Gas on right side spark plug - CB360

Matnetik

Active Member
1974 CB360 - finding gas on the right side spark plug. Left side looks clean.

Bike starts first try every time, idles, I can drive, it has power throughout all the gears, no bogging or anything, literally runs perfect. After warming up, I am getting a light amount of white smoke from the exhaust, once I start going it’s gone, doesn’t smoke while driving at all (at least I can’t see any).

I’ve probably only put 150 miles on it since I rebuilt the top end (new rockers/bolts, camshaft, chain tensioner, adjusted valves, new head and shockwave electronic ignition and oil filter clean, oil change).

Recently discovered my new carb boots weren’t completely seated to the carb, they popped off a few times on startup and I would just push them back on. After removing the clamps last weekend, turns out if you push hard enough they snap in place (had no idea) and now they are seated correctly. Haven’t messed with the carbs since I got it two years ago other than adjusted the idle and mixture screws.

My question is, where do I start? I’d searched a few threads and have gotten mixed answers, any help is appreciated. I checked the plug on Sunday and it was covered in gas and black, used a dremel and cleaned it, threw it back in and went for a 20-30 minute ride, averaged around 40-50mph the entire time with stop and go’s in between. The picture below is after that single ride, doesn’t look too bad but it’s still wet and I can smell the gas. Also no gas in the oil, only on the plug. Thanks in advance for any replies!!
 

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Matnetik

Active Member
Installed new plugs, rode around for about 15 minutes and still smoking. Also smoke coming from the breather tube near the exhaust clamp (which I clearly need to shim and tighten down). Wondering if it’s actually oil and not gas, idk smells like gas for sure.

 

Matnetik

Active Member
New plug after the 15 minute ride -
 

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irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
Your idle is really high. White smoke is oil. Oil will foul plugs too. Your tappets are pretty loud. I'd let it completely cool and go over all of your measurements first, then go from there.
 

Matnetik

Active Member
Your idle is really high. White smoke is oil. Oil will foul plugs too. Your tappets are pretty loud. I'd let it completely cool and go over all of your measurements first, then go from there.
Good note here, think I am going to tear it apart for the winter and check everything over, new gaskets and rings - couldn't hurt I suppose - will check all measurements by the book while I'm in there and report back! Thanks
 

Matnetik

Active Member
I lowered the idle And tried swapping plugs and wires. It’s definitely burning a lot of oil, I topped it off about 50-60 miles ago and it’s back to the “add” mark now. Just ordered a set of .5mm oversized pistons and new gaskets for the entire top end. Going to tear it down, have a machine shop bore and hone the cylinder and reassemble myself. Will report back soon I hope! If anyone has some recommendations for machine shops in the valley of Los Angeles, feel free to let me know!
 

pidjones

Over 1,000 Posts
Let me suggest that you take the old pistons and jugs to whichever shop you find and let them tell you what size piston to order.
 

Matnetik

Active Member
Let me suggest that you take the old pistons and jugs to whichever shop you find and let them tell you what size piston to order.
Yeah? I mean I already ordered the .5 over (it was the smallest next step) - my cylinder could be in spec for all I know but figured if I am going to tear it down, might as well bore it up 1 size - I can always return them if they aren't enough or too much - thanks for the advice here
 

pidjones

Over 1,000 Posts
I had an XR100R bored this summer. Asked the machinest if I should go ahead and order a .25mm over piston (I had already measured and knew it needed a bore). He said to wait until he had bored it to make sure it cleaned up (mostly taper and out-of-round). He called and said go ahead and order the .25 over, than honed the cylinder to fit correctly when I took it in. May not be that easy (or cheap - $30) in LA though.
 

Matnetik

Active Member
Okay, tore it all down today! Also filmed the whole thing and am going to upload it to the tube for everyone - here are a few pictures though, whats odd is how much oil reside is on the left piston and that spark plug was the dry one with no issues. This CLEARLY needed to be done! Some pitting in the cylinder, looks like it’s from the rings. Excited to get it bored, everything cleaned (going to re-paint as well) and already have all new gaskets - thinking about doing some oil mods while it’s all apart. Suggestions?
 

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irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
Keep a search out for the CJ pickup. Drill the clutch basket. Open the valve coming off the oil slinger/pump.
 

Matnetik

Active Member
Keep a search out for the CJ pickup. Drill the clutch basket. Open the valve coming off the oil slinger/pump.
Appreciate this, have seen a few post of CJ’s about oil mods! Also think I should replace the valve stem seals and check the valve guides while I’m in here
 
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crazypj

Split personality, I fake being smart
Do you have any idea of the actual mileage?
If it's below 30,000 it's doubtful that bores are worn and you probably just need rings?
Cylinders will normally last 60~80,000 miles or more but rings wear relatively quick if your using rpm correctly.
You don't need the CJ pick up unless your sloppy about checking oil level or leave bike idling on sidestand (and stand is bent so it leans further than normal) It's a simple upgrade though. Doing the oil transfer piece mod is probably the best thing you can do to make engine last a LOT longer. I did a picture write up over on Vintage Honda Twins on a CB350 a few months ago but 360 is almost identical (slightly more difficult as it doesn't have oil filter cover like 350)
Valve guide seals are pretty much shot due to age rather than wear, unless it was run excessivly with dirty or low oil the guides are probably OK (it's an expensive job to get them changed, particularly if you get bronze guides) If you go to the expense of doing guides, it's probably worth the extra to fit 35mm intake valves (I wouldn't bother with over size exhaust valves though, it doesn't need them)
 

crazypj

Split personality, I fake being smart
Oh, as for the gas problem, probably need shut off valve or maybe just dirt in the shut off? Re-set float level to 21mm if you run E10 fuel (and being in Cali you probably can't get anything else?)
 

Matnetik

Active Member
Oh, as for the gas problem, probably need shut off valve or maybe just dirt in the shut off? Re-set float level to 21mm if you run E10 fuel (and being in Cali you probably can't get anything else?)
Hey crazypj! Thanks a ton for the reply and detailed info! This bike was rebuilt by the person I bought it from about 3 years ago - he also gave me a storage bin filled with parts, said he had 3 CB360 engines and rebuilt one solid one with all the parts - after about 6 months of driving a rocker arm bolt flew out on the freeway - from that point I had to buy new (will used but) rockers with very little pitting, a camshaft, new valve cover and all the gaskets - after that rebuild last year it was running great up until recently with the oil/gas problems I've been having on the spark plug - this is why I decided to tear it down and have revealed all the above - dropping the cylinder at a machine shop today with the new pistons (already have the oversized ones so why not?) - I've definitely seen your post on vintage Honda twins, will read through it again and most likely do the mod - I really only use this bike to putt around town but would love for it to be reliable enough to drive through the canyons on a nice Sunday!

Probably won't do the guides unless it's necessary! Also, I have a shut-off valve and using shut it off before I pull on my street so it burns off some of the gas in the bowls - I am going to rebuild the carbs since they are out - they do have pod filters, I am sure that isn't helping
 

Matnetik

Active Member
Well, took the cylinder and head to a machine shop - looks like the head needs to be replaced, the journal is pretty bad and the machine guy would rather not work on it and charge me know it’s going to fail eventually, found one on eBay for $100 in good condition, going to pick it up and have him check the valves, guides and all that jazz - working with Kurt at Valley Cycles in Los Angeles
 

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