haven't posted in here for a while..

Recently I've been trying to squeeze the mpg as most of us are these days.

I'm interested to know how fellow DMTL owners are driving. As in driving style. Is there any good change up rpm? Or is it a case of just be as gentle as possible?

I have G40 transmission. So I hit 2000 rpm in 2nd at 26mph ish and 2000 in 3rd at 34 ish. I'm aware it goes on the main circuit at around 1800rpm.

Perhaps people have ideas?

Only just saw this.

Top of the spritmonitor Polos from 1982 to 1990 (though with suspiciously few fuelling entries) has a driving style where he turns off the engine when coasting (Hypermiling FAS), accelerates only with foot to the floor in 2nd, then changes to 5th.

This being a German 54PS car it will very likely have the standard Pierburg 2e3!

I cannot condone coasting, because there is no engine braking and Polo brakes are rubbish enough already.

I use a vacuum gauge to tell me when to change, and to remind me to take my foot off the loud pedal.

I use an 8P gearbox (like the close ratio 4 speed GX) with an extra 0.74 5th.

I get max vacuum from 2200 to 3000+rpm, so I try to use that power band, Above that the thirsty DMTL 2nd stage is usually kicking in. When I tried to drive gently my economy was often worse ... I think because I was often in too high a gear to re-accelerate efficiently

(low vacuum).

right then boys and girls. I have read the whole topic but i seem to have an interesting dilemma...

I have the 32/34 dmtl from a larger engined golf on my mk2 mh engine. kept the hedgehog intact and working and has the standard inlet manifold and standard airbox (the elbow bit at the end of the airbox has been removed to get a little bit more air in).

my jets are the standard configuration as follows:

primary idle - 45

primary air- 155

emulsion tube - F22

main jet - 100

secondary air - 185

emulsion tube - F30

main jet - 115

secondary idle - 70

my dilemma is that it runs awesome! It pulls a lot harder than the car ever has and i'm not really getting bad economy even though i often redline it :) or maybe I'm not noticing it but it's not a problem for me.

In theory this should be way too rich right? If i put the choke on all the way i get massive amounts of black smoke out the back but it hasn't needed the choke more than half way before. its easier to start from cold and hot than the pierburg. It doesnt bog down when i accelerate from mid range like some have mentioned but it is a bit slow on the uptake (which I'm not bothered about, i just roll on evenly or keep the revs up high). my only real concern is that this could be way too rich and that i might end up destroying the cylinder walls. so my question is... With this setup could i be causing damage to my engine? does anyone else get black smoke (I'm talking solid black here not just a bit grey) with the choke on full?

any help would be greatly appreciated

"In theory this should be way too rich right?"

It depends on the air flow and fuel supply. You need to get an AFR meter on it, preferably a wideband lambda.

I'm using 112 main primary and 135 secondary and thin(=richer) emulsion tubes.

But larger air correctors than anyone else I know.

Polo show rolling road printout showed 13.5:1 (ish) AFR at hard acceleration and the guys reckoned the main jet could go bigger to aim for 12.6:1 and smaller air correctors. In fact - crucial for me was ensuring petrol went into the carb rather than returning to the fuel tank.

"I'm talking solid black here not just a bit grey with the choke on full?"

Well yes, there's hardly any air in primary barrel so it just sucks petrol.

What you need to do is measure the time from point A to point B on a quiet road both directions a few times,

then repeat with choke on a little. Is the time better or worse?

"With this setup could i be causing damage to my engine?"

No, does not look extremely rich enough to cause bore wash.

(In fact it looks standard so will be fine for standard filter inlet etc) Do the spark plug ceramic noses look sooty at all?

Edited 1 December, 201312 yr by dvderlm

"In theory this should be way too rich right?"

It depends on the air flow and fuel supply. You need to get an AFR meter on it, preferably a wideband lambda.

I'm using 112 main primary and 135 secondary and thin(=richer) emulsion tubes.

But larger air correctors than anyone else I know.

Polo show rolling road printout showed 13.5:1 (ish) AFR at hard acceleration and the guys reckoned the main jet could go bigger to aim for 12.6:1 and smaller air correctors. In fact - crucial for me was ensuring petrol went into the carb rather than returning to the fuel tank.

"I'm talking solid black here not just a bit grey with the choke on full?"

Well yes, there's hardly any air in primary barrel so it just sucks petrol.

What you need to do is measure the time from point A to point B on a quiet road both directions a few times,

then repeat with choke on a little. Is the time better or worse?

"With this setup could i be causing damage to my engine?"

No, does not look extremely rich enough to cause bore wash.

(In fact it looks standard so will be fine for standard filter inlet etc) Do the spark plug ceramic noses look sooty at all?

Thank you very much. Exactly what I wanted to hear :). I will investigate the spark plugs and report back. It seems to run fine and you have put my fears to rest so I am happy to keep it as is... Thanks again for your help

Btw guys before I sold my DMTL (sadly!), I ended up with 115, 120 with standard air correctors etc. The 115 was a bit richer than it needed to be and the 120 was a bit leaner.

Worked very well.

With F30 emulsions?

My 34DMTR with 25/26 venturis is currently running

40/107/F33/230
70/140/F33/220

50 pump

about 7.5mm float height.

I went down on the primary from 48 idle and 112 main, because my old Pierburg only had 37.5 idle and still feels okay (my high compression and squish GK engine likes lean).

oh you didn't get on with the DMTL too well then?

yes F30s

Ran really well, but I think the DMTL was always going to be a slight compromise due to the relatively small capacity engine.

All said and done I would definitely recommend my DMTL days to anyone else. Probably used it for 2 years or so. No problems ever (bought from new).

The richer 115 was to smooth out town driving on the 1st choke. The 120 secondary was because when I belted it it didn't seem to make much difference raising to 125.

oh you didn't get on with the DMTL too well then?

Love the DMTL but the Lancia 34DMTR was a bargain.

Passini reckons a larger carb can use less fuel and have better top end - so long as you have a well heated manifold; I think theory is you drive on the larger primary stage for longer so air velocity is less. Hard part is avoiding a 2nd stage stumble - and using the loud pedal. It's been using about the same fuel until recently needing to use the choke as it has been sticking partly on due to a frayed cable.

34,34? hmm.

I think the problem with my first stage was that the pump jet I had from new was misshapen/ broken. It sprayed horizontally rather than downwards.

Pump jet needs to spray down the inlet manifold into the air stream.

Porsche IDA-3C tuners are careful to select the right pump jet length to match choke size to avoid spraying onto the inner venturi wall

http://www.performanceoriented.com/technical.htm#AccelPumph

But I don't know of any variations that fit except standard DMTL/R part 76407 (or 76413 from the IBF) and both point vertically down.

Maybe yours was a 76402 for new style 48 IDA or a 34 ICT. These look to have no small spout, just a diagonal slash ending.

Edited 30 December, 201411 yr by dvderlm

must have been a faulty/ broken item therefore. Bad luck really as I have a history of stumbly cars :(

Hey ho, to the future :)

Hi guys,

I know this sounds a bit odd.. But I'm seriously considering putting a DMTL or something like it on my AVY (1.6 16v) conversion when I get round to it.

Simplicity is key for a fun car I think, and the DMTL really fits the bill.

thoughts?

my thoughts are vw spent alot getting that injection system just right and working fine for cold starts and all that , i would take that bit of extra effort and make it all work as intended

the reason I consider you see is that originally I was going for the injection, then people told me you can get 140 with bike carbs.. but all the RR curves I've seen from these people is about 125.. which is standard.

I think I should just try to make the standard setup work perhaps.. although that will require lift pump etc.

yeah well id put everyday reliability and fuel economy above a few hp , can keep all the diagnostics and stuff then

Personally, I got better fuel economy with the weber than I did with both injection and the pierburg! And it's the only system that hasn't let me down so far.

As far as I can see the only thing wrong with carbs is emissions.. and even then the 2e3 was on par with spi systems of it's day iirc.

To me they sound better, drive more 'analogue'/smoother (being mechanical).

I'm perfectly satisfied with 125bhp.. more than enough for the car. No point faffing around with bike carbs I think. Of all the options the weber is actually looking the most attractive right now, because of ease/ simplicity.

Let me know if I'm off my rocker! ha