v and the starter is cranking again.

1/5 - 107
2/5 - 92
3/5 - 198
4/5 - 108
6/5 - 92
7/5 - 197

8/9 - 80
5/9 - 300

My only out of range one is the 5/9 circuit, source coil low speed. Would this keep the bike from starting? Or is that a potentially different problem all together?
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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My only out of range one is the 5/9 circuit, source coil low speed. Would this keep the bike from starting?
Yes. You're getting insufficient ignition voltage in the low range.
 

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Discussion Starter · #18 ·
Yes. You're getting insufficient ignition voltage in the low range.
Thanks for the help Randall. So I probably need a Rea-San stock CDI kit or an ignitech to fix this right? Don't know if I need the full hall effect kit or not. Any direction is much appreciated.
 

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If #s 1, 2, 4, and 6 are within spec, you shouldn't need the Hall effect triggers.
 

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Discussion Starter · #20 ·
Finally received my Rae San Hall effect kit (same price as stock CDI) and installed it...

Damn this bike is loud!

So thankful for all the help. Stoked this 40 yr old beast is alive again. Now to finish the rest of this project, hold my beer.

Thanks missing linkage, Randall-in-Mpls, nolimitz, murrayf, D-fresh.
 
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