Twin 40 DCOE running problems!?

[mk2jettakyle]

Guys in need of some guidence, advice and knowledge from genuine experience.
The background info:
So here's what I have, it's a vw mk2 Jetta with a 1.8 8v gti engine I rebuilt, when I first built it I had it running on a 32/36 twin choke weber, it ran great and never let me down but always felt it could do with something more.
So I bought a pair of used weber twin 40 DCOE's which I've seen videos of running. I finally got round to fitting them about a month or so back.
The set up:
They are mounted to the inlet manifold with the metal and rubber style gaskets, as it's an 8v they sit just above the exhaust manifold so to help with heat I've wrapped the manifold. It's still on the standard mechanical fuel pump with a malpassi regulator.
The problem!:
90% of the time they run great, the engine pulls like a train in high gears and flys round the country lanes. 10% of the time though it's not so happy, once warm like 60/70 dregrees and I'm sat idling for an amount of time the revs will begin to drop and it'll run lumpy like an idle valve is blocked (they aren't blocked though I've checked that a few times now) then the revs will drop to the point where it'll no longer idle. If I then get a little drive out of it the idle will once agin level out and hold there.
I've used a CO tester and it seems when the idle dropped it was due to excess fuel the only thing is I can not work out where this excess fuel is bleeding from and if it is my main problem.
The only ideas I have are,
Possible air leak from the metal and rubber gaskets between the inlet mani and carbs?
Wrong jets? What jets should I be running?
Wrong fuel pressure, again what should I be running?
Faulty fuel pump?
To much hot air from the exhaust?
Me and my dad have set these up at least twice now and it still seems to go out of balance and still plays up every now and then once warm.
Can anyone help me please!?

[Dez]

ive just had nigh on identical intermittent/irregular running faults that i though was the carb, and it turned out was an ignition fault. swapped the dizzy (after changing cap/arm/points/condensor twice to no effect) and the faults have gone.

I'm still not entirely sure what it was, but presumably something to do with the advance mechanism, possibly sticking i guess.

id double check your ignition setup before going to deep with the carbs.

[Kieran]

Fuel boiling in the carbs?

How warm are they when it starts playing up?

[mk2jettakyle]

Thanks for the responses guys,
The only reason I haven't thought that it could be something to do with the ignition is because it's only started doing it since fitting the carbs, also correct me if I'm wrong but the advance shouldn't be doing anything on idle which is when it plays up.

When it's at the temp it plays up at you can still touch the carbs but they are hot, at first I wondered about the fuel possibly boiling but I'm slightly sure it's something to do with over fueling, wether it be to much getting in or that is not able to burn it off quick enough but I'm just not sure how to test these theory's

[Kieran]

If you have an electric pump, when it starts to stumble, can you kill the pump to see if its either the float bowls overfilling, or the fuel getting gassy has it boils?

[usedabused]

Are you using the fuel enrichment chokes at all on cold start.,
DCOE's are buggers for the chokes leaking and as the pump on these is so good many blank of the enrichment path completely and start on a balanced throttle........

That's the main reason I use DHLA's though they have there issues the cold start choke is far more reliable...

[usedabused]

[mk2jettakyle]

It's still running on the mechanical fuel pump so unable to stop it.

That's a thought, I don't have the chokes connected with a cable but I've also not blocked them and the mechanisms are still bolted on, maybe I'll pull them off and block them up and see if that helps. Thanks mate!

[frag]

Can't offer any help with DCOE's (although,if you want to cut fuel on mechanical pump while its running,you can clamp outlet pipe with grips as they pump 'to demand'it will be same as floats cutting fuel into chambers)

You say you had a 32/36 weber on....could you please tell me,
Was it a dfev (or dfav) by any chance,what was it off originally ?
What was / is it jetted for (CC) ?
Ta.

[mk2jettakyle]

Ah that's true I could do that, cheers.

I pretty sure it was a dfav, it was originally off a type 4 air cooled engine out of a vw bay van, I believe it was an 1800 as I never had to change the jet sizes. Can't remember what the jet sizes were though I'm afraid. My original peirburg was shot (like most peirburgs end up being) when I bought the car and my dad had that sat in his workshop, it didn't fit straight on but we have a guy the works with c&c machince and he made me up an adaptor plate out of aluminium and the rest is pretty much self explanatory once it's on

[frag]

What I was leading to.....

If you get the 40's running right and would like to sell the weber,I'd be interested in buying it....
Ta.

[mk2jettakyle]

Possibly I'd have to check with my dad as I never actually bought it off him so it's still technically his, but yeah I'll find out for you and get back to you mate

[1980escort]

Now i don't know how your engine bay is layed out but i would check that your coil isnt over heating as i had a similar issue in the past, i relocated my coil further away from the exhaust and my issue was solved

Sent from my GT-I9505 using proboards

[mk2jettakyle]

It's a thought but the coil is in the same place it was from factory and I never had this problem before the 40's even when I was running the twin choke and had no wrap on the manifold

[ChasR]

A silly question but how does the car run if you leave it idling from cold? Have you checked the float levels in the carbs?

I would be tempted to fit an electric fuel pump myself. If you were local I would have been tempted to loan you one.

[Bozwell]

from your description I would say fuel is boiling in the carbs. modern fuel can start to boil as low as 30 degrees C so will be a problem in stale hot air. as soon as you start moving the air in the engine bay will cool slightly.

a shield above the exhaust manifold may help so worth a try.  venting the bonnet above or near the carbs may also help. a cold air feed blowing on the float bowls with a cheap inline boat fan (the sort that they try to sell as an electric supercharger) should keep the carbs cool when stationary.

[Kieran]

Electric pumps can also avoid fuel evaporation.

[frag]

May 23, 2015 20:02:49 GMT mk2jettakyle said:

Possibly I'd have to check with my dad as I never actually bought it off him so it's still technically his, but yeah I'll find out for you and get back to you mate

That would be great,mines 'tired' and the choke mech. is hanging revs up which is annoying to say the least...
It's days are numbered.

[frag]

May 24, 2015 17:38:14 GMT Bozwell said:

from your description I would say fuel is boiling in the carbs. modern fuel can start to boil as low as 30 degrees C so will be a problem in stale hot air. as soon as you start moving the air in the engine bay will cool slightly.

a shield above the exhaust manifold may help so worth a try.  venting the bonnet above or near the carbs may also help. a cold air feed blowing on the float bowls with a cheap inline boat fan (the sort that they try to sell as an electric supercharger) should keep the carbs cool when stationary.

The engine in my van came from an audi 80,looking at the wiring it has a temp sensor (ambient air nr cylinder head) that triggers engine cooling fan if it gets too hot,as well as one into coolant to run fan....(I assume this is to move air around carb if its too hot)
(you could always bridge cooling fan to run constant,just to prove theory and see if it has any effect,revs may drop slightly with alternator load tho)

Uno turbo,tho injection has a cooling fan blowing cold air onto injectors ! sensor for which is situated near to them.

Probably something else that would benefit,having a fuel return to tank,fuel temp should be lower..
Modern diesels have a fuel cooler fitted into return line to fuel tank.

[blower]

A Standard mechanical fuel pump will usualy push fuel in at a Similar rate , on either idle or full chat

Black smoke - overfuelling


A electric fuel pump will slow or steady the flow as the revs come down

Most people will say a mech fuel pump is fine with twin carbs

Most tuners will/should tell you the opposite