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Navy Vet Search & Rescue
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No it doesn't sound right because it's only running on 2 or 3 cylinders. Let it idle for a few seconds or so then feel of the exhaust pipes where they exit the head. See which one/s are not getting hot.
 

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Discussion Starter #3
They are all hot to the touch. I sprayed water on all of them and they seem to vaporize when I hit it near the top. Before I did all this I did check the spark plug caps to make sure they were snapped in. Seems like you don't hear them snap in all the time. I wonder if I should replace those spark plug wires. Not sure how they are removed from the coil though. Here is a vid when I sprayed the cylinders:

YouTube - kz750 checking cylinders
 

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Navy Vet Search & Rescue
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Looks to me like #3 is the culprit in the video and #1 appears to be somewhat weak. Don't wait long enough for the pipes to get hot up top just from conduction from the head. A quicker way to tell is just patting them with your hands as they first start to warm up, but again do no do this right next to the head.
 

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P.S. Looking at the parts breakdown, it appears you have the coils with the screw on caps at the plug wires. Just unscrew the little cap where the plug wire connects to the coil then twist and pull on the wire and it should come out of the coil.
 

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Discussion Starter #6
Each cylinder felt warm after the initial idle. That's right when turning the key from the cold start. I'm thinking I touched it too high though perhaps? Should I touch it more towards the bottom. Does seem like in the vid, #3 doesn't vaporize the water as fast. There might be a tad of soap in the water, doubt that'll effect it. Is there another way to ensure the cylinder is working besides touching it or spraying water on the headers? So if one cylinder isn't working at all there should be significant loss in power. I think I need to get it out on the road and see how she rides. I think I would be able to tell if there is performance loss when hitting the throttle. I mean one cylinder out should severely limit performance I would think.
 

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Navy Vet Search & Rescue
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It could be that it's just partially firing as it would from weak/intermittent spark or carb/compression issues for that cylinder. All that is accomplished by checking the pipes is to help narrow down where the problem is. As in which cylinders have problems. It's ok to use the water but you need to really pay attention to the fact if one will boil/vaporize the water instantly while another one only boils it off after sitting there a second or two. The differences may be small but you need be able to notice that. Also, I've seen some cases where it idles like crap but once you get some rpm going it starts to run somewhat normally.
 

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Discussion Starter #9
Seems to idle right from the get go though every time though. I guess a bad cylinder wouldn't necessarily cause bad starts. Before it wouldn't even idle or run without the choke. Checking the battery again it's at 11.6 volts again. I wonder if the battery isn't good. Think I want one of those batteries where I don't have to keep refilling with acid.
 

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Navy Vet Search & Rescue
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I can totally remove 2 plug wires from mine and start it up and it will idle very nice on only 3 cylinders so don't think it's running on all 4 just because it starts or idles. I've got a vid that I posted for an entirely different reason but it demonstrates that one will idle on 3 cylinders. Listen to the sound on 3 cylinders. It's sort of like a chugging sound. It's very distinct as yours is. When all 4 are firing evenly the sound is totally different.

YouTube - Plug firing test
 

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I can totally remove 2 plug wires from mine and start it up and it will idle very nice on only 3 cylinders so don't think it's running on all 4 just because it starts or idles. I've got a vid that I posted for an entirely different reason but it demonstrates that one will idle on 3 cylinders. Listen to the sound on 3 cylinders. It's sort of like a chugging sound. It's very distinct as yours is. When all 4 are firing evenly the sound is totally different.

YouTube - Plug firing test
You have a 5 cylinder? :confused:
;)

Oh and the video...I so remember that thread.
 

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Discussion Starter #13
So maybe the carb sync. will help? Guess I might as well do that and see what happens. A carb sync is the same as an engine vacuum sync. right? Anyone got a write up on where to make the connections from the carb tune pro to the bike when synchronizing the carbs?
 

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Seems to idle right from the get go though every time though. I guess a bad cylinder wouldn't necessarily cause bad starts. Before it wouldn't even idle or run without the choke. Checking the battery again it's at 11.6 volts again. I wonder if the battery isn't good. Think I want one of those batteries where I don't have to keep refilling with acid.


i think your battery might be toast.....
 

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There should be a vacuum port on the top front of each carb. They may currently have vacuum lines attached to them so those will have to be removed to attach the carb tune. You will need a small aux fuel tank to attach while doing the sync.
 

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I have 1980 750 LTD and I had similar issues. Only thing is mine would do it when the choke was on. Found out the choke circuit on cylinder 1 was plugged, not allowing fuel to flow. But my bike sounded exactly like yours. Have you ensured that that carb is clean? It took me about 6 cleanings to finally get all the crap out of mine.
 

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Discussion Starter #20
There should be a vacuum port on the top front of each carb. They may currently have vacuum lines attached to them so those will have to be removed to attach the carb tune. You will need a small aux fuel tank to attach while doing the sync.
I'm probably just going to get some long fuel lines and vacuum line to do that, and just raise the tank up on something. I'm kind of cheap, lol. I don't think I'll need a long vacuum line if I just set the petcock to prime correct?
 
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