[Tigers] Carb Fire Research

[Tom Witt]

I finally got around to watching this video. It was like watching paint dry. It could have been 30 seconds long, not 20 minutes. But anyway (it’s not Stu’s fault), it did eventually shows the gas boil at a low temperature.  I’ll just throw these things out there:

1. No one ever mentions it, but there has to be some cooling effect of both from the air being drawn into the carburetor and the evaporation effect of the gas (like when you apply rubbing alcohol to your body).  Then again, without cold air ducting..., maybe not.

2. A cooling effect likely offsets some of the heat soak while the car is in use. However, when the engine is stopped that cooling also ceases.

3. It would seem best to isolate and insulate the carburetor from the rest of the engine compartment.  This, however would require some type of hood scoop (or duct) and and an isolation enclosure under an already crowded hood.

4. I’m wondering if the horn opening block off plates some use (that work at idle/stopped) to prevent recirculation are a detriment at higher speeds not allowing cooler air to pass through the engine compartment?  I’ve always through a spring loaded door seemed a better concept. Closed at an idle/stopped condition, but opened from the flow of air as the car moved forward.

5. If anyone is interested, some of the 280Z’s had a fan and ducting that blew air onto the injector rail. The concept would seem somewhat adaptable to blowing cool air on the carburetor after the car shut off. A 555 Timer could control the run time after shut-off.

It seems any attempt for correction deviates from a stock appearance. And, a crowded area under the hood doesn’t leave many options for isolation or ducting. Has anyone run without their hood to see it it makes a difference?

Just some rambling thoughts.

From: Stu via Tigers 
Sent: Friday, September 11, 2015 5:42 PM
To: Tiger Net 
Subject: [Tigers] Carb Fire Research

I've been doing some research, and found an interesting video:

https://www.youtube.com/watch?v=d7AkcjnCTVU



To summarize, this guy does a good experiment that proves that some components of normal gasoline boil at around 170F.


Our engines are usually well above this, so when we stop it's safe to assume that the underhood temperatures spike, heating up our carbs, and everything else.  So there could easily be some boiling in the carb  bowl.  And once the 170F components boil off,  the temperature rises even more.  When trying a hot restart, new fuel is introduced to the much hotter carb when the pump comes back on, perhaps there could be a few moments of additional, perhaps more violent boiling, blowing vapor and fuel out the vent.


Last weekend I tried recreating the problem.  Similar hot day, drove around the same loop, etc.  Parked and waited 10 minutes, about the same time as before.  I had cleaned the top of the carb, so it was obvious that nothing had come out when I opened the hood and looked  But listening closely, I thought I could hear a faint sizzling sound from somewhere within the carb...   I did not try a restart, since I hadn't seen this video at that point.


Any opinions?


Stu
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