I'm struggling a bit to sort out what seems to be a mixture/needle problem but please suggest if you think there are other things I should look at.

I have a Cooper S 1275 + 0.060, twin HS4, 1.5 roller rockers, standard Cooper S cam and LCB extractors.

I've noticed when the engine is doing 3500 - 4000 and above it seems to be starving and not running smooth, it's especially noticable running at constant 100 kph, opening up the thottle it picks up OK. Pulling out the choke, and I mean right out also improves the situation.

It's even noticable if you just rev the engine without load up to 4000 and hold it there, it seems to miss or run rough.

If I increase the mixture to try to recify it the idle then seems way too rich. Besides it seems I would have to screw a long way rich to solve the problem judging by the amount the choke has to come out.

I've also found if I try the correct viscosity dashpot oil (using singer sewing machine oil which is v.similar I've been told) it dies breifly when you try to accelerate, it seems better using thicker 2 stroke or 20w50 eng oil.

(It also seems very rough and jumpy as you decelerate from 2500 - down to a stop. Not sure if that would be related to this problem or not.)

The current needles are M. The springs are red.

Does it sound like I need to try different needles and if so what would people suggest.

Cheers

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68 Morris Cooper S Mk1 (*ex 78 1275 LS 4th last built, 70 Morris 1500 OHC & 70 MiniMatic)

Most people recommend ATF fluid for the dash pot, and also not overfilling it.

The first one's that come to mind is how old is your fuel filter and what is the condition of the butterfly's and spindle's
.

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If you are running twin HS4s I would try either CP4 or #6 needles. M's just don't work in them, I found.
#6s drew a straight A/F ratio line on the dyno, on 2 motors (1293 and 1360) I used them in.
CP4s were used in the Police pack Ss back then, but I found the 6s work better..

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

You can't overfill them. They just squeeze out the extra through the vent hole.

That true, but who wants to clean up a mess they don't have to

I suppose its one way of finding the right level , if it stops making a mess it's right on the money

The other needle to look at is the No 7 fixed
.

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I was just pointing out that it is possible to under fill but impossible to overfill a dashpot.
I have seen repeated warnings about making sure to avoid overfilling in threads about poor running when that is in fact the least of their problems.

Fuel filter is only 3-4 months old.

I had thought about the condition of the carbies. From the receipts of a previous owner the carbies were new in 2002 so I've been assuming they are probably still OK. What's an SU's usual life span before it needs an overhaul?

If I want to check the spindles what is the best method?

...and what should I be looking for with checking the butterflies?

I might start with ordering some #6 needles and see how I go.

Does it still sound like it could only be a carby/fuel issue?

Thanks all

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68 Morris Cooper S Mk1 (*ex 78 1275 LS 4th last built, 70 Morris 1500 OHC & 70 MiniMatic)

I wasn't relating the overfill to the poor running but I can see where your coming from

anyway back on topic





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Thats why they invented curtains
Sorry couldnt resisit

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http://www.youtube.com/watch?v=nDMkVq1jRGU

The old "How does an Aussie drive women crazy" joke.

the 'best' method is with them off the car, it'll be obvious if they're worn. If you can wiggle the shaft up and down, then it's worn. If the butterflies are worn, they'll have steps at the side from where they've been rubbing against the shaft holes, and won't be round - again it'll be obvious

When still on the car, if you can wiggle the shafts up and down (mostly the inner end of the shaft) then it's worn

The shafts wear, and the bodies wear - they can be rebushed easily enough. I made teflon bushes for mine



I've found that #6 needles are the best for me on a similar spec (+.040). I am thinking about trying to go a little leaner at idle, but that's nothing



sounds quite odd - I'd be checking for air leaks and going over everything

do a run at 4000rpm when it's running badly, then shut the engine off and pull out the spark plugs - they should all be the same colour, and mid to light brown

Sorry, I jumped over your post, fuel filters don't cost to much ,you may as well fit a new one once you have someone/ or you fit the new needles and check the butterfly's and spindles and have the carbies re-balanced and colortuned, if you were in Melbourne I,d recommend Russell at Minis-R-Us for SU carby rebuilds and refits
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It will only take one load of bad fuel to clog a fuel filter - easy.

If the spindles are worn, it will really only show up at idle.

Could be ignition, don't discount it.

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If i were faced with this problem, the very first things that i would look at are the fuel delivery to the carbs (Vol per min should be at least one litre within one minute) (((fuel filter & fuel pump checks would definately be involved with that test)))

then i`d be checking the float levels

then if all is good there,,, the next thing would be to enrichen the mixture at the problem area & that can be done via a few different ways,,, "depending" on how the lean-ness is occuring

maybe richer needles ,,, maybe stronger springs

maybe a combination of both

so,,, if the fuel delivery is good & the float levels are right, then yeah CP4 needles may be a good start (going on those engine specs) & see how it runs after that.

there is also another (very often missed) area of concern , & that is the o-rings that seal the pipe into the float bowls,,, quite often they can be fitted in a ruch & may have an issue where the oring isn`t quite spot-on & can peel or squish out & half block the pipe,,, they still may seal well, but the semi-blockage can do wonders making a lean result in the revs, but won`t show up much at idle or low load , low revs

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

OK I will check those things out when I get a chance however I was thinking fuel delivery must be OK because if I pull the choke out when doing 100kph then the problem disappears so I figured there must be plenty of fuel being supplied.

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68 Morris Cooper S Mk1 (*ex 78 1275 LS 4th last built, 70 Morris 1500 OHC & 70 MiniMatic)