37 replies to this topic

[mini-mad-mark]

Hi All,

Kind of run out of ideas

1991 998 HS4 (waxstat) carb with stage one kit from MiniSpares (3 branch, RC40 and K&N for std airbox) otherwise standard

I also got a needle with the kit which I fitted and since then have never been able to get the car to run properly to get to a rolling road.

 

It runs totally black on the spark plugs with so much soot - Dick Van Dyke was dancing on one of them.

 

When I first had trouble it ran so badly i thought it had to be ignition so have now got new plugs, leads, coil, points, condenser, cap and rotor arm all MiniSpares so no Ebay rejects. However I have come to the conclusion it is some way fuel related due to the soot

 

I've tried a different carb, going back to the standard needle (even though in theory this should be too lean with the K&N) changed the piston spring for one out a known good carb and have leaned the mixture (or should have) to the point where I cannot screw the jet higher up into the carb.

 

There is oil in the dashpot, and the float seems correct according to the instructions (and would have been unlikely to be wrong on two carbs?) and the fuel is fresh. Valves adjusted (twice!) and ign timing set OK 

 

It is running seriously rich and once the plugs get cold it wont run properly on the next start

 

Any ideas welcome as I'm just about tearing my hair out (well what bit is left!) - cheers, Mark

 

 

[carbon]

Is the jet height adjusted so the tip of he jet is about 1.5 - 2mm beneath the bridge level? And does jet move up and down freely when you pull out and push in the choke?

 

If the above are both OK then might be worth checking the jet size. There are 2 sizes: 90 thou for HS4 and 100 thou for HS6 and externally they look almost identical. If you have a set of drills take the dashpot off and carefully see if the blunt end of a 2.5mm drill will fit into the jet.

Edited by carbon, 07 May 2019 - 07:27 PM.

[Spider]

Check the fuel pressure just before it enters the float bowl.

[mini-mad-mark]

Cheers both

 

Will try both ideas at the weekend (will try anything as getting a bit desperate)

 

Mark

[mini-mad-mark]

Hi all,

Still no luck - I just cannot get it to run lean whatever I do - I must be doing something fundamentally wrong but cannot work it out. 

 

I just don't understand it, even with the jet screwed in as far as it will go it still runs too rich (doesn't seem possible?)

 

I tried changing the coil for a 12v non-ballast known good one (with a wire direct from a 12v supply before anyone asks) in case there was something wrong in the low tension side or the coil was duff - it ran fractionally better but still completely coked the plugs after 10 mins. Then as before the spark just isn't able to light the mixture as the plugs are fouled and it barely runs at all backfiring through the carb.

 

Normally carb mixture just makes it run rough not run so badly it stalls or wont pull away which is what I have and why i think I must have something fundamentally wrong

But it starts so easily that I can't resolve that with something fundamental as normally fundamental issues prevent starting at all...

 

Kind of losing my sh@t with it at the moment.

 

Any other ideas gratefully accepted

 

Cheers, Mark

[cal844]

Did you readjust the needle and jet as above?

Is the mixture nut wound all the way to the top of its available range? (If so you need to go for a leaner needle)

I'd also suggest a waxstat delete

[Zami]

Recently had a similar problem that came on all of a sudden. Plugs were all black ran like hell. Spark checked out ok. Pulled the domes and pistons on the HS4s and measured the depth of the jet to the bridge which was like 8mm. Long story short turned out to be a stuck choke holding the jet down. Currently the bridge to jet clearance is about 3mm and the plugs are brown and it is back to running and idling perfect. Good luck.

[mini-mad-mark]

Thanks for the further assistance/suggestions

 

Yes adjusted the needle and jet per suggestions/manual (15 flats from level) and have tried going back to the standard AAC needle instead of the AAU that came with the Minispares Stg 1 kit all to no avail did try winding it up to the minimum and still ran sooty black on plugs

 

No issue with the choke sticking 

 

Waxstat delete was on my mind just in case there was something wrong but not sure what parts I need to go back to a standard jet - is there a conversion kit available?

 

But saying that i tried a known good carb from my project (was running fine before I stripped it) so I would be unlucky for both carbs to have the same problem?

 

This is why I think I must be missing something fundamental not subtle but I can't fathom anything obvious - as I say it starts after half a turn so I cant think what could be fundamentally wrong otherwise it would be impossible to start.

 

Working away for a couple of days from Wednesday and busy Saturday so no more chance to work on it until Sunday again....

 

Cheers

[mini-mad-mark]

Still no joy - just checking - I now think this may have started after changing the needle (for the AAU in the Mnispares Stage one kit)

Even going back to the standard needle doesn't work and it still runs black soot rich.

 

Have I made some fundamental error changing the needle somehow that is allowing too much fuel past

 

I cant see it, as it seems pretty simple - trawled the net and here to find a pictorial guide or video but can't find anything except some SU instructions that have pictures but not with the exact step of putting a new needle in.

 

I undid the screw on the piston and pulled the needle and holder out, put the spring onto the new needle and then did the reverse keeping the holder flush to the base of the piston

 

Is there anything I might have screwed up there - as mentioned I changed to the AAU and as it ran rich I went back to the AAC (by the same method)

 

It ran fine before the last MoT which is when i started off on this long road of changing/swapping parts (including a head gasket change for good measure to look at the valves (all good)

 

Does anyone n#know of any other fundamental engine function/malfunction apart from a carb issue that could cause fouled plugs?

 

 

Getting a bit desperate now 

[johnR]

Have you given it a good run after fitting the leaner needle? It can get sooted at idle (where most needles are the same) but clear when driven hard. You could shim/adjust the float lower in the chamber so there's less fuel in there.

Edited by johnR, 18 June 2019 - 05:40 PM.

[imack]

Did you ever check the fuel pressure and jet size? Is it rich without the air filter fitted?

Edited by imack, 18 June 2019 - 06:23 PM.

[richmondclassicsnorthwales]

Me thinks there is a wrong jet in it, it can be on both carbs you have.

 

There are conversion kits you can buy - or there was, so you can change from waxstat to a standard plastic jobby - However -

 

Now, for a 998cc on a 1991 model should use the following parts in the carburetter

 

Jet - LZX1111

 

Needle - AAC

 

If you still have the tag on the float bowl, it should be FZX 1415

 

You need these specifically. Original specification. Buy the parts from Burlen fuel systems  - Tel - 01722 412500.  These are the replacement Skinners Union (SU) now suppliers, don't buy alternatives from any where else.  Don't get a salesman saying that they will supply  "this instead"

 

Hope this helps. Additionally - you can call me on 0759 6541072. Easier to talk than typing all the information

 

Neil............................

[cal844]

AAU is leaner than a AAC needle. The engine will run on an AAU (I have one fitted along with a stage one kit to my 998 and 1275)

I use engine oil in the carb Dashpot on all my minis and they all run slightly rich but are set to the emission limits for the year of car.

When you fit the needle the flange on the needle (where the spring sits) needs to be flush with the base of the dashpot.

There are two jet sizes and thus two needle diameters.

Hope this helps

Edited by cal844, 18 June 2019 - 07:30 PM.

[mini-mad-mark]

Thanks all, been tearing my hair out - so frustrating as the other mini (1330) has a carb lifted from a Maxi (HS6) and I never did anything to it; 15 years later still running fine so this is a real pain as I just cannot see why it is SO bad- not just a bit rich but absolutely choking the engine.

 

Sorry - been reading so much about needles it's fried my brain. MS Stg 1 kit comes with AAU needle I think - anyway still rich with the std AAC which is what is in there now .

 

Never changed the jet so it should/must be the std 0.090 for the HS4 (it worked before) 

 

Engine oil in the dash pot.

 

Tried it without the air filter as would expect that to lean it out a bit but it is a virtually brand new K&N element in std airbox so didn't think it should make much if any difference (it didn't)

 

Tried giving it a real blast after cleaning the plugs (at which i am now the worlds expert having done it about 100 times in the last couple of weeks) - it runs when the plugs are clean but as soon as you stop/slow down then it clogs up and runs bad - OK if I could clean the plugs every third traffic light......

 

The carb worked before fitting the stage one kit so I can't see why the float height  would be wrong/need to be altered but happy to try it - its a solid plastic float so I need to shim the seat if the height/clearance is incorrect right?

 

Have checked the jet level but not sure what measurement it should be as I thought I read somewhere that a starting position was to screw it up as far as it will go then screw it back out 12-15 flats (but that would probably be 1.5-2mm as 2 to 2.25 threads) then of course work from there to fine tune with the lifting pin (before the rolling road but its never run well/long enough to consider being able to get to a RR)

 

I might have misunderstood but I thought checking for excess fuel pressure was done by cranking the engine with carb top off and piston out to see if fuel was being forced out of the jet by pressure rather than vacuum - this was OK no fuel present during cranking - I don't have anything to measure fuel pressure if not this check. But again why would that suddenly change, if anything I would expect not enough pressure as the pump wore?

 

Next plan is to get a new jet (non-waxstat) and needle valve and seat to close those out - thanks for the tip about genuine SU parts

 

Not sure I understood the instructions about how to fit the needle:

 

When you fit the needle the flange on the needle (where the spring sits) needs to be flush with the base of the dashpot.

 

I fitted the needle into the little adaptor piece and put that adaptor flush to the bottom of the piston (per Mr Haynes instructions as not able to find a clear pictorial assembly guide only the SU instructions which are a bit wordy and not that clear)

 

 

I'll do some pictures next time as they might get someone to go "ahh you have/haven't done x,y,z"

 

On a slightly different but related topic someone lent me an HIF38 to try but I cannot get it onto the manifold as it hits the bulkhead (MS stg 1 inlet) - any thoughts on that?

I can only just get the HS4 on/off the studs and the jet is close to the bulk head but no it doesn't foul or bang or jam in anyway.

 

 

I definitely have one petrol problem - I haven't got a gallon to pour over it and burn it....

[Earwax]

I sympathise with your fried brain syndrome. It often occurs with fumble fingeritis, dropping things into the ether.  sometimes you just have to have a laugh or otherwise ,,,, well you know....BUT

 

you need to approach all things systematically and ideally with only one change at a time.

 

Things such as needle valve not closing or some crap in it, choke always on, gasket leaks ( although maybe you could import one to help lean out the mixture.) need to be checked to omit from further enquiry ( just like the officer always wants to take my fingerprints to exclude me from heinous crimes)

 

Whilst banging your head over fueling , don't be afraid to hold onto a HT lead and get zapped as it shorts across your body.. ( said in jest, but seriously be sure you aren't tracking a spark away from dizzy or through the leads)

 

Also our current fuel / spark plugs don't play nicely once run in fouling conditions.  Sometimes cleaning just doesn't bring back the plugs to their full goodness...   So have a new set at the ready.  Don't throw them at the situation until you are sure you have made a 'find'

 

Good luck , hopefully something will show up.