CB360 running issues

[crazypj]

PJ do you run stock airbox on your 360? I know your carbs are something else......

Running genuine K&N filters and a long quietish exhaust.
I have spent a LOT of time making stock carbs work (21~22 yrs ;D )
Without modified air corrector jets it will never run right mid -range
You can check bdn3d comments after he rode it on my build thread (about halfway down page)
http://www.dotheton.com/forum/index.php?topic=11736.375
I will be modifying a set of real cheap filters I got from Sporting For Less (made in China) the mountings are terrible so I'm going to machine some tubes and epoxy them in place to get 'correct' length and a better shape for transition (filter to tube)

 

[MB]

Already referred and re-refered to your build countless times mate. So what are the odds if next time I'm in the Sanford area for a few days and throw my carbs in my suitcase I can pay you to "pj upgrade" them for me.....?

 

[tweakedlogic]

I have been running stock jets with pods and pipes on my 360 for a couple of years now. It ran great. One little spot I can tell it's lean, but I don't stay in that spot often. Then a couple months ago I let a friend talk me into re-jetting. I took it to a local shop that deals a lot with vintage race and street bikes. Now, I have less top end. I want to go back the way it was, but they don't know what jets they took out and swear what they installed is right. But now I can't hit 100 MPH where before 112 was top speed. That is not to say you don't need to rejet. But to say that you ahve to rejet is BS. Especially when you can't even get the bike to idle.

If your plugs are black with soot after just idling, I would say you are too rich. With my set up I have to turn the fuel screws out 3.5 turns. And the fact that your idle jumps when you take the choke off tells me the same thing. It's getting more air with the choke off.

There is supposed to be a little knob under the left carb. That is your idle speed. It may be out of whack too. you haven't mentioned it so it may be missing. That, or mis-adjustment, could be another issue. Points are very important. You will have to make a test light and follow the manual for setting them up right. It's a pain, and tedious, but once they are set you can for get it for a while. Adjusting valve lash is not hard. It takes all of 10 minutes. Remove the tank and you will see the caps to remove. Follow the procedure in the manual.

One more thing to consider is that you may have a torn intake boot. I did at first and thought i would never get it set correctly. I tested them by coating them with a layer of black RTV on the outside and inside. let them dry over night and reinstalled and after a little fiddling, they were perfect.

Good luck.

 

[crazypj]

I have been running stock jets with pods and pipes on my 360 for a couple of years now. It ran great. One little spot I can tell it's lean, but I don't stay in that spot often. Then a couple months ago I let a friend talk me into re-jetting. I took it to a local shop that deals a lot with vintage race and street bikes. Now, I have less top end. I want to go back the way it was, but they don't know what jets they took out and swear what they installed is right. But now I can't hit 100 MPH where before 112 was top speed. That is not to say you don't need to rejet. But to say that you ahve to rejet is BS. Especially when you can't even get the bike to idle.
Good luck.

Post a link to pic of your bike, I'd like to see what pipes your running?
It isn't BS to say you need re-jetting on a CB360 with pods, they run real lean top end with stock 98 secondary mains or real rich mid range with 105~115. (which is correct range for max rpm, depending on exhaust fitted)
If dealer removed stock jets, it's easy to re-fit stock jets, sizes are in service manual.
It sounds like OP has blocked pilots(slow jets), it runs rich on choke ten lean with choke off.
Idle speed is probably set way too high so it will idle with choke on.

 

[teazer]

If your plugs are black with soot after just idling, I would say you are too rich. With my set up I have to turn the fuel screws out 3.5 turns.

And that tells you that you are a mile out on the pilot jet size.

Your comment about idle speed adjustment is right on. So often a bike won't idle, so the owner screws in the idle speed screw to stop it stalling and now it won't start without choke and so it goes on. One bad decision spawns lots of others in an attempt to fix something.

What did that dealer do to your bike. It takes about 10 minutes to strip a carb and check what jets are now fitted and compare those to stock. It is very possible that your jetting worked at full open throttle and high rpms but not so well at lower revs. Getting teh jetting right for more of the rev range makes a bike feel smooth but not fast and it's also possible that their jetting set up improves mid range but may be less perfect at the very top of the range.

Unless we're talking a track bike, that very top end is largely irrelevant - your bike may well be faster now - under normal riding conditions.

remember all those 4:1 pipes that made more or less the same power as OEM but had a hole as it came on the pipe? They felt way more powerful as they came out of the hole, but were actually slower. Same with jetting. Get it wrong, and it often feels more powerful but it's the opposite.

 

[tweakedlogic]

The mufflers are from a 900 thruxton. I had to pack more fiberglass in there 'cause they were way too loud.

After thinking about my lack of top end, I decided to pull my carbs. turns out at least one of the float bowl screws are completely stripped out. So now I need a new carb body. I'm pretty sure it wasn't stripped when I dropped it off for the re-jet. Oh well, I have spare bodies, but it sucks that I have to do it. If I can come up with the money, I'll buy the VM32s I've been eyeing.

I need to take new pics. If you guys don't care about the carbs missing I'll take some pics tomorrow.

 

[crazypj]

If you get VM's, you'll be a lot happier with 28 or 30mm

 

[Kanticoy]

Re: Re: CB360 running issues

If you get VM's, you'll be a lot happier with 28 or 30mm

Amen to that. Been through that, and even with an overbore the 32s were never right. BTW though, you can easily re-tap the threads to the next largest size and not have to change carbs bodies.

Sent from my ADR6300 using Tapatalk

 

[tweakedlogic]

I've been wondering which carbs to get. The stock ones are 32mm bore, but there is a butterfly in the way so I figure it's really a 30-ish. I was thinking the 32s because I have plans for an over bore and a cam + head work.
Go easy on me guys. It's a rat rod. I had it polished and painted all shiny, but was tired of keeping it clean. I haven't washed her in over two years unless you count the times I've been caught in the rain. I actually worked pretty hard to get this look, but I think it's time for a seat change.

 

[crazypj]

I've been wondering which carbs to get. The stock ones are 32mm bore, but there is a butterfly in the way so I figure it's really a 30-ish. I was thinking the 32s because I have plans for an over bore and a cam + head work. I actually worked pretty hard to get this look, but I think it's time for a seat change.

Unless your racing and full throttle most of the time you still only need 28's, maybe 30's with overbore, etc.
I've run 390cc (14mm overbore) with 26mm carbs and it's good for 120 (faster with 30's but not so 'nice')
You can work out surface area for 34mm carb then surface area of throttle shaft.
eg, 'shaft '34x4= 136sq/mm, bore, 34mm = ~908sq/mm (that's just a guess, it may be thicker?)
908 - 136 = 772sq/mm = 31.375mm
This doesn't take into account the turbulence caused by throttle shaft/plate in bore which reduces flow about another 10%
It's usually better to shoot for 25%~35% smaller round slide when swapping from CV

Fit rear sets when you do seat
You'll be amazed how much more comfortable it is when you move footrests back from stock position

EDIT
OK, I just had to go measure some stuff.
The shaft is 8mm dia
the screw heads are 7mm dia and about 3mm high (about 42sq/mm restriction, there are 2 screws ;D )
It's actually slightly more as I didn't measure how far he threads stick through on opposite side of shaft

New Numbers
272+42 = 316sq/mm
908 - 316 = 592sq/mm
592sq/mm = 27.454mm dia

 

[tweakedlogic]

Thanks PJ. The rear sets are one thing that has kept me from doing the seat. I was thinking of a brat or flat tracker style, so I would sit lower and have to do rear sets. But, the exhaust is in the way of the shifter and brake lever. So yeah, I'm still working on that.

 

[raptormeat]

can i assume:
that if i have equal compression and good spark in both cylinders but the right exhaust takes longer to warm up and has a weak back pressure..that my issue is strictly syncronization? or could a clogged pilot jet also cause this?

 

[DC74inc]

Most likely synchronization, because it is a subtle adjustment. A clogged pilot and it probably wouldn't be running very good at all. You could try bench syncing with a piece of wire or something similar. Only expose your first pilot jet and a small and equal air passage