Alright.

A week ago, I was driving and my car starts misfiring and cuts out. When the key was turned it would start up and idle perfectly for 4 or 5 seconds then die. This was with a Pierburg 2E3 carburettor.

The mechanic told me that it was probably a problem with the carburettor, so I went ahead and bought a new Weber carb with the adapter kit for this car. I had been planning to do this anyway so I thought now would be a good time to go ahead and do it.

Having installed the Weber carb and fixed one air leak at the base, the engine with the choke in and cold starts up, goes to 1,200 for a second, then drops to 800, then dies. With the choke out (choke flap set to close off the barrel), it starts, goes to 800, then dies.

I have tried putting a silicon based spray lubricant around the bottom of the carb, around the rubber mount and the gasket from the outside as it sits on the engine. I know the pump is working because I have seen it pump fuel into a bottle when the fuel line to the carb was disconnected and the engine was turning on the starter motor.

Giving it some on the accelerator seems to work, the car revs up OK.

I've totally ran out of things to try, at the moment I can't even get it to a garage.

Any help would be greatly appreciated.

Edited 27 October, 200916 yr by anessen

get someone to start it with the airfilter on ... and lean on the airfilter (push the carb down on the manilfold) if the seal is gone it should idle when you do this... even if only just.... if not you have some other issue.

*does it have fuel in the filter once it has cut out? if not check the fuel lines from the tank... its quite possible you have dragged up some gunk.,,, (this happens alot if you run the tank low)

*check compression < could be any number of underlying faults... i.e cracked or warped head or dropped/cracked valve

*run it till it cuts out.... try and restart it... if it doesnt go pull the coil (king) lead off at the dizzy and get someone to turn it over.... while holding (with thick gloves on) the lead approx a cm from for example a rocker cover bolt... you should get a fat blue spark... if not check ignition wiring for faults... control mods have be known to fail in the same manner as condensors on earlier cars.

maybe the mixture is way off? should be 1.5 turns out as a rough setting (i think) should be some set up papers with the carb

its a basic carb realy...cant be much wrong

will it stay running if you rev it ? might be worth seeing if you can warm it up and ajust the settings

Check the rubber tube that connects to the brass UFO thingy. This is the choke pull down diaphragm. When the engine fires it has to pull the closed tight choke flap slightly open. It can't do that if there's a leak in that tube. I reckon the brass UFO thingies themselves are indestructible unless some cackhanded idiot forced the carb apart.

If not that sounds like blocked idle jet or idle circuit (so long as the needle float valve isn't sticking closed which requires removing top half of carb from bottom half and much faffery to make both floats not rub on the walls).

But it's a Weber -they're so much better for working on than Pierberg's - remove air cover - unscrew the idle jet, pull it from the holder and see if you can see light through it. They're only about 0.4 mm so block easily. Clean it by blowing through it.

To clean the idle circuit you can unscrew the idle mixture screw and pull it out then blow compressed air in (I use a computer keyboard cleaner spray and some windscreen washer tube) . It should bubble in the wells of the jets. If it doesn't bubble there's no fuel in there.

Is the intake filter in the carb clean (large brass screw below feed pipe entry gives access to plastic gauze tube)?

Good luck

(but why did the Pierberg die? Split rubber or electrical failure ? Or rust from the tank?)

Thanks for the advice, I'll get on it tomorrow. Today I did get a chance to put the air box on, and when it was all buttoned up and warm it hunted between 800 and 1000 with the choke out. With the airbox off it's totally useless. So it's running too lean?

OK I fiddled with the idle mixture and the idle speed adjust. I now have the engine idling at 1,000 RPM with the choke flap closed and 800 RPM with it open on a hot engine.

I took it out for a drive and this is what I found.

Choke flap closed, hot engine: Misfiring below 2,000 RPM, no power above 3,500-4,000 RPM

Choke flap open, hot engine: Misfiring at any engine speed, but seems to improve at higher RPM.

Also very high fuel consumption.

OK so the garage had a fiddle with it.

It has a really bad flat spot at low throttle, say in the first 1/4. The engine misfires and stalls, give it a tad more throttle and it takes off like a rocket. Idling is fine.

Focusing on this, what could cause that flat spot? What is actually going on in the carb when it transitions from idle to partial throttle?

Edited 27 October, 200916 yr by anessen

Are you certain you haven't achieved that idle by uncovering progression holes with a too large throttle plate opening, masking that the idle/low-speed circuit is blocked?

Did you check the idle jet?

Did you blow thtough the idle circuit?

At transition fuel is sucked up through the primary jet as well as the idle jet and out to the venturi, to cope with the gap in fuel delivery under vacuum the accelerator pump jet squirts fuel into the throat driven by a cam off the throttle.

Might be this pump jet is blocked or split pump diaphragm or bent or worn pump lever.

There's a ball bearing in the accelerator pump jet. You should here it rattle if you pull out that jet and shake it gently.

Or the primary jet is blocked.

Or your primary jet is too big or your idle too small.

you have the correct jets on your carb yes???

did the garage adjust it the misture???

if not try this

let the car idle and adjust the idle to about where you want it. next move onto the misture screw.from your basic settings 1.5 turn out.start working half a turn at a time. undo it and listen to a engine speed increase. it would be very slight but will be noticed if thats was your listening for..undo it another half a turn and listen for another increase and carry on..once the engine speed will increase no more.wind it in half a turn and check the idle speed drops. then out that half a turn agen.

basically you want to achieve the highest amount of revs but adjusting the misture screw out.but at the point where if you wind it back in slightly the revs drop.

then adjust you idle to suit.

you may find that you might he to do this a few times to get it perfect.

thats if its you carb which is the problem...:/

good luck

and make sure your plugs are ok. could be possible that the mixture was so poor it coked uo you plugs. doubt it but worth checking..clean tem with a wire brush then poor abit of petrol on the metal part and light emm.

The garage basically just blew through the carb, cleaned the jets and left it at that. At least they didn't charge me.

Today I checked for a vacuum leak at the base of the carb by spraying Easy Start at the rubber block. The engine revs increased slightly when I did this. So I removed the carb from the rubber block, cleaned off the surfaces and to make sure I put a bit of silicon gasket sealer on parts of the rubber block where it was looking a little tired. I put everything on nice and tight again and fired it up.

It is better than it was with the flat spot but it's still doing it. There is now a high pitched whistling noise coming from the base of the carb (I assume).

I tried spraying Easy Start around the base again, it didn't do anything this time. Spraying it down the carb venturi makes the revs drop.

Also, adjusting the idle mixture, when it's wound nearly full in, the engine dies . But, I can wind it right the way out and the engine sounds just the same. Is that right?

I think the ignition's all right, everything fires just fine as soon as I give it a bit more on the throttle.

The garage basically just blew through the carb, cleaned the jets and left it at that. At least they didn't charge me.

Today I checked for a vacuum leak at the base of the carb by spraying Easy Start at the rubber block. The engine revs increased slightly when I did this. So I removed the carb from the rubber block, cleaned off the surfaces and to make sure I put a bit of silicon gasket sealer on parts of the rubber block where it was looking a little tired. I put everything on nice and tight again and fired it up.

It is better than it was with the flat spot but it's still doing it. There is now a high pitched whistling noise coming from the base of the carb (I assume).

I tried spraying Easy Start around the base again, it didn't do anything this time. Spraying it down the carb venturi makes the revs drop.

Also, adjusting the idle mixture, when it's wound nearly full in, the engine dies . But, I can wind it right the way out and the engine sounds just the same. Is that right?

no. that means the throttle plate is too far open or too big idle jet.

whistling is not good. is there a spare brass tube still open that should have a pipe to dizzy or temp regulator on airbox?

Primary idle jet is 45, which is the smallest it goes. Need to adjust the idle speed then.

I think everything is connected, it does seem to be coming from the right as you look down at the carb.

Primary idle jet is 45, which is the smallest it goes.

What are you using for main primary ?

I got a bog (but not misfiring) when I experimentally tried a humungous 127/F30/185 with 45 idle.

A 50 idle and 50 pump jet fixed that, but it was too fuel heavy.

Is this DMTR 22/22 or DMTL 24/25 venturis?

I think everything is connected, it does seem to be coming from the right as you look down at the carb.

Those brass tubes can pull loose giving you a whistle and an air leak.

My tube on the opposite side to throttle quadrant goes via a rubber tube to the air temperature regulator.

It's a DMTL 24/25. It is running with these jets at the moment:

Main: 100/120

Air Corrector: 155/185

Emulsion Tube: F22/F30

Idle: 45/70

Winding the idle speed screw all the way out (closing the throttle plates) did nothing for it at all. Mixture screw still goes right the way out without stalling.

I'll check out the whistling tomorrow, vacuum pipe from distributor is connected but the air temperature one was removed because I took the filter off so I could adjust the carb. The whistling started when the engine warmed up, it wasn't doing it cold.

So for what ever reason the progression circuit isn't working properly, because that would give the engine the additional fuel it needs to transition from idle to part throttle, when the vacuum in the venturi is insufficient to pull fuel through the main circuit.

So that's either a blockage or it's not getting enough vacuum to pull through the progression circuit... could an incorrect sized idle jet also cause this?

Plug that hole, use a bolt in the end of a rubber tube, otherwise it's an airleak causing atmospheric pressure and turbulence where there should be a pressure differential so the venturis do their job.

As for jet sizes:

Depends on the rest of the engine (manifolds/exhaust/porting/compression/timing/valve lift)

If its all standard that idle jet and the rest looks okay.

It might be the gasket between top and bottom of carb stopping progression doing its magic.

Or the pump jet or its diaphragm, but this is a 'new' carb you said as in "unused"?

If you accelerate really smoothly does it still stumble?

If so that rules out accelerator pump.

After much fun and games with a 24/25 ? on the derby, Gaz swapped his emulsions to be F30 primary (it's an excellent all rounder)

and F22 secondary (thin walled, good for high compression engines). I think he's finally going injection though.

That's a cheap experiment before jet swap-o-rama.

... so I could adjust the carb. The whistling started when the engine warmed up, it wasn't doing it cold.

I thnk you know you gotta do carb adjustments with the engine warmed up completely.

On a cold day I drive it a few miles first.

On a warm day I let it idle with bonnet closed until the fan comes on.

Yeah, I know the whole thing has to be warm before I make adjustments. At the moment it's not idling at all when cold, regardless of where the choke is. I keep the accelerator held in to about 3k RPM to warm it up.

I'm going to investigate the whistling tomorrow, it's too late now and I just got back from Uni. I really don't think it's the temperature vacuum pipe though, it's coming from the wrong side of the carb.

The carburettor is new, totally unused. It came sealed up, I can see the gasket between the top and bottom parts and see were they used some kind of sealer on the gasket.

The engine and fuel system is totally stock, nothing done to it. It's a 2G engine with 106k miles.

By smooth acceleration, you mean slowly bringing the throttle forward rather than letting it idle at any time?

Accelerator pump is fine, I can see it squirting fuel into the primary venturi. The engine revs up (presumably on that initial shot of petrol), then misfires then dies.

There is definitely no leak at the base of the carb now, found out that the rubber mounting block had a small leak where it met the intake. That's fixed. No difference and no whistling.

All four jets are clear.

Also progression seems to work fine with the choke out a bit.

Also progression seems to work fine with the choke out a bit.

Bigger idle jet is probable cure then. The air just can't be flowing fast enough through the 24mm venturi.

Alfa Romeo Giuletta 1300c with 24mm venturi used 50 idle and 60 pump jet.

Lancia 1100c with 22mm venturi used 50 idle 70 pump

Fiat 1200cc using same carb but 23mm venturi used 45 idle and 70 pump.

I run 50 idle and 50 pump with F30 tubes in 22mm primary venturi.

Ok, until I can buy a new set of jets is it worth swapping primary and secondary idle (45 for 70, secondary should come in later?), or will that just not do anything?