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

[Deanxm]

Chris, it does kind of do that but since it only has 76hp and is an enormous van you can't really feel it, on light throttle it pulls nicely and maintains speed but as soon as you apply that tiny bit more throttle (operating much less than 50% throttle) its like i lose a tiny bit of power and progressive throttle application results in no more power.

Zel, yes i know what you mean, you get a big gulp as the air rushes in to equalise the manifold vacuum but the engine speed does not increase for a second or two, it did do that when i was initially setting the idle mixture but i richened it out to stop it so that the engine speed snaps up when revved. It has started doing it again sometimes but it's very mild, the engine just seems to hiccup and bang the engine mounts when i snap the throttle open.

D

[white exec]

Ring Tom at SGS Cranleigh, Surrey (an ex-colleague of Barry Annells of Shalford Green). He might recall that engine/carb, and whether there were issues with it. Citroen had flatspot problems with petrol engines in the mid/late 80s, and that might have affected Talbot too.
Give me an S.U. any day!

[Zelandeth]

Give me an S.U. any day!

Just not the Peirburg copy of an SU...

Had one on my second Saab and must have spent at least an hour every weekend I had that car trying to get it to behave itself.

I could always have any two choices between running well under full throttle, light throttle and idling properly. However getting all three seemed to be utterly impossible...I hated that carb with a passion...

Only actual SUs I've had were on my Metros, and aside from checking the dashpot oil now and then I never had to touch those...

[white exec]

Tuning S.U.s was a doddle, using the little built-in lifting pin. For twin (and triple) set-ups, once the throttle spindles had been correctly set, you were in business. A finishing touch was a Carbalancer to precisely balance their respective airflows.

The big mistake with S.U.s was either to forget to keep the dashpot filled, or to fill it with engine oil (invariably 20W/50 in those days), rather than the proper thin stuff. This wasn't helped by the BOL and even some owner's handbooks, recommending engine oil.

Never did get on as well with Strombergs, which Triumph used. Not helped by these being mounted on flexible rubber mounts, to insulate them from engine vibrations. This left the carbs free to 'nod', which did nothing for a steady idle. Rover, and even Austin-Morris, balanced their engines much better, so no need for such nonsense.

If all else fails, Dean, . . .

[Deanxm]

Had another look today and tried to get the other three plugs out, one however had the top snapped off it and I'm not sure how......
Fitted a new plug and had a play with the carb and surprisingly with ignition on all 4 cylinders it idles well but I've not driven it yet, I suspect there will still be lean issues.

D

[white exec]

Colour of plugs after a bit of driving should tell.
That is a very strange photo...

[Deanxm]

The plug wells are very deep, I had to take the air filter off and the heater cowling out to get access to look down, the threaded section with the little screw on nipple had snapped off and fallen down the side of the plug so I couldn't get the plug spanner in, good job really as if it didn't I would of taken the plug out and the nipple would have fallen into the cylinder which would of been fun!

I still think it's running lean, fuel pump delivery looks ok, I'm getting 6psi pressure and the fuel pulses out ok but I do get the fuel running back to the tank after sitting for a week so it could be a dodgy non return element in the pump.

D

[Deanxm]

Managed to get a brand new fuel pump for £30 so i fitted that just to rule out the very crusty looking old one, re-piped the fuel line and removed the fuel return line and capped it off, the fuel does not run back now when left idle for a few days and i have gained some power, maybe 10mph max speed, the only issue now is a hiccup at about 1400rpm when accelerating under light throttle, it feels like its bogging as the throttle pump fires in the extra fuel, maybe just how it is?

I have cleaned all the plugs and will run it for 100 miles or so and check again to see whats happening.

D

[xantia_v6]

How is the fuel pressure regulated if you have deleted the return line?

[white exec]

If there is a float/float valve, that should be providing the carb (fuel-level*) control, providing the fuel pump is not so powerful that it overcomes it (which would flood the carb).
Return line on carb-petrol engines is sometimes provided to avoid vapour-locking in a very hot engine bay, otherwise it's not needed.

* On some carbs, it is necessary to set up/check the fuel level in the float chamber, to provide the carb with the right 'head' of fuel. This is usually done by adjusting (bending) the float valve actuating lever, to obtain the correct level. The shut-off valve can also go leaky, and fail to work; this can result in flooding.

All this from memory: been decades since I last worked with petrol/carburettors.

[Deanxm]

How is the fuel pressure regulated if you have deleted the return line?

This is what i thought and after hearing about it being done, a stupid idea, then i heard PSA recommended to dealers the fuel return was deleted due to overworking the fuel pumps.
When i took the old pump apart i found that after reaching a set pressure the pump diaphragm disengages from the cam and stops pumping, so with the fuel return disconnected the pump works less and the carb is supplied fuel at a constant 6-8psi, with the return in place the pump pushes fuel up a 6mm fuel line to a 'T' which runs up to the carb or back to the tank on either side so fuel runs back on shutdown and fuel pressure is probably non existent.

D

[Deanxm]

A further update on progress....

I managed to lay my hands on a strobe this week and had a look at the ignition timing, the marker plate with the timing marks was bent so i unbolted it, straightened it out and refitted it, painted the marks up and connected up the strobe to Cylinder 1.
At this point, my daughter came out so we spent 5 minutes playing star wars laser gun fights before getting back to work.
Static timing for leaded fuel should be 10°BTDC and for unleaded or low octane 6-8°BTDC but the ignition timing was set (as far as i could work out without degreeing the crank pulley) to about 16°BTDC with the vac line removed.

I set the timing to 8° which lowered the idle speed, i then had a tweek of the mixture settings again and re-set idle and it felt OK, went for a drive and it was shocking, torque was improved at or just above idle but the rest of the rev range was flat, course or stuttery so i came back and just turned the distributor at idle to get the highest idle speed and what do you know, it ended up at 18°BTDC with the vac pipe disconnected, i reconnected the vac and timing stayed at 18°, revved the engine and still didnt budge from 18°. When i suck on the vac pipe i can feel the diaphram move and its not leaking so i think the ballance weights have siezed in the distributor so i need to pull that out this weekend, strip it and check.

Given the above, i think that is the problem and i'm surprised it ran so well if that is the case, maybe my expectations were just very low....
I shall report back when i strip the distributor, i hope it is seized

D

[Deanxm]

Think i have sussed it...

Took the distributor apart and cleaned and lubed the mechanism, it was not seized
The centrifugal weights and vac advance mech actuate steel fingers which rotate around an electromagnetic field created by a coil of copper wire in the distributor, i also noticed there is a crank sensor on the bellhousing.

I took the plastic cover off of the coil and lo and behold, it has an ignition amplifier, Ducellier branded but the model number rang a bell, MTR-01
I had this issue with the V6 XM in which the ignition amp stopped controlling the ignition advance and i got stuck with static timing only causing a mid range stutter and lack of power, the ECU was saying it was advancing the ignition timing but the amp was not doing the business.

Given the advance mechanisms work and i have a resistance on the sensor in the distributor then the only other falling down point would be the amplifier....
Could be why the ignition timing was so far advanced, the previous owner just set it well advanced so it ran kind of (Meh) OK ish across the rev range instead of stumping up the redies to sort the problem out.

We shall see.

[white exec]

What a strange distributor, Dean.
Can you post a picture or two of the arrangement?

[Deanxm]

IMG_5249 by Deanxm, on Flickr
top section with coil and vac advance
IMG_5250 by Deanxm, on Flickr
IMG_5251 by Deanxm, on Flickr
bottom section with the centrifugal advance
IMG_5247(1) by Deanxm, on Flickr
these just move the 4 legs around the coil which sends some sort of signal to the ign module which, combined with the crank sensor appears to control advance and dwell. there is no mechanism in the distributor which allows the rotor to shift phase, it is a solid shaft from the drive gear to the rotor

D