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You need to verify you have spark to that cylinder.
Then do a compression test if possible - just so you aren't guessing.
If those check out ok, its your carbs.
I just did my carbs and I was the first one to get into them. Mine did the exact same thing until used a .020 wire on my emulsion tubes. Number 4 cylinder was cold and idle was erratic.
From personal experience:
You can spray carb cleaner through the hole - not good enough
You can look through it and see light - not good enough
Soak it for a while in Sea Foam & ream it with a .020 wire, it will be like new.
The wire has at least a couple thousanths clearance and doesn't damage anything.
Also, when I did mine, I found the mixture screws were only 2 turns out, and the tips were dirty. I have them set to 2 1/2 turns and it idles much happier. My point is, you need to check them and make sure they're set.
After you clean the emulsion tubes well and mess with the mixture screws, the carbs need to be sync'd.
If you run it without the tank on, don't forget to plug the vacuum hose from carb 4 you took off the petcock.
Then do a compression test if possible - just so you aren't guessing.
If those check out ok, its your carbs.
I just did my carbs and I was the first one to get into them. Mine did the exact same thing until used a .020 wire on my emulsion tubes. Number 4 cylinder was cold and idle was erratic.
From personal experience:
You can spray carb cleaner through the hole - not good enough
You can look through it and see light - not good enough
Soak it for a while in Sea Foam & ream it with a .020 wire, it will be like new.
The wire has at least a couple thousanths clearance and doesn't damage anything.
Also, when I did mine, I found the mixture screws were only 2 turns out, and the tips were dirty. I have them set to 2 1/2 turns and it idles much happier. My point is, you need to check them and make sure they're set.
After you clean the emulsion tubes well and mess with the mixture screws, the carbs need to be sync'd.
If you run it without the tank on, don't forget to plug the vacuum hose from carb 4 you took off the petcock.
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