carb running problems

[johhnyboy]

I have been rebuilding a pair of HS4's for my toledo and now have them on the car but can't get it to run well at all.I have tried tuniing them a few times and altering mixtures,balance,timing  etc but they sound rough at low revs and wont rev very high.I was just wondering if it they did a conversion for a twin choke carb or single weber carb as that would be a more reliable way to go maybe?

[James]

I wouldn't call this a reliability issue - twin choke carbs will end up costing you a lot of money and give you no advantage. Far better to just buy a pair of reconditioned carbs for £150.

Check you put them together properly :)

[piman]

Hello johhnyboy,

if you are not familiar with S.U.s, did you have a manual to help you rebuild them. Follow the settings and they should run pretty much straight away?
I don't believe you need to spend any more money if you have replaced the gaskets etc.

Just a brief run through:-
clean the inside of the dashpot and piston with carburettor cleaner (no Brasso or anything abrasive) Check the needle is straight and fitted with the shoulder flush to the piston face.
Check the fuel level, if an electric pump then just switch on and view the jet, it should be about 6 to3mm below, if it is above or is slowly flowing out the float valve is stuck\dirty\damaged and this must be corrected first. (Mechanical pump, crank the engine a few times unless the pump has a priming lever)
Screw the jets flush to the top, then refit the dashpots. Check the jet centreing by lifting the piston and let it drop, it should fall smoothly and stop with a slight click. If it does not, slacken the jet nut (above the adjusting nut) and push down on the piston (after removing the damper)
then retighten the clamping nut.
Ensure the choke works, and the jets return to the top when pushed back home, and that the fast idle screws are clear of the cams.
Adjust the jet (mixture) nuts down by two full turns, (12 Flats).
Release one carburettor's throttle clamp and start the car.  You may need to run at a fastish idle with some choke until it warms up. using both idle screws (not the fast idle screws on the choke control) adjust to a medium speed idle, say about 1000 rpm and using a bit of tube in one ear listen to the intakes and adjust the idle screws until they both sound even and you have a nice steady idle of around 700 rpm. Retighten the throttle clamp.

Alec

[johhnyboy]

I have just disccovered that one of the pistons is half way up its height on tickover while the other is sitting at the bottom of its travel so I will try your method later this week and see what happens
thanks
john

[johhnyboy]

Right I have tuned the carbs as per your recommendations and the car runs a lot better.It is still a bit uneven tickover wise but when accelerating up a slight hill in 3rd gear it will get to 50mph and go no further .Any suggestions on what else i should do

[Scottie55]

To fine tune the carbs, you need to raise each piston up by about 1-2 mm each in turn. You can use a screwdriver to do this but better to use the sprung pins to the underside of the pistons on the carb body. If the revs increase, mixture is too rich so turn jet up one or two flats to weaken. If revs drop, then mixture too weak so turn jet down one or two flats to make richer. Keep doing this for each carb until raising the pistons have no change on engine revs. Throughout be sure to keep chacking and balancing the air flow. Also, throttle rev between adjustments to clear carbs.