Dean's Activa/XM/V6 and now Talbot blog

[Deanxm]

It looks great but the spark plug wells are very deep and a had to grind down a spark plug socket to allow it to fit into them its that tight, its also difficult to get your head in to look down at the plugs so may not be a very good option in this case im afraid.

D

[white exec]

Hi Dean,
Does sound like weak/lean mixture. Air-leak on the induction side somewhere?
If a manual choke, this will need to be opening the throttle slightly as well as adjusting the mixture. Usually an adjustment somewhere for the amount of throttle opening that accompanies choke.
Thermostat correct and OK?
Weak mixtures can also cause some overheating.

Not sure about Talbot, but Cit went through a faze with the BX 1.6 (around 1989) petrol where they opted for carb jets that delivered economy, but not performance. Result was massive flat-spots and indifferent acceleration. Peu, on the same engines (but with heavier cars) did not make the same mistake, and the cure for the problem was simply to fit a set (pair?) of Peu jets, which transformed performance

Agree . . . What are these "carburettor" things?

[RichardW]

Old skool tech means some old skool mechanicing is required! Ideally you could stick it on a gas analyser to see what it's doing. Did you check the fuel level in the carb bowl when you had it apart? What sort of ignition has it got? You should probably get it on a timing light to check the timing, and that it is advancing the spark as the revs rise. How's the dizzy cap and rotor arm?

[Deanxm]

Hi Chris, there is a mechanism that opens the throttle as the choke plate closes, there is the ability to set the throttle plate position with a stop screw but i set that as instructed on some solex training manuals i found online but they were for the Pict 3 not the 34 Pbisa16 but it did drastically improve cold starting, having said that the mechanism that controls throttle opening was broken and needed to be fixed as it was not opening the throttle as choke was applied when i got it so that would more likely be the improvement.

Richard, I did check the float height which was correct, fitted a new float valve and checked again on assembly, the dizzy and rotor are new, i fitted them when i serviced it, the distributor has a vac advance which does not leak but that's all I've checked, i dont know if the vac advance mechanism in the base of the distributor is seized or not, the ignition has no points, i have not checked the coil spec's or wiring yet.

I could borrow a timing light and check, and certainly will in the long term, but it just feels like fueling problems so was going to try that first, a gas analyser would be great but i'm too tight to take it to the garage.

When i set the carb mixture i used a vac gauge to get a max vac and then richened it out about 1/4 turn but it was pulling something like 23Hg which was over the green zone on the gauge, this was with the gauge connected to the manifold fed brake booster line as the vac line to the distributor only produced vac at open throttle, i investigated and put this down to the vac line port being sited above the throttle plate.

I am going to take the plugs out today and see what they look like and then check fuel pressure and flow as a starter, i did suspect an intake air leak as trying to set the carb up i had to have the idle mixture about 8 turns out to get it right instead of the instructed 2-3 turns, could not find a leak though, and there aren't many places it can leak air on this engine but will check again.

D

[bobins]

Purely to assist anyone trying to work out what the problem might be - here's a couple of diagrams of a 34 PBISA 16:

34 PBISA 16 #1

34 PBISA 16 #2

Images taken from https://www.ruddies-berlin.de/34PBISA_PEU.htm


Reading on another forum about a similar Solex problem, they found that the bent pipe at #9 in the upper diagram was missing from theirs. What it attaches to was still there, but the pipe had made a successful bid for freedom.

[Deanxm]

That's the jet for the throttle pump, it is there and squirting fuel ok when the throttle is opened, diagram is handy, just trying to get the plugs out now

D

[Deanxm]

Talbot express spark plugs after 400miles

Here are the new plugs after 400 miles, looks lean, the soothing could be because I was running it on choke coming home yesterday to keep the temps down, time to look at the fuel pump next.....

D

[RichardW]

For someone who claims to know nothing about carbs you are going in the right direction! Running hot can be a sign of lean, and also over retarded(?) timing - but making it go better with the choke out, certainly points to a fuelling problem. The mixture screw only adjusts the mixture at idle - once the main butterfly opens the mixture is determined by the fuel level in the carb, and the main jet. This carb was widely used - my VISA has a 32 version on it. Did the carb look like it had been messed with before you had it off? Could someone have fitted a carb from a smaller engine; or even the wrong jet (no idea how you would tell!!). Has it got a fuel filter, and have you changed it?

[Deanxm]

Well I have done a lot of reading on the subject since I got a troublesome carb in my life, but reading about something and doing it are, as you know, very different things.
I did wonder about the jetting, the carb and engine in general looked completely untouched, there was a £600 bill for a water pump and tuneup but when I got the van the coolant system was full of sludge and no antifreeze, the water pump looks like it's never been touched as did the carb and it ran badly but that doesn't rule out........fiddling
I did not get back out to check the fuel pump today but my gut feeling is that whilst aged, it is fine but will check it, I may just get a new one as they are only £25 for a Valeo unit and that rules it out.
The fuel filter is an inline pleated paper type and I replaced that when I serviced the thing a little while back.
I must stress pulling out the choke makes it pull stronger at low revs, stops the stuttering and stops the temps creeping up when climbing gradients but makes no difference to power at higher revs but I wonder if that is due to the restriction the choke creates at higher engine speeds.

I need time to fiddle but baby was born 2 weeks ago so I have not really seen outside recently let alone done much spannering

D

[Zelandeth]

If you need a timing might I'm happy to lend you one. I picked one up for one job a couple of years back, but it's a bit superfluous now as the Crypton machine has one built in.

If it's running lean under load but not at idle that would suggest a bit of gunk in the carb.

Vacuum leaks tend to cause more trouble at idle (unless we're talking a huge leak) than on the move as once the gas flow rate picks up they tend to swamp any offset caused by a leak.

I had a vacuum leak on the Lada for a while which took me a while to work out. It ran fine under load, but insistently idled on about two and a half cylinders. Turned out that one of the inlet manifold bolts needed to be nipped up by about half a turn...was surreal tightening that up infinitesimally and the engine suddenly idling smoothly - after I'd been chasing this fault around for well over a month.

As for starting out with a "base" mixture, I usually just go for the old approach of twiddling the idle mixture screw until you find where the revs start to drop at each end of the travel, then set it to the mid point. If you've got an engine that tends to run rich or lean, just tweak it a bit in the appropriate direction.

If it's fine at idle but is struggling under load though I'd tend to suggest that either:

A: there's a bit of gunk in a jet. Doesn't take much as the jets tend to be so tiny. I was ticked off when the Invacar still ran poorly after I stripped the carb down the first time...I later found one jet I'd missed and it had a miniscule bit of grit in.

B: Carb air leak (around the throttle plate spindles is a favourite as I recall). Though see earlier comment about that usually being more of an issue trying to set up the idle.

My money is on crud in the carb.

[Deanxm]

I think you could be on to something, when i next get a chance i will check the fuel pump delivery, just because, and then pull the top of the carb off, remove the jets and blow through them with a bit of air, double check the float level and gap the plugs as i forgot to do that when i put them in and they look like they are at 2mm not .7mm.

I will report back on what happens but if there is no improvement i think it will be timing next.

Idle is good, i can get it to idle at stupid low RPM, and pretty smoothly too, its just as soon as the throttle is opened it isn't running right.

D

[Zelandeth]

I've got an old school CO% meter here, sadly I'm not exactly just down the road, and it's not the sort of thing that would likely take kindly to posting given it's got a pretty sensitive analogue meter movement.

Do you get a noticeable "intake of breath" if you blip the throttle from idle before the revs pick up?

[Deanxm]

Thats very kind of you to offer but i should be able to get the mixture right with a little trial and error, if there are jetting issues it may take longer.......

I have not noticed any sudden intake of air, (sharp sucking noise as throttle is snapped?) but i have not run the engine without the air cleaner tbh and it is so restrictive and such an effective silencer i wouldnt notice with it fitted so when i put it back together i will run it with the intake removed and see.

D

[Zelandeth]

Bit tricky to describe I think...If I get a chance tomorrow I'll pop into the garage and demonstrate with the Invacar...

If the engine is running lean (and/or the accelerator jet is clogged) if you open the throttle sharply rather than the revs immediately picking up, the engine will tend to bog down for a few moments before catching up - exactly the same behaviour you see when it's cold if the choke isn't pulled out far enough.

Have the valve clearances ever been set on this recently? I had a 306 with the 1.6 (TU5?) petrol engine which was quite noticeably tappety when I got it, and would tend to run warm and pink a lot under hard acceleration at lower revs. Adjustment of the valve clearances somewhat to my surprise completely eliminated that behaviour. Not sure how awkward a job that's likely to be in the van...Does the cowling over the engine in the cab come off like on mine?

Shudder to think how awkward a lot of work would be without that access hatch. Now I think about it, I realise that I've made the assumption that the Talbot has a conventional in line layout...Engine isn't transverse is it? Kinda shows I've never looked under the bonnet of one!

You've mentioned re-gapping the plugs...Definitely do that and make sure they're the correct ones. I've found (and wasted much time as a result of it) that a poor spark can give very similar symptoms to fuel starvation, so given that's pretty easy to check I'd do that first.

[white exec]

Classic sign of a weak mixture is when driving, and trying to accelerate briskly, if the throttle is opened significantly the engine just 'hangs' - sometimes called 'yawns' - and doesn't put on speed until the throttle is eased up a bit, and only then it responds. Happens on both fixed jet and SU/variable choke carbs.