7 replies to this topic

[zero_wlv]

Having recently fitted a Stage One kit,  I noticed a few days ago that the vacuum advance pipe had completely perished at the carb end, and was hanging on by a thread.   So naturally I went out and bought a replacement vacuum pipe.

 

This is where the problems start.   I've set the timing by strobe light (5º BTDC at 1000rpm,  no vac advance, as recommended by Minispares).   I've tried adjusting the carb mixture in various different positions - slightly rich,  slightly lean,  and somewhere in between.   The engine runs fine in neutral,  at all points through the rev range  (1000 - 5000rpm).

 

However,  as soon as I get into gear and try to pull away,  the engine starts to knock quite badly.    After a few metres I have to stop.  (I assume the sound I hear is "knocking" in the sense of pre-ignition.    It only happens under load)

 

The only way to stop this happening is to pull off the vacuum advance pipe - then the car runs quite well and will happily go on a 20 mile run.  It runs satisfactorily except for perhaps a slight lack of torque or responsiveness under part throttle.

 

I guess it wouldn't be wise for me to retard the timing much more than 5º BTDC at idle.

 

Can the Stage One manifolds change the vacuum characteristics so much that the vacuum causes far too much advance?  Is it possible to modify the vacuum canister to be less sensitive?   Or maybe to modify the slot in the distributor breaker plate to stop it from vacuum-advancing past a certain point?   

 

I've found plenty of previous threads on the forum relating to tuning after Stage One,  and also plenty of threads relating to vacuum advance, but I can't find anything relating to this specific problem.

 

I fully understand that a rolling road session is necessary after fitting a Stage One - the thing is,  I don't want to risk wasting £75 on an RR session until I understand what might be causing the problem with the vacuum advance.   

 

I've read various threads on this forum about vacuum advance and most posters seem to agree that it's highly recommended for standard road cars.  I'd be wasting money if the car had to be RRed with the vacuum advance disconnected.  

 

Is there something I've overlooked that the RR guys would be able to sort out easily,  or should I get the vacuum problem sorted out first?

 

 

PS.  Any recommendations for Mini-friendly rolling roads near Birmingham would be appreciated     I was considering Aldon in Cradley and Hi-Tech in Kidderminster.

 

____

 

Car specs:

 

- 998cc engine,  high-compression variety

 

- Minispares Stage 1 kit   (Maniflow exhaust manifold,  Minispares inlet manifold,  AAU needle, K&N filter in standard box,  1.75" RC40 twinbox exhaust)

 

- Lucas 59D distributor fitted with Aldon electronic ignition    (I can't see how the electronic ignition would make any difference providing I've set the timing correctly with a strobe)

 

- standard HS4 carb

 

[Dusky]

Im at school so if I didnt Read it properly excuse me
But it Sounds like you Have the advance connected to the manifold, it should Be plumped in the carb.

Make sure your timing Marks Are correct, I had 2 White dots on my pulley..

Edited by Dusky, 03 October 2016 - 10:01 AM.

[sledgehammer]

try some anti knock additive - this may confirm if it really is a detonation knock

 

what is the oil like ? condition , spec , smell & age & psi under load

 

how long since the last h/g ? (hot spot in combustion chamber)

 

is it the correct dizzi ? pipe on small carb union ?

 

correct plugs ? - & colour of plugs ?

 

air leak on manifold weakening 1 or 2 cylinders

 

end noise (had a few customer cars that were retarded to stop end knock under load -

 

when advanced they knocked again (not retarded by me)) small end rattle - check oil pressure ?

 

Knock from new exhaust or is it a pinging - pinking sound

 

what fuel - maybe a duff batch - get some known good super un leaded 

 

also check valve lash - not sure that could be the noise - but won't hurt

 

another check is advance diaphragm isn't full of condensation / crud - had that on a different car in the past

 

pic or vid may help

 

cheap stuff first - best of luck

Edited by sledgehammer, 03 October 2016 - 10:12 AM.

[Danyul1275]

As for RR suggestions I have heard brilliant things about Malc at TTP Performance in Bromsgrove

[zero_wlv]

Im at school so if I didnt Read it properly excuse me
But it Sounds like you Have the advance connected to the manifold, it should Be plumped in the carb.

Make sure your timing Marks Are correct, I had 2 White dots on my pulley..

 

Hi Dusky,

 

Thanks for the suggestion,   I've been plumbing the vacuum advance into the carb,  just above the throttle   (although this spot is very close to the manifold).  

 

I'm pretty certain this is the correct place - it's where the blue arrow is on the attached pic.    (The pic shows the remains of the perished pipe before I fitted the new one).

Attached Files

•  20160924_102919.jpg   43.63K   17 downloads

[zero_wlv]

I'll have a look at some of your suggestions.

The one that jumps out at me is the suggestion of big-end noise.

I'm really not quite sure what "pinking" sounds like,  and now you've mentioned it,  the noise I'm hearing certainly could be what I'd imagine a big-end knock to sound like!   (It's a very mechanical lower-pitched sound,   not the high-pitched "pinging" noise that some sources describe).

 

I thought I'd find something on Youtube that demonstrates what pinking sounds like,  but there was very little.

 

It's worth mentioning though,  that a couple of weeks back the car was running fine with the vacuum advance connected,  the only difference being that this was BEFORE the Stage One kit was fitted.    So either there was no big-end problem a couple of weeks ago,   or the Stage One manifold creates more vacuum and exposes a pre-existing big-end problem that wasn't evident before.

 

If it is a big-end problem then it looks as though I'll be running the car with no vacuum advance temporarily,  whilst saving up for a new engine    .

 

Out of interest,   how do I detect whether it's a big-end problem,  other than by listening?

 

-----

 

A reply to some of your other points:

 

what is the oil like ? condition , spec , smell & age & psi under load

 

The oil is fairly clean  (it was last changed 9 weeks ago).   It's 20W/50 mineral.    I have an oil pressure gauge to fit but haven't fitted yet so I don't know the PSI.

I'm not sure when the head gasket was last replaced - I've only owned the car for 9 weeks.   If it helps,  these are the compression test results from a few weeks' back:

 

 

  4 3 2 1 DRY 90 110 110 110 WET 105 120 120 120

 

how long since the last h/g ? (hot spot in combustion chamber)

 

I'm not sure when the head gasket was last changed,  as I've only owned the car for 9 weeks.   I'll have to lift off the cylinder head at some point and check the condition.

 

is it the correct dizzi ? pipe on small carb union ?

 

The distributor is Lucas 59D,  I believe this is the correct one for the engine,  which is a 1989 998cc high-compression Metro engine.

 

I've been connecting the vacuum advance onto the top of the carb,  directly above the throttle.

 

correct plugs ? - & colour of plugs ?

 

The plugs are NGK BP6ES which I believe is the right temperature for this engine   (they were working fine before).

The plugs are currently black and sooty,  but that's because I've been playing with the mixture again yesterday.   I had the same 'vacuum advance' problem before this,  when the plugs were brown/tan coloured.

 

Knock from new exhaust

 

There is a very slight rattle from the new exhaust but that's not what this sound is.

 

what fuel

 

I always use branded 95RON unleaded.   At the moment it's got Tesco Esso in it.

 

air leak on manifold weakening 1 or 2 cylinders

 

Air leak on manifold  -  I'll have to check this  - I believe WD40 is the way to check it?

 

Air leak between carb and inlet manifold  -  this is possible,   because I had to loosen the carb to get the new vacuum advance pipe on.

 

also check valve lash - not sure that could be the noise - but won't hurt

 

Valve lash -  I've checked the valve clearances recently so I don't think that's a problem.

[zero_wlv]

how long since the last h/g ?

 

I've just seen some other posts that suggest that head gasket failure can cause quite terrifying noises under load but not at idle.

I'd be quite happy if it's just h/g failure rather than big end failure!

 

Would this be a likely explanation though,  given that disconnecting the vac advance pipes stops the noise?

[carbon]

Your compression test results: 4 3 2 1 DRY 90 110 110 110 WET 105 120 120 120

 

Cylinder 4 is down significantly compared to the others, could be a leaking valve. And if these are psi then they are not right for a high compression engine, would expect to see well above 160psi across the board.

 

If you think you have engine knock then I would suggest ditching the cheap 95 octane petrol and get a few tankfuls of Shell 99 octane. See what difference this makes, in the long run it's a lot cheaper than a wrecked engine.