Help Cb360 running way too rich

Hi this is my first post on here. I am having some trouble getting my bike running correctly. It is running way too rich. Spark plugs are turning really black after a 10 mile ride and I am only getting 25 miles per gal. I have rebuild the carbs with a Keyster rebuild kit and have new diaphragms from JB industries. I thought my airboxes might have been causing the problem so I cut up a fram air filter and rebuild them. The bike also has ok compression in both cylinders at 155 psi. In addition to running rich the engine rpms will slow at first when rolling on the throttle from idle and the engine have very little power below 4000 RPMs. Air mixture screws are set at 1 and a quarter turns out and floats are set at the stock height of 18.5 mm. Does anyone know what's going on here? Do I need to buy new airboxes, different rebuild kit or is it possible the diaphragm slides are not sliding freely? Any help would be much appreciated.

Sounds similar to troubles I was having recently. I too had installed new JBM diaphragms, but different that you I was trying to run oil coated Uni foam filters and I have a custom made 2-into-1 exhaust. My biggest problem turned out to be that I had the slides installed backwards and one was stuck. You want to make sure the two holes in the bottom of the slide are on the side nearest the intake valves.

After I fixed the backwards slides I changed the float height to 21mm (this may not apply to you if you have mostly stock air cleaners and exhaust, but I have heard many here say they believe 18.5mm to be a mistake in the manual and that it should be more like 19.5mm.)

After these changes the bike was running much better, but still had a bad flat spot. It turned out the oiled filters were not letting enough air in. So I changed them to pod filters after I carefully removed a chunk of the boot near the top of each filter so as not to block the port in the carbs that allows normal pressure air in. I also synced the carbs using vacuum guages and the must-have Motion-Pro 8mm socket/screw-driver tool. I still have additional plug chop tests to do, but bike seems to be running well now.

So I would definitely make sure your slides are moving and are oriented correctly.

did you make sure the jets removed from the carb matched the size of jets in the keystar kit? I know for the cb350 the jet sizes in those kits are often wrong, and the jet sizes varied by year.

wahvtec makes a great point. My carb kit (K&L, I think) came with 100 secondary main jets, but the originals were 110. I used the originals.

Thanks for the quick responses. I do have all of the stock jet sizes except the secondary main jet is 100 not 110 but that should make it lean not rich. I think currently the holes on the diaphragm slides are on the airbox side of the carbs. I'll have to check that this weekend.

kosmoto said:

You want to make sure the two holes in the bottom of the slide are on the side nearest the intake valves.

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Wrong. The vents in the slides are on the filter side. Definitely NOT on the engine insulator side.

here is a map I made to help guys w that a while back. I modified it to show this more clearly.

Thanks trek97. I've been struggling with the slide orientation and very much appreciate the correction. Last thing I want to be doing is putting wrong info out there.


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kosmoto said:

Thanks trek97. I've been struggling with the slide orientation and very much appreciate the correction. Last thing I want to be doing is putting wrong info out there.

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Your welcome dude. I experimented w slide orientation a while back. If you put them in backwards, it will only take a couple minutes at 70mph and the poor bastards will hammer themselves to death. Until they finally mushroom the ends enough they wedge inside the bodies. It took me about 15 minutes of cussing to pry the friggin things out. They were almost permanently destroyed.

pics of my experiment gone wrong here...
http://www.dotheton.com/forum/index.php?topic=60728.0

Hey Bart welcome to DTT.

how did she run before you installed the new diaphragms? Better than she does now?

Hey trek97 are you 100% sure of the slide orientation? Below is from the Honda Motorcycle Carburation manual which is showing the holes to be on the engine/intake-valve side. There is a diagram in the CB450 Shop Manual that has it that way as well.

Moved to 1-800...

kosmoto said:

Hey trek97 are you 100% sure of the slide orientation? Below is from the Honda Motorcycle Carburation manual which is showing the holes to be on the engine/intake-valve side. There is a diagram in the CB450 Shop Manual that has it that way as well.

Click to expand...

Thats a very healthy attitude, to be curious, and its always smart to be skeptical. I understand you dont want to believe everything you read, (especially coming from "some guy on the internet")

The answer is NO, Im not a motorcycle mechanic and I wasn't there to witness the engineers designing/ testing this stuff. So, I can not honestly tell you I am 100% sure.

I have no doubt the college educated boys down at Honda Motors, having years of experience and millions of dollars worth of tools and test equipment and bikes and parts. Do, know a little something about what they publish, especially when it comes to the workshop manuals their own mechanics use to maintain bikes.

that being said...

You may find the result you are looking for. Because there is a major difference when comparing our bikes, you have the uni filters or stock boxes installed? (I have K&Ns) I also have 2 - 2 pipes.

Therefore, in reality I have no idea what will happen.

So, it very well may be the increased airflow did have an adverse effect, in my situation. AND it was just one trial.

I will tell you this, for the first few miles having the slides installed with vents (as pictured in your manual) on the engine insulator side really DID IMPROVE THE RICHNESS PROBLEM I was having between 3500 -4500 rpm.

Afterwards, Be sure to post pics and write up what you find.

Now you have ME intrigued! Damnit.

I have both a complete pair of stock boxes, perfect rubber parts including a gorgeous pair filters sitting in a box next to my bike. Along w a pair of uni filters, right now. Ready to bolt on.

I would be more than delighted to do a write up on my blog...crediting YOU for finding this fix & helping tons of fellow 360 owners.

And I would like nothing less than to publish a written apology for saying you were wrong.

I believe you and I are getting off on the right foot, I have a bunch of respect for guys who read the manuals...rather than just looking here for the quickest and easiest fix, from the first a-hole willing to reply to their thread.

Abraham Lincoln said "The man who can read yet chooses not to, is no better off than the illiterate man."

I believe he is right.

So, get-er-done and post the results.

I forget where I read it but some old honda guru's said that 360 cabs are the ONLY ones they have ever seen with the slide holes on the filter side of the carbs. I can understand the difference in pressure between both sides as well, considering that the pressure SHOULD be higher on the filter side than on the intake side. The slides will RISE sooner if the holes are on the intake side since the vacuum on the intake side is greater.

The Honda Carb manual was published in 75, right after the 360's came out. Funny thing is they make no mention of their specific cabs in that manual, only the 350, 450, and the 4's. I've read it front to back many times, I love the old artwork in these things, that's half the fun of reading them sometimes.

There are a lot of quirky things about 360s that don't show up on any of the bikes AT that time or BEFORE. After them sure.

trek97 said:

And I would like nothing less than to publish a written apology for saying you were wrong.

I believe you and I are getting off on the right foot, I have a bunch of respect for guys who read the manuals...rather than just looking here for the quickest and easiest fix, from the first a-hole willing to reply to their thread.

Abraham Lincoln said "The man who can read yet chooses not to, is no better off than the illiterate man."

I believe he is right.

So, get-er-done and post the results.

Click to expand...

Yup, I'm a software engineer by trade and learned a long time ago to RTFM. But I understand these are modified bikes. Mine has Uni foam filters and a custom-made 2-into-1 exhaust so there's no manual for that. There's only things like your blog posts and posts by you and others on the forum that record the results of the various things that were tried and whether they made things worse or better. My bike is running OK, but not great so I have a lot more tuning to do. I won't be able to start that for a week or so, but I will definitely post the results. We're definitely off on the right foot - thanks!

frogman said:

I forget where I read it but some old honda guru's said that 360 cabs are the ONLY ones they have ever seen with the slide holes on the filter side of the carbs. I can understand the difference in pressure between both sides as well, considering that the pressure SHOULD be higher on the filter side than on the intake side. The slides will RISE sooner if the holes are on the intake side since the vacuum on the intake side is greater.

The Honda Carb manual was published in 75, right after the 360's came out. Funny thing is they make no mention of their specific cabs in that manual, only the 350, 450, and the 4's. I've read it front to back many times, I love the old artwork in these things, that's half the fun of reading them sometimes.

There are a lot of quirky things about 360s that don't show up on any of the bikes AT that time or BEFORE. After them sure.

Click to expand...

That would be interesting if CB360's were the only ones to have them on the filter side. I have a friend with a presumably unmolested 76 CB360. We might have to pull the slides and check 'em. If/when we do I'll be sure to post the results.

kosmoto said:

That would be interesting if CB360's were the only ones to have them on the filter side. I have a friend with a presumably unmolested 76 CB360. We might have to pull the slides and check 'em. If/when we do I'll be sure to post the results.

Click to expand...

I sure wouldnt be surprised if he opens it to find the slide holes are all cattywampus and cockeyed. Ive seen the slides rotate inside stock diaphragms, all discombobulated like.

According to this post the holes are supposed to go on the engine side of the carburetors.

http://www.hondatwins.net/forums/49-fuel-supply-carburation/16124-74-cb360-vacuum-slide-orientation.html

OK OK I give up...just do it, then report back.

Well I changed the orientation of the slide holes around so that they are on the engine side of the carbs but it did not seem to change much. The bike is still running too rich, has lack of power below ~3500 rpm and the engine still hesitates when I roll one the throttle from idle. Here's a picture of some new spark plugs after a ~7mile ride.