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Twin Hs2 Problems


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#1 Fdc907d


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Posted 02 March 2013 - 11:45 AM

We are currently trying to get a 1966 Cooper S back on the road which had been renovated in the 90's and has been in storage for some 10 years. Everything was going smoothly until we realised that both carbs had become gummed up, to the point the butterfly's wouldn't open. When the carbs were still on the car we noticed the jet on the RH carb was a lot lower than the LH one.
We just thought it must have needed some tuning, so we stripped the carbs and blew them out and then realised the jet and bearing were completely stuck and so replaced them with new ones for the specific carbs from SU (at which point it turns out it has one 998cc carb from 61-62 and one 998cc carb from 64-69). Wen arrived we replaced them and when it came to putting the needle and piston in the needle wouldn't sit down properly. We adjusted one jet down a little and it then sat right but on the RH carb we couldn't adjust the jet down far enough to get the needle and piston to sit right. Checking the needles we had against each other it turns out that the RH needle was longer.
I cannot understand why and thought I would ask those with much more experience for any ideas asto why this would be the case.

The carbs are aud104r and aud15r (yes both are right hand carbs for some reason)

Thanks for your help

#2 dklawson


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Posted 02 March 2013 - 12:34 PM

Don't worry about the mixed carbs unless you are/were going for originality. There are many things to look for when reconditioning SUs and I would not get fussy about what car the carbs were originally used on.

That said, I would...
  • Thoroughly read through the carb rebuilding steps in the early Haynes Mini manual, also those in the SU book by Brooklands, and the steps you will find online at the Burlen (current owner of SU) web site.
  • Totally disassemble the carbs and carefully clean all the internal passages making sure to flush them with spray carb cleaner.
  • Reassemble the carbs using NEW matched needles. The Brooklands book will have a list of what needles would be right for your car's engine as it left the factory. Others on the board will have suggestions for what needles to use if your engine is modified.
  • Match the SU pistons to the vacuum chambers. Go to YouTube and search for the video titled "matching SU air pistons" by John Twist.
  • Make sure your new neeldes are installed flush with the bottom of the pistons.
  • CENTER THE JETS as described in the various manuals. (This MAY be the issue preventing the one carb piston from sitting as low as the other. Jet centering is a MUST on early carbs with fixed needles).
  • Make the necessary "first start" settings of the jet height.
The remaining adjustments deal with balancing the carbs and setting the mixture. Obviously they need to be made after the engine is started and up to temperature. Read the procedures multiple times before starting and you will have success.

Edited by dklawson, 02 March 2013 - 12:36 PM.

#3 carbon


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Posted 02 March 2013 - 05:50 PM

What is the length of your 'longer' RH needle? 'Fixed' needles are shorter than 'swing' needles.

Do both needles have the same code on them?

Also if the springs are original then the AUD15 is red and the AUD104 is blue. You need two reds, this may account for the jets being set a very different heights...

Also tagged with one or more of these keywords: engine

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