JamesyCottony
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| posted on 15/4/16 at 08:16 AM |
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Started....but not anymore....`
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]
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COREdevelopments
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| posted on 15/4/16 at 08:23 AM |
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have you tried covering the inlet of the carb while cranking?
Rob
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JamesyCottony
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| posted on 15/4/16 at 08:26 AM |
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quote:
Originally posted by COREdevelopments
have you tried covering the inlet of the carb while cranking?
Rob
Air Inlet?
Fuel Inlet?
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COREdevelopments
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| posted on 15/4/16 at 08:28 AM |
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air inlet. are the plugs wet?
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JamesyCottony
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| posted on 15/4/16 at 08:29 AM |
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quote:
Originally posted by COREdevelopments
air inlet. are the plugs wet?
Havent covered air inlet no.
Plugs are dry :/
I just hate cranking it over and over while the pump is trying to chuck fuel in, makes me nervous
[Edited on 15/4/16 by JamesyCottony]
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nick205
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| posted on 15/4/16 at 08:33 AM |
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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.
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COREdevelopments
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| posted on 15/4/16 at 08:37 AM |
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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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JamesyCottony
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| posted on 15/4/16 at 08:39 AM |
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quote:
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
Ill check that, thanks. We did put some 20w50 in the pot to help lubricate it when we took it apart the first time but when it didnt start we drained
what was in there out. When cranking I was pushing the little button (to the NS of the engine) that raises the piston, but still nothing, Ill double
check the grooves now.
Also would I cover the air inlet because the mixture is too lean?
[Edited on 15/4/16 by JamesyCottony]
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COREdevelopments
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| posted on 15/4/16 at 08:41 AM |
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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]
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COREdevelopments
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| posted on 15/4/16 at 08:46 AM |
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The 2 holes in the piston above should be facing the engine.
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JamesyCottony
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| posted on 15/4/16 at 09:07 AM |
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quote:
Originally posted by COREdevelopments
The 2 holes in the piston above should be facing the engine.
Put my hand over the inlet.... IT STARTED!!!!!!!!!!!!!!!! THANK YOU GUYS!!
now seems to start without covering inlet.
One thing that I think might be the mixture is when i put some throttle on (after it being warm) it dies quickly then picks up quickly, too much fuel?
not enough fuel? too much air? not enough air?
[Edited on 15/4/16 by JamesyCottony]
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JamesyCottony
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| posted on 15/4/16 at 09:23 AM |
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quote:
Originally posted by COREdevelopments
The 2 holes in the piston above should be facing the engine.
Only one groove, and yea, holes are facing the engne
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Andy D
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| posted on 15/4/16 at 09:25 AM |
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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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JamesyCottony
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| posted on 15/4/16 at 09:50 AM |
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quote:
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.
There is a little in there still yes
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JamesyCottony
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| posted on 15/4/16 at 10:21 AM |
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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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MikeRJ
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| posted on 15/4/16 at 10:46 AM |
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quote:
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?
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.
quote:
Originally posted by JamesyCottony
There is a little in there still yes
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.
BTW you should never use abrasives on the needle, dashpot or piston, especially not wet and dry paper.
[Edited on 15/4/16 by MikeRJ]
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JamesyCottony
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| posted on 15/4/16 at 10:48 AM |
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quote:
Originally posted by MikeRJ
quote:
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?
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.
quote:
Originally posted by JamesyCottony
There is a little in there still yes
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.
What oil would you recommend? im guessing it will have to be mineral as synth will ruin the seals
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cliftyhanger
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| posted on 15/4/16 at 10:49 AM |
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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.
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cliftyhanger
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| posted on 15/4/16 at 10:49 AM |
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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.
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ian locostzx9rc2
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| posted on 15/4/16 at 10:58 AM |
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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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JamesyCottony
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| posted on 15/4/16 at 11:04 AM |
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quote:
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.
I dont have a cat, or o2 sensor and its meant to improve octane, but would it do any damage if I put lead in?
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JamesyCottony
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| posted on 15/4/16 at 11:04 AM |
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quote:
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 .
Got it running now thankyou
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britishtrident
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| posted on 15/4/16 at 04:47 PM |
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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.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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JamesyCottony
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| posted on 15/4/16 at 05:34 PM |
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quote:
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.
It's starting now thankyou, just need to get it running smoothly. When I press the throttle it dies but then picks up quickly, not enough fuel
getting in?
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rusty nuts
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| posted on 15/4/16 at 06:39 PM |
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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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