Hi guys, I posted this in the FAQ a few days ago but had no reply so might have been the wrong section.

I recently fitted a weber dmtr to m standard 1.3 2G engine with the following jet set up.

............Primary...........Secondary

Idle Jet ......45.................. 70

air jet ........155................ 185

Emulsion ....f-22 ................f-30

Main jet ......115 ................120

My problems from the start are, the car can sometimes be a bit difficult to start but other times will fire up fine. Sometimes the car will cut out when sat idle at a junction, usually not long after starting the car. Might I have the choke cable set up wrong ?

The other problem is on half throttle the car accelerates excellently but on full throttle the acceleration backs off and bogs down.

Also there is often quite a strong smell of fuel around my car when i park up in drive, possible over fueling problems ? could that be linked to the bogging down ?

Any help would be appreciated.

Cheers.

Do you know if the float height settings have been calibrated properly?

Have you got any spare jets?

Not sure what float height settings are or how to set them up. I was hoping the carb would be an easy-ish swap just needing the mixture and idle setting looks like i was wrong lol.

Not sure if it makes any difference but the cabr is second hand form the same enigne ( i know no two set-ups are the same )

I dont have any spare jets but could buy sum they're only a couple of quid each but i just don't know where to start.

"Starting sometimes hard."

Spark plugs and leads and rotor and coil and ugnition amp all tickety-boo?

When? cold engine, hot engine.

"Cutting out."

Once you've started it with full choke -push it in untiil youi reach 1100 rpm. Gradulally push it further in as you drivea need engine warms.

Or push it all the way in and be prepared to pull the choke on again when approaching junctions while still cold.

You can use a colortune or a vacuum guage to get idle mixture and speed exactly right.

The idle jet is misnamed - it is called 'slow running jet' in italian and is the hard working jet used for most driving upto about 2250rpm

(if you don't believe me take out the main jet and go for a gentle drive somewhere quiet). It's correct setup is vital.

Search for redline lean best idle method.

"but on full throttle the acceleration backs off and bogs down"

At what RPM?

I assume it is a secondary stage lean stumble. Does it go better with the choke pulled on when you do that. That richens the primary stage.

If so - I fixed that with 50 idle and 50 pump jet.

If not its a rich bog, could be too big main jait or float too high.

Plug leads and distrubutor Cap have all been replaced.

It's a bit difficult for me to set it up as i don't have a rev count so doing it all by ear.

I have followed the redline lean best idle method to set it up originally to get it all up and runing.

I couldn't tell you what rpm the bog is at but it does feel through the throttle to be on the second stage.

I think i am going to try a 50 idle jet to try solve the cutting out issue but I am confused as to where i would find the pump jet to check its size and possibly alter it ? and also how to alter the float height settings ?

Not sure if you guys do but i have been told to run an inline fuel filter after the pump but before the carb to allow a smoother fuel flow, is this correct ?

unfortunately this is the first carburettor i have tried to set up and tune it, but i need to learn somehow and theres simply no garages or anyone i know to ask around me so your help is much appreciated !

Setting up by ear is fine with redline's method. You only have to be certain you are not running on the priogression holes (so primary plate just barely touching the wall of the tube keeps them covered). But you can't tell whether you've got the idle at 750 too little or 1000 rpm too much. Might just need a tad more on the idle speed screw to stop the stall at junctions when warm. Idle speed should be 800 to 950 rpm really.

(I once passed an MOT with the car idling at only 200rpm thanks to a partially blocked idle jet - they fixed that for free to drive it to the brake rollers...)

With warm engine will it just about pull the car along in first gear on a flat road with no touching the accelerator pedal once moving?

I switched to 50 idle when I started using F-30 emulsion tube in the primary, so lack of seconadry oomph might be something else. F-22 tube normally has very good pick up.

Swapping pump jet involves taking the top of the carb off. Six bolts in top of carb, plus you have to undo the pull down unit (brass UFO) (two bolts one tiony circlip) and the choke flap operating lever. Once topless you can check the float height.

Pump jet is part 18 in the exploded diagram in this thread from the vaults with pics of float too.

http://www.clubpolo.co.uk/forum/index.php?...t&p=1664804

Edited 20 September, 201213 yr by dvderlm

Have you done the "use choke" experiment yet?

I have an idea that might explain poor starting and full throttle bog.

You are running too rich at full chat and soot fouling the plugs with the combined primary and secondary stage.

The 22/22 venturis of the DMTR have a very high air speed compared to the 24/25 of the DMTL.

That high air speed gives a strong bernoulli effect and pulls lots of fuel and causes good atomisation. But if it's too much fuel to air ratio not all of it will burn leaving carbon on the piston top and plug contacts. Drive hard and it builds up making the spark weaker so you lose power. Ease off to the primary stage and the carbon is burnt off the contacts.

You could try looking at a plug after you get the bog symptom, but it has to be straight after, cut the engine and coast to a stop safely. It (plug cut tuning) is a very inexact science and a rolling road session or wideband lambda AFR gauge is the modern substitute.

I recommend increasing the secondary air corrector which takes effect over 4000rpm-ish to 200 to combat full throttle over-richness

See whether that helps.

If it does then I suggest you lean out the mixture more. I'd reduce the primary main jet to 100 or 105 and if that feels a bit lame up the idle jet to 50.

I've put the jets as standard for an 84bhp 1.3 Lancia beta on here somewhere. It's got a better engine than your Polo, but gets that power from a 22/22 DATR with large air correctors.

(Same as DMTR but auto-choke, not manual choke)

Sadly I have still not found which emulsion tubes it used.

Edited 22 September, 201213 yr by dvderlm

Thats pretty much what i was considering doing just didn't know what sizes to start at. I'll try 190 to 205 air jets in the secondary. I was also going to change to a 50 primary idle and hadn't considered changing the primary to a slightly smaller main but i will order it all up next week ( cars currenty off the road so no point ordering it all nw) and i will report back to let you know how its all going !!

Thanks for the advice really didn't know where to start ! but hopefully, once back on the road, ill be able to get somewhere with your suggestions and ill report back !

Cheers for the help !