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MG Midget and Sprite Technical - 45 DCOE help

Hi,

I'd like to put a little problem to the collective wisdom on here. I have recently got my MG back on the road, and am having a bit of trouble getting the carb set up.

I know a trip to a rolling road, preferably Peter's, would be ideal, but I haven't yet located _any_ RR in France that has weber know-how and a selection of jetting parts, so I'm stuck until such time as I bite the bullet and go back to the UK.

It's currently set up :

45 DCOE 152 (the venturi bypass are closed on both chokes, if that makes a difference, simply because it doesn't seem to make any noticeable improvement and listening to both chokes they both seem to be flowing the same)
38mm chokes
4.5 Aux. Vent.
F16 Emulsion tubes
175 air correctors
165 main
45F9 idle
40 accel. pump jet

It has a somewhat lumpy idle (but I don't know if the cam has been changed the PO had the block out at some point and it was bored to 1330 so I don't really know what else has been done) but I can live with that. It also needs quite a lot of advance at idle (17° @ 1000rpm) but my biggest niggle is that at part throttle (around 2500-3000 rpm) there is sometimes a hesitation. I previously had 45 accel. pump jets, and moving down to 40's has improved, but I'm not sure that's the only problem as even on very slow throttle opening (where the pump shouldn't really matter) it does it too. It makes town driving (which I don't really do that much of) really quite a PITA.

If it's relevant the carb sometimes will "spit back" at very light throttle @ around 3300 rpm. I thought it needed more advance, so have dialed that in and it improved tremendously, but it still does it once every couple of hundred kms, and if it's relevant it will _sometimes_ stall coming back onto idle from wide throttling openings, though it does idle correctly if it's slowing down for a junction.

I think I've got the setup as good as I can on my own (and I'm a bit stubborn, so I do like trying to do things myself as well as I can :/ ), so any further advice is welcome because I'm somewhat stumped.

I'm actually even toying with fitting a lamda sensor and wideband, but they cost a fortune and it seems like overkill just to do the setup :/

Thanks in advance for any wise words. Any yes, I have the owners manual on DVD (in fact, I have it twice because the older DVD's are compatible with XP but not W7, so I had to buy it again. No bad, I keep a copy in the laptop and a copy in the desktop :) )

OrangeSpyderMan

Get des hamil's book about webers and delorto's
I has very clear descriptions about how to setup a weber
Onno Könemann

I have it, and that's what got me this far, but try as I might I can't totally iron out the hesitation.

One other remark about the book is that it (like many weber books, I have a few...) don't consider the specifics of the DCOE 152, particularly that the idle adjustment screws are different and usually not set around 1.5 turns out with a reasonable idle jet, but somewhere closer to 2.5, and doesn't mention the venturi bypass at all.

At least not the edition I have, maybe there's an update.
OrangeSpyderMan

I do not know that exact type weber but how many progresion holes does it have?
I believe the book mentiones the type more preferable and the fact that the "wrong" type can give progression problems.
Onno Könemann

send your current spec and set up to Eurocarb, they will advise any changes by return. It worked for me and saved a rolling road session and a lot of trial and error. I cant remember the guys name but he claimed to have taught Des everything he knows!
S G Macfarlane

Hi,

The 152 is one of the recent spanish ones, with the 3 progression holes.

I'll contact Eurocarb and see what they advise - they've been very helpful in the past.

Thanks for taking the time,

OSM.
OrangeSpyderMan

The only drawback with just asking for help....we have Ike at Chatsworth Motorspares who gets so close with guesstimates it is uncanny....how do you know it has saved you a rolling road tune if you havent any hard numbers to compare?

People spout off ideal AFRs or %COs or whatever from the safety of 'armchair tuning', be wary, we find the best performance, whether cruise conditions or WOT vary considerably for best effect even from car to car, remembering mosr older cars are not factory clones anymore but individuals.The same obtains to igniton advance requirements, it will not come out of a book. Sadly( or good to my thinking) life is not Black and White but most wonderful multishades of Grey :)

38 mm chokes are up at competition size and will be biased for top end flow, the sidedraft does not run sweetly part throttle driving, you are also fighting the ubiquitous charge robbing of the A and B series. In practice the sidedrafts with chokes which allow the high rpm power to develop run like a crock of the old proverbial until 2500 rpm or so, add the effects of a hairy beastie cam and you will not have 'good manners' at low rpms. Put throttle bodies on if you really want to get the best advantage of weber type performance top end and su tameness at low rpms.

Advancing the low rpm advance helps but also disguises problems, make sure you dont have too much top end advance because of this and risk destroying pistons and head gaskets.

Peter

Peter
P Burgess

mgb bookbr>Yes - I know that it's going to be about guesstimates, and I'm still toying with taking it to the UK and putting it on a RR to "do it properly", but as I've said, that will mean a trip to the UK, and I don't really have time because of mundane things like having to work :(

I realise the 38mm are at the high end, and did wonder about going down to 36mm, and it even sounds like I'll probably not get it to be much better behaved than it is without a significant change, which doesn't surprise me that much. Part of my reluctance of going down choke size is that I suspect it'll mean starting the jetting all over again, and it's take me forever and a day to get it this good :( (I confess to having despaired on many an occasion, but it came with a Weber and when I price up moving back to SU, it does make me shudder somewhat...)

It's got quite a lot of advance, and it's running a 123/tune (that I bought from Peter at the end of last year when shipping was difficult because there was snow everywhere if that rings a bell - I'm guessing you don't ship many to FR :) ) that's been very useful in adding bottom end advance without going over 34
OrangeSpyderMan

I would be interested if you email me the advance curve files and whatever the max is you set it to(maybe curve different from reality)? We can fire them up and have a look. The trouble with changing chokes is, as you say, cost! We tend to use drill and solder so we can alter the jetting to suit.

Peter
P Burgess

Sticking my neck out here but if your jet choice for mixture on full throttle is correct would a pair of F15 or even F11 emulsion tubes be worth a try if you have some or can borrow some -- they should bring the mains in a tiddle earlier than your F16's and might just get rid of that little flat spot
Having said that I would have thought you would be on 175 - 180 mains with 38mm chokes

What do you think of that
Willy
William Revit

Now i have a related question.
Why do people always jump from 38 to 36 chokes?
Is 37 a best or worst of both worlds?
Or is 37 not available for a weber (it is for my new dellorto)
Onno Könemann

Or bore some 36s to 37s, not as good a venturi shape but still works well.

Peter
P Burgess

Hi,

I have a pair of F15's that I can try, and I'll send a copy of the curve that I'm using in the 123, Peter.

Another "armchair tuner" (to use Peter's excellent term) suggested F2's, which I have also and seem to recall having used but seemed much richer (too rich?). The carb is using MED dual cone which they say needs the jettings leaning off a bit from standard trumpets, but I'm uncertain how much difference that would actually make.

Thanks again for all the help and suggestions, and the one thing that does please me is all this fiddling around and all the good ideas I'm getting do help me understand how this carb works, though clearly I'm never going to put Des Hammil out of a job :/ .

OSM.
OrangeSpyderMan

If you have the money to buy a MED DCR system get to a RR!
Even in France they have racing cars running on 45's and roling roads to put them on.
Go to the nearest classic race meeting and ask around most wil be very happy to help
Onno Könemann

Mon Dieu Onno! " Męme le French",ŕ la guillotine avec toi ! :)

Peter
P Burgess

Off cours going to the UK is better an mostlikely will result in a perfect set up.
But France is not Mallorca ;)
Onno Könemann

Hi Onno,

Thanks for that advice :) I've spoken to many classic car afficionados here, and none can recommend a RR with weber know-how. One pointed me to a RR not too far away, but the guy said quite clearly that "he'd done it before" but had no jets/tubes etc and that hardly filled me with confidence. He wanted 200 € for a run on the RR and to start looking at the carb. Labour would then be charged on top of that. Makes even a DCR look cheap ;)

If you have any addresses to recommend (that are at least closer than driving it to St. Malo and then up the UK to Peter's shop :) ), I'm all ears.

OSM.
OrangeSpyderMan

Having looked at some of the work done by the PO's "specialist" garage on the car, and having tried to get any sort of expertise, at least around here, I have come to the conclusion that the French have a very different relationship with cars than I do.

Every RR I've spoken to, with one exception, only do ECU programming. That exception is over 800 kms away :/

I'm still toying with the Ferry + drive to the bacon sarnie shop up the road from Peter's RR. While I'm getting the sarnie I could drop in and see Peter.

Time is the deal breaker at the moment, though.
OrangeSpyderMan

I can recomend several RR's in the Netherlands but i do not know how far that is for you.
Though the prices are simulair to what you state from your RR.
I know one cheap one but have heard he does mostly full throttle work and is not concerned with part throttle work etc.

That is one of the reasons my next RR trip will be combined with a holiday in the UK.
The ferry is just €50,- and the hotel and other costs are not that crazy.
But indeed time!!
Onno Könemann

I've also just noticed that the route from Portsmouth to Alfreton will take me right past Abingdon.

My wife wanted a holiday in the sun, so I'll need some help convincing her what nice weather there is in Derbyshire :/
OrangeSpyderMan

"If you have any addresses to recommend (that are at least closer than driving it to St. Malo and then up the UK to Peter's shop" -
would help if you said where you are - France is quite large.
David Smith

Netherlands will be as far as Derbyshire - I'm about 70 kms from Le Mans, on the "wrong" side for going to the Netherlands.

As an aside, it staggered me that there is only one RR near Le Mans (or only one I can find) and he clearly stated "I don't do carbs because I don't know how to".

*sigh*
OrangeSpyderMan

Yes, David, realised that, sorry. In the middle of nowhere between Le Mans and Rennes.
OrangeSpyderMan

Thanks for sending the advance files, I reckon, if you are running the timing at 35 degrees measured at high revs it maybe too much with your tuned engine, do you know what sort of comp ratio you are running?

Peter
P Burgess

The calculated comp ratio is around 10.5:1 with that head. I haven't actually measured the chamber sizes to confirm, though, but that's what we aimed for.

I can always try and take it back to less advance (the Curve 1 I sent that I used for a while has 34° all in). I was also surprised that the curve looked quite "flat" and seemed to advance pretty quickly, but my "seat of the pants" scientific testing ;) seemed to feel OK with that.

Thanks a lot for taking the time to have a look and for the feedback.
OrangeSpyderMan

I think I would be looking around 30 max with the specs you have given. As much advance as you can get away with at low rpms. the beauty of the 123Tune is the starting point (cranking) seems to be zero so the engine spins over and starts easily.

Peter
P Burgess

I think you can get pretty close to a decent set up with a weber without too much problem so long as you are sensible about it.

Firstly the 38mm chokes are FAR FAR too big. This then means that depression (suction) in the carb is very limited so any jets you size up are hopelessly weak. The symptoms you describe endorse this assumption as they are classic symptoms of weak idle jets.

As Peter has suggested setting the timing advanced will ALWAYS make the idle better but this is just a mask and as many have said in the past setting the timing by ear at idle will always cause the overall timing to be too far advanced.

I would agree with Peter that probably 30 degrees max all in would be ample for your engine and 32 would make that a definate as it does the vast majority.

In my very humble opinion you should have the following

34mm chokes
140 mains
190 air corrector
F15 emulsion tubes
and 50/f9 idle

This will be a good starting point and can be tweeked from there. The price of bits is not too high so it is a cheap alternative to get you going.

It should be remembered that unless the car is accelerating hard or is travelling above 55MPH it will be running on the idle jets.

Robert (Bob) Midget Turbo

Firstly, I'd like to thank everyone for the feedback.

I'll certainly try taking the advance back to 30 or 32 all in. @ Bob, the 123/tune was part of my plan to avoid having overall advance too far; at least if it is now, it's my own fault :(

I must say, as Peter says, that the 123/tune is good for at least one thing and that is setting cranking speed advance to 0 or not very much... The bad thing about it, unless you visit Peter is that it opens up a bag of possibilities that I, at least, can't really make the most of... (hence this thread)

I realise now that the chokes are big, though for a 1330 I didn't think they were "FAR FAR" too big for enthusiastic road use. As I mentioned to Peter in a separate email I'm now on F2 tubes and 170 mains with 180 air correctors and it seems to have improved the issues.

My understanding of the spit back is either retarded timing (which I don't think it is, given the curves I'm running) or lean mixture, hence my change to bigger mains and F2 tubes.

Once again, I'm _very_ novice about all of this, and I'll happily admit having bitten off more than I can chew on this one (hence the post.. :/ ) so I am in no position to correct anyone at all. All the feedback has been useful, and perhaps at some point I'll change the chokes that were on the car to something more timid, but I'm a bit worried about the can of worms that will open and the cost and energy of getting something "bearable" again.


Thanks again everyone for the feedback.
OrangeSpyderMan

Just a quick update. I've now gone up to 175 mains and backed the overall advance off to 31 (Curve 1) or 32 (curve 2).

It feels a whole lot better, the part throttle behaviour is much nicer, and while it's certainly not scientific the plug colour looks much nicer after a good long drive (sunshine in abundance made that bit a positively pleasant experience, though my nose will be redder than usual tomorrow, I fear :*) ).

The change in advance also feels (again, seat of the pants, not science) much betterat the top end.

Thanks again to all who took the time. I'll leave it at this until such time I can get to a decent RR. I've also asked about RR's on one of the more active French mini forums, and drawn a blank, so I really do think that it'll have to be a trip to the UK.

OrangeSpyderMan

Bob, I'm glad you said that, as I was feeling a worried. My car will run on bigger chokes than 34, just not very well. Loads of top end, big hole at the bottom. I consider my car reasonably highly tuned, and it certainly is not slow. (1380cc, 11.1 comp, 1.5 roller rockers, 276 cam, big valve head, maniflow etc. etc. 15.5sec 1/4 mile). Even with the 34's, it is very sensitive to timing settings.
Shawn

This thread was discussed between 23/06/2011 and 07/07/2011

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