Is the carb sealing well to the manifold
Do you know if the throttle shaft holes on the carb are round and are both sealing well
Butterfly in backwards reducing airspeed across the bridge:?:

will add more to this when i think of them......sorry eating nom nom nom nom nom nom........

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

The e-type had 3 x 2 inch sus. They were not that bad really - the only problem is that they wouldnt hold tune for long.

It doesn`t matter how many SUs there are in-line,,, twins, tripples, quads, whatever

it`s the very same process to get them right & if you go over & over the same process, over & over, do it again & again,,,, then """IF""" everything is wonderful & in good order with nothing wrong with them,,, then you will """ALWAYS"""" end up with them exactly the same & perfectly in tune & they should stay that way

You obviously have a small problem wghich you havn`t found/sorted yet,,, when you discover the problem then all will be wonderfull

& if you`d like to test my theory about setting them over & over & over again,,, by all means pl\ease do so,,, because as i said--> """IF""" everything is in good nick & working correctly, then each & every time you adjust them correctly, you will end up with the jets in exactly the same place , ---->"""every time""".... (((Providing there are no problems & you know what you`re doing))).... but obviously in this particular case you have an issue

sorry my days of helping sort carb issues over the net are gone, because there are simply way toooo many variables & i can`t trust what anyone says they have checked everything out & all is spot on etc etc etc & the typical response is--->

"""It`s all been checked out & everything is perfect, so why am i having these prooblems???""""

sorry,,, if they were sitting on my bench i could source the problem for you

edit,,, But i`ll ask you this--> are both jets the same size???

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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.

Thanks matt...

Yeah they are both new and rebuilt from a twin SU kit a year ago..so all the parts were sourced from the same box. The spindles are all new so no movement and leaks from there...I've checked everything I can but I'm missing something small...

The odd thing is, with the colortunes on the car (I've got two thanks to Rob Duca...thanks Rob!), the 3/4 cylinder carb will do the same trick if the cylinder mixture is either very rich(orange) or very lean(light blue)...at 800 rpm idle..so it kind of vindicates an air leak issue I thought..but sometimes you can argue your way out of anything..I'll keep looking...

Compression test brings up 200-200-190-200 That new head is a little shallower than I thought it was...

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Are both float bowls positioned at the same angle? Is the vent on the 3/4 carb clear?

If it's drawing fuel in at low RPM regardless of the jet position, it sounds like fuel is finding its way in without needing to be dragged out by air across the bridge. Extra pressure in the float bowl will do that...



I chased a carb problem for months believing this too. I put a new butterfly shaft in and by eye and finger it looked/felt leakproof, but after I gave up and gave it to Scott at Minitopia he determined it was sucking air past the shaft, had it rebushed and it's good now.

That one idled brilliantly too, and checked out with the colourtune at low RPM...

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Simon

The adventures of an owner builder in the Tallarook Ranges

Does the dominant 1 wear stillettos and fishnet stockings and does the other 1 have a leather mask with a zipper. Perhaps a role reversal will work

I was waiting for that Maxx....no fishnets but she is wearing the pants around here...



I should have explained a little better, the behavior is the same if it is either really lean or really rich or anywhere in between...

I'll play with the spindles in the morning and put a little oil on the ends to check for air leaks..but they still seem very new..

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Were the bodies rebushed at rebuild time?

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Simon

The adventures of an owner builder in the Tallarook Ranges

Yes, the bushes are still in nice and tight, idle will go down to stall too it seems.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

A few things to check.

You do have the airflow through each carb set the same? If this isn't the same you wont get the same response when you lift the piston. You need to listen to the airflow through each carb through a piece of tubing and adjust the idle speed until both carbs sound the same and the idle speed is around 1100- 1200 RPM. You need to set the mixture strength at this higher speed not at the final idle speed of around 800 - 900 RPM.

Make sure the stopper pin is in place on the underside of the piston adjacent to the needle. This is a small pin, plastic or brass, that stops the piston closing completely. The engine wont idle properly if this is missing.

Are the fuel floats set to 1/8" to 3/16" for an HS type carb? To do this hold the float lid vertical with the float pointing down and measure the clearance between the lid and float at the closest position to the lid. If you have the one piece plastic float this is at the opposite end to the needle. Use the go/no go principle using a 1/8" and a 3/16" drill bit to set the float height. Dont let the float compress the spring loaded float needle if you have one fitted.
If the float levels are different you wont get the same mixture strength at the base setting of 2 turns down from the jet being level with the top of the jet holder.
If you have the one piece plastic float you have to adjust the float height using packing washers between the jet and the lid. They are 0.010" aluminium washers and each washer changes the float height by approx 1/16". There is about a 1:6 ratio involved.

Did you replace the piston springs? These tend to fatigue over time and should be replaced at regular intervals. If you have replaced them make sure they are both exactly the same. I fitted new ones recently and even though they were the same colour code - Red - the new springs were different lengths and made of different thickness wire than the old ones. This means the spring rate is different and even though they may test OK at the test length they will give different piston heights at part throttle which may be enough to upset the mixture. While this doesn't directly address your idle problem it may be a contributing factor.

Hope this helps.
RonR

Thanks for all the help, I appreciate the efforts people went to in replying...now its only good manners that I get back and let you know what I found.


The problem was that it was missing...........that is the carb was missing a whole gasket

When I the manifold back together the other week I had a problem with one of the carburetor-manifold studs...so I took one of the top studs out in the car and cleaned up the thread a little before putting it back in..while I did that one of the gasket between the sandwich plate and the spacer took the opportunity to swing down to 6 o'clock...I put the stud back in and tightened her up and away I went...

So today I swapped the gasket back out, and put it back together..and it works much better now....

Sometimes you want a sophisticated problem to crop up so you don't have to admit to a dumb mistake...

The really god news is that with the new head, higher compression, now tuned twin SUs and a dizzy with a better advance curve, the donk's a stack more snarly than it was before....now when's that track day?

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Excellent

I'll take a dumb mistake every time, sophisticated problems are too expensive

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Simon

The adventures of an owner builder in the Tallarook Ranges

I will second that!

Now you can join mini maxx and prompt punch yourself in the head !!

Glad you found and sorted it, often these things come down the the simplest things.

So it was the top one.......glad it was a simple, cheap fix after all the time you put into them before they were fitted to the engine......did you end up putting the richer needles in

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