Hi guys,

I recently did a weber conversion on my 1.3 mk2 golf due to my pierburg being very thirsty. The DMTR i bought was used off ebay.

After i fitted it the idling was very poor going up and down, and the RPM was put up to about 1300 just to keep it running.

After around 20 miles of driving the idling got better so i lowered the RPM to 900. This was fine for the first half mile, then every time i dropped the clutch and slowed down the battery lights would come on and the car would cut out unless i quickly lifted the clutch. The car did cut out at every junction, and whenever i stopped. The idling has also gone back to the lumpy state it was in, revving up and down randomly.

I'm pretty sure this isnt carb icing because this happens even after 15 minutes of driving. My hot air feed pipe is fine, and i am using the standard circular airbox. The plastic "flange" was replaced when the carb was fitted, as well as its gaskets.

This did happen to my pierburg on the odd occation in the cold, but was never this bad. As a temporary fix to stop the car from cutting out i have got the car on a constant higher choke. This has not imiproved the lumpy idlinig though.

i would very much appreciate any advice as all this carburettor business is turing my hair grey and I'm only 17!

Kind regards

Rajan

Edited 20 March, 200818 yr by rajan_mk2

Check the mixture adjustment screw and any places where there could be an air leak. Also check the mechanism is giving the car a bit of throttle to idle but you probably already know this...

Cant just fit a carb from one car and expect it to work on another

Needs idle mixture adjsting and then idle speed

Idle jet might be blocked. It's only a small jet on the DMTR and can block easy. Be worth taking it out and giving it a clean.

Cant just fit a carb from one car and expect it to work on another

Needs idle mixture adjsting and then idle speed

Sorry i forgot to metion I got a full carb setup at a garage with an emissions test, they would have done this.

Thanks for the replys though guys, i really appreciate your help.

Idle jet might be blocked. It's only a small jet on the DMTR and can block easy. Be worth taking it out and giving it a clean.

Ill give that a try thanks mate!

Update:

I bought some carb cleaner today to check for any blockages in the carb but as i sprayed the cleaner around the exterior of the carb the revs started picking up - indicating a vaccumm leak. However i could not source the leak.

Can anyone suggest common places of leaks on these carbs, or a way to source the leak.

Thanks for the help guys, i really appreciate it.

Rajan

The rubber block underneath the carb which its bolted too

Whip the carb off and put some blue gasket sealant on the surfaces. Wait for the solvent to evaporate and then bolt it back down.

If there's still a problem it could be one of the pipes is disconnected or perished in the vacuum system.

take the jets out and clean them one by one...

did you use new vacuum hose?

Thanks for the replys guys i appreciate it.

I took the carb off today and inspected all the gaskets, vacuum hoses etc. I found the leak in the most inobvious place - one of the bolts holding it down to the manifold had a very poor and rusty thread which i replaced, i also cleaned the idle jet. The idling problem has now been fixed, but i took it back to the garage to get an emissions test done and the level was very unstable and kept changing.

The car also feels a bit less responsive and has the odd "flat spot" where theres no power. Does anyone have any suggestions on what it could be??

Thanks for the help,

Rajan

There is a small screw inset into the carb at the very bottom in-most (nearest the the bulkhead) corner of the carb, approaching from the passenger side. It's not visible whilst the carb is on the car - This is the idle mixture screw, different to the spring-loaded idle speed screw at the back of the carb.

Get a small screwdriver in there and turn clockwise - if no change occurs whilst turning the screw, it's been set way too rich. Continue turning clockwise until the engine starts to slow down - when this happens, stop and back out about a quarter or half a turn. If it's what I think it is, follow those instructions to know for sure.

I think - Before now, you were experiencing an air leak and the carb was running lean. Now that it's been fixed, the carb is running way too rich and causes the dodgy emissions and flat spot (hesitation) you describe.

another way to know that the mixture is somewhere near...turn the screw in until it stops then out 1 ,1/2 turns ...that should be close enough to run ok

dont be affraid to mess with it...they're very easy to play with

the idle speed will need re setting after any ajustments

Thanks for the replys guys -

As for adjusting the idle mixture i will give it a try when it stops raining. Also when starting the car its a bit hesitant and takes a couple of seconds as well as quite a bit of throttle as if the engine is flooded. Is this another symptom of a rich idle mixture?

it should start up cleanly into a fast idle, you should then push the choke knob in so that you just have a fast idle

have you used a manual choke before? maybe you are leaving the handle out too long

nah I'm not flooding the carb steve . I try to use the choke as little as possible - only on cold mornings. Just takes a while to start thats all..

hmm doesnt sound right

are you pulling the choke right out for the start up? i use full choke and no pedal for the cold starts

i dont pull the choke right out on cold mornings unless i have to. Thats probably it...

yeah pull it fully out on all cold starts(thats cold engine not just cold days) ...if it runs wayyy to fast on choke theres a fast idle ajustment screw

Yeah it does run very fast when the choke is fully out. Wheres the fast idle adjustment screw then?

Yeah it does run very fast when the choke is fully out. Wheres the fast idle adjustment screw then?

The idle speed screw protudes from the carb body at 90 degrees

to the idle mixture screw at the back of the carb.

It has a hex head with a slot and a spring around it.

The fast idle adjustment requires demounting the DMTR and inverting it

to set a 1.25mm gap for the throttle plate by adjusting a bolt that goes through a lever.

See

Figure 6, page 247 of this document 'Lancia Y10 turbo Weber DMTR'

All Lancia carbs 1972-1990 PDF including DMTR

Or it may be your float valve is not closing or float height is too high giving a too rich mixture.

Nice one I've bookmarked this thread from a while back, glad it's being kept alive. That Lancia link is great.

Cheers.

Your avatar... What's a DTMR ?

DTMR,It's a limited edition carb from a Hillman Imp special edition sub 6 sec. Drag car.

Actually no ,It's been like that for ages never even noticed. It should read DMTR lol.

Corrected now cheers.

I've always read it DTMR/L anyway, sounds like it should be...