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Discussion Starter · #1 ·
Hey guys
Long story short I’m trying to get an 81 cx running that’s been sat for a good while. I’m at the point where it runs but on the left cylinder only. carbs are clean, had them off a few times. I’ve not really worked with cv carbs before, I took a video. My question- Shouldn’t the slides rise smoothly when I’m winding the throttle open ? Left moves a bit, right one kind of flutters.
help much appreciated.
 

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It would be helpful to know what other things have been done to the bike. Have you checked the stator (How to check or test the stator and pickups on a CDI Honda CX500 | MotoFaction )? Have you done a compression check? How did you clean the carbs? Did you follow this procedure (https://sites.google.com/site/cx500gl500/correct-carb-cleaning-and-idle-jet)?
If you haven't already, visit the wiki (link in my signature line) and download a copy of the factory service manual for your bike. See the trouble shooting guide.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Thy should move smoothly, together.
Is it possible the vacuum domes have been switched? The vacuum pistons and domes wear together after a while, and I've found them to stick sometimes if the pairings are confused.
 

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Discussion Starter · #4 ·
Thy should move smoothly, together.
Is it possible the vacuum domes have been switched? The vacuum pistons and domes wear together after a while, and I've found them to stick sometimes if the pairings are confused.
I didn’t switch them but I suppose I could pull the carbs back off and switch them around and see if it makes a difference. When I push them up by hand they seem to move quite freely.
 

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Discussion Starter · #5 ·
It would be helpful to know what other things have been done to the bike. Have you checked the stator (How to check or test the stator and pickups on a CDI Honda CX500 | MotoFaction )? Have you done a compression check? How did you clean the carbs? Did you follow this procedure (https://sites.google.com/site/cx500gl500/correct-carb-cleaning-and-idle-jet)?
If you haven't already, visit the wiki (link in my signature line) and download a copy of the factory service manual for your bike. See the trouble shooting guide.
I checked compression and spark initially and am running it off some fresh fuel from an auxiliary tank. When I spray some carb cleaner down the inlet it starts firing on both cylinders which is why I assumed a carb problem.
cheers
 

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I checked compression and spark initially and am running it off some fresh fuel from an auxiliary tank. When I spray some carb cleaner down the inlet it starts firing on both cylinders which is why I assumed a carb problem.
cheers
When cleaning the carbs did you remove the idle jet? See CX500Gl500 - Correct Carb Cleaning and Idle Jet If you decide to remove it there is an alternative to using the screw extractor which requires taping the first bit of the jet and using a screw, bolt and washer. This side of the pond we would use a #4-40 screw and the appropriate tap.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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When I push them up by hand they seem to move quite freely.
If they were sticking in the domes, you'd notice it trying to move them by hand.
Are the atmospheric ports unobstructed on each carb? A blockage could keep the pistons from lifting as they should.
 

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Discussion Starter · #9 ·
When cleaning the carbs did you remove the idle jet? See CX500Gl500 - Correct Carb Cleaning and Idle Jet If you decide to remove it there is an alternative to using the screw extractor which requires taping the first bit of the jet and using a screw, bolt and washer. This side of the pond we would use a #4-40 screw and the appropriate tap.
Ahh, you’re right I didn’t I didn’t see anyway of removing it so I assumed it was a factory set part. I’ll have a try at getting them out this weekend. Enlarging that hole by screwing something into it won’t effect it ?
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Discussion Starter · #11 ·
So I removed clean and refitted those idle jets and now it fires on both cylinders and idles nicely. I took it for a spin, it’s fine up to about 1/3 throttle then you don’t get any more acceleration out of it.
i think it’s those slides not traveling up and down nicely. The right one particularly, it requires more force when you operate by hand. Is there anything I can do to help this.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Try switching the vacuum domes. The pistons and domes wear into each other. If they get mixed up, they might not move smoothly.
 

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Discussion Starter · #14 ·
I’ve got the slides moving nice and smoothly now but it hasn’t made any difference at all. When riding it it’s fine until 4K rpm then acceleration drops off suddenly.
 

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I checked compression and spark initially and am running it off some fresh fuel from an auxiliary tank. When I spray some carb cleaner down the inlet it starts firing on both cylinders which is why I assumed a carb problem.
cheers
I’ve got the slides moving nice and smoothly now but it hasn’t made any difference at all. When riding it it’s fine until 4K rpm then acceleration drops off suddenly.
It may be time to revisit the ignition system. The CDI has essentially two systems, one which operates at low rpm (0 to about 4000 to 5000 rpm) and one at higher rpm. Do the stator resistance checks as mentioned in post #2.
 
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Discussion Starter · #16 ·
1 - 5 = 107.7
2 - 5 = 88.2
3 - 5 = 197.7
4 - 5 = 104.6
6 - 5 = 91.1
7 - 5 = 196.4
9 - 5 = 1
9 - 8 = 79.3
This is what I got.
infinite resistance between 9-5
The diagram says this is the low speed source coil. Does that seem right ?
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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You might need to change the range on your DMM to get a 9/5 reading.
Or you've got a broken connection somewhere on the 9 wire.
 

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Some stators give slightly different readings, yours may be OK. You have a baseline reading for future reference.
Did you do the test engine cold or at operating temperature?
 
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