1.7 B172 Fuel Layout Help

B14, B172, B19/200, D16 engine, ignition, cooling, fuel & exhaust system, gearbox, variomatic, final drive... | Tuning: engine swaps, welded diff, clutch upgrades...
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LadbrokeOB
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1.7 B172 Fuel Layout Help

Post by LadbrokeOB » 10 Sep 2014 01:52 pm

Ok.. so below I have drawn my fuel set up on the B172K.

Image

Firstly does it look correct? I'm guessing its not far wrong as the car runs.
From my picture, which of the two lines that go to the tank are the return and supply? top or bottom etc.

Secondly where do can I source a 3 port fuel pot / filter like the one in the red circle? Is it even needed?

Thanks
Last edited by LadbrokeOB on 11 Sep 2014 08:41 pm, edited 1 time in total.
1988 1.7 340 Redline

Nick-340GL
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Re: 1.7 B172 Fuel Layout Help

Post by Nick-340GL » 10 Sep 2014 03:08 pm

Just run without it, you'll notice the difference in fuel aswell. Just put the pipe from the pipe *can go through another inline filter* straight to the carb.
1987 1.7 340 4 door saloon, 2" drop on 13s with a welder :D

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LadbrokeOB
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Re: 1.7 B172 Fuel Layout Help

Post by LadbrokeOB » 10 Sep 2014 03:54 pm

i think im being slow.. I cant really understand which pipes to go where? do i just do away with the return?

or could you tell me which numbered pipes go where... i've even done another photoshop to help :D

Image
1988 1.7 340 Redline

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mac
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Re: 1.7 B172 Fuel Layout Help

Post by mac » 10 Sep 2014 05:45 pm

It's not a filter - it's a swirl pot/vapour separator.

You can run without it but you would need an alternative fuel pump - you must maintain the return to tank.

On your system the pump feeds the swirl pot, the return is taken from the swirl pot, and the swirl pot feed the carburettor.
From chassis no.735603 the swirl pot is discontinued and the pump feeds the carburettor directly and provides for the return to tank (pump has an extra connection).

Mac.
88 5door Redline 1.7 52k - 19 XC60 Momentum Pro D4 AWD 17k
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Nick-340GL
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Re: 1.7 B172 Fuel Layout Help

Post by Nick-340GL » 10 Sep 2014 05:47 pm

Loose 1 & 5 and connect 3 (plus another inline filter) straight to the feed for the carb

mac, why do u need to maintain the return? My mk2 fiesta had a return but wasn't used and the pump just fed the carb. I dont see why the return is necessary myself but happy to be told otherwise. :)
1987 1.7 340 4 door saloon, 2" drop on 13s with a welder :D

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mac
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Re: 1.7 B172 Fuel Layout Help

Post by mac » 10 Sep 2014 07:10 pm

Hum! Why indeed,
I'm tempted to say "because that's the way it was designed" but there are at least two obvious reasons why a fuel return is a good idea (can't speak for your Fiesta - it probably knows more than me).

The "simple" reason is that the pump operates at a higher pressure than is ideal to be controlled by the carburettor float valve - a calibrated fuel return reduces the pressure being fed to the carb. Without a return anything other than perfect valve sealing would result in fuel bypassing the control and "overflowing" from the float chambers into the venturii. Result grossly rich mixture.

The second reason is more complex and requires an understanding of how a combustion engine works. Basically your engine is a device that converts chemical energy into kinetic and heat energy. Fuel is mixed with air and compressed within a cylinder and rapid oxidisation is initiated by an electric spark (an explosion may not seem to a chemical reaction but that's what it is). The reaction creates an over pressure event which translates into kinetic energy (piston moves down and crank rotates) and a great deal of heat which is wasted to atmosphere (ie:- heats the air up in the engine bay). The colder the air surrounding the engine is - the more chemical energy is wasted as heat (leaving less to "do work").

If the design of the car allows the engine bay to run hot it minimises this heat rejection from the engine block and allows the engine to "turn" more of the fuels chemical energy into "work".
However it is NOT a good idea to allow the fuel to become too hot as this leads to vapour formation (and mixture fluctuation) or even to vapour lock (where the pump simply compresses gaseous fuel rather than pumping). On the B172 especially, the pump (sitting on top of the cylinder head) is very susceptible to heat soak.
A return to tank (whether from the pump directly or from the vapour separator) allows a constant flow of cooler fuel (from the tank) to replace fuel from the engine bay that has absorbed heat. The fuel tank act therefore almost as a radiator or thermal sink.

Mind you, a bloke dahn the pub may well have a different view.

Mac.
88 5door Redline 1.7 52k - 19 XC60 Momentum Pro D4 AWD 17k
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Re: 1.7 B172 Fuel Layout Help

Post by classicswede » 10 Sep 2014 10:09 pm

Most carb engines do not use a return but the pump is driven via a cam in the block with a plastic isolator to keep heat down.

On the B172 the pump is neat the exhaust and up high so the pump is exposed to a lot more heat than most engines. Allowing a constant flow of fuel through the pump keeps the temperature down and stops the fuel vapourising in the pump.


Basically what Mac has written but condensed down
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Nick-340GL
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Re: 1.7 B172 Fuel Layout Help

Post by Nick-340GL » 10 Sep 2014 10:26 pm

Hmmm interesting, i knew obviously it was susceptible to heat soak, but you learn something new every day :) think i might put mine on an electrical pump with a regulator then and do away with the mechanical one :) plus i can put a kill switch in the car aswell :)
1987 1.7 340 4 door saloon, 2" drop on 13s with a welder :D

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LadbrokeOB
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Re: 1.7 B172 Fuel Layout Help

Post by LadbrokeOB » 10 Sep 2014 10:40 pm

mac wrote:From chassis no.735603 the swirl pot is discontinued and the pump feeds the carburettor directly and provides for the return to tank (pump has an extra connection).

Mac.
I took a quick look at the setup on my friends 88 1.7 earlier and i couldn't work out why i had the swirl pot and his didn't... well that explains it! upon looking i saw his had the 3rd port for the pump. i'm tempted to do away with the return feed just for now to get me by as i think im having issues with my swirl pot? will the 3 port pump fit exactly the same housing as my 2 port one? probably best to keep the return in the long run and ill just use his reg plate number when ordering and make sure they supply me with a 3 port one.
1988 1.7 340 Redline

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LadbrokeOB
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Re: 1.7 B172 Fuel Layout Help

Post by LadbrokeOB » 10 Sep 2014 10:53 pm

very interesting to hear about the heat soak issue and using the new fuel as a 'coolant'. i only started the thread as i'm quite unsure as to what is causing my poor running. i've had the car cut out numerous times and it doesn't seem to want to start until i leave it for an hour or so.

i'm rebuilding my carb at the weekend with a full service kit and floats, only thing i cannot source is the jets. so i printed off the full 15 page pdf that mac has written on the solex 28/34 z10 to keep me on track and i'm hoping that once replacing the various parts, gaskets and cleaning it all out etc. that it will allow it to run smooth again!

so far i have tried replacing fuel hoses, the new fuel pump, new inline filter, i've cleaned off the earthing strap and ignition module to try and clear the hesitation / missfires and i've even had a little tweak with the choke cam and idle mixture screw to see if that helps at all. still nothing! not sure whats left in the system to replace other than the vapour separator and the carb itself.

so new parts on the way are camshaft oil seal, as mine seems to weep a bit which might disturb the distributor contact.. a new ignition module incase mine has broken down over time, the carb rebuild kit with floats etc. and failing to find a vapour separator, i might as well try the 3 port fuel pump instead so as to retain the fuel return line.

am i right in thinking that there is a tea bag type filter in the actual tank which could be clogged up?

thanks for all your answers, ill hopefully get to the bottom of it soon!
1988 1.7 340 Redline

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mac
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Re: 1.7 B172 Fuel Layout Help

Post by mac » 11 Sep 2014 09:15 am

The later fuel pump will fit fine.

Have you changed the cap and rotor - the B172 is especially susceptible to rotor arm failure which can give symptoms easily identified as fuel problems?

Mac.
88 5door Redline 1.7 52k - 19 XC60 Momentum Pro D4 AWD 17k
1950 pair of legs that don't work very well.

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LadbrokeOB
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Re: 1.7 B172 Fuel Layout Help

Post by LadbrokeOB » 11 Sep 2014 09:54 am

Oh yes, I forgot to mention that. I've had a new distributor cap and rotor, new leads and plugs.. all within the past 500 miles.

Just after I got home last night it broke down. Before hand it was spluttering and misfiring like mad. Managed to get it started once, with just enough splutters and bangs to power it onto the driveway and it died and wouldn't start again. So that's where its going to stay! Had to cycle to work this morning! brrrrrr

Sooooo....

Would a blocked crankcase breather be an issue? Does this happen?
If there is an in tank filter, could that be clogged up?

I can't really think of anything else that is left in the system to check?
1988 1.7 340 Redline

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mac
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Re: 1.7 B172 Fuel Layout Help

Post by mac » 11 Sep 2014 10:08 am

Blocked crankcase breather - possible, very unlikely, would not cause your problem.
Blocked fuel filter on base of sender unit pick up - possible, very unlikely, could give your problems.

A few suggestions,

Air leak at base of carb - warped base or broken insulator block,
Air leak from crank breather - large pipe into insulator block,
Failing coil unit,
Failing Renix (very unlikely),
Blocked exhaust silencer (internal collapse - more common than you might think),
Failing fuel pump, fuel blockage, (pops and bangs could indicate very weak mixture),
General carburettor contamination, blocked main jets,
Incorrect cam timing (unlikely),

Mac.
88 5door Redline 1.7 52k - 19 XC60 Momentum Pro D4 AWD 17k
1950 pair of legs that don't work very well.

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Re: 1.7 B172 Fuel Layout Help

Post by macplaxton » 11 Sep 2014 01:21 pm

LadbrokeOB wrote:new distributor cap and rotor
Double-check these?

Some of this new stuff is shoite.
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LadbrokeOB
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Re: 1.7 B172 Fuel Layout Help

Post by LadbrokeOB » 11 Sep 2014 03:57 pm

to be honest I had it off yesterday when I was checking to see if the camshaft seal was weeping, everything looked ok. Might as well buy another set for a couple of quid off the local motor factors and hope for the best :lol:
1988 1.7 340 Redline

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