7 replies to this topic

[blue redtop]

hi all,just planning ahead. ive got my self a set of twin carbs su 1 1/4 and wondering what the best way was to set them up diy style.
was thinking of getting a colourtune kit but then thought would it really help me as there is 2 carbs.

am i right in thinking that a colour tune kit wont help with twin carbs.
thanks.

[Big_Adam]

Ah twin carbs.

Whole world of setting up troubles.

1st you need to balance the carbs so they both run at the same idle speed. So your not running two pistons insted of four. Do this either using the "suck" method whereby you stick a tube into the carb and listen to it running. Or buy a carb balancing tool. Motorbike one or car one will work.

Once their balanced you need to do the fuel setup. Colortune works lovely here as you can change the mix to account for things like filter clog or indifference. Or use the lift pin or a screwdriver (to lift the piston in the carb if you have no lift pin) and set the mixture to engine rev. Thing is each carb will rev the engine up or keep it running if their out of wack. So once you've done the mixture you need to re-do the idle speed.

Or read le plom

http://www.mintylamb...page=sutune.htm

[blue redtop]

cheers for that ill have a read.
am i being thick in thinking that getting the fuel mix set up will be a pain,because if i change it on one carb and use the colourtune so there is a nice blue spark.how will i set the other carb up as there will already be a blue spark. if im making sense .
cheers

[Sam Walters]

halfords do these kits.

[blue redtop]

ebay are cheaper lol.
never go to halfords.

[blue redtop]

Ah twin carbs.

Whole world of setting up troubles.

1st you need to balance the carbs so they both run at the same idle speed. So your not running two pistons instead of four. Do this either using the "suck" method whereby you stick a tube into the carb and listen to it running. Or buy a carb balancing tool. Motorbike one or car one will work.

Once their balanced you need to do the fuel setup. Colortune works lovely here as you can change the mix to account for things like filter clog or indifference. Or use the lift pin or a screwdriver (to lift the piston in the carb if you have no lift pin) and set the mixture to engine rev. Thing is each carb will rev the engine up or keep it running if their out of wack. So once you've done the mixture you need to re-do the idle speed.

Or read le plom

http://www.mintylamb...page=sutune.htm

thats a great help.it doesn't look as hard as i thought, not really much point in getting a colourtune after all. but i think i will invest in a air balancer tho just to get it as close as possible. i know it will never be perfect with out a rolling road.
thanks again.

[Big_Adam]

cheers for that ill have a read.
am i being thick in thinking that getting the fuel mix set up will be a pain,because if i change it on one carb and use the colourtune so there is a nice blue spark.how will i set the other carb up as there will already be a blue spark. if im making sense .
cheers

thats a great help.it doesn't look as hard as i thought, not really much point in getting a colourtune after all. but i think i will invest in a air balancer tho just to get it as close as possible. i know it will never be perfect with out a rolling road.
thanks again.

I would still get a colortune. Although today I found I can do mine by ear (I was so proud) but thats single carb so meh. Their handy bits of kits for checking it fairly well. I mean the lift pin is handy but with the filters off the mix will be richer when the filter is on. By no means a very bad thing but still if you want to go full bubble then you'll be pedantic about these things.

On the 1st quote the design of the A series is like two engines glued together. So when you get one side done (say cylinder 1 and 2 both fed from one carb) you move on to the next two cylinders (3 and 4) with the CT tool.

Might want to pick up some new jet for them carbs unless their brand spanking new.

[Dan]

The carb balancer will not allow you to adjust the mixture, only to balance the flow between the carbs. Colortune works very well, for twin carbs you just need to use two. Put one in #1 and one in #4.

Don't balance two cylinders at a time, that could be quite bad for the engine if there is a real imbalance in mixture at any time. Also it will decieve you as the cylnders that are closer to tune will be seeing the other two as a load and that will change the mixture requirement for the two you are working on slightly. Work on both carbs together.