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Mike G

Petrol Freeze-up

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Now that the decent weather is back, and the mornings look brighter, I was tempted to take my Exmo to work. Air temp was in the low single figures centigrade. Car started no trouble, but about 2 miles down the road engine spluttered and eventually ground to a halt in the most inconvenient piece of road.

 

Diagnosed petrol freeze-up (or failure to atomise). With the engine heat and two minutes of going nowhere, the car restarted and did the remaining 20 miles without a problem. This has happened in the past twice before under the same weather conditions.

 

The engine is 1600cc Pinto with twin-choke Weber, with none of the Winter gubbins to suck heat off exhaust (- that's bandaged up, so most of the heat goes out the silencer).

 

I was thinking a small 12 volt element or a headlamp bulb installed in the air filter might provide sufficient heat to overcome this. Anyone sorted this one out?

 

Cheers

Mike G

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I've never heard of this but I think to place an element or even a headlight bulb in the air filter would be very dangerous! I have a 2.0L pinto with a 32/36 DGV and had a pipercross foam filter. I would occasionally see wisps of fumes come up from the filter when the engine popped and backfired. There is also a vapour stain on the underside of the bonnet. You wouldn't want to ignite any of this :help:

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does the carb have a auto choke because it sounds more like you have trouble with that

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I got rid of the auto-choke when I had the carb rebuilt years ago. When the engine starts to misfire, it doesn't matter what I do with the manual choke knob (excuse the expression!), the misfire continues with lots of smoke out of the silencer until the engine eventually dies. Trying to re-start immediately is a waste of time and battery power.

 

This has happened three times over the past few years, and only occurs when the air temps are below say 6 degrees, and the car has travelled only 2 miles. Parking up for a few minutes (no choice as the engine is dead), I believe the accumulated heat under the bonnet, even after 2 miles, is enough to thaw out whatever area has caused the fuel to 'freeze up'. The engine then starts OK, and will run for the remainder of the journey without a hitch.

 

A possible safe cure I have in mind, is to coil some micro-bore copper tubing inside the air filter, and plumb it into the heater circuit. Advantages are that there will be no electrical element or whatever to ignite fumes, and only works when my feet are cold and I therefore need the heater 'on'.

 

Cheers

Mike G

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i would go for the copper pipe plumbed into the heater, i did the same on my mini years ago but for the washer bottle that used to freeze up in winter

pete2b

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It isn't the petrol that freezes, it's the water vapour in the air.Iwould look for a way of ducting warm air from around the exhaust system into yhe air intake.That's trhe way car manufacturers overcome the problem.

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The water-vapour freeze-up makes more sense - probably as a result of contrast between cold & hot surfaces. I've bandaged up the exhaust manifold and pipes, so there isn't a lot of heat coming from that area anymore. To offset hot-weather problems under the bonnet, I also arranged trunking to suck cold air in front of the rad straight to the air filter. Helps to stop over-heating in Summer, but does no good I suspect at this time of year (although judging from my biking days, the engine probably prefers the cold air intake).

 

Think I will pursue my copper pipe idea. Should be a fairly cheap solution if it works!

 

Thanks guys for your help

Cheers

Mike G

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its a common problem on piston engine aircraft.usually associated with carb icing. ice forming in the venturi . they have a warm air outlet from a shroud fitted round the exhaust stacks and draw warm air from there this is selectable via a cable connection and flap valve so its only tends to be used on descent with throttle partially closed. but you can get carb ice form at all altitudes /speeds/ etc depending on the dew point of the atmosphere.

i would suggest you take off the cold air intake for the winter and try again.

steve

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I had this problem many years ago with a mini marcos with SU carbs and no room for the air intake heater from the exhaust.

Hot water pipes will not totally cure the problem because these do not get hot enough until the car has been run a few miles by which time it will have frozen up and stopped.

Electrical heaters are possible, I suppose, but over complicated, in my opinion.

The best cure is to duct warm air from around the exhaust. I think that this will work even with exhaust bandage around it. You only need to get a few degrees warmer to stop this from happening.

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Blank off your air run to the front of the car & instead take the air in from under the bonnet in the winter, that will solve the problem. If you are really clever you could make some kind of vented box with swivelling vents, Open the vent in winter (I suspect drawing air from both sources will still be warm enough) & shut the vent in summer, you could even make it dash operated with some thought.

 

Dan :)

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If you can find an inlet manifold from a sierra that had the bigger DFTH carb it has an electrical heater in the base of the manifold. You could hook that up electricaly with a relay and timer to get around the problem.

 

Nigel

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On my 1st car - a Fiat Panda (yes how embaressing) the air box had a top that you could turn to switch between a cold air feed from the grill or a hot air feed from the exhaust manifold area.

 

On my old carb 32/36Dgav i never had any problems with carb icing but i know someone got it when fitting the top hat adapter with cold air feed.

 

Either remove cold air feed or fit some kind of blockage into the end of the pipe during winter?

 

Andy

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It isn't the petrol that freezes, it's the water vapour in the air.Iwould look for a way of ducting warm air from around the exhaust system into yhe air intake.That's trhe way car manufacturers overcome the problem

Had the exact same problem with a K&N on an XR2, solution was a simple 2" foil tube from exhaust manifold to K&N.

Nothing fancy just tied one end to the manifold with some welding wire and the other to the filter, did not even blank any of the filter off.

The extra few degrees seemed to stop the freezing.

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