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Discussion Starter · #1 ·
I got this 360 that will start up great. It idles, but if you ope the throttle at all it jumps up to about 4,000 rpm, and takes a long time to come back down, if at all.

I figured this was a sticky advance, so I opened it up and cleaned and greased everything. Now, when I operate the advance the arms are not that quick to close and don’t quite close all the way on their own. So I am assuming my springs are too weak. I don’t really want to have to buy a whole new unit, especially a used one that might have the same problem. Does anyone have any suggestions on where to source springs?
 

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The springs were NEVER sold separately, and fine parts oil (not grease) is the correct lubricant, used sparingly
 

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Correct Steve. If I recall correctly there have been some members that came across close equivalents on the web that still needed modifications to work just right. That was beyond what I was comfortable doing, so I don't have experience in what was purchased and what specific mods were done.

For the advancer, I just used some general purpose mechanic oil on the springs and the arm joints. Can you confirm that the carburetor is tuned properly (A/F mixture screws and both carbs are in synch). In my initial startup this past weekend, my CB360 did the exact same thing until I started messing with the mixture screws and idle screws. Is the throttle "snapping" back after releasing the grip?
 

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I cut half of the hook on each end of the spring, and reform the ends. I have seen folks using springs from mikesxs, but I don’t know if they are plug and play.
 

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Could easily be not enough slack in throttle cables....
 

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Discussion Starter · #6 ·
Throttle cables have ample slack and snap back to closed position. I did a LOT of reading on here before decided to take off the points plate.

I did read about people on the do the ton forum trimming the springs to get more tension. However I also read on here (specifically in an old post by you, sprint, that if you don't get the right tension the advance curve will be off.

I have not messed with the mixture screws yet. I read the manual and was a little bit confused about "finding the highest idle." I do have the screws set to the spec'd position which is 1-1/8 turns out (754A carbs).

In any case I will need to get the advance unit back on before starting again, and it is definitely not snapping back as it should. I supposed if the springs are not in existence without buying the whole unit, I can begin by trying to trim them.
 

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Regarding the mixture screws, you set them to a base setting (such as 1-1/8 out like you state) and then let the bike idle. You slowly turn the mixture screw left or right and you may hear the RPMs go up slightly and then taper off and decrease. Right at the "peak" RPM spot is where the mixture screw should be set at. Repeat for the other side's carburetor. The HSM spec is just a baseline for getting the bike running, but needs to be fine tuned on an individual basis, as this setting will depend on elevation, temperature, humidity, etc.
 

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Discussion Starter · #8 ·
Thank you, that's a great explanation. I'll trim the springs and try air screws and see if it improves the condition. These carbs honestly probably do need a rebuild but I'm trying to be lazy ;)
 

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Discussion Starter · #10 ·
I rebuilt the advancer unit, cleaning with acetone and then applying some light lubricating oil. The spring-back action was a bit improved. I did not trim the springs at all, they were too hard to bend with the tools I had so I left them.

The problem (idle won't go back down after throttle is released) was improved with the bike on the stand. However when I started riding it around the problem persisted.

I can see that throttle cables are not obstructed and spring back in place when released. What is the next logical conclusion?
 

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Discussion Starter · #11 ·
Found a good post with a list of things to check. I'll start with chasing air leaks. Does anyone know about "centering the throttle butterflies?" Can this be done on the bike? I'm more familiar with slide carbs. Really don't want to take carbs off.. stupid scrambler pipes...

https://www.hondatwins.net/forums/48-engine-discussion/36918-cb350-hanging-idle-weird-idle.html

List:

Carburetors:
1. Leaking carb boots
2. Carb/throttle cables not synched
3. FELT Washers that seal the Throttle Shaft on these carbs. They are supposed to be
soaked in oil to seal the shaft from allowing air behind the throttle plates.
yours could be simply dried out
4. Carb floats
5. Clogged pilot jets


Ignition:
6. sticking worn ignition advancer, the advance springs not pulling back
7. End play of the Breaker Cam
8. Check timing with strobe
 

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I had the same running idle on my Cl350. I would have to put her in gear to bring the revs down. I tried nearly everthing to fix the issue (fidled with the advancer springs, timing, sought out air leaks, I even thought at one point it was weak carburetor diaphragm springs). I gave up on it. I don't know why, but one day I decided to fiddle with the timing again. I spent an entire afternoon setting the timing absolutely perfect using a continuity light. Prior to starting the bike, I also installed a radioshack rectifier (best mod to-date by the way). I had no intentions of fixing the idle issue, like I said, I had already given up. The bike started right up and idled for as long as I wanted, reved, and came right down. I haven't had a problem since. I barely know what I'm doing half the time, but that's what I did to inadvertly fix the problem.
 

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Discussion Starter · #13 ·
Thanks, I set the point gap and timing today. It unfortunately did not fix the problem. I also adjusted the air screw. Symptom was more like hesitation when you blip the throttle, then if it comes up, it wants to stay up.

So, the bike came apart and carbs are ready to rebuild tomorrow. There was fuel on the inside surface of the carb boots, the surface that mates with the head. Also a lot of fuel in the bore of the boots. So I know there was a carburetion problem, most likely float height if not more. Maybe slightly leaky boots too?

I have a couple questions since I’ve never rebuilt these carbs before.

1. I have an ultrasonic cleaner. I read that there are felt washers on the common throttle axle. Do I need to separate these carbs from the rack and remove those before throwing them in the bath?

2. These diaphragms seem to have been messed with by a PO. Seems they should be replaced. The fiche calls it all out as one part. Is it possible to buy just the rubber?
 

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Interesting, I have always seen these rubber pieces as being black (or faded black due to age), never blue! They do seem like they have been messed with...

Unfortunately they only come as a complete assembly with the carb slides included (and they are $$$). I know that there is a mod that is touted by Common Motor Collective to replace the diaphragms with a new set from JBM industries, which requires ripping off the old ones and press fitting the new ones on, but there has been some operating experience here on this forum that concluded that they aren't a perfect substitution.
 

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Discussion Starter · #15 · (Edited)
I also found the common motor collective parts. I am considering trying them. 4into1 has a set that is meant for 350's and is supposed to be installed without detroying the retainer like the CMC one's. I emailed 4into1 about the compatibility of the 350 diaphragms on the 360, just in case.

I got my carbs apart. The bodies are marked 754A. That is not one of the carb types mentioned in the manual. My jetting was:

68 Primary main (same as manual)
100 Secondary main (manual says 95 for 744B and 68 for 745B and 747A)
35 Slow (same as manual)

I am not sure what the difference with the bodies is, but the only one that is called out in my manual with a secondary main even close to 100 is for the 250 twin, and it is only a 95. So I am thinking that it may be possible that the secondary main should be a 68, and that could be contributing to my problem.
IMG_E8223.jpg

Edit: just read another thread on here saying that the manual is mistaken and the secondary should be 110.

https://www.hondatwins.net/forums/49-fuel-supply-carburation/5531-cb360-carb-main-jet-debate-excerpt-brett_bike-project-2.html

Edit: ok also seeing 100.
 

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Note that ordering from JBM industries directly can get you a MUCH cheaper deal than CMC...as usual.
 
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Discussion Starter · #17 · (Edited)
Note that ordering from JBM industries directly can get you a MUCH cheaper deal than CMC...as usual.
Thanks, I just requested an invoice from them. should be $47.50 with shipping as opposed to $60 before shipping on CMC.

edit: just realized there are supposed to be gaskets in between the insulators and the head, and I had none. lol
 

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just realized there are supposed to be gaskets in between the insulators and the head, and I had none. lol
Yeah looks like another source for an air leak = more headaches with tuning.

Good catch!
 
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