[Rockatanski]

'75 360 and the left spark plug soots up fast, that after two miles I can barely make it up the driveway.
It had 13,000 miles on it when a buddy pulled it out of a barn. New ignition components, timing checked twice, points checked three times, spark advancer is clean and works which I took off again and verified. New diaphragms in both carbs and I have replaced the float valve and seat. I got the new seat (Common Motor) in as far as it would go but I can see a trace of the 'O' ring. Also before replacing the seat, I had the float height as far as 24mm and I think it was fuel starved. Regardless, the plug fowls as much as before I replaced the seat. Float height currently at 19mm. Float valve moves freely and the float floats. Idle screw turned all the way in but makes no difference. Other than the diaphragms, all needles and seats looked good for wear as one would expect a bike with 13,000 miles. Fuel NEVER seaps out the overflow.
What so I do next? I had monkeyed with the float height before changing the seat, but I think I wound up starving it for fuel and put it back at 19mm at some point. Should I try it walking it lower again? I think that's my only option but it helps me to bounce these things off others.
The right plug soots a little but nothing like the left. The left side is my largest problem.
Thanks.

 

[Rockatanski]

BTW, the carbs are stock and I while I don't have the jet #'s off hand, I have already verified from other posts that they are the stock sizes.

 

[gogodirk]

Try a hotter plug

 

[Bill H]

You might check the jet needle and see if they are the same on both carbs. raising the needle a step will lean out he mixture in the carb. Also sounds like idle circuit is plugged in both carbs.

Bill H

 

[Rockatanski]

You might check the jet needle and see if they are the same on both carbs. raising the needle a step will lean out he mixture in the carb. Also sounds like idle circuit is plugged in both carbs.

Bill H

I assume then that a plugged idle circuit blocks air rather than fuel. I had assumed both.

I should have mentioned in the initial post that when I managed could get the RPM's high, then it ran on both cylinders, sounded good, and had power. Backing off to mid-range made it sputter some. Three blocks from the house I was on one cylinder. Therefore plugged lower circuits makes sense. I've got fuel filters installed but the carbs had a bunch of rust in them when I got it so crud might be breaking lose from somewhere. I don't use ethanol and have verified that the float is actually floating.

I will check the needle but I don't think there is more than one notch. I will also ensure the idle circuits are clear again.

Is there a unique method to clearing those out that I'm not aware of? For example, I know on a completely separate carb on a different make of bike that there is a specific method to cleaning some jets or they won't be cleared. Can you tell me is such is the case with these?

After the above and short of advice from others, I will reassemble and depending on what I find, lower the float for giggles.

Thank you very much for the advice.

 

[Bill H]

The idle circuit works or not when the throttle is closed. as you open the throttle the needle moves in the needle jet and allows fuel to increase wide open throttle is high speed jet only the needle doesnt do anything . so if you are having low to mid range problems you need to look at the needle and needle jet. Pick up some NAPA carb cleaner , tear down the carbs and let them soak for 2 -3 days. then blow out with high pressure air. If the needle only has one setting make sure the needle jet is clean and the idle circuit is clean . reassemble and set the floats to factory setting. Now try the running the the motor and let me know whats its doing.

Bill H

 

[Bill H]

You might take a look at this on the net. Kevin Cameron Explains How to Tune Carbs.

Bill H

 

[Rockatanski]

I thoroughly cleaned the carbs, blew every orifice and atomizer there is, and started it. It won't idle, runs on both cylinders but sputters. I ran it about 2000 RPM's and let it get good and warm and it sputtered worse as it did. After shutting it down, I checked both plugs and the left is coated with dry soot again just like last time.

 

[Rockatanski]

I may have solved it. I lowered the fuel level on that side and the difference is like night and day. When the weather warms in a few days I'll take it out and later walk the fuel levels in.

 

[Rockatanski]

I may have solved it. I lowered the fuel level on that side and the difference is like night and day. When the weather warms in a few days I'll take it out and later walk the fuel levels in.

Praise the Lord!

 

[Montanabill]

It won't idle and turning the idle mixture screw all the way in doesn't affect it? You might be able to tune around it by changing the float level but you are kidding yourself.
Make sure part numbers 3 and 14 are still there (and 14is super clean) and pull out 3 and see how tight it fits on the slide needle.

https://www.partzilla.com/catalog/honda/motorcycle/models-with-no-year/cb360t-a/carburetor

If you have the stock old carbs all bets are off when trying to use the standard tuning axioms. Look for missing or worn parts and good luck. If you can't seriously slow down the engine by turnig the idle mixture screws all the way in something is wrong. One to three turns out from lightly bottomed works.

 

[Rockatanski]

It idles fine now that I dropped the fuel level 2mm thus leaning it out. It's running the best it has yet. When the weather warms, I'll ride it and see what happens. I may have to tweak float levels and pilots, and will check synchronization. I got in this mess because the carbs were so corroded that I had to replace the floats and float valves which threw the levels out of whack.

 

[Rockatanski]

The problem hasn't completely gone away, just better since I lowered the float height and installed hotter plugs. After a 4 mile ride, the plugs showed some soot. After a 6 mile ride, the left is very sooty again and it died twice going up the driveway, but at least I made it farther. The slides move freely but I'll double check. Short of other advice, I'll lower the fuel level more. At least I feel I'm making progress.

 

[Rockatanski]

This is an update to close the post. The culprit was high fuel levels in the bowls. A last float bowl adjustment has either solved the problem altogether or I'm darn close- close enough to make other repairs and then ride it a while. I did about 10 miles today and it hummed right along, sounded REAL good. Got back and made another slight adjustment to one carb causing it to idle about 100 rpms faster.