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Discussion Starter · #1 ·
We've actually been referring to this excellent forum throughout this construction project, but haven't posted anything until now. Got a chainsaw for free at a garage sale, gave it to Bentley, age 24, who traded it the same day for a cb360, not running. I found another one on Craigslist for $100 (both are 1975 models), and we've been making a hybrid over the last few months. Finished to the point of running, now, Bentley loves the sound it makes, I, Michael, wishes it were quieter! We've had a blast working on it. My first ever motorcycle, Bentley's second, We have a technical question...shall I ask it here or in the technical section? How about both.

The bike seems to run strong, but acts like the mix is too lean: some backfiring, hesitation and tendency to stall on take-off, some missing while cruising. This last problem happened most noticeably when I had my wife on the back, accelerating up a hill. Sound like lean mix? Clues:
-- One of these bikes had 3300 miles on it, the other about 7000. Used best parts to build with.
-- I cleaned the carbs twice, the last time within an inch of their lives, with carb dip, compressed air, and careful probing with guitar strings in passageways. Adjusted floats, set both throttle plates exactly the same. Photo below, if I can figure out how to add one.
-- I cleaned out the tank with the nuts and bolts agitation technique, rinsed very clean, installed two in-line fuel filters -- glass cylinder with replaceable screen element, new fuel hoses.
-- Did extremely careful job of timing with the excellent tutorial provided here by tbpmusic.
-- Adjusted valves painstakingly.
-- Adjusted cam chain tensioner exactly as instructed in manual.
-- Installed new after-market mufflers, Dunstall is the name, if I recall it correctly.
--Compression is 155 on the right, 159 on the left, after ball honing and new rings.
-- Pilot screw on carbs, set as in the manual, to maximize rpm at idle, is open on both carbs 2 and 1/4 turns.
-- Strong sparks on both plugs.
-- Here's a baffling one: right cyl. plug is sooty, left one is light tan.
-- Have driven only 200 miles so far.

Anyone have any ideas?
A thousand thanks to the moderators and the contributors to this forum. What a delight to read your stuff! Proves two heads are better than one. Onward! :D
 

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You're already tackling things the correct way. Nice organization while cleaning those carbs. Props to you for that.

I assume the 200 miles were put on it after the hone work?? The compression numbers seem a little low to me but I forget the proper numbers..

The tan plug sounds like that cylinder (carb) is tuned nicely but the sooty one still has to be too rich for some reason. Is it a powdery type of soot or a baked on black soot? Powdery would suggest too rich of a mixture but baked on would suggest burning oil..

Are you sure that the jets and needles are identical in both carbs now? Pay careful attention to the needles. They may be different as well but it's a little harder to tell.

Have you synced the carbs??


GB :mrgreen:
 

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bentley said:
--Compression is 155 on the right, 159 on the left, after ball honing and new rings.
Correct compression is 171 lb/sq.in.

My guess is your cylinders are not excellent, but close enough. Good luck :D
 

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You should have changed the valve seals while you were in there.
 

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I see the stock side covers, leading me to believe it's running stock air filters. How is the air filter on the sooty side ?

Oh yeah, Vancouver here. Welcome to the site.
 

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Discussion Starter · #8 ·
FIXED!!!
Wow! Thanks for the deluge of advice! Thanks a million. What a treat.
I pulled off the air cleaners, and that fixed everything! WooHoo! It runs beautifully, and the plugs now look identical, a clean brown.
In fastidiously cleaning everything, I had blown the air cleaner elements thoroughly with compressed air, but decided to go one better and I soaked 'em in white gas, scrubbed 'em with a parts brush, and blew 'em dry. An old-timer around here told me it was a mistake to use the white gas, throw 'em away, they're ruined, he said. I was skeptical, but I guess he may have been right. He runs a motorcycle shop, said he had some foam to replace the paper elements in an inexpensive kit. I'm heading to his place tomorrow.
I was skeptical that that could be true, but it was IndieSol's question about the air filters that convinced me to try running it without the filters. Thanks, Man!
Dirtbag said I should have replaced the valve seals....I forgot to mention that I'd lapped the valves. Did not replace the valve seals, but the machinist who helped me with the project said they were ok.

[b]The compression: I'd love your opinion about what's going on there.[/b] I re-tested the compression tonight. The machinist who assisted me with this project recommended boring the cylinders and buying new pistons etc., but he knew I didn't have a lot of dough to put into this machine, so he said let's try the ball hone, with new rings. The cylinders had a little rust, all evidence of which was gone after the honing. I don't know the piston-to-cylinder clearance that 665 Sprint asked for. I recall that the machinist saw it as borderline. He had the factory specs. I carefully installed the rings the right side up.
So tonight, elated with how well it was running with the air filters off, I took new readings. Left, 158. Right, 157. Squirted oil in the holes, got 195 left, 178 right. Based on a tiny education in these things, I understand that to prove that the moderately low compression readings are due to rings, not valves. Why so much better on the left? How am I doing?

If you're still with me, one more question: Due to the loudness of this machine, I'm inclined to run it at really low revs in my urban neighborhood, when I'm cruising at 25 to 40 mph, like around 2500 rpm, unless I'm accelerating, I know what lugging is, and this skirts close, but feels ok. If I need power, I downshift.

One more: The bike feels stable at 55, and a little wobbly at 60. I almost never see bikes this size on the freeway anymore, and wonder if I'm unrealistic to consider riding this thing on the freeway. Few people do, so maybe they know something I don't. There must be something that inevitably draws motorcyclists toward bigger bikes.
Thanks, All!
Michael
 

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I'm glad I could help on the fuel mixture thing. I had a similar issue with my CJ360T. I went with the stock air filters for now, which were somewhat hard to find, but I was able to locate two new ones. Admittedly, they cost a pretty penny.

I can't really help you on the compression thing. It's a bit above my pay-grade, unfortunately, but I hope to get there sooner or later. I just know low compression is not good mojo.

As far as the low RPMs in the neighborlyhood, I'd suggest dealing with some annoyed neighbors. From what I understand, these things don't really charge well unless they're up around 4 or 5k or higher. If the majority of your trips are going to be short jaunts in urban settings, I'd imagine you're going to do a fair amount of idling (stop lights, traffic and such), and your bike might benefit from a bit of charging when ever it can. If you've got a battery tender, maybe this isn't something that will concern you. Just throwing it out there, because if your battery starts to run low the bike won't run right. Plus, they sound cooler up at higher RPMs, am I right?

On the freeway thing, perhaps steering stem bearings? They should be checked regularly. Same with the wheel bearings. I've taken mine up to 75mph with no wobbles, so I don't think it's normal. I know a lot of people don't like to ride these things on the freeway simply because their small size makes wind gusts/drafts a bit sketchy. I'd agree a bit with that, but don't mind hopping on the interstate for a bit if I've got someplace to go in mind. The back roads are just funner, in my opinion. At least where I live, you don't see these bikes often anymore, period. Whether on a back road or a highway. I feel that the abundance of cheap, powerful 600cc and larger bikes that have popped up in the last 20 - 30 years has a lot to do with it.

I'm curious to know how the replacement air filters work out for you. Obviously my NOS replacements won't last forever and I don't know how lucky I'll be the next time I need to find them.

Also, have you gotten yourself a manual for that bike? I'd suggest getting the Clymer manual as well as a digital copy of the shop manual if you can find one. I've got the shop manual for the '77 CB360 and CJ360T, which has a "Late Model CB360" supplement. I don't know if your bike fits in that category, but if it does, I'd be happy to send you a download link. The file is nearly 100mb.
 

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Look im running 155 and 160 in my cylinders. The bike still hauls ass. If you want it done right, bore your cylinders, get new pistons, machine the head surfaces etc. Then you'll have a fresh motor. Last you for years.

I welded a gsxr steering damper to my bike and it's now less wobbly at speeds.

ordered a 33mm clamp from ebay.
 

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MIke,
Good to hear it seems to be running OK. Different muffler back pressue and air filters will affect the mixture and usually the carbs will need to have slightly larger jets.
Keep running the bike. It is possible the rings will bed in. However, cfhances are it will need a rebore.
If you can stand the vibrations, a CB360 is fine on the freeway. I bought one new in 1975 from the Nave exchange in Subic Bay RP. It came home on board the USS Kitty Hawk. I rode it from San Diego CA to Whidbey Is WA. My hands were numb but the bike performed flawlessly.
 

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Discussion Starter · #12 ·
Cut the paper out of the air filters, used silicone caulk to glue in the filter foam by it's edges....not sure if it's different than standard issue upholstery foam...but got it from a motorcycle shop, it had instructions for installing as an air filter, $16, enough to replace the elements on two cb360's. When the silicone was dry, I sprayed 'em lightly with a mix of kerosene and motor oil (oil thinned with the kerosene to make it easy to spray with a typical plastic spray bottle nozzle), and they seem to work great. Engine runs better, but I can't say that the filters are as good at filtering out the fine dust that paper would.
Yep, I've got a Clymer manual and a downloaded shop manual, found the link here somewhere, I think. Amazed at what the Clymer manual leaves out sometimes...e.g., it makes no mention whatsoever of the oil filter screen in discussing cleaning the centrifugal oil filter. Found out about that in the shop manual.
Taking my first trip out of town tomorrow, about 150 miles altogether. I'm excited! :p Washington state is gorgeous in the summer. It'll be a blistering 83 degrees in the afternoon!
Oh, here's a tip young Bentley discovered: Rather than investing in the special Honda tool for removing the magneto from the shaft, the bike's own rear axle is perfectly suited to the job!
 
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