fuel starvation issue

wondering if anyone had any ideas,
mk1 1.3 pierberg carb. completely restored from shell by myself, new filler neck, cleaned tank before reinstall, filter ok, fuel pump seems to work fine. have done carb clean and new gaskets.
fuel lines original with new flexi + clips in engine bay. tank pick up clear.

problem - had an issue where no fuel to filter previously, primed whole lines + pump + carb reservoir and issue was solved till month ago when did run tank low and problem recurred.

today spent couple hours checking can suck fuel into filter, primed pump and filled reservoir and car ran nicely for approx a minute till fuel filter dry again. not vacuum in tank as tried again with filler cap off. return pipe clear.

could it be pump working sufficiently to empty filter but not enough suction to pull fuel through lines ? thinking of just replacing fuel pump but GSF only stocking pump for 1.5 carb and up, would upgrade improve fuel pump power and ensure fuel actually gets to carb?

trawled through forum and all issues already discussed don't seem to fit my probs. any help much appreciated.

keep the mk 1's on the road as they seem to be dissapearing fast !!!

cheers

Breather on fuel tank correctly fitted ? Mechanical pump ? Suspected faulty ? Replace it they are cheap enough .

issue was solved till month ago when did run tank low and problem recurred.

Could also be rust in the lines / filter / pump ?  Sucked in when the above happened .

cheers for feedback.

anyway, swapped feed and return pipes over, drawing good flow through with syringe and no air bubbles, replaced fuel pump in case substandard and new filter, only small amount crud in old filter. repaced flexi pipe from rigid to filter, now good flow into filter and very good squirts from carb side fuel pump but still stalls after minute or two when carb reservoir runs dry.

GSF guy did say pump could deteriorate to point clears filter but not enough suction to draw fuel from tank and always check flexi hoses for very small cracks which draw air rather than fuel - this has solved low amounts of fuel getting to filter.

thinking current problem is needle valve in carb stuck shut as pump not able to keep carb reservoir full ? agree ? will get some time this weekend to pop top off carb and blow everything through and fiddle with needle valve - poss tin bit of crud has got into carb and blocked fuel intake to reservoir. when fill up reservoir then car starts and runs great for approx 60 seconds before dies now with adequate amounts of fuel in filter.

sorted the problem! hopefully MOT'd later today.

small piece of rubber like stuff stuck in ball valve at fuel inlet to carb reservoir - had jammed shut so all fuel being diverted back to tank.

here's a quick checklist i've worked out to sort out fuel issues on small block mk 1's:

1. check for crud in filter - replace as v.cheap

2. syringe onto fuel line prior to filter (should be able to draw very good flow clear petrol without any air bubbles)
- if not - take out back seat, lift carpet, remove tank inspection panel, check flexi pipe connections to tank outlet, mark up which flexi wet to which rigid and remove, unscrew petrol tank header unit, check filter at end of long pipe (feed intake) if still fitted for crud blocking it, can clean/replace/remove filter(as lobg as place inline filter further up), then finally check tank for crud/rust (if present check your filler neck for rust and if posible replace). rebuild and recheck can get good flow from feed pipe in engine bay. check your rigid fuel lines and flexi jubilees underneath if still an issue.

3. check can blow air/petrol easily back via return pipe from carb wtihout leaks from underside of car (usually cracked flexi pipes, poor jubliee clips or worst case cracked rigid lines).

4. check fuel pump - remove fuel pipe from carb siide of pump, using glass jar check when turn car over (take off king HT lead to prevent sparks and fire up), make sure solid powerul spurts of petrol are coming out. sime pumps have small filter that can get clogged up too. if in doubt of adequate pump function easily replaced for very little money.

5 . check carb (Solex) - remove air filter housing, note position of manual choke and release cable, undo fuel feed and return pipes, undo 5 bolts at top of carb and remove top (care if not done for while as most likely will damage gasket which will either need to be pelpaced or as I did made up new from gasket paper). remove float noting postion of small white plastic retainer, check bottom of reservoir for crud and clean out if neccessary, check outflow not blocked at bottom of reservoir, , if possible blow throgh all openings in carb with air line, replace float, check valve on underneath of carb lid - remove using spanner (hex head) check not blocked and can blow through easily when valve not depressed. bow through fuel inlet to clear debirs - rebuild reverse of above.

these steps should ensure adequate fuel getting into carb reservoir to allow normal running.
Lumpy running or cutting out are probably carb set up, air leaks at carb/inlet manifold, vacuum hose failures (experienced all of these).
Also check earth strap between carb and fuel pump not deteriorted as this caused a carb earth failure leading to idle solenoid not woking once on my motor.
Also once had problem with reduced current in idle solenoid feed preventing it opening fully when runnning causing the motor when allowing to idle (diagnosed as deterioration in wireloom, rerouted).

hope this helps anyone with similar issues,

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