The phenomenon of Vapor Look:

[NitroR/C]

Small guide I had in my database to share with you.

The phenomenon of Vapor Look:​

Vapor look is a phenomenon that occurs in micromotors due to overheating of the
themselves due to various reasons.
It manifests itself, more so in the summer period, and in two ways:
- visual way through the occurrence of air bubbles present in the mixture tube that goes from the tank
to the carburetor;
- acoustic mode in the sense that when the mixture reaches the carburetor, it can be heard to
"fizzles" as it is called in technical jargon and evaporates instantly due to the significant
thermal difference between the temperature of the mixture itself and the temperature present in the
carburetor at the time the mixture reaches it.
The reasons that cause said phenomenon can generally be identified among the following
Which are given in random order;
- engine with little or no ventilation due to the body lacking the relevant holes to let
fresh air to flow to the head and crankcase;
- engine too compressed;
- unsuitable spark plug;
- lean carburetion so less mixture enters than is needed;
- mixture with too much % nitromethane than the manufacturer indicates on the
engine instructions;
- No. of washers present in the underhead;
- clutch worn or not properly adjusted in such a way that the engine increases
RPM significantly without increasing in speed in such a way that it cannot
enjoy a sufficient supply of fresh air thus not ensuring its cooling;
- difficulty in advancing the model due to incorrect adjustments in the transmission (e.g.
brake linkage partially locked, or incorrect adjustment of the "trim" function
on the radio always relative to the brake - wheel bearings with limited sliding due
to dirt or wear and tear on them).
Therefore, to solve the inconvenience and without upsetting the model car, one proceeds step by step to
example;
- turning without bodywork (although this would not be advisable since in case of
overturning the model one could suffer considerable damage from it) one can already verify a
possible attenuation of the phenomenon;
- by replacing the spark plug with a suitable one following this table;​

- possibly lengthening the mixture tube running from the tank to the carburetor to a
maximum length of 15 cm.;
- trying to run with a mixture with a lower % nitro than the one in use when the
the problem occurred (e.g., from 16% you can change to a 10%);
- greasing the carburetion i.e., opening the maximum needle by half a turn or one turn depending on
depending on the type of engine;
- insert a filter on the pressurization tube that runs from the muffler to the tank that acts
as a heat sink as well as preventing the entry of oily residue from combustion that would
would go to foul the mixture in the tank.
​

 

[WickedFog]

I assume this is supposed to be vapor lock?

 

[NitroR/C]

Basically, the mixture evaporates inside the carburetor because it is too hot, causing difficulty in shutting off and hot starting because bubbles also form on the tube.

consider that the methanol in the mixture evaporates at about 67 degrees Celsius So it would be better in the summer when it is very hot to keep the mixture in the tank as cool as possible, perhaps by mounting a specific filter or radiator on the pressure pipe to cool the exhaust gases coming from the muffler . Another reason is that a lot of carburetors are made of plastic material and not aluminum for this reason.

 

[WickedFog]

Basically, the mixture evaporates inside the carburetor because it is too hot, causing difficulty in shutting off and hot starting because bubbles also form on the tube.

consider that the methanol in the mixture evaporates at about 67 degrees Celsius So it would be better in the summer when it is very hot to keep the mixture in the tank as cool as possible, perhaps by mounting a specific filter or radiator on the pressure pipe to cool the exhaust gases coming from the muffler . Another reason is that a lot of carburetors are made of plastic material and not aluminum for this reason.

Yeah, I think that is supposed to be vapor lock, not look

We used to fix that by putting clothes pins on the fuel line in front of the carburetor.

 

[tudordewolf]

by replacing the spark plug with a suitable one following this table;

Which manufacturer's numbering scheme is that? There's no standard for glow plug numbering.

We used to fix that by putting clothes pins on the fuel line in front of the carburetor.

Interesting, what does that do?

 

[NitroR/C]

A generic reference chart… this was in the guide I retrieved many years ago from a Nitro RC racer and mechanic.

 

[WickedFog]

Which manufacturer's numbering scheme is that? There's no standard for glow plug numbering.


Interesting, what does that do?

It's like a heat sink for the fuel line. On straight sixes with long tubes it would have the carb right above the header. Adding the clothes pins was a quick fix until you could get some aluminum finned tubing on the line or reroute it. I can't tell you how many times I saw clothespins on a fuel line back in the early '80's.

I can imagine similar reasons on nitro RC's can cause vapor lock, though I'm not a nitro RC guy. Having the header right there, and cramped spaces would seem to me could cause this issue.

 

[NitroR/C]

This is an example I adopted on one of my rc model cars. i remember years ago when i was new to nitro rc, turning in the summer I often encountered this problem with an old kyosho pure ten. and solved the problem more or less with a self-made aluminum heatsink on a lathe.

 

[WickedFog]

This is an example I adopted on one of my rc model cars. i remember years ago when i was new to nitro rc, turning in the summer I often encountered this problem with an old kyosho pure ten. and solved the problem more or less with a self-made aluminum heatsink on a lathe.
View attachment 162218

Very nice. That is kinda what you would put on a fuel line on a car to prevent vapor lock.

 

[Greywolf74]

Very nice. That is kinda what you would put on a fuel line on a car to prevent vspor lock.

I'm assuming that is supposed to be vapor lock?
Sorry, I couldnt resist

Back when I first joined this forum, IIRC, all the old nitro heads said those "fuel line heat sinks" were a gimmick. They dont have enough surface area to do any substantial cooling. People used to just suggest creating more airflow under the body to fix the issue and make sure the fuel line is routed in such a way that its away from heat sources as much as possible.

 

[WickedFog]

I'm assuming that is supposed to be vapor lock?
Sorry, I couldnt resist

Back when I first joined this forum, IIRC, all the old nitro heads said those "fuel line heat sinks" were a gimmick. They dont have enough surface area to do any substantial cooling. People used to just suggest creating more airflow under the body to fix the issue and make sure the fuel line is routed in such a way that its away from heat sources as much as possible.

I already edited it before your post, so that don't count

I'm assuming that is supposed to be vapor lock?
Sorry, I couldnt resist

Back when I first joined this forum, IIRC, all the old nitro heads said those "fuel line heat sinks" were a gimmick. They dont have enough surface area to do any substantial cooling. People used to just suggest creating more airflow under the body to fix the issue and make sure the fuel line is routed in such a way that its away from heat sources as much as possible.

And you might be surprised how much heat that thing will dissipate. The ones we put on our fuel lines weren't much bigger.

 

[Greywolf74]

And you might be surprised how much heat that thing will dissipate. The ones we put on our fuel lines weren't much bigger.

I got have any data on it, I'm just repeating what people used to say about those.