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D. Sherman
User Rank
Gold
Re: Ignition failure & carb icing
D. Sherman   1/16/2012 11:58:23 AM
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Carburetor icing does occur in ground vehicles, but not commonly unless there's a malfunction. Carb icing requires humid air, usually at temperatures in the 30s. Sub-freezing air is already dry enough the futher cooling in the carburetor is not likely to condense any moisture out of it. My first encounter with carburetor icing was when I took my new (to me) 1952 Tucker Sno-Cat out for its first big drive on a warmish winter day. The route involved going up-hill for about 10 miles with the throttle wide open, and then turning around and coming back down. The engine was a Chrysler 230 flat-head with a ver y simple 1-barrel carburetor. In deep snow, the machine takes a lot of power, and the engine is barely up to the task when also climbing a hill.

When I first started down, between the combination of going downhill and driving in my old tracks, I was able to get up to maximum speed (15 mph) so I backed off on the throttle. About half way down I began to lose power, and soon I had the throttle wide open and was still barely making progress even in my old tracks. The engine ran smoothly so I couldn't imagine what was wrong. When I got back and opened the hood, it was obvious -- the carburetor bas was covered with iced and the ventury was narrowed down to a small diameter. Apparently going uphill under full load generated enough heat in the engine compartment to keep the carburetor thawed, but once I cut back to partial throttle, the ice buildup began. This engine has a manual heat riser used on industrial and military 230s rather than the thermostatic ones used on cars and light trucks, and it was set to the "summer" position.

I can't imagine why anyone would set the heat riser on a snow machine to "Summer", but someone had done so and done it a long time ago because the only way to set it back was to take the manifolds off, separate, them, break the shaft loose from the rust, and clean out a large accumulation of carbon that had blocked the heat riser passages. Once the heat riser was cleaned, re-assembled, and set to the "winter" position, the machine has never iced up. I've thought about putting a manual control cable on it so I could adjust "carb heat" from inside the cab, but I suspect it's not necessary on a snow machine.

 

 

RobLewis
User Rank
Gold
Ignition failure & carb icing
RobLewis   1/16/2012 10:42:47 AM
NO RATINGS
The MGB presumably had Lucas electrics, right? There's a reason Mr. Lucas was affectionately known as the Prince of Darkness.

On carburetor icing: pilots of small planes are trained to be on the lookout for this, but I'd never heard of it happening in ground-based vehicles. In the air, it's most likely to happen in humid (and not exceptionally cold) conditions during part-throttle operation. Planes have a Carb Heat knob on the dash that selects preheated intake air from the exhaust manifold. If you don't wait too long before pulling it you can avoid an engine failure. You're taught to turn on Carb Heat when you reduce power for deceleration to a landing.

burntpuppy
User Rank
Silver
Re: Snow and Carburators
burntpuppy   1/16/2012 9:53:33 AM
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 The more likely cause is that the crack opened up more when warm, this is fairly common.

3drob
User Rank
Platinum
Re: Snow and Carburators
3drob   1/16/2012 9:39:30 AM
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Ahhh, the good old days when you could actually work on your car, and do it on the side of the road (but before cell phones so you HAD to fix it there, or walk).  For my first 15 years or so of driving, all my cars (and I went thru a few) were old junkers.  Usually when faced with problems (many of them over the years) my focus on the side of the road was to just fix it well enough to get me to my destination where I could safely fix it right. 

My two consumable materials that I always had on hand were duct tape (actaully capable of sealing spewing radiator hoses without turning off the car) and wire (or coat hangers, for exhaust and other issues).  Apart from the standard small set of tools, my indespensible tool was a pair of vise grips.

The only thing you can do with a modern car is call AAA.

jccubs
User Rank
Silver
Re: Ingenious
jccubs   1/16/2012 9:39:11 AM
NO RATINGS
I have used WD-40 for so many things I've lost count.  The WD in the name does refer to water displacement, but the number of times it is used for that application are probably a very small fraction of the overall uses!

Charles Murray
User Rank
Blogger
Ingenious
Charles Murray   1/13/2012 5:35:07 PM
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"I sprayed some WD40 to displace the water..."

As is so often the case I am amazed by the ingenuity of our readers. I have to admit, I never would have thought of it.

Rob Spiegel
User Rank
Blogger
Re: Snow and Carburators
Rob Spiegel   1/13/2012 1:24:26 PM
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Good story, Bob. If you fleshed it out a bit, we could use it as a Sherlock Ohms posting. You would just need to add a couple examples of your sleuthing to find out what was wrong and an explanation of how you finally figured it out.

If you're interested, you can reach me at: rob.spiegel@ubm.com

Please include a short bio if you choose to send it to me.

bob from maine
User Rank
Platinum
Snow and Carburators
bob from maine   1/13/2012 10:42:06 AM
NO RATINGS
Had a Volvo that would run in all circumstances and temperatures except during very heavy show storms. The car would run fine until it just seemed to lose spark and die. It was so consistent I bought an extra coil and distributor cap "just in case". It turned out that the SU carburators (same as the ones on the MGB) would ice-up just behind the throttle plates. Stopping the engine allowed the heat conducted from the engine to melt the ice and the car would run for another 5 to 15 minutes depending on how hard it was snowing, the longer you shut it off, the more of the ice melted and thus the longer it ran before quitting again. This short paragraph in no way covers the tens of times I tried to troubleshoot this problem, of course always in near blizzard condtions. The fix was to make a shroud that covered the air cleaners with a snorkel that took air from the exhaust header. After making this, I found that it was available as a stock part for an earlier model year. It cut down on performance but the car soldiered-on for 375K miles through 13 winters. My 1920 Model-T has the same problem when driving in very thick fog.

Tim
User Rank
Platinum
WD-40
Tim   1/13/2012 6:26:45 AM
NO RATINGS
WD-40 and duct (duck) tape have been saving lives for decades.  These two go down as two of the most handy tools available.

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