Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Damp membrane and fuel line

Greetings All

Couple of things I thought I would consult the collective wisdom about.

Damp membrane between the frame and the chassis... Is there a preferred product?... I noticed what was left of the stuff on my car was several mm thick (3 to 4 at least) but beyond that hard to tell much about it. If there's a 'proper' way to go with this I'd appreciate a steer in the right direction.

The underbonnet of my car was a hugely untidy mess of pipes and stuff (doubly irritating as it's a simple old pushrod crossflow with about 12 moving parts)..... Amongst the things I'm thinking of doing is removing the return petrol pipe.... I understand this feed/return system is to prevent vapour lock... In all the years I've driven (including taking an Austin A40 overland into the Sahara and repeating the trip later in a 2cv) I've never had a vapour lock.... The underbonnet of the Morgan doesn't seem overly crowded by any standards and the fuel system is on the opposite side from the exhaust... Is this really an issue or will me deleting the return pipe and blocking off the outlet at the carb cause some unforseen catastrophe?..... I have to say that in all the old carb cars and motorcycles I've ever had this is the first return system I've ever seen and caused me to scratch my head a bit til I worked out what it was for... .. Your thoughts Ladies and Gentlemen?

K

My crossflow engine only has a single feed from the petrol tank no return. Feed from the tank goes to a bulkhead mounted filter, not original, then to the mechanical fuel pump and then in to the carburettor.

What sort of fuel pump do you have? My limited understanding is that engines (esp. carb-fed engines) with low-pressure electric or mechanical fuel pumps don't need a return system, but if you're running a higher pump pressure and there's a chance of "overwhelming" the induction/injection system, then a return line deals with that, sending un-needed fuel back to the tank and providing a sort of pressure relief against an overenthusiastic fuel pump.

A previous owner had fitted an electric pump... Not sure of its condition so I'm intending to ditch the pump and blanking plate and go back to the original mechanical pump... Should be no problems with overpressure...... I must admit I was surprised to see anything other than a single pipe system when I opened the bonnet.

K

The only time you need to fit an electric pump (and associated pressure regulator)on a Crossflow is if you are running a pair of side draught carbs.

The original mechanical pump is perfectly adequate for the standard carb.

Regarding the membrane, I use very thin rubber strip about 2mm thick with a skim of mastic on the top.

Arwyn

I cant see the need for a return for the reasons stated.

I found this on gomog recommending tar paper between the chassis and the tub!
http://www.gomog.com/allmorgan18.html

Arwyn... Those were my thoughts..... The electric pump is overkill.... I'm trying to keep the car as basic and simple as possible... Mechanical pumps are compact and cheap.... I could carry a spare if I felt the need.

John... I've seen a few option's mentioned..... I'm wondering what the factory uses?... And also if they just sell it like any other spare part?... Tho I fear it might be eyewateringly expensive for what it is.

K

Image, the damp course used to be a sort of bituminous strip, like cheap roofing felt without the green grit

A better modern option is Hyload (brand name) DPC from builders merchants, as it won't squish under load & won't leach out messy bitumen, just use 2 layers if you need it thicker

I remember only seeing return pipes introduced when fuel injection became the norm, given need for constant higher pressure for the injection system. Only advantage I can see for electric lift pumps is having ability to get fuel to carb without churning engine over. Grateful for such when one of two tanks on an old XJ12 ran dry and fuel pump changeover didn't work, at 12am on the M4!

Richard.... Having seen the pressure bleed return on my injection systems was what made me do a double-take when I saw it on the Morgan... Turns out that the idea is that the constant cycling of the fuel keeps it cooler and prevents vapour lock.... On my previous experience I'm willing to risk it for reduced opportunities for leakage and simplicity.

K