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The 100-Six Forum

Austin Healey 100/6 1959 Loss of power/torque

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AJPope Andrew Pope
Derby, Derbyshire, UK   GBR
Hi, I cannot rev beyond 3000rpm in second gear when under load (climbing a hill) . Runs fine on the flat. Compression test is all good. Fuel pump new, air filters new, With my foot to the floor it just won't push on. Engine revs fine otherwise.
Anyone experienced this? Could it be the carbs setup?
I have electronic ignition, new ht leads, new high power coil. I'm sure it should have a bit more grunt than it is providing ☹️

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rusty1c Avatar
rusty1c Peter D
Antioch, CA, USA   USA
1961 Austin-Healey 3000 BT7 "RUBY"
1963 Chevrolet C10 "Rusty"
Andrew,
Sounds like it isn't getting enough fuel at the top end when the engine is under full load. Check the needle and jet. Also check for clogged screens at the inlet to each carb and any fuel filters that you may have in the system. Remember always start with the simple things first and you will usually find the problem.
Pete

AJPope Andrew Pope
Derby, Derbyshire, UK   GBR
Hi Pete,
Thank you for responding. I suspected the in-line fuel filter, and have a replacement on the way. I know all the fuel line and strainers on the carbs are clean and clear.
I was wondering if a thinner oil in the dash pots would help? Jets and needles are good. Not sure if the mixture is set correctly though
Regards Andy

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rusty1c Avatar
rusty1c Peter D
Antioch, CA, USA   USA
1961 Austin-Healey 3000 BT7 "RUBY"
1963 Chevrolet C10 "Rusty"
Andy,
Have you checked the distributor to see if the vacuum advance unit is working? You should get approximately 35 degrees total advance at around 3000 rpm.
Pete

AJPope Andrew Pope
Derby, Derbyshire, UK   GBR
Hi Pete, I have a 123 Electronic ignition fitted, so that should not be a problem. I can set up the advance curve via an app on my iPhone
Regards Andy

rusty1c Avatar
rusty1c Peter D
Antioch, CA, USA   USA
1961 Austin-Healey 3000 BT7 "RUBY"
1963 Chevrolet C10 "Rusty"
I’m at a bit of a loss then. I’ll have to assume it’s fuel then.
Pete

Leyburn, North Yorkshire, UK   GBR
I think I'd switch back to points ignition , just to eliminate the electronic ignition before doing anything else. Good luck.

AJPope Andrew Pope
Derby, Derbyshire, UK   GBR
Cured it!!
Removed the in line fuel filter , fitted new fuel line from tank to pump, without any filter, replaced SU pump , again!
Now works , pulls well in all gears on any incline !!
Fuel pump was pulling air in from one of the connections.
Next option was to remove cylinder head!!

Leyburn, North Yorkshire, UK   GBR
Hi Andrew,

Glad to hear you cured it before taking the head off, it certainly wouldn't have revved or pulled had you done that, lol smiling smiley

Well sorted.

Stan

Leyburn, North Yorkshire, UK   GBR
A lot of opinions here on this problem, including mine. I had the same problem coming to light last years, mostly in 3rd hear under heavy hill climbing load. I had already decided that over the winter I'd take a good look at the distributor, as tick was rubbish to non existent, and got faster the hotter the engine, a sure sign of vacuum advance problems. The vac advance, I found wasn't working at all, so the rotted diaphragm was replaced. At the same time it was noticed the the low revs centrifugal advance spring was slack allowing free movement , at will of rotor. Genuine springs are not available, though various possibles and combinations are, which I bought. But before I try these I decided to solder the slot in the toggle to shorten it just enough to take up the slack in the spring. This all worked fine, except that the lack of power at 3000-3500 rpm was still there, maybe worse. My next step was the bit by bit advance the timing, all this did was move the rev range a little that gave the problem. So by now, like some of you became convinced it was a fuel shortage problem, and it is, again I bit by bit made the mixture richer, each little move lessened the problem, so I kept at it until the problem was gone. However another problem that I had greatly reduced by weakening the mixture some years ago, is back, and that is popping in the exhaust on over run of unburnt fuel. My conclusion from this is that what we have all been experiencing here is nothing more than a flat spot, that in the general way of things has to be lived with to a degree in old cars, or does it, well no it doesn't, but it does take time and effort to cure, and here is the answer, you'll need to read it through a few times I think for it to sink in properly. Read pages 62-64 of this link to a book on SU carbs, it describes how to test for, flat spots on the needle and how work it to remove said flat spot. I do know someone who has done this on MK2 Jaguar in Australia, if I can get his source of info, which may be better, I'll post that link in time, meanwhile,

Stan

https://books.google.co.uk/books?id=CTz2EAp2ua8C&pg=PA63&lpg=PA63&dq=Working+needles+on+SU+carbs+to+eliminate+flat+spots&source=bl&ots=gv-urcqDjK&sig=HaidctXaK0m8OT7j1jJzoagV33E&hl=en&sa=X&ved=0ahUKEwiCo4WRyO_bAhXpMewKHXngAAUQ6AEIbTAG#v=onepage&q=Working%20needles%20on%20SU%20carbs%20to%20eliminate%20flat%20spots&f=false

petnatcar Avatar
petnatcar Silver Member Peter Carbone
Watertown, NY, USA   USA
Andrew,

Check the setting of the float levers in the caps of the float bowls
and
be sure you're getting full advance out of the distributor.

Unplug a fuel line and turn on the pump to check fuel flow/pressure.

Use a can to drain the gas into and a bunch of rags to soak up any spill.

Good luck,
Peter


Attachments:
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Float Level 1.jpeg

Float Level 2.jpeg    53.8 KB
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Leyburn, North Yorkshire, UK   GBR
Hi all,
Further to a previous post I made on this subject, I have now found the site I wanted regarding needle polishing to get rid of flat spots, certainly worth a read even if you're running
ok. you never know when you won't be, fuel as we know is now constantly changing, and each change can bring a problem.

Good luck,

Stan

http://www.terryhunt.co.uk/tech/picsb/pics.htm

johnbn6 Avatar
johnbn6 john nieuwenhuizen
kerkrade, limburg, Netherlands   NLD
To my knowledge there are 2 different springs in your 100/ distributor. One is under tension and the other (heavy) spring has some slack. This is done to get a two stage advance curve. The light spring allows
the weights to swing outwards advancing fairly quick from low revs. When the slack is taken up from the secondary spring the advance slows down to give full advance at around 2000 distr.revs.

Leyburn, North Yorkshire, UK   GBR
johnbn6

Exactly my understanding, but as I found, the weak spring over time also stretches and ends up with some slack, allowing the rotor to float.

Stan

David8831 Avatar
David8831 David Halliday
Thame, Oxfordshire, UK   GBR
I had a similar issue with a car I had bought as a relative non-runner, it had sat for about 5 years. It revved fine with no load but when driving, just wouldn't pull past ~3,000 revs.

I tried all sorts of things, fuel pump, fuel filter, different distributor, new coil, pulled carbs apart and cleaned them up, pulled out the fuel tank and cleaned out, plugs and more. Plenty of fuel as coming through, float levels were okay.

In the end, I had a carb rebuild kit for an MGA so just thought that I'd have a look at the new needles that are in it. They had far more taper than the needles in the carbs. I changed needles over and the car ran beautifully. How on earth those needles, which were like straight rods in comparison, ever go in there, I have no idea at all!

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