My CBX smells of petrol/gas

[zalle]

Hy guys,

I recently moved house, and I built a wooden shed, because I don't have a garage.

In this smaller space, I notice the CBX smells like petrol. Especially when the shed is hot.

I don't see any leaks, where should I begin to check what is wrong?

Someone told me to check the rubber around the tank filler cap, I haven't done it yet.

Thanks for your help

[EMS]

I wouldn't worry too much if you don't see an actual leak. But...they can be small and gasoline evaporates easily. That being said, all carburetor bikes will have some gas evaporating through the overflow or vent tubes when sitting just after a ride or in a warm/hot environment. And you may smell that, especially when the enclosure is small. Make sure you religiously close the petcock. The filler cap is vented and gas can evaporate through there also

[CBX-tras]

If you park it "hot" without running the fuel out (as you should be doing), the heat of the motor, rises up, and will "cook off" the residual fuel in the carbs.
Run the bike dry before putting it away and your problem will probably go away.

I recommend this for all vintage, carbureted bikes, regardless of size, make or model.

[CBX1000chris]

Absolutely with EMS, make sure the fuel tap is off when you park up. Unless you have a source of ethanol free fuel rubber parts will degrade with the ethanol. I recently had to replace the float valves on a 1996 GPZ900R because they wouldn't seal, not a massive issue because the bike has a vacuum fuel tap and when the bike is running leakage past the float valves is less than the rate of consumption. But the fuel tap has a 'prime' position that bypasses the vacuum control of fuel flow and some idiot left the tap in 'prime' when the bike was parked up and it flooded a cylinder and hydraulic locked. As far as I can tell GPZ900R carbs do not have an overflow which is plain bonkers. The idiot was me by the way.....

It is possible your CBX is leaking past the float valves, even if you turn the fuel tap off any fuel 'higher' that the float valve will leak and evaporate off and if it's slowly you may not see any signs.

In the UK 'most' Esso Synergy Supreme+ 99 fuel is 0% ethanol. You can read about it here:

https://www.esso.co.uk/en-gb/fuels

I always try to use this fuel in old bikes.

Chris.

[zalle]

Só, guys, should I turn the fuel tap to OFF, and then let it burn all the fuel until it dies?

Only then store it?

[CBX1000chris]

What I do is switch the tap to off as I get home, any fuel between the tap and carbs is used up as I ride the bike into the garage. I'm not worried about any fuel in the float bowls but I use fuel without ethanol. When I rebuilt the carbs I ordered a rebuild kit from the US that I believe was ethanol tolerant, even so I would be reluctant to leave 10%, or even 5% ethanol petrol in the carbs to evaporate off.
I have a clear plastic fuel filter just after the fuel tap and it always surprises me just how much fuel runs into the carbs when I turn it on if the bikes been stood for a week or so, I think pretty much all the fuel in the float bowls must evaporate off in this time.
Cheers,
Chris.

[CBX-tras]

FYI, float bowls hold about 2oz of fuel each. That's about 12oz total that needs to be run out/burned off/drained, prior to short or long term storage.

Also, don't think for a second that the AVF is your savior to stop the flow of fuel. The diaphragm inside is made of the same material that gets old/damaged and non-compliant with age and the various fuels that have run through it since new. They do go bad.

The easiest way that I know to ensure that the petcock is actually working (without disassembly) is to turn it to OFF. The carbs should run dry in a few minutes. Apply the choke, start it, and run it until it dies again. Do this on ANY carbureted small motor, regardless of make, model or displacement to help prevent damage from fuel additives and varnishing.
If the petcock is found to be defective, many can be rebuilt some will need to be replaced.

[wessi]

When you new build a wooden shed, maybe the smell could come from the wood impregnation or from some protecting paint ?

[zalle]

Hi guys, thanks for the answers.

I really need to put a fuel filter in mine. I had one but it went bad, so I removed it and need to buy a new one.

I started the bike yesterday, fuel off and let it burn the petrol in the carbs. It seems that most of the smell has gone.

[daves79x]

CBXs have done this forever. If you put your bike away hot, without draining the carbs (or even if you do sometimes), in a small enclosure, it will smell like gas is leaking everywhere. As JR said, the hot engine will cook most of the gas out of the carbs while it cools. Just the way they are.

But you should take heed of the real issues here - turn the gas off EVERY TIME you park. If you can live with the smell, and are riding the bike regularly, no need to drain the carbs every time (but shutting the gas off a mile before home is easy enough). For storage more than a couple of weeks though, absolutely drain the carbs, to keep the old fuel from clogging them up.

[Duffey Lake rd.]

All good advice.
I also add about 15 ml / Litre of Seafoam Gas Treatment to the tank, it also stabilizes.

-Scott

[Larry Zimmer]

As Dave said, "DRAIN THE CARBS!!" If either of my carb bikes are going to sit longer than a day, drain the carbs. Takes 10 minutes or less. In 45 years I've never had a carb issue other than oring crap due to alcohol. Fix that with Viton.

[EMS]

Oh my! The "drain-the-carb" crew. If I would drain the carbs every time I ride a bike and want to let it sit for a week, I would lose the desire to ride. The drawback of draining carbs is the restart, which is going to be hard. As everybody knows, who still runs a vacuum petcock in a CBX, it is a PITA to start the thing after it sits for a while and the float bowls are empty. I am running ethanol-free gas in all my bikes, even the FI ones and I never have a problem with anything "clogged up" during the season. But whatever....you need to do what works for you.

[daves79x]

I've described a million times how to fill the bowls with a vacuum valve in place. Takes 15 seconds. Starting is not a problem then.

Dave

[EMS]

Yes, we all know. And I am sure we all have our systems. Getting a hose plugged to the vacuum valve vent and blowing in it until the bowls fill takes longer than 15 seconds, however. Everything is nice in theory. Real world works a tad different.
Let's talk about theory a little: If you are concerned about stale fuel clogging up the jets, draining the bowls will not do a thing. Just by draining the carbs, your are not getting all the fuel out. Even when running the bike until it dies, will not completely clean the carbs. You have six carbs and the bike will starve long before they are all dry. You are looking at a process of at least 20-30 minutes form draining the carbs, running the engine and continue cranking until they are completely clean. It is a stupid recommendation. Use ethanol free fuel or an enzyme additive like Startron, you are better off and have an easy restart. That's my take, I am operating 14 carbureted bikes like this very nicely and I will avoid the elaborate discussion that will follow.