Fuel Vaporisation

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Neil Evans
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Location: Boston, Lincolnshire
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Fuel Vaporisation

Post by Neil Evans »

Via email...
In normal traffic conditions my a35 runs ok. but in slow moving traffic and queues (getting into shows) it stalls. Two goes on the starter and it starts. Five minutes later it does the same. When traffic returns to normal it runs ok.
The vaporisation usually comes about because the fuel supply to the carb is marginal due to partial obstruction or wear to the pump components.

Examine the pump and check that it's working as it should and that the filter is clear. Renew or recondition as necessary.

Disconnect the fuel line at both ends and blow through it with an airline to ensure it is clear. If the pipe is the original steel one, check that it isn't holed by corrosion, allowing it to pull air in (usually towards the rear of the run).

The tanks originally have an internal filter that's impossible to service and the cars were obviously never intended to last 50 years. It can be disabled by poking a rod up the fuel outlet and forcing it through the gauze. I recommend you use brass as a steel rod could cause a spark.

Install a new inline filter in the pipe near to the tank.

If you've done all of the above and still have the problem, some people find that routing the pipe that runs between the pump and carb further away from the hot exhaust manifold can help.

Check the colour of the spark plugs, they should be a straw colour. If they are lighter or white even, the mixture is too weak. Zenith carburettors are renowned for running weak. The carb body distorts where it joins the manifold and also where the float chamber attaches, allowing air to be pulled past the gaskets.
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ansemic
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Joined: Mon Jun 15, 2009 9:36 am
Location: Reading, Berkshire

Re: Fuel Vaporisation

Post by ansemic »

Having similar problems with mine. I did wonder if the supply to the Zenith was getting hot as it's very close to the manifold. Does the higher ethanol content make the vaporisation worse?
Mike

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Re: Fuel Vaporisation

Post by Tight Yorkshireman »

Never had any problems with mine thast I know of and thats the Zenith. Problems I have had were down to lack of fuel supply through carp in the system and a dodgy lift pump

John G
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First referred to as the Tight Yorkshireman in editions of the Clubs Spotlight: Autumn 1996 Page 40 and Autumn 1997 Page 15
Big Daddy
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Joined: Fri Jun 10, 2011 7:33 am

Re: Fuel Vaporisation

Post by Big Daddy »

ansemic wrote:Does the higher ethanol content make the vaporisation worse?
Good point Mike and something I know little about. So I dug around the web and discovered ethanol blending does increase volatility. Search for "Reid Vapor Pressure" if you're interested. There's lots of deep technical papers... :whistle:

However doubt whether current E5 (5% ethanol blend) has much effect on vaporisation although E10 and more aren't far away: http://www.whatcar.com/car-news/new-e10 ... ts/1229022
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Eric
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Joined: Wed Jan 08, 2014 6:39 pm
Location: Durham

Re: Fuel Vaporisation

Post by Eric »

Had this problem with my mga.fitted thicker gasket between carb and manifold and fitted electric fan...
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