Morris Minor Owners Club

Is anyone out there running a 1275 engine with a Kent 266 cam?

My 1275 Marina-engined Morris has never run smoothly since the introduction of unleaded fuel - it’s jerky at low speed (though it idles smoothly at 900-1,000rpm and pulls like a train when you open the throttle). I wondered if the low speed jerkiness had anything to do with the 266 cam fitted?

(Other mods include a gas-flowed head with a slightly higher compression ratio, HIF44 carb with BDL needle on a Metro inlet manifold and Janspeed exhaust headers. I’ve recently fitted a new BBC 45D distributor with electronic ignition and vacuum advance, renewed all the gaskets on the intake side and by-passed the manifold’s heating, as advised by previous threads.)

Also, I’m planning to check the fuelling using my friendly MoT station’s exhaust sniffer next week, which I think might be more accurate than the ColorTune I used before, but I wonder if I should re-set the timing first?

(I’ve adjusted it ‘by ear’ so far but am wondering if I should re-set everything from
scratch.)

Could anyone suggest what the dynamic ignition timing should be for a modified 1275 like mine?

Thanks all

Hello Omm,

adjust the timing after the mixture is adjusted, the latter affects the former.

Alec

Should run nicely - the 266 is effectively a copy of the excellent MG Metro cam. although with a little extra lift. Ignition timing - advance till you hear some pinking in top gear acceleration, and then take it back slightly. Colour Tune is completely useless - as will be MOT sniffer. These things only work at idle - and tell nothing of the combustion when the engine is working - which is after all what matters..... A portable CO sniffer which can be used on the move would be handy. Meantime - what oil is in the carb damper and what colour are the plugs after a decent run?

Hi bmcecosse

I use 20w/50 in the dashpot.

As for the plugs, here it gets a little odd: they used to be a light chocolate brown around the base with a light dusting on the insulator nose and electrode. However, since I fitted the electronic dizzy, they're more sooty all over. I tried to lean off the mixture but the engine started hunting at low revs and wouldn't idle properly - hence the thought of testing the mix with a sniffer or Colourtune.

You're right about tuning at idle - I had my engine set up on a Cryptontune/Sun Diagnostics kit a few years back by a garage that claimed to know about classic cars, and it ran like a dog afterwards. I know a rolling road is the only way of setting up an engine under load, but it's out of my price range at the moment!

Obviously a more 'sporty' cam like the 266 does lose some power at low revs to gain at high revs. Try 3 in 1 in the carb. And advance the timing till it pinks etc. The plugs should be light beige after a decent run.

Definitely worth getting a rolling road session done - if you are near(ish) to Croydon there is an excellent one there, and he keeps a huge range of SU needles as well - BDL is a good starting point for your spec. Paul at FastParts is the name (020 8683 2748).

I had a 266 in our 1380 (now a 276) and it is a really excellent cam - loads of torque and power from 2,000 to 6,500 rpm. Reasonable idle (we have a lightened flywheel) of ~1,000 rpm and very smooth with no vices at all. Aldon 'Yellow' distributor, vacuum advance connected and the inlet manifold is water-heated. Result was 100bhp at ~5,800 rpm and 100 lbf. ft. torque all the way from 2,500 - 5,000 rpm. 20w/50 in the dashpot, but I would be very surprised if this is the cause of your problem.

The distributor needs to have a maximum of 12° of centrifugal distributor advance (24° engine), which when added to 8° static advance, gives an 'all in' of ~32°, which is about right, depending on the CR - what is yours and what is the advance spec of the distributor you have? Without this information I would be very concerned about using the engine - apologies for the 'dramatics', but you could very easily wreck it. You will find that the 266 will idle more smoothly with the idle advance up to around 15°, but just imagine what the distributor advance on top of that will do to your engine! Don't do it.

The distributor advance could usefully be less than 12°as unleaded fuel need a bit more low speed advance as does the cam.

Yes, you do need to start from scratch with this spec, as nothing is as it was as standard.

Some things to try (1 at a time!):

Unless you know the full spec of the distributor, you cannot set the timing on static or idle, as it is the maximum total advance that is the limitation. Make sure the total timing advance is correct, and I would definitely NOT use the 'advance until it pinks method' for a modified engine. At best you might hear the low speed detonation, but the high speed detonation is inaudible and is the real engine destroyer. With a CR of ~10:1, the maximum advance at 5,000 rpm should be no more than ~32° BTDC, may be a bit less and super unleaded fuel required for this. For 95 Octane, probably 28-30° BTDC maximum.

What 'all-in' advance are you getting? Without this, you have no way to set up the dsitributor.

Make sure that the vacuum advance is working properly - if not low speed 'town' running is very uneven (forgot to to reconnect after adjusting the tappets, and wondered what I had done wrong. Could not believe the difference!)

The manifold heating has been discussed many times, with as many views expressed! I do have it connected, as again I found the low-speed warm-up running was slighly lumpier without it. Current spec has 112 bhp on the same rolling road in Croydon, so it can't be restricting things that much.

In my experience - the 'advance till pinks' works well - as long as you DO hear it of course as you accelerate in top gear - and then take it back so it's NOT pinking. It will need N6Y plugs -and yes it MUST have working vacuum advance. But I much prefer a very low static ignition advance - no more than 2 or 3 degrees - the vacuum will pull it up nicely at idle, and then the mechanical advance (which I use at ~ 15/16 degrees (= 30/32) brings up the total advance to that 32/34 degrees. After a good hard run -switch off (no idling) coast to a halt and pull out the plugs. Should be a nice beige colour. Water heated inlet - each to their own.. For economy yes - but not for best power/reduction of detonation risk. I'm not aware of a twin manifold with water heating!! Must be a reason......

Just to offer an opinion regarding the fact that vacuum advance will work at idle- I don't think it will unless you've got that rare beast of a HIF with the vacuum port on the manifold side of the throttle flap(as I have just discovered I have- this gives maximum vacuum advance at idle- not what I want!). Most HIFs, and definitely standard Minor HS2s etc, have the vacuum port just on the other side of the throttle flap, giving zero vacuum advance at idle, but large amounts at low throttle settings. Hence I suspect with your HIF 44, you will need high static advance, but as Islip Minor says, you'll need much less total advance as standard in the distributor to compensate for this and ensure it doesn't go over the 30 degree mark.

Ahh - but you need good advance at idle, and very little when starting, to ensure good reliable starting without any 'kicking' against the starter. My vacuum comes off the manifold - can't see why it should come from anywhere else !

Hi BMC,
The standard vacuum outlet on all HS2s from Minors that I've seen is just on the air filter side of the throttle flap, giving minimal vac advance at idle. My trouble is that with the full manifold vacuum I've got with the HIF 38 (which looks in just the same position as the take-off on those HIFs with the take off on the other side of the throttle flap), I get around 25 additional degrees of advance at idle. I know extra advance helps (especially with the MG Metro cam in my 1030), but that's going a bit far! I guess the signal from this carb is stronger than what you are getting with yours (maybe due to vac pipe diameter or something?)... It's worth knowing that there are these different types of vacuum take-offs on the HIF carbs, as if you did try to set the timing without disabling the vac advance first using a strobe, it could result in the timing being miles out because of the effect at idle.

Hello Liam,

"I get around 25 additional degrees of advance at idle",
that's a very large amount of vacuum advance, general average is around 8 to 12 degrees? What distributor do you have? By the way don't mention strobe to BMCE, he doesn't believe in them?

Alec

Too late - he said 'strobe' hahahahahahaha......oh dear. Actually - If folks want to use a strobe, good luck - but what will they do with it? I also doubt that 25 degrees additional advance from a vacuum unit ....... - seriously - is your 'strobe' working correctly?? I don't think vac advance can do 25 degrees. However - the mechanical advance could be kicking in if the springs are weak!

Good advice Alec- I kicked myself for mentioning strobe after clicking 'submit'... I think that the strobe is totally unecessary on a standard car, but more useful with a modified engine. The fact is that the advance figures I quoted, however unbelievable, correct (God knows I've checked them enough times!!!), and I think the issue comes from running a standard 948 distributor (well, a copy of a DM2) along with the incorrect vacuum signal- i.e. a mismatch between the carb providing the signal and the advance unit on the distributor. The mechanical advance is working as it should. This phenomenon that has been seen before by respected engine tuners when HIF carbs using full manifold vacuum are used. I think even BMC holds AC Dodd in high regard, and I discussed it with him when I took the car down to get the needle reprofiled last summer. He said the best course of action to remedy the massive idle advance is simply to relocate the advance port on the carburettor to the more standard location found on HIF carbs, then the signal will mimic the that found when the standard carb is used.The current huge advance causes horribly high hydrocarbon emmisions at idle- not a problem at MoT time on a 1962 cqar, but indicative that the engine is not happy!

Unfortunately, when you start modifying engines like this, problems do come to light due to the mismatch of parts, and it's been necessary to try to sort out the timing nicely, as the engine I've got, with it's high compression ratio and today's low octane fuels, is prone to serious pre-ignition with the standard distributor advance curve. I've also had serious problems with brand-new 'quality' camshafts (which affected the timing due to distributor drive gear wear), which have resulted in 2 engine strips of a rebuilt engine, but I'd best not go into details of that in public...

I just doubt that a vacuum unit can provide 25 degrees advance no matter how much vacuum it sees. And at idle - I doubt it will see all that much vacuum anyway!

Hi BMC,

I wonder if we're talking at cross purposes. I've just looked up the terminology, and I think what I've got on my set-up is manifold depression vacuum, as opposed to the more normal (and standard Minor set-up) of throttle edge depression. This means that I have absolutely maximum vacuum advance at idle, which then gradually tails off with increasing throttle openings. Obviously that's not what you'd normally see with throttle edge depression vacuum- a little increase at idle, followed by a large increae in advance under light load, tailing off under full load. Basically, what I've got is wrong for my car. The Mini forums have discussed it a bit

http://www.theminiforum.co.uk/forums/to ... m-advance/


Possibly the slightly dodgy Indian-built 'Lucas-TVS' distributor has contributedd to the massive advance. It's just worth other people knowing about in case they end up with the same combo of parts, as it's been a bit of a nuisance in my case, and took me a while to figure out as i thought the vacuum advance wouldn't affect anything too much at idle... Hey ho, you live and learn.

To the original poster- I think that the MG Metro cam is not too far off your 266 duration-wise (252 inlet and 268 exhaust I think), and a bored-out 948 idles quite well and pulls from low revs well, so your engine should be fine I would have thought. Your standard distributor will struggle though- I need lots more static advance (around 10 degrees) to get smooth pick-up from idle.

I don't think an idling engine develops all that much vacuum - would need a vacuum gauge (which I despise.... ). And can any vacuum unit really pull up 25 degrees of advance ?? But I don't see what the problem is - my vac unit connects to the manifold - the engine starts well/idles well - and is nippy on the throttle. I have absolutely no idea what the static ignition setting is. And it 'just' pinks initially as I put my foot down - then settles in to the slog with no further pinking. I'm happy with it!

There's no major problem- just a slightly rougher idle than there would be with a little less ignition advance with that cam, and high HC's, which doesn't matter as no emissions test on MoT- just a stinky idle! Like yours, it starts and drives well. Like you, I've no interest in using a vacuum gauge...

Hi Islip Minor

Thanks for a very comprehensive reply. However, I think some of it might be a little beyond my level of technical understanding!

Good to hear your experience with the 266 on unleaded is good, so clearly my probs are about adjustments. I realise a rolling road would be the ideal solution but my unemployment means it’s out of my reach, so for the meantime I need to set up the car as best I can using conventional methods.

I always prefer to err on the side of safety so have backed off the timing well below pinking stage – I can’t hear any pinking when accelerating hard up a steep hill.

My strobe is very basic and doesn’t give a readout of the exact number of degrees, so I’m not sure about the ‘all-in’ level of advance. However, based on the alignment of the timing marks on the pulley and pointer, the timing would seem to be about 10-12 degrees advanced at 1,000rpm with the vacuum pipe disconnected.

(I’ve been unable to borrow a decent strobe light – could you recommend a cheap but decent one that would allow me to measure the exact number of degrees advance? I looked at some on ebay but the ad doesn’t say whether they give a readout or are just the basic flashing light type like my existing one.)

Not sure about the exact compression ratio – the engine tuner was rather vague about it – but would guess it would be around 8.7:1 and certainly no more than 9:1. Fuel is branded (not supermarket) unleaded but not super.

Simon at BBC mapped the electronic dizzy to the spec of the engine (see original post), so it should be OK.

What do you reckon? Should I retard the timing a tad for safety until I can afford a rolling road?

What would be the point of wasting money on a strobe? What would you do with it? Just advance the timing little by little until you do hear some pinking - then back off. Hard to comment on the idling advance - since I don't know if the mechanical advance will have started - I suspect it will have....... 1000 rpm idle is very fast - slow it down!

Hello OMM,

"Simon at BBC mapped the electronic dizzy to the spec of the engine (see original post), so it should be OK."

When he did that did he not give you a sheet with the curve, or at least give you some figures?

Personally I do use a strobe, it saves me having to road test every time I adjust or replace the points as I know what to set the timing to, also it enables a check on the working of the advance mechanism. I also do have a vacuum gauge, mainly for my mechanical injection Triumph as the operation of it depends on engine vacuum. Figures for manifold vacuum at idle for most engines are in a range of 15 to 20 ish inches of mercury, my Triumph being slightly different at 8 inches of mercury. However, although I've never really got into using it as a diagnostic tool, it was commonly used many years ago and can help pinpoint a variety of engine maladies.

Alec