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fuel tank neck repair

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No, had to give up and head back home before I even reached the A14. Engine was dying at roundabouts, but pulling well when pumping the gas pedal or over 3000rpm.

I had put 20 more litres of fuel in so the Isoproponal must be very small proportion and no trace of water.


Managed to misplace a screwdriver after one side of the road stop. Did I leave it in the engine bay, or on the verge?

Did not want to risk 2 hours of lean driving at moderate to high speed. Maybe the Aldon guys would have helped if I made it all the way.


So did a compression test and it's all good, Thought it might be HG between 1 & 2, which were running cool from IR thermometer at exhaust manifold.

Siphoned out both carbs fuel bowls, and measured how much in a jam jar, and they were about equal, so I think needle valves are not blocked closed.

Then looked at the plugs and 3&4 show white of lean but 1&2 are nearly normal to slight ash.


Rechecked the balance left/right and it's tipped towards 1&2, uncovering one more progression hole.

Had to take off the cable-mech to  see the throttle plate through the holes with a small torch.

With good access cleared out number 3 idle circuit and found a tiny sliver of black rubber.

Did it come from the o-ring or fuel line?

So small it blew away when I tried to pick it up to take a picture.


Refit cable-mech etc.

Drove and still rough and far too lean at cruise..

Tried fitting some big 48 idle jets, just in case there was still Isopropanol affecting the mixture.

That went real smooth, but obviously too rich - like 11:1 AFR or 9:1 at overrun.

Had to wind in mixture screws to nearly closed to reach 13.3:1 idle, black soot and moisture at tail pipe.


Switched back to the 43 idles and could not get cylinder 4 to change engine speed or influence AFR, unscrewing the mixture.

Removed and pulled the jet from the holder.

Looked through that idle jet up to the light and it was partly blocked with some yellow/grey/brown crud!

Fuel varnish?


Some carb cleaner spray and compressed air through that, refitted.

Yes, back to normal.


Balanced using vac gauges. Number 1 is still 2psi below the others but all at -13psi with some bypass valve opening.

Mixture around 14.4:1.



Wish I had been able to do all that during the week.

Disappointed I did not make it to the Rolling Road.


Time for a cup of tea.


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Think I might put a dab of paint on the left/right balance screw, so I can see if it moves, and I'm not tempted to mess with it and just mask a different problem. 


There's a spring on it to keep it still I think, but the thread is quite coarse and it takes very little movement to  partly reveal a progression hole.

Idling on progression holes on one half of engine is not good. Surprised it didn't shake more. I suppose I mis-compensated with the mixture screws

for the starved cylinders. 


Wonder if the AFR gauge log would reveal the imbalance? So busy with screwdrivers and siphon hoses and compressed air cans I forgot all about using the computer.

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It's driving really well. Had a couple of stutters when I'd expect the accelerator pump to operate, then wheel spin. Think fuel and carbs are all clear.


But I finally filled the tank, and it sagged down and towards offside, disconnecting the fat breather hose which had no hoseclip, just push-to-fit.. 

I think tank is only held on to bodywork by the strap and front edge. I did not fit one nut at rear edge. 

Might need to file or drill a hole in the tank seam to line it up with the stud.

It's a 42 litre tank in a 36 litre space. 

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The strap was not fully tight, because the rear edge was pressing on the threaded stud.

Drained 15 litres out of the tank. Used an axle stand to hold the car up and a hydraulic jack and piece of wood to push the existing seam hole over the stud.

Tightened the strap retaining nut fully home (it had 1/4inch to move ).

Realigned the filler and breather tubes.

Have ordered  an 11 to 13mm herbie clip to hold fat breather tube on the filler neck. No idea how you could tighten a jubilee clip or squeeze a self-tightening clip in that space.

Image result for herbie clip image


Was a bit worried about filing or drilling the tank with fuel in it, to be honest. 

Edited by dvderlm

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… and that clip is too small to lock by squeezing the ridged tongue into place.

Maybe a jubilee clip and 7mm flexidrive?


Sorted the last bit of stutter. Had sat in a queue with it idling and I could hear the faint pop of occasional lean, sure enough drive through the traffic lights and 18:1 on the AFR gauge and power down, rough sounding  at low to medium load.

Drove home with starter device assistance to try to stop any engine damage using the AFR gauge for feedback to push pull the "choke" cable as needed.

Reckon the main jets operate from 3800rpm or higher. Might try without them 

I think the starter device mini carb feeds from very low in the well.


Wasted third of a can of carb cleaner on the idle passages and mixture screw and air bleed orifice and found nothing in the progression hole chamber that has acted as a sieve previously.

Suspected both cylinder 3 and 4, so took the carb cover off to check the needle valve and new filter around the banjo bolt. All clear.

Fuel level was a bit low in that carb. Found partial blockage at the T joint for carb feeding 1 and 2.


Inside of carb looking good after 2 and half years, though that might be the Seafoam.


But still could not get cylinder 4 to completely behave. I could get it to idle with good exhaust manifold temp and 14:3:1, go for a test drive and hit 18:1 on overrun and stayed there.

Even checked compression (just in case I had a burnt exhaust valve) and spark plug lead for that cylinder as it was not contributing to engine turning at all.

Suspected leak at brake servo take off, but, no, all good condition too from a Cold Start spray test.

Could feel the pulse of cylinder descending with intake valve open in the tube to the servo.

If there was a leak there would surely be no pulse.


Finally found tiny yellow fuel varnish flakes in the bottom of the that hole number 4 idle jet sits in at bottom of well. Sucked those out, reset mixture and re-balanced just bypass screws a tad

not the carb1/carb2 see-saw.

I reckon when you unscrew the idle jet stack to blow it clean anything partly blocking falls out, to be sucked up again next time there's high engine vacuum.

Idle jet is smallest hole so it's bound to be the point for any fuel blockage.

Air carried blockage could come in the top of the idle holder, not emerge from its emulsion holes and then sink inside the tube I suppose.



Edited by dvderlm

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Got the bigger Herbie clip on. I hope I don't have to do that again for about another 10 years.

Had to push pipe from inside the car to get it far enough onto the 12mm side outlet, then get the clip over in opened position (like  a spiral)

then squeeze it together - took one hour and my left middle knuckle has no skin!

Wheel off and on, jacking, metal, ring around the rubber flap seal off and on. Torch that made no difference. Some snipe-nosed pliers for the Herbie clip  and molegrips on pipe inside the car helped.





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Drove on the newly cleaned sparkplugs, and went lean and running on 3 cylinders after a roundabout.

Some idle jet crusty stuff. Limped home.

Got it to idle nearly smooth.

Suspect it is dirt washed off carb float chamber side walls. Lifted car left and right to simulate corners, then siphoned out both carbs, poured fuel through a sieve. Let sieve dry and found varnish!



so now letting carb chambers soak in Seafoam/petrol mix.


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Siphoned out the Seafoam/petrol mix after overnight soak. It's golden coloured, like it dissolved years of petrol. 

Took out all jets and mixture screws, which looked spotless.


Checked the fuel filter which only had a little dirt. Fuel from tank is much clearer pale yellow.

Refitted jets and mixture screws, maybe a bit too wide open to let any crap pass, and avoided the starter enrichment.


Was very hard to restart, occasional fire, actually got blue smoke back out of the carbs, let it rest, recharged the battery, and another set of clean plugs 

(ones in engine were wet oily of none ignition),  and then vroom.


Revs, idles, pulls smoothly.


Reset mixture to 14.6:1 AFR with engine hot. 

Feels like a new engine. It managed one roundabout no problem - I'll drive further tomorrow.


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So drove front wheels on to ramps to try to replace the preheater from below, but only managed to remove old one. New preheater is a bit too big to fit without removing brake servo or carbs or getting longer pipework.

That meant rear of the carb float chamber got a good petrol washing too.


So. no big surprise when this morning got about 4 corners from home and went lean again. 

Number 1 idle jet with a blockage that blowing would not dislodge - used a toothbrush bristle.

Ok, siphoned out, still quite golden, and back in with Seafoam/petrol from last time, but added through a filter paper in a cone. 


I suppose I'll have to keep at it until no more crystals and/or it changes colour. 

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Seriously considering an ultrasonic cleaner or turning the car upside down and shaking it.

Maybe inserting siphon hose down main jet well is not going deep enough?




Yeah, there is fuel below number 37, main jet, and the pump diaphragm 30, is lower still.



Edited by dvderlm

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