Trying out a 34 DMTL with 24/25 venturis. It's got a label saying Weber 11702 124 4.

No idea what it's off. But importantly for me the accelerator cable pulls from bulkhead on the battery side of the carb. I have had a reverse mounted DMTR with 22/22 venturis from a Golf 1.3 since 2006 with a re-routed cable that was too close to the heater resistor.

The float hinge is meant to face direction of travel.

Unlike my DMTR there's only one vacuum port - and it's air filter side of the throttle plates.

So I guess this is for the hot air flap. Can anyone confirm that?

I've tapped a hole in the alu base mounting plate and fitted a 6mm stainless caliper bleed screw as manifold side vacuum port. This I'll connect to my Bosch Dignition manifold pressure sensor (MAP).

I've also fitted the carb to the rubber base mount using a bakelite carb-spacer and thick cork giving 5cm from inlet manifold to bottom of carb. This lengthens the inlet tract and insulates from engine heat.

new toy

manifold tap

Unlike my DMTR there's only one vacuum port - and it's air filter side of the throttle plates.

So I guess this is for the hot air flap. Can anyone confirm that?

No you are wrong.

No I am wrong.

Vacuum advance port has to be atmosphere side of the throttle plates.

Hot air flap vacuum should be engine side.

Mix them up and you're heading for 45 degrees ignition advance when take foot off the loud pedal -> possible detonation.

And the DMTL does have three ports.

1. on the front above secondary plate.
2. on front but higher for the choke pulldown UFO unit.
3. in the side opposite choke at the very bottom near front corner.

.

But number 3 had lost its 4mm brass pipe and my huge cork gaskets seem to have blocked it up.

Oh well, can always use the caliper bleed tap for a vacuum guage or boost reference .

How is it driving with the DMTL? I preferred it on mine. It seemed to be more economical, Mine had an extra pull down unit on it over the DMTR for part throttle economy; That Y shaped thing in the 2nd pic was absent from my DMTR. Landrover Haynes describes it as a 'power valve'

Not got around to fitting it yet.

Yeah, the Y shaped thing with three screws - as I understand it the full power valve that operates at low vacuum (W.O.T) means the main jets can be smaller.

http://dimequarterly.tierranet.com/article...ning_guide.html

More about the power jet in Hypojam's DMTL pic

photobucket clicky

I fitted a brass pipe to carb body for manifold vacuum. It should be 5mm outer diameter.

The modelling shop only had imperial brass tube (from Chicago, Illinois :rollseyes: ) and no 15/64 inch, so I used 3/16 inch and expanded it around a punch and used some PTFE tape. Attached a bike pump and no air would blow though it...

I've now cut away some cork from my thick cork gaskets for all the small satellite vents of the venturis and blowing through the new tube air does flow, so I can now get manifold vacuum from two places. The other ports will let power valve and full throttle enrichment operate.

Fitted this finally in time for the Polo show.

Did n't even bother setting the idle right as it sounded sweet.

It died half a mile from home as one jubilee clip was leaking fuel from the swirl pot.

Sorted that. No real issues driving to show.

Second stage pulls really well from 4,000rpm to 6,500-ish.

Vacuum gauge said -20psi upstream of throttle plate at the show (and snapping throttle closed went to -25psi so all healthy).

http://classicinlines.com/Vacuum.asp

Forgot the spark plug spanner and had too much beer to safely borrow one.

Was not quite as smooth driving back.

I checked the idle mixture with the Colortune once home.

Idle was slightly rich. Set it to bunsen blue. About 1 turn in.

But spark plugs were a bit white not tan, so upped the primary main to 105.

Idle had risen a bit and now at cruise there's some surging.

Suspecting the PTFE tape around the vacuum port causing an air leak. I had disturbed this at the show

using the guage

I'm running

Primary 50/105/F33/185

Secondary 70/127/F33/220

Edited 10 July, 201214 yr by dvderlm

The surging was not an airleak from the PTFE tape as spraying carb cleaner and even cold start spray

made no change to engine note.

The surging problem was because the primary main was too lean.

Plugs were still white with 105 main.

Car drove better above 2000rpm with choke on slightly.

I had exposed the problem by correctly setting the mixture for lean best idle

(everything overlaps).

Tried a 125 main and all is amazingly good.

Well not checked fuel consumption yet.

I had thought/hoped that moving to 105 main with 185 air corrector would be enough

to compensate for the reduced airspeed of a 24mm venturi versus

a 22mm venturi (where I used 100 main and 220 air).

That was based on a Fiat 127 Sport but I had not realised the jet sizes

were for the Mk1 1040cc version with only 22mm primary venturi.

My mistake, should have based it on the Fiat 127 1300cc Sport.

I'm still running a DMTL on my ABD engine, I will compare jets when I get some time tomorrow. Good write up though!

Perhaps I should have done a mini-build thread.

In the FAQ you had this for your ABD

http://www.clubpolo.co.uk/forum/index.php?...t&p=1318574

So I should be able to reduce the mains.

Sure I had a 117 main jet somewhere but I cannot find it.

I'd be interested to hear your comparison between running the DMTL over the DMTR.. To me I feel in some situations the DMTL lacks road drivability. On full chat acceleration it just feels like you have all the power in the universe.. but then it struggles to pull away at 70mph in a high gear.. just a bit frustrating really. I'm wondering wether the DMTR would be smoother at lower rpm.. well it should be, shouldn't it?

I think DMTL beats the DMTR just (but I do have a less restrictive air intake and 2inches more heat isolating plenum and electric fuel pump and a new coil and a vacuum guage).

Better economy (by 7% if I measured right):

DMTR Usually happy with 48.3mpg.

DMTL Did 51.7mpg this week (warm weather with less traffic yet more fast motorway).

About the same top end (but my exhaust is restricted for noise reasons):

DMTL Plant my foot at 70 on the speedo in fifth, revs climb from 2600 and keep going.

(not exceeded 3000 in 5th yet).

DMTR Plant my foot at 70 in 5th, revs rise with gusto, especially once over 4000

0 to 30mph in 1st/2nd:

DMTL doesn't really pickup until 2500rpm. It moves but it just feels noisy.

DMTR could spin its wheels at launch or gear change.

Need to compare the off the lights acceleration to a mate's scooby or a Toyota Auris HybridSynergyDrive which I think is same rated bhp per tonne but with electric assist sport mode.

Edited 22 August, 201214 yr by dvderlm

Been driving paying attention to my vacuum gauge for the past 500 miles.

The power band has moved up the revs with larger venturis, so when not in a hurry I've been delaying changing up a gear until 3000rpm or so, rather than 2500rpm-ish that I used to do with the DMTR.

This keeps the vacuum up around 18" of Hg.

It's paid off.

DMTR I was happy with 48mpg.

Previous best with DMTL: 51.7mpg

Since last fill up (461 miles in 40 litres) 52.7mpg.

I have not been doing as much motorway miles, but I'm quite shocked by that improvement.

Was my custom DMTR jetting so bad?

Maybe not, John Passini says

"On a Mini 850 with manifold heating that is no more than a gesture, the venturis for a 28/36 DCD are 21 and 23, while with a well heated manifold they are 23 and 25 giving better top end and better economy at the same time."

(edited from original 54.5mpg claimbecause I had forgotten about tyre size - which I had allowed for when I calculated 51.7).

Edited 12 September, 201214 yr by dvderlm

A quick queary,

So the line for the vacuum advance needs to be from the atmospheric side of the throttle plates?

A quick queary,

So the line for the vacuum advance needs to be from the atmospheric side of the throttle plates?

Yes, that is best.

Will work either side but I'm sure I've posted a good link of the choices and reasons before.

Here

http://www.clubpolo.co.uk/forum/index.php?...t&p=2372756

Edited 13 September, 201214 yr by dvderlm

QUOTE (dvderlm @ Wednesday 22nd August 2012 - 11:53pm) <{POST_SNAPBACK}>

0 to 30mph in 1st/2nd:
DMTL doesn't really pickup until 2500rpm. It moves but it just feels noisy.
DMTR could spin its wheels at launch or gear change.

Solved that nearly. Reset the idle for maximum vacuum with engine really warm and then turned in the mixture screw 1/5th turn which is about 1/3rd inch of Hg.
But then I found I could not get idle revs below 1100 rpm with speed screw.

Went down from 50 to 45 idle and changed nothing. Revs at rock steady 900.

It now zooms up to 3000rpm sounding much crisper, not quite as aggressive as the DMTR.
I think the DMTl economizer/power jet is also en-richening the mixture.

Need to look with the good ol' colortune.

Oh yeah, my pump jet is 45 - I thought it was 40.

Edited 22 May, 201412 yr by dvderlm

It now zooms up to 3000rpm sounding much crisper, not quite as aggressive as the DMTR.

Last fuel economy measurement a little disappointing

Dropped to

328 miles in 31.6 litres = 47.2mpg.

Maybe the smaller 45 idle and lean best idle mixture set for nearly max vacuum means I'm on the 112 main jet sooner. But, I've been driving an extra mile to work and queues have been quite bad coinciding with end of school holidays.

Also, and this is more likely the reason, been trying out a 150 secondary main, because 127 sec main I got dreadful power loss after hard acceleration at 50 to 70mph range, so hills and empty roads have been very heavy right foot territory to try to provoke it again.

This power loss might be the cold air feed upsetting the carb operation.

Mght be fuel starvation at tank/pump/swirl pot/pipes.

So you'd expect a bigger secondary to make that WORSE.

It hasn't...

Maybe it's high speed lean.

So current jetting is

45/112/F33/185

70/150/F33/210

45 pump

Need to get the tank nearly empty and try again.

Over a year since first fitting.

It managed 76.1 bhp on the rolling road in Jan.

45/112/F33/230

70/150/F33/195

Could be more but exhaust is restrictive for noise reasons and that secondary is too rich, but was worth the play.

So now I'm on

45/112/F33/230

70/120/F33/195

Still seems to pull very well.

I've been driving carefully for over 1000 miles.

And logging the fuel purchases.

I'm pleased. It's definitely adequate for a distributing manifold single carb.

Edited 25 June, 201313 yr by dvderlm

Another rolling road (at the Polo show) and slightly different jets.

45/112/F33/230

70/135/F33/220

produced 80.6bhp (and 93.0 lb.ft of torque at 3900rpm)

Which is a hefty gain from 76.1bhp (and only 75.4 lb.ft of torque at 4190rpm) at Aldon with the 150 main.

Well different rolling road - different day?

(For comparison old DMTR on the Polo Show RR was 73.6bhp and 85.5 lb.ft of torque at 3700rpm

Is that optimistic torque given 1984 GK spec with the 22/26 Pierburg ?)

The really interesting thing was the AFR graph.

It was around 13.2 to 13.4 upto 5000rpm then heading near 16 at 5800rpm.

Discussion with the operators suggested reducing the main to try to get 12.8 at W.O.T acceleration (well, duh)

and reducing the air corrector as it was running out of oomph due to high speed lean-out.

So I went down down down with air correctors. All the way to only 145 air in the secondary.

And it made no noticeable difference. Above 5300rpm (in 2nd up a hill I know well, or joining a motorway with a long acceleration lane sometimes) it would still not have that high rev punch the old DMTR had.

Yet, oddly, from standstill in first gear it would easily do 900 to 6800rpm and hit the limiter.

Huh, the engine does not know what gear I am in!

So perhaps it is not too much air, it is too little fuel.

Despite a bigger main jet.

And unrelated to amount of fuel in tank.

I had a theory that the pump to swirlpot vapour separator flow, was preferring to let petrol back down the 6mm return pipe to the tank than into the float bowl through a 1.5mm needle valve.

So I clamped the return line. I have an electronic self-regulating pump, it turns off when no demand.

That seems to have sorted it.

I've now replaced the temporary clamp with a one way valve -fuel cannot return to the tank.

I was worried there's nothing to remove bubbles, but the carb's float bowl will do the same as the swirl pot.

I reckon the lines are always pressurised now.

Have I just changed the shape of the curve and kept the same area on the graph?

Time will tell.

(still sipping fuel too...)

Edited 29 August, 201313 yr by dvderlm

My dmtl has a vacuum pipe on the back of the carb as well as the front... its a 32/34 but reading previous comments, i'm a bit worried about having too much advance! is this the right pipe to have it on? the vacuum is pretty weak when it's idling (put my finger over the end)

Advance should be on higher of the two pipes.

http://www.clubpolo.co.uk/forum/index.php?showtopic=290280#entry2372756

Lower pipe is constant vacuum to operate things like the hot air flap for exhaust warmed inlet air.

"operators suggested reducing the main to try to get 12.8 at W.O.T acceleration (well, duh)"

No, not well duh. 13.2:1 is leaner than 12.8:1 AFR. That means a richer than 135 secondary main.

Bit surprising as 1.8 golf are specced 127 main jet by Weber replacement kit and tuned to 140 main.

Need to mend my AFR gauge to find out - or another RR session.