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Coughing and spluttering 100/6

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Leew

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My fuel tank is clean, I have a silver in line filter and a Powermax in line fuel pump which is sited under the back seat, which leads up to two inline filters just in front of the carburettors
The car starts and runs great but after driving for a while it starts coughing and spluttering and backfiring, so much so I have to pull over
When I lift the bonnet and look at the transparent filter just in front of the carb it is only half full of fuel
I switch off, wait a moment and switch the ignition on and the bowl fills to the top, then the car will start and run great again for half a mile
My diagnosis is the silver in line filter is clogged and the fuel pump is low not high pressure
I intend fitting a correct SU high pressure pump........unless anyone knows different?

Ta
 
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Cheers Steve...just edited my post, must have been drinking some funny stuff
I agree too many filters, but I also think the pump is incorrect
 
Vaporisation? Fuel filters often look half full, but the engine is generally okay. One filter close to carbs is good.
 
Fuel pressure should be limited to 2-3 psi. Higher pressure will overcome the float valves and overflow the carbs. Too many filters sounds like the cause.
 
I've ordered a new correct SU fuel pump, removed the metal in line filter that was between the tank and the powermax pump, which was clogged with rust and obviously never changed when the tank was changed and am going to put back the original copper fuel lines rather than the mish mash of rubber piping
Brinkerhoff....my first thought was coil as years ago I had a problem with a cracked coil that when it warmed up would short to ground and cause a similar problem

I will keep you all up to speed
 
Our 100-6 was doing that also and I tried lots of things. It seemed to be a form of vapor lock as it only did it when the car was hot and in stop and go traffic, never when under way. It finally stopped once I removed that clear filter in the engine bay near the front carb. I assume the plastic filter was absorbing the engine heat and vaporizing the fuel as it traveled through it causing the fuel surging.
 
UPDATE !! New SU pump installed with all new copper lines and just the one filter close to the carbs.....Bingo, drove it yesterday no issues, went like a dream
However, two things, when the car is running you can see that through the fuel filter that the fuel is almost bubbling through....never noticed that before
Also when the car is not running, but the ignition turned on, the pump is chattering more than I would expect given it does not need fuel at the carb as you can see in the filter it is full
I have to admit the copper line from the tank to the pump was not my finest piece of engineering and did get a little compressed in places.....could this be causing the pump to keep trying to draw fuel?
Also the olive that I soldered on to the pipe that goes into the tank was my first attempt and may not be great even though it does not leak and fits nice and snug
 
Leew said:
... when the car is not running, but the ignition turned on, the pump is chattering more than I would expect given it does not need fuel at the carb as you can see in the filter it is full...
Click to expand...

When you turn the ignition on after the car has sat for a couple days the pump should pump for 5-10 seconds--gradually slowing down--then stop, and pump once every 10-15 seconds or so thereafter. If it keeps pumping, you likely have an air leak on the intake side.
 
Leew said:
Fitted all unions with PTFE tape to prevent the sucking of air....all good
Thanks everyone
Click to expand...
It's been so long since this has come up, but I'm thinking that Teflon is no match for gasoline.

Teflon tape__or paste__IS NOT a sealant, its purpose is to lubricate the threads to allow a tight fit up. At most, two (2) wraps or layers of tape, in the direction of turning (clockwise on typical RH threads) is sufficient, and one should always leave one-half (1/2) to one (1) whole thread exposed__the tape should never overhang to the opening of the fitting.

Hylomar is a sealant, and one of the very few that is gasoline resistant, but that should only be needed if there is a problem with the fittings themselves. That brings to mind something posted previously though, that the olive was soldered to the tube. Did you mean the fitting that the olive (ferrule is the correct term) goes into is soldered to the tube? The ferrule is supposed to be slipped onto the tube and then compressed by the ferrule nut. The ferrule itself shouldn't be soldered to the tube.
 
Have to agree with Randy,especially with ethanol. Ferrell nut should be brass to compress and maybe have a cupped washer.
 
What I did was used a 5/16 copper compression olive, cut the pipe, slid the threaded nut over the pipe then soldered the compression olive to the pipe end and filed it down to sit flat and flush, seems to have worked.
I will look into Hylomar ( not sure it is available in the UK ) but given the Teflon PTFE does not come into contact with fuel I'm not sure why you cannot use it?
 
Hylomar was invented by the good folks at Rolls Royce, possibly during the development period of the Merlin aero engines. The can I have has a UK phone #: 44 (01)1942 617000.

Even if it works, it goes against tube-fitter installation practices__but hey, we Yanks put honkin' V8 engines in our Healeys (and BMWs) so what do we know?!?!
 
I agree that ferrules or as they are commonly called in the UK olives are not usually soldered to the pipe . However in my very humble opinion as a nuclear industry engineer with over 35 years experience I d rather trust a soldered olive to seal to the female conical surfaces of the fitting and nut and the pipe OD than be wholly reliant on PTFE tape or Hylomar. The best option would be new clean pipe and a new olive. However if it's now sealed leave it alone till next time. If you must use a sealer loctite 242 is excellent as is permatex.
I,ll get off my soapbox now !!!!
 
Randy said: Hylomar is a sealant, and one of the very few that is gasoline resistant...."

I'll attest to that as I once got a bit of it in my fuel tank when sealing up the sending unit. A few months later I found that it had made its way into the inline fuel filter and it appeared like it had just come out of the tube.
 
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