Um ... fuel boiling in the gas tank?!

Rider 5280
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6/10/2022 11:59pm Edited Date/Time 6/13/2022 11:25pm
Guys - I ran into something I've never encountered before today.

I was running my carbureted 2008 Honda CRF450R at an elevation of ~ 8500-ft (and it was ~ 90 degrees F out) on Colorado mountain trails and the bike started to run weird/fuel-starved like, so I pulled over, removed the gas cap, experienced a major pressure release, and then when looking down into the tank, the gas appeared to be boiling. Literally ... a rolling boil like this:
https://www.youtube.com/watch?v=0c1aeLm-Z7o&t=34s

I checked my gas cap's venting system (I use a check valve vent) and it was still breathing OK on vacuum. The engine coolant wasn't particularly hot at ~ 175-200 degrees F. Lastly, I was running 91 octane pump fuel with Yamalube Fuel Med Rx additive to combat ethanol issues.

I haven't dug into this yet, but it was the oddest thing.

Has anyone here seen this before and if so, what was your fix ultimately?

*** I can upload a video of the actual event later this weekend if that helps anyone diagnose this ***
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CarlinoJoeVideo
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6/11/2022 3:19am
I had my fuel boil at the mammoth MX race once. The techs there suggest a different fuel. For hot days at high elevation.

Ethanol boils at sea level at 173f and about 160f at 10k feet. So maybe start with a non ethanol fuel and see if that helps.

Water boils at about 190f at 10k feet for reference.
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sandhills
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6/11/2022 6:43am Edited Date/Time 6/11/2022 6:43am
Gas starts to boil at 95f at sea level, so the question of what made it boil is easy, would only take a little heat at elevation.

In a vented container it would just cool itself by evaporation though, and not actually boil. The boiling comes from being warm under pressure and then the pressure being released.

So what kind of check valve are you using on your vent hose? It's supposed to allow some pressure venting but it closed, but I've heard even the OEM ball valves can have the same problem.
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Rider 5280
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6/11/2022 9:27am Edited Date/Time 6/13/2022 2:42pm
sandhills wrote:
Gas starts to boil at 95f at sea level, so the question of what made it boil is easy, would only take a little heat at...
Gas starts to boil at 95f at sea level, so the question of what made it boil is easy, would only take a little heat at elevation.

In a vented container it would just cool itself by evaporation though, and not actually boil. The boiling comes from being warm under pressure and then the pressure being released.

So what kind of check valve are you using on your vent hose? It's supposed to allow some pressure venting but it closed, but I've heard even the OEM ball valves can have the same problem.
The check valve definitely wasn't allowing any pressure to escape, so I will go back to the OEM fuel cap hose and see how things go.

I recall years ago having a similar but different problem with a check valve add-on, so I think I am just done with these devices.

Thanks guys - you gave me some great advice!

Rider 5280
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6/11/2022 9:34am
Another question:
Do you think I damaged my fuel tank and now it's potentially unsafe to run?

I rode it like this for 5 hours on/off. Was kinda stuck in the "way back" trails as I made my way out after realizing what was happening.

The Shop

seth505
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6/11/2022 9:47am
Rider 5280 wrote:
Another question: Do you think I damaged my fuel tank and now it's potentially unsafe to run? I rode it like this for 5 hours on/off...
Another question:
Do you think I damaged my fuel tank and now it's potentially unsafe to run?

I rode it like this for 5 hours on/off. Was kinda stuck in the "way back" trails as I made my way out after realizing what was happening.
Just give it a once over for cracks and maybe inspect the petcock/gasket. I wouldn’t be surprised if it’s all fine.
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sandhills
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6/11/2022 10:24am
I don't think it would hurt anything. Sealed gas cans are fine even if they bulge a little and a gas tank is stronger than that.
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RGaede
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6/11/2022 4:10pm
Last year i had that happen at Aztec in Colorado springs toward the end of a moto on my 19 kx450, and have gotten it many times on my old 06 crf250r here in Albuquerque during the summer (riding spots are all 6500 ft and temps if 95 in the summer). If the tanks not leaking you should be good. Thinking if riding my smoker tomorrow instead of the 450 because the smokers don't generate as much heat and i don't want to boil the fuel.
yz133rider
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6/11/2022 4:29pm
It’s the ethanol in the fuel. Shits such junk. More politics where it doesn’t belong that there’s even ethanol in fuel.
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RGaede
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6/11/2022 4:59pm
yz133rider wrote:
It’s the ethanol in the fuel. Shits such junk. More politics where it doesn’t belong that there’s even ethanol in fuel.
I agree on the ethanol, i treat it personally. Here vp is going for 125 per pail and i can't stomach that price. Very few no ethanol pumps, and there all under 91 octane so id need to cut it with vp anyway.
willbilly
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6/11/2022 5:14pm
The aluminum fuel tap on the tank sits less than an inch from the head. Insulate that and the bottom of the tank with heat tape and that will stop the boiling.
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harescrambled
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6/12/2022 6:38am
RGaede wrote:
I agree on the ethanol, i treat it personally. Here vp is going for 125 per pail and i can't stomach that price. Very few no...
I agree on the ethanol, i treat it personally. Here vp is going for 125 per pail and i can't stomach that price. Very few no ethanol pumps, and there all under 91 octane so id need to cut it with vp anyway.
Buy Sunoco 260GTX. 98 octane, has no ethanol and costs less than VP
RGaede
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6/12/2022 1:47pm
Buy Sunoco 260GTX. 98 octane, has no ethanol and costs less than VP
No sunoco here, there's torco at the dragstrip and vp at 1 dealership. That's it for race fuel.

Back on topic, rode the 450, boiled the fuel, had a great time.
btroxler
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6/13/2022 9:15am
Also you can get you some gold foil and wrap the bottom of your tank with it. It helps reflect the heat, you can get it from Motosport or RMATVMC.
2
Rickyisms
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6/13/2022 2:35pm
I bought a couple rolls of the gold tape from eBay for pretty cheap. I’ve had race fuel boil and interrupt the vacuum to the carb. Haven’t had a problem since.
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Rider 5280
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6/13/2022 2:43pm
Perfect - this ^^^ is what I'll do.
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