CBX Carb Spewing Gas After Hard Time Starting? | GTAMotorcycle.com

CBX Carb Spewing Gas After Hard Time Starting?

U

unL33T

Well-known member
So I tried to ride my CBX to work today. Took FOREVER to start. Probably 10 minutes. I'm surprised the battery didn't go dead actually. Once I got it started I noticed a large black spot on my driveway. Turns out it was spewing gas out the side of the engine, I believe from one of the carbs, the whole time I was trying to start it and even after. I shut it all down, turned off the petcock (at least I hope I remembered to do that), parked it, and rode the RS125 into work instead.

I presume this is not at all normal even if I flooded it while trying to start it? Does this for sure mean I gotta pull the carbs off again for some more cleaning/rebuilding?

I was going to have the guy that did most of the restoration work on it do some more work this winter anyway so if the carbs have to come off again I may just park the bike for the rest of the season and haul it to his place. Probably not a great idea to try to ride it while it's dumping gas all over the engine and exhaust. I should probably ask him to put the vent tubes back on so if this happens again at least it just dumps out the bottom of the bike instead of all over everything.

I'm still (slowly) learning about how carbs work. I'm going to start it up back at home after work today and see what I can see going on, with a catch tray underneath.

Thanks in advance for any help!
 
bitzz said:
Could be a carb float hung up. Fairly normal occurrence.
Try tapping the float bowls to loosen it.
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Thanks. I'll try that tonight.
 
Stuck carb float or debris under float needle was my first thought. Just need to figure out which one of the 6. Do you need to pull the carb assy to remove the fuel bowls?
 
DJM said:
Stuck carb float or debris under float needle was my first thought. Just need to figure out which one of the 6. Do you need to pull the carb assy to remove the fuel bowls?
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I'm pretty sure you do.
 
bull958 said:
I would also check your oil level before you start it again. If its the petcock, you have a chance of gas getting into the crankcase.
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VERY important! I know of a few motors that have gone boom because of hydraulic lock.
 
Will do.

I did find out the hard way not to try to check the oil on the sidestand. :LOL:
 
If the engine slows cranking very slowly - STOP!!!!! ZZZ ZZZZ ZZZZ ZZZ Zuuuuuuuuuh ZZZZ ZZZZ ZZZZ. This is a hydrolock condition, not uncommon on CBX and 400x4 Hondas. This is a sign that the vacuum petcock has failed AND you have a stuck float on one of your carbs. On early models, all 6 carbs overflow into one hose and this can hydrolock the low cylinder Starting a hydrolocked engine will fook it from bottom to top.

If the engine cranks fine and does not start, 1 stuck float on a 6 carb bike would not make it hard to start. Check for a split fuel lines, leaky petcock, or bad fuel line connections.

You might also have more than one issue. The CBX has a vacuum petcock that will fail if you use ethanol based gas -- not if, but when. You can try Viton rebuild kits, I'd stick with Ethanol free gas. Also, those bikes use a very small fuel bowl, put a bike away hot, leave it for 10 days and the carbs will have to refill themselves. Some old Honda riders add a marine primer bulb to speed up the re-prime so starting is quicker and easier.
 
Mad Mike said:
If the engine slows cranking very slowly - STOP!!!!! ZZZ ZZZZ ZZZZ ZZZ Zuuuuuuuuuh ZZZZ ZZZZ ZZZZ. This is a hydrolock condition, not uncommon on CBX and 400x4 Hondas. This is a sign that the vacuum petcock has failed AND you have a stuck float on one of your carbs. On early models, all 6 carbs overflow into one hose and this can hydrolock the low cylinder Starting a hydrolocked engine will fook it from bottom to top.

If the engine cranks fine and does not start, 1 stuck float on a 6 carb bike would not make it hard to start. Check for a split fuel lines, leaky petcock, or bad fuel line connections.

You might also have more than one issue. The CBX has a vacuum petcock that will fail if you use ethanol based gas -- not if, but when. You can try Viton rebuild kits, I'd stick with Ethanol free gas. Also, those bikes use a very small fuel bowl, put a bike away hot, leave it for 10 days and the carbs will have to refill themselves. Some old Honda riders add a marine primer bulb to speed up the re-prime so starting is quicker and easier.
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It seemed to be turning over fine although I did notice sometimes if I cranked too long it was like the starter would come disconnected and freewheel? That was odd but I'm not sure if it's a sign of something bad. It seemed to be cranking over fine other than that the battery seemed a bit low. I assumed it was just because I've been out of town most of the summer so I haven't started it in probably 2 months or more.

When the bike was restored the guy that did it left the "vent tubes" as he called them, off the carbs. Claimed they did next to nothing. I presumed the vent and overflow are just different terms for the same but I could be wrong there.

The fuel petcock is brand new from Honda as far as I remember. That's the valve where you select off, reserve, and on, correct? I didn't know that about the ethanol in the gas though.

Does this primer bulb just go in line between the tank and the carbs? That sounds like it might be a good idea because I ride infrequently. I think my carb'd RS125 has a similar issue as it is also very hard to start after sitting for awhile. Well, hard as in I have to hit the starter many times over and over. Not like it requires any real physical effort from me although it is annoying when I'm late for work or it's really hot out. I just assumed that was the nature of carbs.
 
There's an overrunning clutch on the starter. If it was anything like my old Honda twin it was basically some roller bearings on a ramp. Lack of lubrication or excessive wear in that clutch will cause the starter to disengage while in operation. You'll have to pull the starter to get a look.
 
DJM said:
There's an overrunning clutch on the starter. If it was anything like my old Honda twin it was basically some roller bearings on a ramp. Lack of lubrication or excessive wear in that clutch will cause the starter to disengage while in operation. You'll have to pull the starter to get a look.
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Good to know. Thanks!
 
unL33T said:
It seemed to be turning over fine although I did notice sometimes if I cranked too long it was like the starter would come disconnected and freewheel? That was odd but I'm not sure if it's a sign of something bad. It seemed to be cranking over fine other than that the battery seemed a bit low. I assumed it was just because I've been out of town most of the summer so I haven't started it in probably 2 months or more.

When the bike was restored the guy that did it left the "vent tubes" as he called them, off the carbs. Claimed they did next to nothing. I presumed the vent and overflow are just different terms for the same but I could be wrong there.

The fuel petcock is brand new from Honda as far as I remember. That's the valve where you select off, reserve, and on, correct? I didn't know that about the ethanol in the gas though.

Does this primer bulb just go in line between the tank and the carbs? That sounds like it might be a good idea because I ride infrequently. I think my carb'd RS125 has a similar issue as it is also very hard to start after sitting for awhile. Well, hard as in I have to hit the starter many times over and over. Not like it requires any real physical effort from me although it is annoying when I'm late for work or it's really hot out. I just assumed that was the nature of carbs.
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If the engine spun over more than a few times and didn't start the risk of hydrolock goes away. If a hydrolocked engine starts, it usually breaks a rod which usually punches a viewing hole in the case.

As for pet cocks, that bike may have a 2. The first is the mechanical on/off fixed to the tank, the second is called an AutoLock located downstream near the carbs. The Autolock cuts fuel when the engine is off, and lets fuel thru when the engine is on. If you forget to switch off the tank petcock, this minimizes the chance of leaking fuel into the cylinders (oil dilution and hydrolock). The Autolock is vacuum controlled, opening when the engine is spinning and making vacuum, closed when it's not. It gets minimal vacuum when cranking off the starter motor, almost none when cranking slow. If your bowls go dry -- which is a common issue with CBX carbs -- it can take a lot of cranking to get them filled again because the starter doesn't let the engine create enough vacuum to hold the Autolock full open. This is why you would want a primer, it bypasses the Autolock so the bowls can refill in a few seconds.

Other options:

1) Remove the Honda Autolock (increasing risk of hydrolock)
2) Remove the Honda Autolock AND remove the 6 into 1 vent hose (reduces risk of hydrolock, increases chance of fire)
3) Remove the Honda Autolock and replace the CBX fueltank petcock with a Honda VTR vacuum petcock == they have a built in prime setting.
4) Add a primer bulb off an outboard motor. Tee the inflow between the tank petcock and the Autolock, and tee the outflow after the Autolock.

Finally, you want that 6 into 1 carb vent tube. That bike runs very hot and the fuel evaporates from those vents when the bike is hot. When they are open, they evaporate fuel faster, they also vent under the seat (boom) instead of into clear air below the bike.
 
You need to become intimately familiar with carburetors if you are going to own a motorcycle that has them.
Good news is, almost 100% of your problems will be in the lower half, that is where the fuel is.

Carburetors have to be vented, yes. There are hoses on there to do that and they are routed to somewhere they are unlikely to suck in water and dirt, like the air box. Same with your crankcase, needs to be vented, also needs to breath clean air and spew oil mist, water and blow-by gasses somewhere, like the air box.
 
Trials said:
You need to become intimately familiar with carburetors if you are going to own a motorcycle that has them.
Good news is, almost 100% of your problems will be in the lower half, that is where the fuel is.

Carburetors have to be vented, yes. There are hoses on there to do that and they are routed to somewhere they are unlikely to suck in water and dirt, like the air box. Same with your crankcase, needs to be vented, also needs to breath clean air and spew oil mist, water and blow-by gasses somewhere, like the air box.
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Ok. I'll have to reinstall the vent hoses. They aren't installed right now. The nipples are just free in the air pointed towards the front of the bike.

My crankcase vent is connected to the airbox but I noticed the hose is split on one side and not connected on the other. Oops. Rosey Toes didn't mention either when he did the safety.

Would having the crankcase vent not connected mess with the tuning? I have a bad dead spot around 3500-4500 rpm the other guy couldn't get tuned out no matter how much he played with the carbs. He assumed it was related to the crazy loud exhaust installed but Tim's CBX said they don't normally change the needles for this exhaust so that was confusing. The carbs were fully rebuilt over the winter and he had them out 5 times to play with the tuning.

The second carb from the left of the bike (driver's side if it was a car) is leaking. There does not appear to be any leaking when the bike is off. The other vents look fine.

Oil level looks low if anything. I'll have to look up how to read the dipstick built into the filler cap.
 
Wingboy said:
Nothing to do with the safety.
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Fair. He did lube the chain for me which I also wouldn't think was part of safety. Wasn't really a criticism. Just mentioning that a few people have looked over it and didn't catch anything. Doesn't really matter anyway, I'll put it back on.

One of the little clips that holds them on appears to have fallen off the assembly (I kept it even though it's not installed) so I'll have to source one of those. I should probably put new hoses on anyway rather than the old ones.
 
Do you have the OEM shop service manual yet?
you really do need that for every motorcycle you own, quality well maintained motorcycles can out-live the mechanics.

Small zip tie will hold an air tube on as good as anything.
 
unL33T said:
Oil level looks low if anything. I'll have to look up how to read the dipstick built into the filler cap.
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Typically you drop it in the hole and then lift it back out while the bike is level then read it.

btw: were your carburetors balanced? you don't do that by taking it for a spin and turning screws.
 
Trials said:
Typically you drop it in the hole and then lift it back out while the bike is level then read it.

btw: were your carburetors balanced? you don't do that by taking it for a spin and turning screws.
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Far as I know but I'll make sure to ask again.
 
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