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Discussion Starter · #1 ·
I thought i'd post a few teaser pics of my current modification project on my old 360.
anyone who owns a 30 probably knows the best thing you can use the stock carbs for is paperweights.
I have never been able to get the rich stalling fit right off idle out of mine no matter what i do.
The carbs are one half of a rack of Mikuni BS32 CV carbs from a Yamaha XJ600.
I had a partially parted out rack of them laying around with two complete carbs left.
After much studying carb specs & carb mountings i realized it should be a fairly simple swap.
That brings me to the point of this rather dirty, greasy mock up.
 

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Discussion Starter · #2 ·
Well, guys, I know you all probably think my choice of carbs is weird judging by the lack of interest but I thought i'd update this thread a bit anyway. Unfortunately, i didn't snap any pics tonight.

After a bit more work, i have two complete carbs ready for fuel. It seems they were nice & clean inside. Even the emulsion tubes were nice & clean. All they needed was a quick clean, a few O rings & a ballpark float setting. The float level on these are actually checked mounted & wet. Now I just need to figure out how to connect the linkage between the carbs since I altered the spacing (increased it) to fit the 360.

After a bit of messing i have even come to the conclusion the stock Honda throttle cable will hook up. The return cable will simply be removed from the bike.

The jetting even looks close. Pilot & main jets were #40 & #100 on the 360 stock. On the Yamaha they are #37 & #102.5. The airflow should be very close too, considering that each cylinder of said 600cc FOUR makes 18hp at 10,500rpm versus the 360 TWIN making 17hp at 9200rpm for each cylinder.
 

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I totally think you are playing Dr Frankenstein here...and I like it. Krukster managed to tweak a carb set from a 450 to run OK on his 360. What year and style is the 360? If its a CB the pilot is a #35, and both mains #68's. But a few members have been experimenting with the larger jets that appear in the re-build kits these days. Good luck with it.
 

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Sensei
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No reason they can't be adjusted to work, but there is a 20% volumetric difference in the amount of fuel/air mix that needs to drawn through each carb... You may have to "tinker" with the jetting.... :D
 

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I applaud you for trying. Well done sir, well done.

I'd love to hear the outcome.
 

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Discussion Starter · #6 ·
leethal said:
I totally think you are playing Dr Frankenstein here...and I like it. Krukster managed to tweak a carb set from a 450 to run OK on his 360. What year and style is the 360? If its a CB the pilot is a #35, and both mains #68's. But a few members have been experimenting with the larger jets that appear in the re-build kits these days. Good luck with it.
You are probably right there .. . lol.

Actually, had I had a pair of 450 carbs on hand. I would have started with Krukster's specs & installed them.
The nice part of using what i have is I have two almost complete carbs left over for parts.

My carbs are totally shot though, I actually had to plug off the discharge port for the emulsion tube above the #68 jet to get them to run decent at all. No matter what I do these carbs a a rich spot off idle so bad they blow black smoke & often kill the engine. (yes they have new floats set to 19 mm) Every screw in them is stripped from simply being taken apart at least a hundred times by me & the previous owner (my other half) trying to fix the problems created by whoever seems to have cleaned them with a drill (yes I have replaced jets). Both Diaphragms are worn out (one has the silicone fix).
The needle jets are shot & unavailable.
That is why I am " playing Dr Frankenstein" ;)
They are paperweights as far as I am concerned.

On to the jetting. The jet numbers I listed correspond to the positions present in the Mikunis which do not even have the circuit the #68 is in. What i referred to as the "main jet" is the one below the needle jet. Both specs were taken from Bike Bandit's parts fiche for the 1974 CB360. The Jet numbers for the Mikunis were simply read from the parts I removed as I cleaned them.
 

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Discussion Starter · #7 ·
66Sprint said:
No reason they can't be adjusted to work, but there is a 20% volumetric difference in the amount of fuel/air mix that needs to drawn through each carb... You may have to "tinker" with the jetting.... :D
I expect to have to "Tinker" with the jetting as you put it. ;)

The airflow for each cylinder at peak hp calculates out to 27.8 cfm at 10,500 for the Yamaha and 29.04 cfm for the CB360 at 9200 rpm. Which looks pretty close considering that to be slightly small on carbs is always better than slightly large for a street machine. :D
 

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Your calculations show only a negative 3.6% difference in flow rate, but displacement alone shows you'll need a 21.333 increase in flow rate/volume to "fill the cylinders" .... This alone leaves you 24.9 % lacking in fuel mix supply.... While the CV carbs will attempt to compensate (open further at less throttle), unless the throats are the same bore, you will "run-out" of acceleration (supply) at lower RPM (theoretically)......
However, we both know that they may function fine once jetted to compensate, and the only way to be sure is try them.........
 

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Discussion Starter · #9 ·
I got a nice surprise today.
It seems my 32mm Mikunis are actually 34mm Mikunis.
I think they may actually be off a mid 80s Yamaha Seca 750 (they were with an 1100 Maxim i got hold of as spare parts & all I could read of junkyard writing on them was XJ and 84 on one of the caps)
Well, anyway, on to the fun part. :)

I had them mounted up on the 360 and started up.
The bike idled perfectly at 1000 rpm once i set the idle mixture. :D
The carbs were even within 1/16 turn of properly synced according to the hand on tailpipe test. :eek:
(yes, I know the spec is 1100rpm.) I like 1000rpm.
No more belching black smoke & stalling coming off idle either. :cool:
I'm pretty sure the pilot jets are to small since I had to set the idle mixture screws to about 4 turns out.
Oh well, I have a spare set & the tiny drill set needed to open them up a step for testing.
It will be interesting to get everything hooked up properly for a test ride.

I am going to have to make a modified throttle cable due to the sharp bend needed right out of the carbs.
I was afraid of this when i mocked it up on the junk head.
The other annoyance is the tank must be removed or propped up to set the idle mixture.
(The screws are on the top above the throttle blades)
It even looks like stock are filters may work.
 

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Sensei
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Excellent!.... 34's should be much closer, and I'm sure you can "tweak" them to work..... Sounds like you may have found a viable replacement proceedure/part.... :D :D :D ...Keep us posted!
 

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Discussion Starter · #12 ·
Well, after a bit more work i actually rode the bike today.
After drilling the #37.5 pilot jets that came in the carbs from .016 to .018 the bike pulls like a turbine from 2000 rpm to 8000rpm at part throttle.
The bike feels lean between 1/2 and 3/4 throttle and actually cuts out above 3/4 throttle. Since Mikuni & Keihin jets interchange (I tried) and I have a pair that were very close in the Keihins I will try them. I suspect these jets will be close.
 

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Discussion Starter · #13 ·
After a bit more minor tweaking i rode it some more today.
One part was adding some reinforcement to the linkage as pictured.
I installed the larger main jets also.
The results speak for themselves as the bike revs very freely.
After about 10 miles of riding the plugs came out a nice, light tan.
It looks like I am getting fairly close on the jetting already.
 

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FYI for others planning to use CV Mikuni 34's...you can purchase all the jets and diaphrams etc from MikesXS.com as they are the carb type for the post 1980 XS650's.
 

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Discussion Starter · #15 ·
Well, time for a bit of an update since I have actually been riding and enjoying the bike with said Mikunis on it.

The bike starts nearly instantly . .just hold starter plunger in & hit the starter button. Let engine run on fast idle for 30 seconds or so & its ready to ride. No more start it and juggle the choke and throttle to keep it running. (usually took multiple tries)

Once running the bike idles like a clock, whether just warm enough to idle or after being run hard. With the old carbs it was nearly impossible to get it to idle right at all. It never idled consistently or decently. It takes off smoothly whether you have just stopped for a second or idled for several minutes in traffic. Before it would simply go rich and die if you tried to take off with anything less than a hard whack on the trhottle after idling for a couple minutes. This bike does seem to like the idle mixture set as lean as it will idle smoothly also.

I do think i will end up changing needles to get it tuned right in the 1/2 - 3/4 throttle range, but it runs ok now with one shim washer under each needle. These carbs have very lean needles in them. I wonder if the adjustable needles Mikes XS sells for the 34mm carbs would work?? The bike is smooth and responsive. It no longer stumbles on throttle position changes or loads up on fuel cruising at steady 30 - 45 mph speeds any longer like it did with the stock carbs.

Right now I have a set of drilled main jets left over from the stock Keihins in the carbs since i do not have any more jets around. These jets are enough to get the bike to run well wide open. I believe they are close to a 115.

If you are doing this conversion for yourself, 110 - 115 main jets, 160 air jet, 40 pilot jet and one shim washer should get a set of these in the ballpark for initial settings. This is assuming you have early 80's EPA calibrated 34mm Mikunis without adjustable needles.

I had to fabricate a throttle cable . .in my case that involved using a Yamaha cable modified with Honda ends and connecting it to the carbs with a modified Yamaha cable bracket. I think I can mount the Yamaha choke lever on the bottom of the right hand 360 switch housing and use a fabricated cable to control it just like most other bike equipped with these carbs.
 

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Discussion Starter · #17 ·
Well, time for another update.

Since the last update a couple weeks ago I have gotten the choke lever mounted to the left side handlebar switch. This was actually very easy. The two mounting holes for the Yamaha lever assembly lined up nearly perfectly with a pair of holes already present in the bottom of the Honda switch assembly. After seeing this, I simply ground the holes in the switch housing slightly oval with a Dremel and bolted the lever on using the bolts, nuts, washers & lock washers pirated from a set of junk points. (I also had to sand off the Made In Japan lettering on the switch to get a flat mounting surface)

The choke cable is a shortened Yamaha XJ1100 cable but, I believe a bicycle brake cable could have been used to fabricate this cable also. I used what I had since I parted out an XJ1100 recently.

After riding the bike for a couple weeks I have come to the conclusion that my original choice of pilot jets was in error. Installing the 37.5 pilots that came with the carbs confirmed this. The bike Idles smoother, sounds sharper and runs like a clock at light throttle. I may have to try some 35 pilots.

The bike is very responsive and revs very freely like this. It's not uncommon to see 9000 rpm on the tach at light throttle without realizing it.

While the carbs were off for the pilot jet change I also took out the drilled Keihin jets I initially installed, as they proved way to rich. By checking with number drill i determined that the stock jets from the Mikunis were between .040 & .041 and the drilled Keihin jets were .046 so I drilled the stock Mikuni jets to .043 to try. These jets feel lean, but I did not have the .044 drill i wanted. As far as i can tell, .044 should be very close to a 107.5 jet so that is what I will try next.

Now for some comments on running in general. The bike starts great, just pull the choke lever, hit the starter and let the revs stabilize. The RPMs will stabilize around 4500 rpm, push the lever back in till it runs around 2500 - 3000 rpm while I back it out of the garage and close the door. I usually leave it like this till the first stop two blocks away. Treated this way the bike never stalls, even from the normal cold, sticky clutch bit.

The engine will idle reliably as slow as 800 rpm once warm (accidental setting for a test ride). 1000 rpm works great. It never stalls, not even set at 800 rpm even though it is barely running at that rpm. The bike is just delightful to ride around town now.

The engine even has a nice uniformly sharp exhaust note to it at all speed & throttle setting now. With the worn out stock carbs it randomly changed from sharp to dull & thudding with throttle and rpm. At some throttle and load combinations it even loaded up on fuel and would miss.
 

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Great to hear your getting it dialed in. No better feeling than getting it tuned perfectly like that, makes riding that much more enjoyable and one less thing to worry about.

Nice KZ in the background. What are your plans for it? I love KZ's :D
 

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Rampage1967 said:
The other annoyance is the tank must be removed or propped up to set the idle mixture.
(The screws are on the top above the throttle blades)
Hobby shops have small plastic fuel tanks make for larger rc airplanes, maybe a pint or quart size. You could use one for for a remote tank hanging from the handlebar or a rafter so you don't have to prop up your gas tank until you get the idle mixture right and then use it in the future too and for other projects. It would give you more room to work around the carbs until you get them right.

Great idea on splitting a rack of carbs from a bigger bike. I've thought about trying this before with 350's & 360's before. I'm glad your doing it I hope you get it right so it will open up options for 350/360 owners. Perhaps my 350 parts bike will become a 350 driver.

Keep up the experiment, I'm sure you'll have it soon.
 

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Discussion Starter · #20 ·
HerrDeacon said:
Great to hear your getting it dialed in. No better feeling than getting it tuned perfectly like that, makes riding that much more enjoyable and one less thing to worry about.

Nice KZ in the background. What are your plans for it? I love KZ's :D
Thanks :D

The KZ650 is a Frankenbike project as a rider for the other half.
It was gotten as a non runner with title, but with a carb cleaning & fresh plugs it started right up.
It has CB750 bars & XJ1100 controls on it & I'm in process of rewiring it.

mitchellsk said:
Hobby shops have small plastic fuel tanks make for larger rc airplanes, maybe a pint or quart size. You could use one for for a remote tank hanging from the handlebar or a rafter so you don't have to prop up your gas tank until you get the idle mixture right and then use it in the future too and for other projects. It would give you more room to work around the carbs until you get them right.
My auxiliary tank is actually a folding table with the bike tank sitting on it. I leave the petcock hang off the edge & use about 3 feet of fuel line to connect it to the bike. It helps only having to have one line now too.
 
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