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Petrol evaporation - solution?


jordan_meakin

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What carb are you running? My twin strombergs are a devil for this, and run rich when the under bonnet temperature gets above a certain point. I've come to the conclusion a little fan to move some air over them when not moving is about the only way to deal with it. I'm running an electric fuel pump and regulator - it doesn't make any difference. 

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I've previously had great succes with covering a plate with powerwrap and fitting it between the manifold and the floatbowl. I did however close off the hole in the exhaust manifold at the same time (the hole where it connects to, and preheats the intake manifold. It helped a lot but can't tell you which part did the most. You could also powerwrap the Whole downpipe and exhaust manifold to remove a lot of heat from the engine compartment

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  • 3 weeks later...

The answer is  leave the mech pump on and fit a facet lecky pump back by the tank  Wire it to switch

just prior to start switch on lecky pump  this will overcome vaporizing in either mech pump or carb .

When running switch of lecky pump .  This gives you a standby pump if mech pump fails  as well , same sytem is used on all piston engined aircraft ,  I have done this mod to several petrol engined vehicles .

http://www.ebay.co.uk/itm/Red-illuminated-LED-Toggle-Switch-With-Missile-Style-Flick-Cover-Car-Dash-12V-/262254582103?hash=item3d0f975957:g:zBYAAOSwnDxUlv6g 

used this type switch to save inadvertently leaving on

Edited by tacr2man
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On 21/01/2017 at 10:06 AM, tacr2man said:

The answer is  leave the mech pump on and fit a facet lecky pump back by the tank  Wire it to switch

just prior to start switch on lecky pump  this will overcome vaporizing in either mech pump or carb .

When running switch of lecky pump .  This gives you a standby pump if mech pump fails  as well , same sytem is used on all piston engined aircraft ,  I have done this mod to several petrol engined vehicles .

I kinda get the point on a light aircraft but not on a car, by all means leave the mechanical pump in the block and pipes available for backup but if you fit a lecky pump then use this as he main. Why faf about with turning it on and off when it is a better pump than a mechanichal diaphram pump anyway?

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I doubt an Electric pump will solve all your issues, my S1 was fitted with one from the factory and still had the problem. In some instances it's actually worse, as the hot starting issue usually is caused by the fact that the engine has to start in a way too rich environment because the intake is filled with hot fuelvapour. And especially if your carb has an acc. pump, because then you'll squirt in even more fuel when you go to open the throttle which in turn is necessary to start the already very hot engine filled with fuel. In my experience (and I have learned it the hard way sadly) the best way is to make that carb cooler.

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The whole point of having both on aero-engines is to have two independent pumps running from separate power sources, so the mechanical pump will work if the aircraft has an electrical failure and the electric pump can prime the unstarted engine as well as back up the mechanical pump at critical times (low altitude and aerobatics, mainly).  Having both on a car is no problem, but not essential like it is in an aircraft.  It's not a direct comparator.

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On 25/1/2017 at 9:41 PM, jordan_meakin said:

Mine's a Zenith. Refurbed it which solved a multitude of sins, replacing all gaskets and replaced the anti-heat block but didn't solve the evaporation. Did anyone have one new from the dealership? Did LR not acknowledge this problem? Do other carbs suffer it too?

I think, back then it was just a part of owning an Automobile, a long with basic knowledge of how to clean and adjust your Points, and remove condensation from your dizzy. Nowadays you frantically browse through your touchscreen in the center console to find an app to tell your dealer the car needs to be picked up.. :hysterical:

Seriously though, all vintage cars, motorcycles and tractors I've had/come across have suffered from heat soak one way or the other, some worse than others. The problem on cars/lorries/tractors at least is that the intake is often heated by the exhaust to get proper atomization of the fuel. Sounds very daft now, but maybe it was necessary with the fuel quality back then? I don't know but there must be a reason why so many did it, and that it doesn't seem necessary these days.

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Vapourisation is a common theme that affects v8 powered rover P6's - in this case the cam driven pump has to pull fuel quite a long way forward from the tank, and the fuel line runs along the side of the block just above the sump to the pump so is in a nice warm environment. 

The theory on the Rover forums is that it was never really a problem back when the cars were new, but that the addition of Ethanol in modern fuels makes it worse. 

On my car, back when it was carbed I fitted a facet pump to the rear of the car pushing fuel forward to the engine bay(rather than pulling) and deleted the mech pump entirely. I never had any vapourisation issues at all after that. 

I think having a carb with a return to the tank and an electric pump is the best way to avoid vapourisation - the circulating fuel acts as a coolant for the carb and stops it getting hot enough to vapourise.

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The op was asking for a solution , that is what I posted , having used on various vehicles for over 40 years

the info regarding aircraft was just an interesting ( I thought ) aside  from a similar set up that i came across when flying .  Putting an electric pump in circuit pushing from near the tank  as mentioned by subsequent poster is most efficacious , where you have a built in backup ie a mech pump left in situ , with an electric pump select-able has to be an improvement over having a single system  Just as I have dual battery system so I can switch in an instant jump start standby .  The old 6 'P' s.  :) 

The flow and return system was used on RV8 several models also

'

Edited by tacr2man
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  • 5 months later...

Bowie beat me!

My 2.25 powered 90 was fitted with the equivalent of one of these from the factory:

http://www.glencoeltd.co.uk/facet-fuel-pumps/facet-cylindrical-pump-12v-24v/

you only need the basic spec version. 

The pump has done zillions of miles with no issue, infact it lives on as a low pressure pump feeding the swirl pot on my daily.

Here's a copy of the Facet on Paddocks. 

http://www.paddockspares.com/prc3901-fuel-pump-ecternal-electric.html

 

 

 

 

 

 

 

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