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I'm definitely considered an amateur when it come to working on engines, but I do know what Dad taught me, so please be patient. I have a 1975 Honda CB360 that has been sitting dead for about 2 years. I'm feeling motivated and I finally have a little extra cash to pump into it each month. So far I did what I know how to do; replace the battery, check the spark plugs, change the oil, drained and replaced the fuel, and broke down the carbs. I didn't replace any seals or parts in the carb, but I did clean it out and soaked the parts in a carb cleaner.

Put the bike back together and started to kick it. After about 30 kicks I was able to get the bike started with the choke half open, however, I was immediately sitting in a cloud of white smoke. I ran it for a bit and even managed to get it around the block, but if I let off the throttle it dies. Also important to mention, it has an oil leak (probably needs new gaskets). Any advice is greatly appreciated.
 

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Ya really gotta distinguish between WHITE smoke (water vapor) and even the lightest BLUE smoke --- oil.

White smoke, you could have some water in the crankcase, in the muffler, whatever. Burning gas PRODUCES water, and white smoke....before the exhaust manifold, tailpipe, etc, warms up.....is somewhat NORMAL.

If it's got even the slightest tinge of BLUE to it, however, or SMELLS like oil being burned....

You may have a piston ring that's stuck and not sealing, so ..you're getting a lot of blowby; or valve seals that are toast from sitting too long... or simply worn rings/cylinder and your'e due for a rebuild ...or even a crankcase ventilation system that's FORCING oil into the intake.

Or even just a wad of oil that dripped into the cylinder past worn valve guides. Pull the plug and see if it's nasty with carbon... or wet with oil.

Honestly, I'd RIDE it a bit more till you are 100% certain it either is or is not BLUE smoke. Your'e not going to make it any worse, and the ring may unstick itself, all the oil collected in the muffler burn itself out, etc.
 

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You say you cleaned the carbs with carb cleaner. Did you also blow through the pilot and man jets? The running problem you described might be down to clogged pilots. The orifice is really small and needs compressed air to blow through it. Don't jam a wire or other object through it, carb cleaner soak over night, and blast through with compressed air. Hold on tight as an air compressor can put a tiny bit of metal into orbit. Look through the jet at clear sky to see if you can see daylight through the jet. If you can't, start over. The jets and the jet holder/emulsion tube might have some side holes and those need tending to as well. .
 

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I used to boil my carbs, but that declares the need to do some sealing, rebuilding, gaskets, etc. But, I have had more success with that method than any other. I have taken carbs that sat 12+ years and had them like new in an hour by boiling them for a few, then letting them cool in the water, and then cleaning manually afterwards. A complete tear down before the boil is needed, and all rubbers, floats, etc should removed, only the jets and carb housing parts should be boiled!

I do agree though on the carbs subject. If it had low compression I would wonder if it was burning oil.. If cleaning the carbs really well does not do it, and there is not like really old fuel in the tank, I would run compression checks and hope to determine whether the rings are needing a replacement.
 

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NAPA has a carb cleaning kit. A paint can with a basket and handle that sits inside a cleaning solution. Use in well ventilated area and avoid skin contact.

The key to any cleaning, boiling or chemical is to remove all rubber pieces from the carbs.

For carbs in a bank I'll brush clean them with kerosene after removing the bowls and all jets, etc. Only the bowls and jets get dipped and rinsed. Then compressed air is blown through jets and any passages. Most of the crud settles to the bottom of the bowl where the jets live anyway. Seldom do I see much in the way of deposits in the carb body.

I also recommend keeping all parts with the original carb in multi cylinder engines.

Yamaha has a cleaner that is supposed to be safe for rubber - or at least they used to. The NAPA store is closer to me though.
 

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Discussion Starter #6
Great advice guys! I really appreciate the help. I started her up today and I was happy that it started on the first kick with the choke wide open, and the throttle slightly open. However, it wouldn't idle and it was very smoky. It was difficult to keep the throttle open and inspect the engine and carbs, but I did see some fuel dripping from the bolt at bottom of the float bowl. Hopefully this is the source of the smoke!

ACTION: It looks like I also have an oil leak at the base of the cylinder block. I've decided to tear the top end apart and replace all the gaskets. I'll probably replace the piston rings while I'm at it. During the teardown, I will replace all of the parts in the carbs as well. This is new to me, and will be a very valuable learning experience. I appreciate all the help I can get!

QUESTION: I don't have any intention of ever selling this bike, so should I tear the bottom end apart as well? The transmission seems good IMO. Also, how do I know if the cylinders and pistons all look good? Should I run a compression test first?

Thanks again
 

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Great advice guys! I really appreciate the help. I started her up today and I was happy that it started on the first kick with the choke wide open, and the throttle slightly open. However, it wouldn't idle and it was very smoky. It was difficult to keep the throttle open and inspect the engine and carbs, but I did see some fuel dripping from the bolt at bottom of the float bowl. Hopefully this is the source of the smoke!

ACTION: It looks like I also have an oil leak at the base of the cylinder block. I've decided to tear the top end apart and replace all the gaskets. I'll probably replace the piston rings while I'm at it. During the teardown, I will replace all of the parts in the carbs as well. This is new to me, and will be a very valuable learning experience. I appreciate all the help I can get!

QUESTION: I don't have any intention of ever selling this bike, so should I tear the bottom end apart as well? The transmission seems good IMO. Also, how do I know if the cylinders and pistons all look good? Should I run a compression test first?

Thanks again
Running a compression test is a great idea. So is running a leakdown test. So is reading the Motorcycle Repair Course located at dansmc.com.Cannot be beat for the older bikes. Start with topics 11,12,13 and it covers a lot about getting an old bike running. Reading the entire manual will improve your understanding immensely,
It is entirely possible that the valve clearance is wrong from not being adjusted in years, and if out of spec badly enough,it can affect compression.Get everything set to factory specs , You have already changed the oil, run it 200 miles,and change it again.
 

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Ayup, make certain valve clearances are done properly. That is a must before doing any compression testing. A leak down test is not a bad idea at all. They're an absolute must for a 2 stroke but very handy on a 4 stroke. They do require having the gear to do a leak down test though.

You say you're seeing fuel coming from the bolt at the bottom of the carburetor. That would be the drain screw. If it has a bad rubber o-ring and has a little corrosion around it then it might not seal well. If you were having issues with a float valve sticking open you should see gas coming from the overflow tube that is stuck on the nipple on the bottom of the float bowl right next to that drain screw. If you remove that screw you'll see a grove around it near the head that is supposed to have an O-ring. It will also be tapered at the tip and that fits into a tapered opening to aid in sealing the bottom of the bowl. This is right up against the overflow pipe that is press fit into the float bowl.

A minor oil leak isn't the end of the world. Ask a Harley owner :)

You need to determine if that smoke is actually white, or if it has a blue tint to it as that is useful info about what you need to do. Also, does it eventually stop smoking or does it continue to smoke the entire time it is running?

If it stops smoking and is light blue, your valve guide seals are letting a little oil by while the bike sits overnight. If it is continuous there is the possibility it is getting by the rings.

DID YOU blow through the jets with compressed air when you cleaned the carbs?
 

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I don't know if this is the exception to the rule,but my CB 750 was blowing blue only after very low speed runs through town. I took it to a shop that restores vintage, and the guy said the idle was set too high. He also said that once he re-set it that DO NOT mess with it because that bike sounded great!

No blue smoke since..... I take extra care with the carbs and make sure Sta-bil goes in the gas any time the bike might sit. BTW,the shop did not charge me a dime. The one weird thing about that 750 is the gas does tend to go flat in a week or so if allowed to sit. Hit the drain screws on the carbies and it fires right up. I used to think I was a "cold Natured" bike,but all along it was gas going stale at a fast rate.----Not in the tank,but in the carb bowls.
 

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I know what you mean about the gas in the bowls.

I put an electronic ignition in mine and it starts much easier. Higher voltage at the coils gives a better spark.

Are you running ethanol blend or are you lucky enough to have a good gas station nearby?

One of my favorite places on the internet:

http://pure-gas.org/

I think there is one called real gas too.





Actually I've put two electronic ignitions in it. The first one failed at a really good time. A friend of mine was in a club and invited me to a club party at his house. We were gearing up to go for a ride and mine fired up, died, fired, died, dead. It was the only rice burner on the property. The laughing stopped when I slapped the points plate back in and it fired right up. I could still see the marks on the slotted holes in the plate where I'd timed it previously. It was on the money when I checked it with a timing light.
 

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Flat gas

It is some of the Hondas that do that. I always figured it had something to do with the bowl vents. The XL175 was the worst. We would keep the street bikes inside and did not have the problems, that the bikes outside gave us. Like Slumlord said, drain the gas from the bowl, and they would run. Gas would go orange and smell like rotten eggs. Gas in the tank would be fine. This was in the 70s well before blended fuel.
Another strange thing also happened. The tyres on my race bikes would turn a weird purple / blue colour. Did not happen to bikes in the Seattle area using the same tyres.


Forgot: white smoke can be too rich mixture. As in choke stuck open or float bowls puddling.

Unkle Crusty*
 

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We are in a farming state and around here 200+ bushels per acre is not uncommon. The only non-ethanol as is at marinas.... or possibly aviation gas?
 

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If you ever have problems with winter storage you might want to consider running the bike dry and then going to the marina for a fill up, then ride home.

I've had discussions on other boards with folks and there is no consensus on whether folks have troubles. I have had loads of troubles and others have had no issues at all. It may be a storage/blending issue before it gets to the pumps. It could be an issue with the storage tank at the retail level. So if it ain't broke don't fix it. However, if you have problems the extra cost at the marina pumps may be cheap insurance against headaches the next season.
 

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Discussion Starter #15
Ayup, make certain valve clearances are done properly. That is a must before doing any compression testing. A leak down test is not a bad idea at all. They're an absolute must for a 2 stroke but very handy on a 4 stroke. They do require having the gear to do a leak down test though.

You say you're seeing fuel coming from the bolt at the bottom of the carburetor. That would be the drain screw. If it has a bad rubber o-ring and has a little corrosion around it then it might not seal well. If you were having issues with a float valve sticking open you should see gas coming from the overflow tube that is stuck on the nipple on the bottom of the float bowl right next to that drain screw. If you remove that screw you'll see a grove around it near the head that is supposed to have an O-ring. It will also be tapered at the tip and that fits into a tapered opening to aid in sealing the bottom of the bowl. This is right up against the overflow pipe that is press fit into the float bowl.

A minor oil leak isn't the end of the world. Ask a Harley owner :)

You need to determine if that smoke is actually white, or if it has a blue tint to it as that is useful info about what you need to do. Also, does it eventually stop smoking or does it continue to smoke the entire time it is running?

If it stops smoking and is light blue, your valve guide seals are letting a little oil by while the bike sits overnight. If it is continuous there is the possibility it is getting by the rings.

DID YOU blow through the jets with compressed air when you cleaned the carbs?
Sure enough, there is fuel coming from the nipple. Sounds like a stuck float! Also, I didn't use compressed air on the carb parts, but I will this time. It's obvious I have a leak, so should I do a compression test prior to taking the top end apart?
 

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Compression test.

Always check compression, check spark, and check fuel flow.
In between, check everything else. But is nice to know the engine will run first.
However, no compression and you are spinning your wheels, unless it is an easy fix.

Unkle Crusty*
 

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Noooo! If he ain't got compression he ain't ever gonna spin a wheel. :)


Yes, always best to do simple diagnostics before taking something apart.

It might be necessary to break it down if the gaskets are leaking. If it is just a little spot I'd want to confirm that it is actually leaking there and not something that ran down from another location. Fer instance, the seal on the tachometer drive at the valve cover of my 750 has a tendency to leak just enough to leave a spot on the valve cover to annoy me. The tensioner for the timing chain could also be a source for a leak and not require much wrenching.

So, good compression may mean you can delay repairs to see if they're really needed or if the problem is actually coming from another location.

Getting a new valve cover gasket on is simple.

Getting a new head gasket on requires removal of the cam and making sure you don't drop the cam chain down the hatch. It also means you have to check to be sure you get the cam and the crank properly oriented to each other. Failure to do so can cost you heartache if the piston comes up and has a meet and greet with the valves.

Getting a base gasket on means all of the above and the cylinder must come off. That means the piston rings will need to be monkeyed in back in place to get the piston back inside the cylinder. There is a special tool for this but the piston pin has to come out so that it isn't in the way when you're done (at least mine works that way, some others don't). Otherwise you have to use your fingers to compress the rings back into their grooves and feed the piston back into the cylinder.

If you go into it that far, get some good rags without any crud on them or a lot of loose ends might get caught and stuck in places you don't want them.

Stick that into the top of the crank case where the cylinder slips in to fully seal that area off. That will keep dust out while you're working on it. Then cover the entire assembly, rod and piston included while you're not poking around in it just to keep the dust down. You want to seal that space from stray stuff. Like the wrist pin clips you're going to be shooting all over the garage to get the wrist pin back in should you take it out to get the piston back in the cylinder. Even without the ring compression tool it can be easier to get the piston back in the bottom of the cylinder while it is on your work bench instead of the gymnastics that might occur trying it on the bike. Not so much for a single, but adding cylinders creates access and logistical nightmares.
 

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Sure enough, there is fuel coming from the nipple. Sounds like a stuck float! Also, I didn't use compressed air on the carb parts, but I will this time. It's obvious I have a leak, so should I do a compression test prior to taking the top end apart?
Look at the float needle and float needle seat this time. As close and clear as you can get. If you have great near vision go for it, otherwise you may want a hand lens. The float seat needs to be cleaned as well as the jets. If it has gunk in it then it will probably leak. Boil or chemically clean as discussed in a few previous posts. Just be careful in the handling and disposal of any chemicals. Usually you can reuse the cleaner so store it away. Use in an open/well ventilated area if you go that route. Wear gloves and eye protection and any other precautions given by the manufacture/label.
 
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