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Do Nitro's Vapor Lock?

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Old 08-24-2003, 02:40 AM
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ZipZap
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Default Do Nitro's Vapor Lock?

I'm running a Picco XP12. If the motor is above 150F it will not start. When on the bump starter, I see that the fuel runs up to the carburetor nipple, and then heads back towards the tank. I'm guessing that the fuel is vaporizing at the warm temps. This situation makes any flame-out the end of a heat. Is this normal? Is there any way to cool the carb quickly?
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Old 08-24-2003, 04:21 AM
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Default Do Nitro's Vapor Lock?

Blow on it to cool the heatsink, and carb. What's a vapor lock BTW?
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Old 08-24-2003, 05:48 AM
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Default Do Nitro's Vapor Lock?

Vapor lock is when the fuel vaporizes before entering the combustion chamber and sometimes even before getting through the carb.

150 degrees is not hot enough to vaporize methanol and nitro methane at such a speedy rate. Well it is for the methanol but the carb inlet isn’t as hot as the heat sink so I’m saying “impossible” in your case.

Do you have a primer on the tank? When hot, does the engine feel like it has compression? (I mean comparable to when it’s cold).

If you’ve got a primer, give it a few extra pumps forcing fuel into the engine. Does it get tight, like if it were flooded? Does it try to start then?

Or

Do you have to put your finger over the exhaust hole to prime the engine?

If you intentionally flood the engine and it doesn’t get any tighter, your engine has had it.

Have you tried changing your glow plug?
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Old 08-24-2003, 11:33 AM
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Default Fuel line

Like previous post state 150 is nowhere close to vaporizing fuel.

You would need to be up in the top end of the 200's to sizzle fuel at the carb, maybe even a little higher.

If you are getting the correct temp with a gun or whatever then you may have an airleak somewhere.
If you prime and see fuel in the line then all of a sudden it drops you have some sort of leak.
Check the lines, tank and so forth.


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Old 08-25-2003, 01:31 AM
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ZipZap
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Default Do Nitro's Vapor Lock?

I don't have a primer on the engine. It starts and runs great as long as I start it when it's cool. As far as 150F being too cool for vaporization, how much alcohol is in nitro fuel? I agree that the carb nipple should be cooler than the plug/head, but the metal portion of the carb is very hot to the touch at this point. I thought it should be cooler due to the composite carb body. Lines and tank are good, although I don't know how to check them when everything's hot. However, fuel line is cheap, so I'll replace it and see if that helps. Glow plug is good. I've tried the finger over the stinger trick. I can get the fuel to pull into the cylinder (I can hear the bump starter bog down), and I can get it to spark a bit, but never stay running. I got some advice today to pull the plug and totally flood the cylinder. I'll give that a try too.
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Old 08-25-2003, 04:01 AM
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Default Do Nitro's Vapor Lock?

Quote:
Originally posted by ZipZap
As far as 150F being too cool for vaporization, how much alcohol is in nitro fuel?
Methanol is an alcohol fuel but doesn’t evaporate or burn at the same rate.

Methanol is a chemical composition making it an ethanol.

(CH3OH)

Methanol is actually a methane with one hydrogen molecule replaced by a hydroxyl radical (OH).

“Nitro” is Nitro Methane and guess what, you could douse a card board box with pure nitro and you’ll go through a full box of matches and never set it a fire.

Nitro Methane isn’t flammable unless it’s under great pressure (or compressed) and even then it’s combustible not necessarily flammable.

A typical mix...let's say...10% fuel, is 10% nitro methane, with 25% castor oil and 65% methanol.

Do the math to figure out your 20% nitro mixes. The oil isn’t lessoned much but the methanol content is.

As far as your 150 temps and vapor lock goes….

You’d need an acetylene torch to create a vapor lock situation on your RC engine. My Velocity .17 runs 200 degrees any given day and I’ve no problems starting or running it.
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