7 replies to this topic

[Tumbletim]

Good Morning,

 

I have a 1984 998cc Mini City. Just fitted twin HS2 carbs. Told they came straight off another mini and have just fitted them to mine. As soon as you start the car it revs right up. My twin carb knowledge is limited so was so happy to hear they came straight off another mini but now wonder if they’ve been “adjusted” in some way before they got to me? I’ve fiddled with return springs and checked everything I can see and now I’m just Looking at them all confused. Any ideas as to why it revs right up and nearly flat out on start up? 
 

Many thanks in advance. 

[malynch27]

A few questions first off.

Did the carbs come off of another 998 and was the spec of the engine the same as yours? Does it settle back down again after the initial high revs?

The carbs may have been tweaked with new needles and a richer mixture if they came off of a 998 that has been modified. Your best bet is to re-set the carbs to a standard set up and then make them work for your engine by playing with the fuel mixture and needles.

If the car doesn't settle down after starting, something in the carb could be sticking, causing the engine to rev. It could be either carb so as above, set them up and make sure everything is working as it should and then strap them back onto the car and see what happens.

The Haynes manual gives a good step by step guide for setting up carbs. Let us know how you get on and post some pics if you get stuck, need help with identifying something.

Good Luck

[unburntfuelinthemorning]

Sounds like the throttle plates aren't closing properly. 

 

Check return spring is working correctly;  check throttle return stop is screwed right out;  check for sticking throttle cable.

[nicklouse]

That sounds like an air leak. Letting air in.

[imack]

Intake manifold seating against head probably? Can foul exhaust manifold flanges preventing it seating or have different thickness flanges to the exhaust manifold and cause the same problems.

[Tumbletim]

Thank you everyone! I’ll have a look and let you all know how I get on! So grateful for the advice! ??

[blacktulip]

Check that the throttle cable isn't set too tight. Undo the throttle cable linkage screw so the cable is free and push the link down then do it up.

[carbon]

There should be three return springs attached to the throttle connecting rod which sits between the two carbs. Also there is not a lot of clearance between this and the centre exhaust pipe, particularly if you're using an aftermarket freeflow or LCB. Check it's not fouling the manifold.