8 replies to this topic

[Zami]

Twin hs4 - Car had been in storage for 6 months. Put in new plugs and fresh fuel. Took it on a 50 mile run at 60 mph.  Checked plugs 1 and 2 looked good slightly brown with 3 and 4 plugs black and smelling of fuel. Looking for suggestions on possible causes.  I am thinking check for sticking choke  Then  Maybe the float valve.

[timmy850]

Could be lots of things:
Uneven needle placement
Uneven idle mixture tuning
Air leaks on one side
Fuel bowl level inconsistent

Was it missing or running poorly?

[Zami]

It runs great through out  the rpm range.  No hesitation, starts right up.  I pulled the pots and pistons and checked to make sure the needles were instated evenly. Checked the jets to make sure they all matched 2 mm from top of carb body. Piston drop seems to be fine no sticking. I also did the piston lift adjustment and both carbs seemed to be working ok.  Ill check the following:

- air leaks around throttle shafts, manifold gaskets

- float bowel level and needle shut off 

 Thanks

[bpirie1000]

How is the fuel pipe feeding the twins? Did you check the jets? Also check oil in dash pot.

Maybe even try swapping the dash pots over to rule them out..

[Zami]

Replaced float valves with new ones.  Made sure dash pot oil (SU oil) was at the correct level.  Checked fuel flow to each carb.  Switched piston. No change I did notice that the floats are plastic and are not adjustable.  I seem to recall years ago having some SUs with small metal tabs that could be lowered or raised to get the correct height adjustment.  Should I change the floats to adjustable ones?  Or is there a way to adjust height?

[timmy850]

You can adjust the height on the newer ones by adding shims under the needle valve

[mad4classics]

Burlen (SU) now offer the adjustable Stayup float

https://sucarb.co.uk...ayup-float.html

[PACINO]

That the floats cannot be regulated? That is hard for me to believe. Why don't you take a picture of it and post it here?

[Zami]

Thks Pacino. I’ve ordered some shims. I think I will do a leak down check as well.