1968 Mini - Mini throttle response issue

Honest John Back Room » Technical matters
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Thu 22 Sep 2011 16:38
1968 Mini - Mini throttle response issue - AndyUSC

Good morning I am a new member,

I used to live in the UK and owned a 1968 mini, when I moved to South Carolina 5 years ago I brought it with me. It ran well and I never had any issues. However 18 months ago, I parked it in the garage and it had some petrol in it which contained up to 10% ethanol. The next time I tried to start it the battery was dead, and due to other things that came up I did not have the time or money to sort it out. I have recently replaced the battery, oil, oil filter and spark plugs, with an air filter on order (My local store wanted $72 for a replacement).

I also put some ethanol free 93RON gas in it, it took a while to start and when it first fired there was some black smoke and it struggled to idle even when choked and would die when the accelerator was pressed. I put some seafoam in the gas, which helps remove water and also help clean the carb and now the car will idle, but when the accelerator is pressed there is a delay from when it is pressed to actually revving.

Does anyone have any ideas, I would like to avoid dissassembling the carbs, as not many people round here have ever seen a Mini never mind worked on one, and I do not want to make the issue worse.

Any help would be gratefully received.

Thanks

Andy

Reply | Report as offensive | Link
Thu 22 Sep 2011 17:09
1968 Mini - Mini throttle response issue - Quicksilver

What carb is on the car? I assume an SU or twin SUs?

A 1968 mini did not have a fuel filter fitted as standard, (at least mine never had).

I guess you have had a lot of crap pulled through, (rust particles etc.) from the fuel tank.

I assume that this car has the electric fuel pump which will pump to fill the fuel line without the engine running.

Check the float chamber(s) of the SU carburettor(s). If full of crud you have probably got a blocked jet(s). Not to diffcult to clean with an air hose.

Another thing to check is the dynamo regulator, (too old for an alternator?). Possibly some issues there with it swiching in and out.

Good luck

Q.

Reply | Report as offensive | Link
Thu 22 Sep 2011 18:08
1968 Mini - Mini throttle response issue - AndyUSC

It is the SU carb, I cannot see a fuel filter, where would it be if there was one fitted?

The car has an alternator on it,

How do I check the float chambers? Is this an easy job?

I appreciate the help.

Andy

Reply | Report as offensive | Link
Thu 22 Sep 2011 18:55
1968 Mini - Mini throttle response issue - Quicksilver

I am surprised it has an alternator. This must have been retrofitted since in 1968 I am sure they were still dynamos. Is the alternator a Lucas 16ACR?

If you do not see the fuel filter in the engine bay it is probably not fitted. I do not recall any of my cars everhaving one.

The float chamber is the small cylinder next to the carb. where the fuel pipe enters. It held on with two screws, (do not overtighten when reassembling). There is a float valve wich feeds the SU main, (and only!) jet. Take off this cover anl look for crud in the float chanber. Depending on what you find you should then attempt to clean the carb main jet.

I suggest you purchase a Haynes manual. You can get them reallycheap on ebay.co.uk. This will really help in pulling the car apart and putting it back together.

www.ebay.co.uk/sch/i.html?_nkw=haynes+austin+mini+...3

I have owned 4 Mini's in my life so far. All owned in the 1970's and 1980's. The oldest was a 1962 model and the youngest was a 1976 clubman. I have repaired most items apart from a gerbox which I just swapped over from a "donor" car.

Good luck!

Q.

Reply | Report as offensive | Link
Fri 23 Sep 2011 01:07
1968 Mini - Mini throttle response issue - AndyUSC

It looks like it is the SU HIF carb, as I believe the car has a different engine from when it was new, so the float chamber is at the bottom. Have you had any experience removing these? It looks like it will be more tricky. Is it best left to an expert?

Is there anyway I can send you a pic of the engine so you can tell me what you think? Can you send messages to members on this forum?

Thanks

Andy

Reply | Report as offensive | Link
Fri 23 Sep 2011 09:50
1968 Mini - Mini throttle response issue - Quicksilver

This sounds like you have a modified engine and you probably have some sort of Mini Cooper set up. What is the engine size? I am guessing probably 1275cc or 1098cc or 998cc. you are unlikely to have the 997cc or 848cc engines.

I am not familiar with the SU HIF carburrettor however, google is your friend!

www.google.com/search?q=su+hif+carb&hl=en

www.youtube.com/watch?v=ASeMfXfjNpw

It is very likely that you have crud from the fuel tank in the float chamber and this has partially blocked the jet.

I have also had this in the past when fuel lines rusted through as they pass through the rear subframe.

Since the car is running why not take it out for a good run keeping the revs up to try and clear the jet? I have also done this in the past with SU and Stromberg carbs. As long as the oil is good and the cooling system is working OK this might be the best and easiest short term approach.

I assume that there are no USA - NC emissions controls on this car?

Also check the engine breather hose(s) to make sure they are clear and are not pumping oil mist into the air intake etc.

Finally purchase a Haynes manual. It will help solve many problems. Even with shipping to the USA from the UK it will not be much.

Good luck!

Q.

P.S. I know several Mini owners in Northern CA. There might be a North American club you could ask for help.

Reply | Report as offensive | Link
Fri 23 Sep 2011 09:06
1968 Mini - Mini throttle response issue - TeeCee

Impossible to get blocked jets on an SU as revving it will withdraw the jet needle and cure the problem. One of the main advantages over fixed-jet carbs that.

What does happen is:

1) Gunge in the dashpot. This causes the piston to stick and is where I'd start, especially if its been run on gasohol, which gunges SUs nicely. Remove dashpot damper (black thing on top with brass bit on it) unscrew screws holding down dashpot. Remove. Remove jet piston spring and piston / needle assembly. Clean piston and deshpot interior thoroughly with clean petrol. Reassemble, filling tube at top of piston with engine oil before inserting damper.

2) Sticking needle valve in float chamber. Bit of a swine on the HIF series with the integrated float chamber. On a mini, almost certainly requires removal of the whole carb to access. Once removed, unscrew plate from bottom of float chamber. Tap out roll pin retaining float. Remove needle valve. Unscrew needle valve seat. Clean both and reassemble.

Reply | Report as offensive | Link
Fri 23 Sep 2011 15:01
1968 Mini - Mini throttle response issue - AndyUSC

Thank you again Quicksilver,

Also TeeCee I will check the dashpot and thank you for the detailed instructions, I appreciate it and will update you once I have followed the instructions.

Thank you

Reply | Report as offensive | Link
Fri 23 Sep 2011 21:47
1968 Mini - Mini throttle response issue - Railroad.

Carburettors don't come much simpler than SUs, and it's unlikely that there's anything wrong with it. Based on what you describe I'd say the problem is the fuel itself. Petrol goes stale after a while. This is because the lighter parts of the fuel evaporate leaving the heavier liquid that does not burn. Only gases burn. Liquids and solids do not. They merely provide a source off of which comes vapour. It's that vapour that burns, and so I think your problem lies here. Also 93RON fuel is low octane and not really suitable for your engine. I'd try draining your fuel tank and refilling with 98RON fresh fuel. I'm sure you'll see an improvement.

Reply | Report as offensive | Link

From which small car to buy at which price point to the best UK-built cars, our Top 10s have the lot. Click now for your shortlist.

Unsure of what to buy? Our Top 10s are here to help you....