Map sensor on Twin SU carb'd mini?

goldminijohn · Post by **goldminijohn** » Tue Oct 18, 2005 10:34 am

Hello everyone,

I had a quick search through the forum and couldn't find anything about this but sorry if I'm repeating old stuff. I am thinking of putting mjlj on my 998cc A series mini. It has twin carbs and one of the carbs has a take of for the distributor vacuum advance. Will using this with the map sensor cause any problems? Would it be better to take off from the vacuum servo hose in the balance tube?

Cheers

John

Josh_b · Post by **Josh_b** » Tue Oct 18, 2005 2:21 pm

best to take off from a balance pipe so you get a smoother vacuum reading

PioneerX · Post by **PioneerX** » Wed Oct 19, 2005 11:22 am

I agree, this is best as you would avoid the pulsing effect from only taking a vac reading from once cylinder. I personally have a manifold that has vac point at cyl-1 and servo point at cyl-4 no balance pipe. As I have no need for the servo point, I have linked cyl-1 & 4 together, this gives a quite smooth reading.

goldminijohn · Post by **goldminijohn** » Wed Oct 19, 2005 3:36 pm

Thanks for the replies, sounds like the balance pipe is going to be the best take-off point. Would just have been a bit less work taking it from the origional vacuum advance take off. I've ordered the kit now so will hopefully be starting the project fairly soon

hotrodfil · Post by **hotrodfil** » Sun Nov 13, 2005 9:13 am

I wouldn't worry - bear in mind you have siamesed ports, then one carb is actually linked to two cylinders anyway.
BUT, personally I'd throw the twin carbs away if they're 1-1/4"s, they'll never make as much power as a single large SU! Especially on a factory manifold.
I used to pull 85hp at the wheels through a single 1-3/4" in my last Mini powered device...

<img src="http://img.photobucket.com/albums/v321/ ... ling-2.jpg" alt="Image hosted by Photobucket.com">

goldminijohn · Post by **goldminijohn** » Mon Nov 28, 2005 9:24 pm

Hi again,

That's a good point about the siamesed ports. Are there any telltale signs that pulsing would be causing problems? i.e. could I just attach the map sensor to the one carb and somehow test if it worked allright?

Slightly off topic, but I'm afraid the twins are staying on. I've only got a 998 so it breathes fine through them. Gives better power than my old 1.5in su carb and response is great. But I do accept they aren't ideal for all setups.