Hi there,

Basically, I couldn't get the car started so dad called one of his friends that is building a MG A. With only being there 20 mins the car started!! HORRAY!! But once you let go of the choke it was cutting out, so my dads friend said take the bell housing off the carb. He lightly sanded (WITH 2500 GRIT, SO VERY FINE) the needle and the piston inside, there are no scratch marks WHATSOEVER from this, so I know there isnt a leak from the piston end of the carb. He then blew out with a compressor the jet and the mixing chamber (while still built up, didnt take jet out). After putting back together......IT WOULDNT START!!!!!!!!

So i took the bottom of the carb off and cleaned all of the float ect out, but left the jet in.

Back together....still wont start.

There is fuel there and it is all sparking correctly.

Please help

EDIT: Austin Metro 998cc 1984

[Edited on 15/4/16 by JamesyCottony]

have you tried covering the inlet of the carb while cranking?

Rob

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Originally posted by COREdevelopments
have you tried covering the inlet of the carb while cranking?

Rob

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air inlet. are the plugs wet?

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Originally posted by COREdevelopments
air inlet. are the plugs wet?

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As above, get someone else to crank it while blocking (with your hand) the air inlet. That may well let it fire up.

The other way is to get some "easy start" in an aerosol can and spray it in the air inlet while cranking. It's worked for me before to get engines going.

take the dashpot off and check to see if the piston is fitted the correct way, some su's have 2 groves in the piston for location. looking from the top of the piston you should have 2 holes approx 3mm in diameter, these should be facing towards the engine. this is what gives the vacuum. sounds like your pistons are not rising easily.

hth

Rob

quote:

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Originally posted by COREdevelopments
take the dashpot off and check to see if the piston is fitted the correct way, some su's have 2 groves in the piston for location. looking from the top of the piston you should have 2 holes approx 3mm in diameter, these should be facing towards the engine. this is what gives the vacuum. sounds like your pistons are not rising easily.

hth

Rob

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Do you mean the button on top of the float? That allows more fuel into the float chamber not the piston on the main carb body.

Covering the inlet up will force the piston to lift if it is said problem that I mentioned. Have you palyed about with mixture?

Rob

[Edited on 15/4/16 by COREdevelopments]

The 2 holes in the piston above should be facing the engine.

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Originally posted by COREdevelopments


The 2 holes in the piston above should be facing the engine.

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quote:

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Originally posted by COREdevelopments


The 2 holes in the piston above should be facing the engine.

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Have you put the oil back in the dash pot? It's not for lubrication, it's for damping the piston.

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Originally posted by Andy D
Have you put the oil back in the dash pot? It's not for lubrication, it's for damping the piston.

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I didnt get a lot of history with the car, so Im not 100% sure that it has been converted to unleaded, the guy before me seems to think so, he recalls something to do with Valve timing was changed. My wallet doesnt mind me spending out on Lead additive, should I just use it anyway? even if the engine is unleaded? just to be on the safe side

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Originally posted by COREdevelopments
Covering the inlet up will force the piston to lift if it is said problem that I mentioned. Have you palyed about with mixture?

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Originally posted by JamesyCottony
There is a little in there still yes

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Originally posted by MikeRJ

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Originally posted by COREdevelopments
Covering the inlet up will force the piston to lift if it is said problem that I mentioned. Have you palyed about with mixture?

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Covering the inlet won't make the piston lift up. Piston height is a function of airflow and covering the inlet reduces airflow. Choking the inlet simply lowers the pressure in the carb and pulls more fuel up through the needle jet.

It's possible that a jet was partially blocked, chocking the inlet to help pull any crud through is an old trick that often works.

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Originally posted by JamesyCottony
There is a little in there still yes

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Fill it to the top of the damper tube. The damper is the equivalent of the accelerator pump in a fixed jet carb, if it doesn't have sufficient damping then you get a lean mixture and hesitation when opening the throttle.

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Just use it. I haven't converted any of the (10 or so) old cars I have owned (except the one I bought with the engine already machined and in bits, seemed silly not to spend £80 on converting it...)
If you suffer valve seat recession, then get unleaded inserts fitted. It is a big if, none of mine ever suffered, and many got driven hard.

Just use it. I haven't converted any of the (10 or so) old cars I have owned (except the one I bought with the engine already machined and in bits, seemed silly not to spend £80 on converting it...)
If you suffer valve seat recession, then get unleaded inserts fitted. It is a big if, none of mine ever suffered, and many got driven hard.

If you have a spark at the plugs and after cranking the plugs are dry then it's a fuel issue has it got fuel in the tank ? Is fuel getting to the carb ? Pour some fuel into the carb ( little bit ) half an aerosol cap if it starts and runs for a few seconds then you know engine must have compression and the timing is ok or close to correct .

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Originally posted by cliftyhanger
Just use it. I haven't converted any of the (10 or so) old cars I have owned (except the one I bought with the engine already machined and in bits, seemed silly not to spend £80 on converting it...)
If you suffer valve seat recession, then get unleaded inserts fitted. It is a big if, none of mine ever suffered, and many got driven hard.

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Originally posted by ian locostzx9rc2
If you have a spark at the plugs and after cranking the plugs are dry then it's a fuel issue has it got fuel in the tank ? Is fuel getting to the carb ? Pour some fuel into the carb ( little bit ) half an aerosol cap if it starts and runs for a few seconds then you know engine must have compression and the timing is ok or close to correct .

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Really not a good idea to use any kind of abrasive no matter how fine on the piston or dashpot bore or jet needle in an SU carb.
Cleaning with and sof trag is all that is required. If after cleaning the piston isn't returning freely slacken the 3 screws very slightly and wiggle it a little then tighten them gradually and evenly. If that dosen't work try centering the jet by slackening the jet holder wiggle it and re-tighten.
If that dosen't work try it without the needle fitted if it OK without it the needle is bent, if it still sticks it is highly probable the dashpot has been damged by getting dropped.

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Originally posted by britishtrident
Really not a good idea to use any kind of abrasive no matter how fine on the piston or dashpot bore or jet needle in an SU carb.
Cleaning with and sof trag is all that is required. If after cleaning the piston isn't returning freely slacken the 3 screws very slightly and wiggle it a little then tighten them gradually and evenly. If that dosen't work try centering the jet by slackening the jet holder wiggle it and re-tighten.
If that dosen't work try it without the needle fitted if it OK without it the needle is bent, if it still sticks it is highly probable the dashpot has been damged by getting dropped.

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I was taught to clean SU piston and dash pot with brake fluid 50 years ago, it still works and is cheaper than carb cleaner. Clearances between pistons and dash pots are critical and as BT points out never use any abrasives.

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Originally posted by rusty nuts
I was taught to clean SU piston and dash pot with brake fluid 50 years ago, it still works and is cheaper than carb cleaner. Clearances between pistons and dash pots are critical and as BT points out never use any abrasives.

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You will not have done it any favours, but not all may be lost.

Anyway, depending on the carb it may have a lifting pin on the underside which raises the piston slightly when pushed, little rod, Spring and circlip if not use a screwdriver to lift the piston 1/4" when idling.

If the revs increase it is running to rich so back out the mixture screw, to weak and the revs will drop, set correctly and the revs may rise slightly or stay the same.

If it stalls or does not Rev cleanly when you crack open the throttle the oil in the dashpot is to thin so try a heavier grade.

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Originally posted by mark chandler
You will not have done it any favours, but not all may be lost.

Anyway, depending on the carb it may have a lifting pin on the underside which raises the piston slightly when pushed, little rod, Spring and circlip if not use a screwdriver to lift the piston 1/4" when idling.

If the revs increase it is running to rich so back out the mixture screw, to weak and the revs will drop, set correctly and the revs may rise slightly or stay the same.

If it stalls or does not Rev cleanly when you crack open the throttle the oil in the dashpot is to thin so try a heavier grade.

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Have you topped the damper oil up? (20/50 oil best, thinner oil reduces the enrichment, thicker increases it)
Lead additives don't contain lead (ok, a couple do but hard to find, even if they are still available) most contain a brew of other stuff that hopefully does the same job as lead, but do your research as to which ones work. There was some proper lab tests a few years ago, IIRC the castrol one was OK. And another which I can't remember. Most others did nothing very much.

But as I said, these cars will run for years with no issues as the seats harden up with lead memory from when leaded fuel was about. Our mini has been with us for several years, never used additives. Head off recently, no recession at all and no sign of unleaded seats either.

How much oil goes in the dashpot and where does it go? In the small hole and to the top?

The oil to the dash pot going in the top unscrew the cap on the top of the carb you only need a tiny bit of oil in it 20/50 is best but 10/40 will work ok .is it idling now if so make sure it hasn't got any air leaks around the carb and inlet manifold spray carb cleaner/ wd40 around the area if the revs change you may have an air leak ,also worth putting the area you live as I'm sure there would be someone locally on here that could take a look .

[Edited on 16/4/16 by ian locostzx9rc2]

quote:

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Originally posted by ian locostzx9rc2
The oil to the dash pot going in the top unscrew the cap on the top of the carb you only need a tiny bit of oil in it 20/50 is best but 10/40 will work ok .is it idling now if so make sure it hasn't got any air leaks around the carb and inlet manifold spray carb cleaner/ wd40 around the area if the revs change you may have an air leak ,also worth putting the area you live as I'm sure there would be someone locally on here that could take a look .

[Edited on 16/4/16 by ian locostzx9rc2]

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Glad you have got it running

I have noticed like a light brown sludge stuff coming into the coolant tank, would this just be old sludge that has built up due to lack of running? It's not sitting on the top, oil on dipstick looks nice

Probably just rubbish coming through, skim it off.

SU's are very clever devices, much underrated.

Once warmed up do as I suggested above, air filter off you can see the piston sitting just off its seat with engine vacumn, using a flat bladed screw driver insert in the gap between the body and piston and gently twist to lift the piston by 1/4" and if set correctly the revs may rise slightly or stay the same.

quote:

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Originally posted by mark chandler
Probably just rubbish coming through, skim it off.

SU's are very clever devices, much underrated.

Once warmed up do as I suggested above, air filter off you can see the piston sitting just off its seat with engine vacumn, using a flat bladed screw driver insert in the gap between the body and piston and gently twist to lift the piston by 1/4" and if set correctly the revs may rise slightly or stay the same.

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10w/40 oil as 20w/50 causes problems in winter weather

Autotrans oil also works