10 replies to this topic

[drummerian]

Hey people,

Some of you may relise i am going through a dilema with engine choices. Anyway, since i have the bits i plan on ust stage 3 'ing my 998 for now and check out the performance gains from this!

So i have a couple of sets of hs2s to use, and a stage 3 head from smart01c on here.

My question is what needles should i go for in the carbs? And is it possible to get a good tune on them using just a timing gun or will i need a balancer?

thanks

Ian

[jaydee]

If you have no experience with twins, just go to a good rolling road.
Otherwise..
Try GY needles, unless you are fitting an high duration cam too.
Using a balancer will make things loads easier, a timing gun an a gas tester are necessary to set everything right on tickover, then its just a matter of putting load on the engine and then reading spark plugs.

[drummerian]

are there any twins tuning guides out there? i have got a good tune on my current hs4 using just a timing gun (and some expert advice from a neighbour)

any other needle ideas? (cam will be standard....for now )

[jaydee]

Have you got the good old SU handbook?
(..send me an email if you need one..)

Err..i've just read your other topic, the twins are going to a 998 or a 1275?
Because for an MG 1275 you need richer needles, like M needles or even something slightly richer.

Edited by jaydee, 15 December 2009 - 12:03 PM.

[drummerian]

they will be going on a 998, had a bit of a change of plans for now

any ideas anyone? i want to purchase the bits tonite for the alst day of the minispares sale!

[bmcecosse]

Just stick with the HS4 on a decent manifold!

[drummerian]

i have a water heated inlet mainfold, you think the hs4 will be good enough to supply the stage 3?

[bmcecosse]

Of course! Just don't connect the water. If you think about it - each piston sucks in air individually - with 'twin SUs' - the balance pipe is useless - so each piston can only suck in through a single small 1.25" SU ! With a good single 1.5" SU - each piston gets to suck in through the larger carb! Provided the manifold is good(ie MG Metro or copy) - it's better to have the large single carb. Even BMC discovered that - and started fitting large single carbs to the engines rather than twins.

[drummerian]

Of course! Just don't connect the water. If you think about it - each piston sucks in air individually - with 'twin SUs' - the balance pipe is useless - so each piston can only suck in through a single small 1.25" SU ! With a good single 1.5" SU - each piston gets to suck in through the larger carb! Provided the manifold is good(ie MG Metro or copy) - it's better to have the large single carb. Even BMC discovered that - and started fitting large single carbs to the engines rather than twins.

so which needl would you reccommend? thanks

[jaydee]

What bmcecosse said is correct, infact, although i love twin carbs, I use a single HS4 on my 998, tuned as per works car.
Twin HS2s give a better throttle response than a single HS4 carb, but you'll loose 1 or 2 bhp with the twins.
A single carb is easier to tune, you just need to do some work to get out the most of it. First of all, you need a red spring inside the dashpot.
Then doing some works on the elbow, edges and butterfly will improve throttle response.
Stick on an aftermarket alloy inlet without plumbing the heater pipes. i'd reccomend the Minispares' alloy inlets, which are a rough copy of the MG inlet, they're just bigger and work fine. To make the inlet work at its best, you have to flat out all the imperfection on the inside of the manifold and on the carb spacer due to bad castings, then use a drill with a grinding bit on and crack on the inside which have to be smooth but textured to give the best flow and the best fuel atomization.
You should try AAM needle on the HS4, but probably needs a re-profile.

[drummerian]

What bmcecosse said is correct, infact, although i love twin carbs, I use a single HS4 on my 998, tuned as per works car.
Twin HS2s give a better throttle response than a single HS4 carb, but you'll loose 1 or 2 bhp with the twins.
A single carb is easier to tune, you just need to do some work to get out the most of it. First of all, you need a red spring inside the dashpot.
Then doing some works on the elbow, edges and butterfly will improve throttle response.
Stick on an aftermarket alloy inlet without plumbing the heater pipes. i'd reccomend the Minispares' alloy inlets, which are a rough copy of the MG inlet, they're just bigger and work fine. To make the inlet work at its best, you have to flat out all the imperfection on the inside of the manifold and on the carb spacer due to bad castings, then use a drill with a grinding bit on and crack on the inside which have to be smooth but textured to give the best flow and the best fuel atomization.
You should try AAM needle on the HS4, but probably needs a re-profile.

what do you mean by a re-profile?

thanks for the advice so far though!