20 replies to this topic

[minimininut]

Hi mini people!

I would really appreciate some help with sorting out Arthur's ongoing ups and downs - this is all in attempt to resolve odd idling/running behaviour - eliminated loads of things so focusing in on the carb now! (i searched for this but there is sooooo much on carbs that I didn't have any joy).

1988 City E, 998, "stage one kit"

Single HS4 carb.

The Haynes manual gives the setting for adjusting the plastic float height for a sprung needle valve without its spring compressed (it says the distance between float and underside of float chamber lid as 3.18mm to 4.76mm this is a huge range ... )

Should we aim for a mid-way figure? And if using a solid unsprung needle valve, is the ideal figure the same?

Any recommendations please? The float in question is all plastic so the adjustment has to be done with washers under the needle valve seating.

Thanks in anticipation!

[lrostoke]

To be honest I've stripped 3 different carbs on 3 different minis with the plastic floats, non of them have any washers. I just leave that bit of the carb appart from cleaning out all the jets etc.
I'd be suprised if thats your problem.

A lot of stage one tuning problems seem to be down to wrong needle.

Just had a quick flick through one of your other topics, have you tried richening the mixture and upping the tickover. Seems to be cold weather related

Edited by lrostoke, 10 February 2010 - 07:08 PM.

[minimininut]

Hey lrostoke, thanks for your reply and your help. I think you're right and the needle is on the list as well...

Lots and lots and lots of experiments with tickover/richness have been done - he got to the point where he was just a nightmare to keep running without stumbling/stalling or flooding. My garage said they thought it was a sticking exhaust valve although it wasn't - we know because the head has been off and all was fine (but it was an opportunity to try out the head I bought on ebay as a spare last year).

It's getting to the point where nearly everything has been replaced!!

[lrostoke]

Mine does more or less what your describing at least once every winter

Normally what cures mine is

remove rotor arm and sand up the brass section
give all my leads a good drying off
give dizzy cap a good clean
up tickover a touch. turn everything on and then set so its just under the 1000 rpm
check oil in dashpot, I only have enough in so I can feel resistance on the plunger.

mixture I do with my gas tester, I set it to 3 % at tickover

Edited by lrostoke, 10 February 2010 - 07:29 PM.

[minimininut]

Mine does more or less what your describing at least once every winter

Normally what cures mine is

remove rotor arm and sand up the brass section
give all my leads a good drying off
give dizzy cap a good clean
up tickover a touch. turn everything on and then set so its just under the 1000 rpm
check oil in dashpot, I only have enough in so I can feel resistance on the plunger.

mixture I do with my gas tester, I set it to 3 % at tickover

Thanks very much for the help Steve, interesting to know that at least I'm not alone!

He was consistently being naughty, but there has been some change since accelorator cable/head gasket/dashpot oil relacement, along with replacing side plate gaskets/dizzy cap/electronic ignition back on ... and so the list goes on and on and on! Certainly seems to be cold weather related, so it'll get better when the spring arrives at least...

[Minimininut's Dad]

Hello, Minimininut's Dad here!
I asked Minimininut to ask the question about fuel height/float level adjustment because the wide range given in Haynes seems excessive. Coupled with the fact that we changed the needle valve originally because so much fuel had poured out of the overflow pipe it ate a hole in the tarmac drive! I was surprised to find that they were still using the needle valves with the small sprung plunger that used to wear a deep hole in the copper/brass float arms used in the '60s. So we replaced this one with a new ball type one and washered it to bring the float within the specs. given.
Then later Arthur Mini developed another flooding problem causing half a tankful of petrol disappear in one 2-hour trip, and stalling every time the accelerator was released, we changed the valve back to the original. Now, although it's not obviously flooding, the idle speed keeps changing all on its own (sometimes speeding up or more often, slowing down) when no one is touching the controls!
So I am thinking that the fuel height is possibly varying too much and perhaps because the pump pressure sometimes overcomes the spring pressure of the needle..?
I have ordered another new needle valve (PET7010) from DCN Classics which looks different to the others, and when it comes I want to be able to set the float height accurately and with confidence! Hence the original question about the figures in the manual.
Any suggestions on the right distance so set the float from the underside of the chamber cover would be very much appreciated. Thanks

[Dan]

I've given up getting needle valves from anywhere other than directly from Burlen (the genuine SU manufacturer). There is another type of valve out there, not made by Burlen I think but by one of the companies who remanufacture SUs and who's parts should be considered non-genuine. I'm not sure which is which now but I believe that the ball-bearing type are not genuine Burlen, whichever is non-genuine of the two is nothing but trouble. I know that it doesn't help you because I can't remember which is which but given that you have now ordered a new and different type you might be on the right track. I've never found a genuine valve to need any packing to adjust the float height to be honest and Burlen have deleted both the procedure and the tollerance from the technical manual for HS carbs because of the accuracy of their parts. The most important point is to make sure the float bowl is horizontal.

Check Burlen Fuel Systems' web site to see if there is a picture of genuine valves on there.

[Minimininut's Dad]

Thanks Dan,

I have looked at the Burlen/SU site and found a useful anti flood kit  image_2342.jpg   5.21K   19 downloads

or a complete float chamber top, valve and float -  image_2813.jpg   8.13K   8 downloads

The needle valve I ordered from the other firm was -  pet7010.jpg   28.57K   10 downloads
The same type as the SU/Burlen one was actually supplied.

Many thanks for your help and advice - by the morning I may well persuade myself to order from Burlen

Edited by Minimininut's Dad, 13 February 2010 - 10:59 PM.

[Boycie]

I've been experiencing exactly the same problems..

I, too have also gone for a replacement, traditional style needle valve, but unfortunately I can't test the new part yet as the car is a fair-weather vehicle and the roads are currently covered in salt.

Hope it sorts it for you, let us know how it goes.

[Minimininut's Dad]

Varying idle speed - now constant!

AUE 277 - The new float chamber lid, assembled complete with Viton needle valve and float, arrived from “The SU Carburetter Company” (Burlen). I checked the gap between float and top flange as per the manual and it was close on the smaller measurement just over 1/8” (3.4mm) which would give something close to the highest fuel height. I could see no washer between the valve seat and cover.

I removed the carburettor to check it thoroughly before fitting the new lid assembly. I found nothing wrong. I even did a drop test on the dashpot piston – it was just outside the 5 – 7 seconds recommended, at 4 secs, but I believe that is a satisfactory result. I improved the choke lever action to provide a finer control of fast idle speed before the jet starts to move. Refilled damper with SU Carb oil (had been testing 3-in-1 but found no improvement with that).

Reassembled and refitted. As soon as fuel reached the float chamber the engine fired and ran really smoothly and was still good after reaching working temperature. A road test found the idle speed consistent at every stop. It’s rather burble-burble (uneven) on even throttle, e.g. when trying to drive at a steady 30 mph on the level, but that may be mixture, not the correct needle or timing?... Time will tell, hopefully, but I am now reluctant to change anything because he is going so well otherwise.

The ball bearing ‘needle’ valve from Mini Spares which was in there when all the flooding occurred has a bore of 3/32” 2.35mm which may have allowed the fuel pump pressure to exert more downward force on the float. The new “Viton” valves from SU and DCN Classics seem identical (they come in Genuine SU Parts bags) and have a smaller bore of about 5/64” (0.07”) 1.75mm, so it will be easier for the float to shut off the fuel. See picture for detail.
 New_needle_valve.jpg   222.52K   20 downloads

The ball type valve may possibly have leaked because I did not tighten it very well as its hexagon is slightly larger than the SU size and so my only spanner that fits SU needle valves, in the confined space, did not fit it.

[Minimininut's Dad]

Yet more problems...
Minimininut's "Arthur Mini" has been set up of a rolling road - Yuck
Many have said it's the only way to make sure we're getting the best from the engine with its stage one stuff.

I drove back from the two-and-a-quarter-hour session, very much poorer and with a Mini not pulling nearly as well as he had on the way to the tune! Timing was deemed as OK, various needles tested and the ABD one in there was put back as being by far the best of the ones available on the day.

Well it's turned out badly and we're back to the erratic idling/stalling problems... and I don't need a meter to realise that it's changing from being too weak to too rich. Having fitted an in line filter (after we had the flooding problems) I can see no dirt or water in there but there is a varying amount of air, and occasionally a few air bubbles come up the line from the pump.

All the joints on the fuel line from the tank to the pump look sound, so now maybe it is time to turn to the fuel pump? It's about the only component (apart from the engine itself) that has not yet been changed!

When will the end be nigh?

[lrostoke]

I wouldn't worry to much about occasional air bubbles. If theres fuel in the filter then theres fuel in the float bowl.

ABD is a very similar profile to AAU , AAU often supplied with stage 1 kits but not always best choice.

Is it suffering flat spots when trying to accelerate then you get a woosh and the power comes. ?? sort of a lag

[bmcecosse]

AAA is the normal/best starter needle for stage 1. I'm not surprised at the RR result - ask for money back ? Unless they are very familiar with Minis/SU carbs - they are just a waste of time and lots of money. You can easily set the car up on the road - if all it's had is a stage 1 kit! Advance the ignition till it pinks - then retard slightly. Check the vacuum unit is working. Adjust idle mixture for best/smoothest idle - then run it hard on the road - switch off after a good few miles and whip out the plugs to check the mixture. Black = rich, white = weak, tan/beige is just right! Simples.

[Minimininut's Dad]

Thanks Irostoke - Normally I would agree about the fuel and a few bubbles in the filter, but am desperately seeking an explanation for the erratic behaviour of the carb. How can it change in minutes/a mile from being rich to weak and or vice versa?

Yes I tried AAU it was pants! Rolling road tried it and others too, also no good.. What the rolling road did tell us was that the ABD (which may have been thinned slightly around stations 3 to 5) is fine for speed if it's set a bit rich at idle. I will do some more on this later, but there is no point until I can get the thing to run consistently in the first place.

Thanks bmcecosse - I will check out the AAA needle spec as soon as I win this stupid battle with the erratic behaviour. When I booked the RR he was running very well apart from being uneven on even throttle at around 30 - 40mph, and I hoped the RR would spot this and come up with an answer.

On the way to the test, the erratic running of some weeks ago returned, to completely disappear once the little car saw all those dials and the rollers (a bit like toothache going when you get to the dentist!). After the RR he was smooth enough (but not exciting) on the road test, but on the way home he went into stalling again mode, but by the time I got into the driveway he was ticking over fine again. Checked everything today and drove about 12 miles, first he was obviously too weak, so 3 or 4 flats down and all is lovely for another 10 miles, then he get unhappy again, so check again and it's too rich.. and so on.

[timmins]

Hi there,

I'm tackling a very similar problem with a 1098 Clubman. The idle RPM shifts from around 800 to 1200. One one occasion, it sat at 2000 before deciding to fix itself! It's also a bit of a gas guzzler (at best, around 30-35mpg, out of town driving). When I stop at traffic lights, then set off, I can smell fuel.

I've stripped the carb apart, checked the float chamber, and can't see why that should be a problem. If it fills too much, then it'll escape out the top, and become pretty obvious where the problem is.

The needle is true, and doesn't appear to be worn. Even if it was, i can't see why that would make the idle erratic.

My best guess is a vacuum leak. The variation in the amount of air drawn into the engine *after* the carb, I guess, would alter the idle speed (but mixture?). The throttle spindle does have a tiny amount of side-to-side play. The exhaust gasket is also suspect.

If you find anything else out, then let me know!