DG with constant, stubborn hesitation

[MGP]

How hard did you have to suck on the vac advance unit to see it move? If the spring inside it is weak then it may not actually move when you open the throttle.

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[NicBeeee]

Lots of questions for you, sorry but I have another, I am assuming the engine hesitates at standstill whilst revving

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[ajsimmo]

Is the centrifugal advance working in the dizzy? If not it'll run fine stationary/at idle, but lack power due to retardation at revs/under load.

[bruce3927]

Quick update to answer some of the questions.

I have blown through the vacuum drillings for the second stage and they appear clear also I have checked (well my long suffering wife checked by peering into the top of the carb while I drive) and the second stage does open when on the road.
The centrifugal advance on the distributor does move when sucking (quite hard) on the vacuum pipe, yes it does run fine at tick over but under load lacks power.

When asking to see the plugs after a run are you looking to see the state of the plugs (like the old pictures in the Haynes manual) or do you need to see the spark colour? What is the best way of safely checking the spark colour?
Mentioning possible earthing issues got me thinking of my old mini with a snapped earth strap so I have had the earth cable below the distributor off, cleaned it up (it was thick with oil) emery papered the contacts and reconnected, not sure it helped but at least I think its not that now, or is it?? The earth cable, having sat on top of a hot engine for 30 years, is very stiff and the insulation is quite brittle, I did notice one small break in the insulation so taped it up. Am I barking up the wrong tree here?

Been a bit short of time this week but the van has been in to get the leaking thermostat housing replaced today (could have done it myself but the lad who did it used a socket attachment with an air chisel to shock the bolts free without snapping them in the head like I would probably have done).

While it was in the garage he hooked it up to the CO which was 7% (ish), it is now adjusted to 2%. Not sure if its just psychological but it appeared to be running better on the way home???
I'll have time to run it properly over the weekend so will be able to give a better update.

Like a soap opera this one isn't it!
The next thrilling instalment is that I'm off on a 2 week tour of Ireland next weekend, would love to have this sorted by then!

[NicBeeee]

7% is very high for CO reading, my concern is that this issue happened suddenly so altering the mixture is possibly just masking the real issue. High co means its running to rich, poor spark/timing or lack of air in mixture.

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[itchyfeet]

pull plugs out fit ht lead to them lay on engine so they have good contact and crank, look at spark colour.

yes dizzy needs a good earth, fit an extra one. if insulation is split it may be corroded inside.

yes 12V feed via ignition switch to coil needs to be good, use a temporary bypass from 12v stud in black box to coil + terminal.

[itchyfeet]

worth checking none of your wheels are binding, would have thought you would notice but worth checking anyway.

I once drove miles with the handbrake on and wondered why performance was bad.

[MartinR]

Recently fitted a new (second hand) engine, and changed all the usual stuff including the fuel pump pushrod. All seemed good, except for the van being a bit unenthusiastic when under pressure at low revs. Decided it felt fuelish, and wondered if pump was not pushing enough through at low revs.

Thinking about it, realised the pump had been on for probably 100k, and on inspection, while all seemed to work, the lever the rod bears on appeared very polished and possibly worn, so possibly making the new pushrod operate as if too short.

Took a punt and fitted a new Brickwerks pump and all problems went away.

Good luck

Regards

Martin

[ajsimmo]

The centrifugal advance on the distributor does move when sucking (quite hard) on the vacuum pipe

That's the vacuum advance you're checking. The centrifugal starts to operate at a given revs, and is progressive up to a maximum at a higher rev threshold. If stuck, it won't increase the amount of advance with more revs, and performance will be "flat" at mid to high revs.
To check the operation, connect a timing light, note the position at idle (vacuum disconnected) - should be on the timing mark (5 deg BTDC), then slowly increase revs, mark should move to the left (progressively, and quite substantially by 4krpm). If you have an adjustable timing light you can measure it against the spec, which is reproduced here, (courtesy of Brickwerks very helpful info page).

ignition timing 5°±1° BTDC without vacuum

Ignition advance checks 0°-2° @ 1500RPM w/o vacuum and basic timing (0-1 @1160)
10°-14° @ 2400RPM w/o vacuum and basic timing (13-17 @2400)
24°-28° @4200RPM w/o vacuum and basic timing (24-28 @4200)
(figures in brackets - later dizzy 85-92)

vacuum advance range 12°-16° engine degrees

and just for information...
idle speed 900±50 RPM
oil temp for CO test 60°C
CO content @ idle 1.5±.5 % volume
HC content @ idle 300 parts per million

[bruce3927]

Thanks for the input so far everyone,
Looks like I've got a busy day tomorrow...
I'll check coil LT side, remake the earth cable, check spark colour, check centrifugal advance...
Not sure if I answered Nicbeeees' question but ticks over fine and yes a bit of a fluff when first accelerating.

[bruce3927]

MartinR, I've changed the fuel pump pushrod, mine was 0.5mm short, can't remember the level being badly worn but it's probably worth a look

[NicBeeee]

Not sure if I answered Nicbeeees' question but ticks over fine and yes a bit of a fluff when first accelerating.

Question was designed to lead onto another, just to rule out any non engine related mechanical issues, but if its doing it whilst stationary then it answers that.

[ajsimmo]

Worn out camshaft would drive very much as described. I'll leave it at that for now, as I hope it's not that.

[bruce3927]

Worn out camshaft would drive very much as described. I'll leave it at that for now, as I hope it's not that.

That's the two of us then!

[bruce3927]

To check the operation, connect a timing light, note the position at idle (vacuum disconnected) - should be on the timing mark (5 deg BTDC), then slowly increase revs, mark should move to the left (progressively, and quite substantially by 4krpm)

Unfortunately I have a basic timing light so the results are not very scientific but I tested the centrifugal advance as you recommended.
The timing is at 5 degrees at 900rpm and when revs are increased the mark moves anticlockwise but at 4500rpm its only moved to about 11 o'clock,
As a comparison when the vacuum hose is reconnected it moves to slightly anti clockwise of 10 o'clock.

I had the plugs out as well but I could not see a specific colour, it seemed to vary from orange to blue to white Not really sure what I am looking for with this so its probably a false result!
I have also made a new earth lead and remade the connections for the 12v side of the coil.

On a test run it still hesitates badly !