Author Topic: '82 CB650SC cylinders drop out and fuel smell  (Read 9375 times)

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Offline bryanj

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #25 on: October 11, 2024, 05:32:43 PM »
Recently had to change the pg's on a gl1500 that wouldnt start and run right, all these coils are getting old now plus heat and wet is not friendly
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Offline M 750K6

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #26 on: October 11, 2024, 10:09:51 PM »
Are you certain the fuel tank is venting?

Offline PeWe

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #27 on: October 11, 2024, 11:09:56 PM »
Are you certain the fuel tank is venting?
+1 on that.
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Offline Depco

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #28 on: October 12, 2024, 05:58:13 PM »
Are you certain the fuel tank is venting?

I'm not sure how I would test that. I certainly don't have any indication that the fuel filler cap is having issues.

Offline scottly

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #29 on: October 12, 2024, 06:12:00 PM »
Are you certain the fuel tank is venting?

I'm not sure how I would test that. I certainly don't have any indication that the fuel filler cap is having issues.
Besides, you've already found a smoking gun with the obviously faulty pulse generator. ;D
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Offline M 750K6

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #30 on: October 12, 2024, 08:17:10 PM »
Are you certain the fuel tank is venting?

I'm not sure how I would test that. I certainly don't have any indication that the fuel filler cap is having issues.
Besides, you've already found a smoking gun with the obviously faulty pulse generator. ;D
True, but it's easy to test. When you experience the fault, open the gas cap. If not venting, it will resist opening and you may hear air being sucked in as it opens. Start it up. If the fault has disappeared, suggests your tank's not venting.

Offline Depco

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #31 on: October 13, 2024, 05:48:35 PM »
True, but it's easy to test. When you experience the fault, open the gas cap. If not venting, it will resist opening and you may hear air being sucked in as it opens. Start it up. If the fault has disappeared, suggests your tank's not venting.

Ill have to get another key. The gas cap needs the ignition key to open. I only have one key. LOL.

Offline RAFster122s

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #32 on: October 13, 2024, 06:21:18 PM »
It has an actual lock on the gas cap? Lots of them are able to open with anything the fits in the slot.
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Offline Depco

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #33 on: October 15, 2024, 07:06:54 PM »
***Final Update... hopefully***

I received the replacement pulse generator in the mail today. I came home from work and went directly to the garage to get it on the bike. It is cooling off here in the midwest and the todays top temp was in the upper 40's F. I tested the new pulse generator and found it to be showing resistances within anticipated tolerances. The boy and I put the new generator on and fired up the bike. It was humming right along as expected. While pulling the old one off I tested it again and it was also within tolerances. I was not surprised since it had not warmed up and usually the bike was good while cold. I may hit it with a heat gun and see of the readings fall off as it warms up, but that is a post mortem for another time.

After letting the bike warm up I decided to go for a spin. I got the cold weather gear out and bundled up. To my surprise the throttle was much more lively and it was responsive through the entire rev range. From a stop to red line it was pulling. It has been many a year since this bike has run this well, and I had a stupid grin on my face the whole time. There was part of me that kept waiting for the bike to have the 2 cylinders drop out, but nothing of the sort happened. As an FYI I ride an '01 Road King so this bike is a completely different experience. Nimble and compact. The sense of speed is significantly more pronounced. It is a great bike for a young man learning to ride.

I rode for about 12 miles and was satisfied with the result, if not a bit cold as my gloves were not as warm as I had expected them to be. Luckily I had a warming machine between my legs and I was able to wrap my hands around it at stop signs. (I mean the engine, you degenerates) This weekend promises to have temps back in the low 70s F. Me and my father-in-law are planning on taking the boy out for a ride on Saturday to let him feel the bike running as it was intended to be. Without hesitation or lack of power. I am hoping this will erase his previous poor experiences with this bike, and get him into enjoying riding without anxiety of being stuck on the side of the road on a busy highway.

It has an actual lock on the gas cap? Lots of them are able to open with anything the fits in the slot.

Yup the gas cap uses then actual ignition key. No other slotted tool will work without breaking the cap.

I would like to thank everyone here who responded and helped troubleshoot this problem. I have been chasing this issue off and on for nearly a decade, in some form or another. Although this is the first real serious attempt at getting the bike back to its original running condition, it had been a long frustration every time I took the bike out to try and see if I could fix it. I doubt highly that I would have come across the solution without the help of the knowledgeable posters here.

Now with the bike running like new I am inspired to finish finding the replacements for the missing/damaged parts for this bike to bring it back to newish condition. I still have to replace the Mirrors, Right side cover,  and rear tail lamp cover, as well as try to rehabilitate the paint on the tank from the glass shower it took a few years ago. I have found a source for some of the parts but I suspect it will be through the winter to get the parts together and on the bike. I will make sure to put up a photo of the bike on the road as soon as I can get one of the boy on it. Again, Thank You, and keep up the good work.

Offline scottly

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #34 on: October 15, 2024, 07:21:52 PM »
We all love to hear when a problem finally gets fixed!! 8) 8)
Don't fix it if it ain't broke!
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Offline fizzlebottom

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #35 on: October 15, 2024, 08:17:34 PM »
Wild. I've never actually seen one of these fail. I'm super curious about what actually failed internally in one of the pickups. I think they're basically just hall effect sensors, which just take a magnetic signal and amplify it via a transistor. They're probably sealed from the elements, so taking one of the pickups apart to investigate would probably destroy it. The engineer in me sure wants to though.
1982 CB650SC Nighthawk

Offline scottly

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #36 on: October 15, 2024, 08:55:10 PM »
I think they're basically just hall effect sensors, which just take a magnetic signal and amplify it via a transistor.
No, the pulse generator is a coil of wire like an electromagnet, but in reverse. ;)
Don't fix it if it ain't broke!
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Offline Depco

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Re: '82 CB650SC cylinders drop out and fuel smell
« Reply #37 on: October 16, 2024, 09:16:51 AM »
Wild. I've never actually seen one of these fail. I'm super curious about what actually failed internally in one of the pickups. I think they're basically just hall effect sensors, which just take a magnetic signal and amplify it via a transistor. They're probably sealed from the elements, so taking one of the pickups apart to investigate would probably destroy it. The engineer in me sure wants to though.

I want to heat it with a heat gun and see if the readings start to fall off as it warms up. If they do I then want to see what's inside... But I also want to salvage the working circuit in case It is needed to repair another bike down the line.