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Discussion Starter · #1 ·
Hello! So I just finished rebuilding the carbs on my 75 CB360. So I got it bench synced and vacuum synced as best I could. Got it up and idling just fine other than it was hanging out around 1500 rpms at idle(Yes I'm going to get that down to 1200 rpm). So one thing I noticed taking it around the block a couple times is it's definitely slowly than before. It doesn't accelerate as fast. Could that be because I added inline fuel filters and they weren't there before? Or did I miss something?

Also, here's a video of it idling at 1500 rpm.
 

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Two things, are the jets in the correct holes and how about the float levels???
Also, air leaks in the carb boots??? If the petcock filter is in place you do not
need the extra fuel filter. That added fuel filter is probably not the problem but
remove it just to see if that helps the bike.
 

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Discussion Starter · #4 ·
I just realized that I forgot to do the timing and valve clearances before vacuum syncing. So once I do that I'll report back on how it runs.
 

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Discussion Starter · #5 ·
Note to self, make sure the kill switch is turned to the on position so that you can actually set the timing.
 

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Discussion Starter · #6 ·
And now that I've done the valves and timing and such, it still runs poorly. It seems to have half, if not less, of the power before the carb rebuild. I'm going to take the carbs off again, and clean them really good. I will also make sure that I get them on correctly so there aren't any vacuum leaks. Anything else I should try? Also, if it helps, the left cylinder and exhaust are definitely hotter than the right cylinder and exhaust. Also, when idling, taking the right spark plug boot off, does nothing to change the idle.
 

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Discussion Starter · #8 · (Edited)
The right spark plug is wet when I shut it off. The left cylinder is a lot hotter and seems like it's starting to get the look of a plug with a lean condition. Also, when I synced the carbs, they were both pulling the same amount of vacuum.
 

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Discussion Starter · #9 ·
Update, I got the timing done correctly. Now the problem is that when the boot sits fully on the left spark plug, it won't fire. Yet when I'm taking it on/off it will complete the circuit and fire. I bought a new boot, put it on, and it didn't correct the problem. So now this is more of an electrical issue and this thread can be moved. But anyway, what's my next step? Check the coil and wire?
 

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Discussion Starter · #10 ·
JK, lol. So I tested for spark at the left spark plug and it was there! So it's down to a fuel delivery issue now. Yay!!!
 

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Just for the record, I cleaned the carbs 3 times on my CB400T II and it still ran on 1 cylinder.
Finally figured it out, I need a new coil.
 

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Discussion Starter · #12 ·
So it turns out that fuel is getting through! My left spark plug(the cylinder not running) comes out wet and I can smell gas coming out of that exhaust. Could the spark plug spark when outside of the cylinder, but when put back in the cylinder not fire correctly? Oh, I also checked just the spark plug wire and that sparked as well.
 

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Yes - Spark Plugs will allow the spark to jump the gap and look good outside of the cylinder but when placed under compression no longer be able to do the same.

Plugs are cheap replace them.

I have on many occasions (more than I would like to admit) Pulled and Pulled on either a Chain Saw, Weed Whacker, etc checked the Spark at the Plug only to find replacing the Plug was the solution.
 

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Discussion Starter · #14 · (Edited)
So today I bought a new plug for the left side and it worked for about 30 seconds before dying. So now I have absolutely no idea what's going on.
Edit:
I'm going to try switching the coils and see what's happens then. Can a coil give too much power to a spark plug and cause it to fail?
 

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I clipped the plug wires about 3/8 inch and reinstalled the plug caps.
Bike ran good for about a minute then went back to one cylinder. With
help from a forum member I was able to test the coil. coil tested bad.
A new coil wil fix mine and probably fix yours.
 

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A cylinder running lean will run hot. It can burn a hole in your piston. Get rid of the filters, you don't need them. It is likely impeding your fuel flow. Other than that, it's the usual culprits with fuel flow. Check your jets and float levels.
 

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Discussion Starter · #17 ·
Well after reading my manual (note to self: do that more often) and going through the coil diagnosis, it turns out that I have a bad left coil! I've got a new one ordered and on the way.
 

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Discussion Starter · #18 ·
The mystery continues. So I got the new coil on today, the bike ran beautifully for like 3 minutes then it went back to a one cylinder bike with the cylinder not running on the side with the new coil. Pulled the plug and it wasn't fouled. When I get time again, I'm going to check the coil, and if it passes I'm going to go up the wires and see if there's a short up the lines somewhere.
 

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Discussion Starter · #20 ·
Alright, so I finally got time to start playing with my motorcycle. I had put the battery on a trickle charger for a couple weeks beforehand. I stick the battery in, pump the kick start about 10 with the switch off to get oil in the upper parts of the engine. Flip the switch, one kick and it starts up right away running on BOTH cylinders. Apparently it rethought its life over the winter and decided to be a two cylinder bike again. The one thing I did change was I put a new carb throttle shaft seal in the non running cylinder before I started it up.
 
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