Fuel Filter Confusion and possibly bad diagnosis

[finalarena]

Hello. I'm feeling dumb and confused after talking to the assistant as my local car parts store!

After putting my 1979 Spitfire 1500 back together following a chassis disaster (!) I'm having new problems. I think I've diagnosed it to being gunk in the fuel from the tank getting into the carbs etc. Basically, it drives brilliantly for a few miles, gets quite hot but no alarm bells, but when I try and drive in slow moving traffic with lots of 1st/2nd gear work it just wants to stall. It can go for a long time with the power on seemingly fine, but then try and idle and its like there is no fuel getting through.

If i let it rest a couple of hours, or overnight, the next day its fine again and the circle repeats.

I did things like opening the fuel cap to see if their were vacuums etc, and the engine certainly needs a good tune up. But I'd like to fit at least one fuel filter to see what it catches. I'd like to fit it in the boot to begin with. So, to my dumb questions:

a) The fuel line hose coming out the top of the tank in the boot is approx 8mm external diameter. What size filter inlet do i need? I assumed I'd need a smaller one, say 6mm, but the shop is telling me 8mm to match the hose (with something like 13mm pipe clips).

b) what is the correct way to refer to hose sizes? The internal or external diameter?

c) Will i need to empty my fuel tank? Or does the fact that it comes out the top mean that I can cut and paste in the filter with minimal covering of self in fuel?

d) I'd like to also clean out the filter in the fuel pump, but for the life of me I can't see an easy way of doing it. The Haynes manual makes it sound simple (just unscrew the single screw on top and away you go). Is anyone able to draw an arrow to the screw on their car and describe the a step or two in the process?

Many thanks for any help. I'm learning - slowly!

[DougBGT6]

Most people fit the fuel filter in the rubber hose just before the fuel pump. That way you don't have to buy any extra hose! Use jubilee clip hose clamps. You don't have to empty the tank. Here's a typical filter, this one is glass but you can get plastic if you prefer:

http://www.ebay.co.uk/itm/UNIVERSAL-IN-LINE-FUEL-FILTERS-TO-SUIT-TRIUMPH-T140-/390607688813?pt=UK_Motorcycle_Pars&hash=item5af208546d

Here is a picture of the fuel pump from Canleys:

http://www.canleyclassics.com/?xhtml=xhtml/diagram/spitfire1500petrolpump.html&xhtmlcatalogue=xhtml/catalogue/spitfire1500.html&category=fuelandexhaust&xsl=diagram.xsl

[finalarena]

thanks. The hose by my pump has little slack, so extremely fiddly to cut it and splice in the filter, whereas in the boot there is loads to spare, so its easily severed to insert the filter. Assuming I can work out what diameter of filter nozzle goes with my hose.

[MK3]

Vapour lock ?

[finalarena]

4277 wrote:

Vapour lock ?

I suspect so. With limited time and experience I'm trying to move one step at a time from easy things to solve to harder :-p My float bowls look to be seeping a bit. I thought they might be getting too hot, so I created a temporary heat shield and monitored temp but made no difference. Then I suspected too much pressure (its the original pump), so working backwards wanted to ensure the fuel was actually getting there clean.

[ferny]

Does sound like fuel vaporisation. Has it got heat shields for the carbs? And also, is it still running the dreaded waxstat?

The glass fuel filters linked to are what I use but be warned, the casting in mine which holds it all together was terrible. A slight whiff of petrol around the car for a few weeks turned into the whole tank draining onto the garage floor one night as it disintegrated without being touched. Luckily they're easy to make if you've got the capabilities. If not, I'd second guess buying one you can't visually inspect before purchase.

[DougBGT6]

Don't think you need to worry, just get the filter for a Spitfire and try it on one end of the hose before you cut it.

I had a lot of sludge in the fuel line which caused similar problems, kept stalling. My fuel filter was near the pump and I noticed it was empty when this happened. Dawned on me I had a temporary blockage further back. I cleared it out with a length of strimmer nylon cord.

Had to do it in sections, there are two short rubber pipes in the fuel line which are convenient points to insert the cord. One at the pump and one near the back. Good idea to replace the rubber sections as they go brittle and loose their rubber springiness. Might even be that one of these has bee squashed and not sprung out.

[DougBGT6]

If you're worried about the quality of filters, get one from the TSSC shop.

There's always a tendency to jump to something complex as the cause, human nature I guess. But before you start worrying about vaporization and heat shields clean out your fuel line and carb reservoirs. Also beware the dreaded rubber slivers blocking your reservoir inlets.

[finalarena]

Awesome, yes I'm hoping its a blockage == simpler :)

For reference, I have the small heat shields behind to each carb (hs4) - quite small just shielding the bowl. It occurred to me if it was boiling, it could be as far back as the pump?

Rough plan of attach:
- fuel filter (I'm hazarding a guess that if the external diameter of my hose is 8mm, I opt for the filters with 6mm ends?)
- clean pump filter
- clean fuel line
- clean carb reservoir (err...are their handy instructions somewhere? Haynes is a little vague)
- check for evil dreaded rubber slivers I've only just found out about (more things to look for :-p)

Thanks :)

[DanM]

How long was the car out of use? If the tank is left without fuel for long periods a huge amount of corrosion and crud can accumulate and cause intermittant blockages. You may need to remove the tank and give it a good clean out, Marine clean is a good product for this.

[finalarena]

I suspect only out of use for 6 months or so (that's what looks looks the gap looking through receipts and talking to PO. Its been used recently, but only on short runs of a mile or so. I think me driving it from the PO to my garage was its first long run in 6-12 months. But I thought fitting a fuel filter was a 1st step / easy and cheap way to see if there is gunk.

[nang]

Don't want to muddy the waters, but another cause of your symptoms is a coil breaking down when hot. Why not temporarily bypass your fuel tank bit running a bit of hose from a suitable container straight to the fuel pump and see what happens ?
Tony.

[Pete Lewis]

you dont want a filter with a smaller internal hose spout than the size of bundy running along the chassis

some filters have a stepped spout to accomodate 6 0r 8 mm internal diameters

in the boot is fine and easy,

no fuel will come out as the suction tube is above the fuel level,

the pipe into the tank is a simple union with a rubber olive which rotates a curved pipe inside the tank to make a sort of reserve
operation.   you cant take this out without removing the tank.

check the hose to this is not hard and loose sucking air,



dont over tighten the clips on a plastic fiter it can compress the spout bore  to nearly nowt.

old fuel can jelly up in the small tube to the jet.

make sure the coil is wired  OK the dizzy wire has to be same polarity as the battery earth eg  neg earth then dizzy on the -ve
ign feed on the +ve.

dont use plugs with an R in the suffix.

check the dizzy spindle has no side float,

some new stock condensers are rubbish.


just a few more idea's

Pete

[Velocita Rosso]

For low pressure use, eg on fuel lines , these spring clips are quite adequate when the hose is a perfect/tight fit to filter tails
http://www.ebay.co.uk/itm/like/161223415976?limghlpsr=true&hlpv=2&ops=true&viphx=1&hlpht=true&lpid=108&device=c&adtype=pla&crdt=0&ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=108

[Velocita Rosso]

My first impression with the faltering when hot, is the need for a stainless carb heat shield to alleviate fuel evaporation
Also, when faltering, stop the car, unscrew the fuel bowls and check for level. If not OK then remove the needle valves and blow through to see if clogged. Also remove the bowl to jet tubes and blow through for same reason
That should keep you going for a while

[junkuser]

Runs OK at larger throttle openings.  Stumbles at lower throttle openings after a while.  Carburetors weeping. (Fuel level should be below gasket level, if this is where it is weeping from)
OK next day for a while.  (Hope this is roughly what you have described)

Could just be the fuel level in float bowls gradually rising due to gunk in needles valve(s)

[finalarena]

Awesome advice, thanks all. Really appreciate it. I'm going to work through everything Sunday/.Monday and will let you know how I get on. I jerry rigged a very insulating heat shield last night and took for a spin with same symptoms, so It really does feel like "gunk" to me either in jets or pipes or bowl etc. This is my first real experience in the fuel system - I've only just started learning so things like "unscrew the fuel bowls and check for level." scare me :-p I've always assumed the carbs were a complex/difficult thing but I guess I'll find out :)

Are the bowls and piston tube feally as easy to take off and clean as it sounds?

[Velocita Rosso]

1.To remove the bowl to jet tube, there is a brass nut that screws to the bowl.
Undo (7/16"af spanner)
Then with a small cross point undo the bracket that holds the jet to the carb body
The tube will pull out of bowl when undone, but carefully pull out as there is a small washer, olive and rubber seal on the end
Lower tube and jet into hand and put on a bench and blow through
Sometimes the rubber seal disintegrates and that can , when assembled fall to pieces and cause a blockage(been there)
Reassemble in reverse
2. To take out the needle valve, remove top of bowl with three screws,turn upside down ,pull pin holding float, check float has no holes and is full of fuel(if so ,need new float)
Unscrew needle valve and make sure no crud in the inlet
Reassemble in reverse
Make sure needle valve moves freely

[finalarena]

Amazing thanks! That's my Sunday afternoon sorted then :-p Was going to start this evening but on driving my old landy to a concert venue for tomorrow, the steering kinda....stopped. So I've had to divert some time to using a hammer on the A40 instead of learning about carbs!  

[finalarena]

Well, a bit lat but got going tonight. CLeaning existing rubber hoses. Acma across an interesting fault:

There are two small diameter hoses running out form the side of each carb: the forward one clips onto the radiator pointing downwards, the one nearest the bulkhead just disappeared down. When I removed it this is what I found:


BAD:



GOOD:



PIC of outermost bowl, with pipe coming out rh side:




I'm assuming these are breather/overflow pipes? After trimming the melted section, tightening and cleaning other hoses and popping for a spin in certainly seems somewhat better. Although it needs the choke on for a long time (10mins) before being able to idle without it, i didn't get the same amount of gasping for fuel type splutters.

Nothing drips from either tube.

Bowls look very dirty...but I wasn't quite brave enough to remove them tonight, so that's fo tomorrow.

[Dannyb]

They are just overflow pipes to allow flooded carbs to dump the petrol on the ground rather than going over the hot engine.

[finalarena]

Filter fitted  - between pump and carbs. Thought I'd start at the front and work back. Interesting symptoms:

Initially great: small clear filter can see fuel being pumped in till its about 3/4 full, car running really well. I also lightly cleaned the bowls and floats.

After 15mins on dual carriageway, it felt coughy again. Great when the power is on, but anywhere near idle or first gear and it just felt starved. Parked, and looked at the filter, and it seemed tome that very little fuel was getting into it...little dribble and only looked 1/5 full.

Get home, leave for 2 hours and restart and again there is much more fuel visible in the filter.

Feels like, when hot, the fuel pump is failing - or is this normal?

I haven't replaced the pipe between the pump and carbs yet - it goes small section of rubber into longer metal pipe, then back to rubber to connect to the carbs/new filter. Is it a no-no to replace this connection completely with new Rubber?

[DougBGT6]

Yeh, sounds like a blockage/constriction further back. That's how it was with me anyway. Filter varied from half full to nearly empty.
Cleared out the piping and change the whole section from the pump to the carb with the armoured rubber tubing. Sorted.

[junkuser]

Could it be that the filter in the pump is blocked with debris?

[rotoflex]

Don't SU's have little brass basket filters in them where the fuel line attaches?