Su hif carbs

#1
I have some Su Hif carbs fit to my 3.5Ltr v8. I have cleaned them up as the pistons were seized. They move freely now. I have now put oil into where it goes but since then the pressure has increased a fair bit to raise the pistons. Obviously this is supposed to happen but it there anyway of measuring that resistance as you have to put a fair amount of pressure to lift them
 
#2
perhaps the oil you put in the damper (dashpot atop the piston) is too thick,could you try some atf or even 3in1
the oil IS meant to damp the piston - but if TOO thick it'll slow acceleration too ...
-i had to experiment loads with souped up mini engines so some carb mods were needed to suit the engines different specs/requirements from a std setup.
neil
 
#4
have you tried squirting a little petrol into the carb intakes - are you sure you have a good spark-at the right time and to the right cylinder -and to clean plugs that want to spark
lot to check/confirm first
neil
 

sdibbers

Well-Known Member
#5
The main thing is to have the same rate of fall on each carb piston. Lift each piston and release together. They should drop at the same rate. As for speed, as others have said, oil choice makes a difference, along with temperature. It’s not uncommon here in the states for folks to use atf instead of oil. I just use 20/50.

Also, look at the spindles, they wear and leak air on the manifold side making it impossible to tune. New spindles, rubber spindle seals and bushes are an easy home fix on HIFs that’ll make a huge difference to running.
 
#6
have you tried squirting a little petrol into the carb intakes - are you sure you have a good spark-at the right time and to the right cylinder -and to clean plugs that want to spark
lot to check/confirm first
neil
I tried petrol directly in and have also tried easy start. It's definitely a good spark and as for timing I have it at no.1 tdc and have adjusted the timing in both directions a tiny bit at a time. They are brand new plugs. I have just removed them and some have black soot and dry, some are slightly wet and some are clean but slightly wet. It sometimes turns over normally other times it seems to struggle but I've been told this could be the timing.
It has a new starter and battery. It's like the car is seizing if that makes sense.
The oil is correct in the engine but when I brought it it was 3 times what it should have been
 

cobraboy

Well-Known Member
#7
How are you trying to fuel it ? from the tank ? did you drain the tank and put fresh fuel in it ? If you take off a fuel line at the carbs and spin the engine do you get fuel coming out ?

I started my car after a 34 year lay up by suspending a 1 litre bottle of fuel from the bonnet latch and piped it straight to the carbs, it fired up after about 5 mins of cranking and then idled like a little sewing machine, three blokes stood around it in absolute disbelief.

Edit
I just read you tried fuel directly in, try tapping the carbs at the base with a screwdriver head in case the floats are stuck. The pistons will be hard to lift, and no that wont stop it starting. You should really remove the dashpots tho' and polish the insides so the pistons drop nicely.
Beware of taking the HIF6 bottoms off without a new seal, the old one will grow as soon as it is released and will not go back.]
Do the wetter plugs smell of fresh fuel ?
Have you worked out if all the wetter plugs are from one carb and all the dry ones from the other ? it could be that only one carb is fuelling the motor.

If it sounds like it is seizing that is a sign of too much ignition advance.
 
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#8
Yes I have been trying fuel from a 5 ltr can to eliminate the tank. I had a previous car and the tank was basically slurry. That had sat around 30 to 40 yrs. I stripped the carbs and pots so they are all clean and running freely. I have had the fuel line off the carbs and there is fuel coming out. I didn't realise the carbs fed different cylinders so that is something I can look at. As I've previously said I don't know a deal about engines. I have a 1968 vw beetle so have tried to learn on a easy engine.
Plug 2 was definitely sooty and dry and I think plug 4 was dirty but slightly wet. All the odds were clean or cleaning and wet
 
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