Misfiring stag

[al-stag]

Hello all,

I've just acquired a Mk 1 Stag. This Stag was totally rebuilt in 1996 with both a body and engine rebuild and has only done 6,000 miles since then , with only 500 miles on the clock since June 2002 according to the MOT's. The owner since the rebuild was a top lawyer, so I am inclined to believe the history. From his bills, the heads have been off once really early on and the waterways cleared of gasket cement, a Kenlowe Fan has been fitted and the alternator, battery and water pump have been replaced. The oil on the dipstick was absolutely clean and there was no oil on the garage floor where the car had been kept. The guy had had the car 'restored to order', but his enthusasm for it had waned.

I, and my son, who is a Stag owner too, test drove the car which seemed fine at the time, but on collection after a 70 mile drive home the engine seemed to be running a bit rough. I don't know whether it had been like this when we test drove it around country lanes and we hadn't detected it, or whether it had developed after the drive home. It ticks over smoothly, but at low speeds its lumpy with obvious misfires, and it isn't until you floor it, that the engine seems to pick up with plenty of oomph. The Stag is fitted with Lumenition and an examination of old bills shows that the plugs were replaced in 2006 and that the car was tuned and road tested in September 2007 by a 'Classic Car Specialist', who also fitted new fuel, oil and air filters The fuel filter is in a clear plastic holder and although there is air in the top of this but you can see petrol being pumped though. There are no leaks of oil or water evident, and the water temp gauge runs normally at the first mark increasing to near the centre mark if you are stuck in a traffic queue for 10 minutes or so. The Oil pressure is a little more than 50, dropping to 25 on tickover.

I have both the Haynes and the manufacturers manuals. I bought the car, not only to enjoy, but to tinker with, soI am happy to try and trace and fix the fault myself so that in future I can keep the Stag in perfect tune.

Its many years since I tinkered, but now i am retired I have plenty of time. My question is, where to start to fix this problem and the order in which tocheck things out stage by stage?

Looking for some expert help!

TIA

Al

[seaside bill]

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Al

Welcome to the forum.
I suspect your problems are down to the car not being used much. Sometimes an 'italian' tune-up will help in these circumstances e.g. take it out for a good blast and don't be afraid to rev it close to the limit - sometimes that will loosen everything up and clear out any crud in the carb etc.
As an ex-tinkerer, you'll be aware that other causes may involve fuel supply or ignition, but I'd start with the basics and don't assume something is ok just because you've got a bill for it!
Check the plug gaps, ignition timing and condition of leads, rotor arms etc;
Check the fuel/air mixture - lift the piston in the carb slightly and listen to the RPM. If the revs continue to rise as you lift the piston, it's running too rich. If it tries to stall it's too lean. You'll need a Stromberg special tool to adjust the mixture - also make sure the air fiter isn't choked;
Check the rubber diaphragms in the carbs - make sure they're not split/damaged
Check the choke lever isn't stuck half open or so; and
Check for any air leaks betweeen the carbs and cylinder heads - with the engine running spray some carb cleaner around the joints - if this makes an obvious difference to the RPM it indicates a leak.

There's loads of other things to check, which no doubt others will suggest, but I've experienced all of the above at some stage.

Good luck

[Andy Rundell]

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Welcome Al,

Bill's advice is all good, the only thing that i would do slightly differentlywith a newly aquired car is to cut straight to the chase with the things you will change anyway: replace the plugs (i always use NGK BP5E's but opinions vary !) , leads, distributer cap and rotor arm and the air filter if it looks grubby.

While buying these bits i'd also get a pair of stromberg diaphrams - you'll need them eventually even if they are OK now.

With all the ignition consumables changed then you can investigate the fuel aspects from a known starting point.

enjoy! cheers...Andy

[DJT]

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"It ticks over smoothly, but at low speeds its lumpy with obvious misfires, and it isn't until you floor it, that the engine seems to pick up with plenty of oomph. "

Prime suspect is one of the carb diaphragms. Change them both, top up the dashpots with engine oiland try again. Cheapest things to change and one of the easiest.

Dave

[nib]

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Hello Al I had a similar problem when I first bought my Mk1 Stag and it turned out to be the ngk plugs which I replaced with Uniparts and touch wood havnt had no trouble since,but I know most people prefer ngk,I can only go on my own experiances.

[stustag]

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Hi AL Stag and welcome to this insane life on the forum! I had this problem and found it to be the spark plug leads which after a three year lay up had deteriorated.

Buy a spark checker and connect to the plug one end and the lead the other and this will show you if you have a weak spark without getting a shock up your arm!

Also check everything the other guys have said and change the diaphragms anyway just for peace of mind.

Stuart

[al-stag]

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Dear all,

Thanks so much to everyone for the advice. There seems to be general agreement as to the possible causes. Thus I have ordered some diaphragms, plugs, a complete set of silcone leads a distributor cap and a rotor arm. I will start with the diaphragmsI think and will check the slides to see if they are gummy from the resdue of dashpot oil. Having been a frustrated sufferer offaulty ignition components over the years, the other bits will be fitted for future peace of mind as the Stag is being kept in an unheated concrete garage where it could feel the damp. I did an "Italian Tune up" around the Chilterns in bright sunshine before I posted my query.

I never examined the MOT's closely before purchase but examining them now the Stag did 124 miles last year, 225 the year before, 95 miles in 2005, then 69, 47, 83, 227, 305, 503, 2130 and 1756 back in 1996. So, there has been plenty of time for things to gum up and deteriorate. I did realise that this might be the case and drew a bit of blood on the asking price to cover the cost of the inevitable new parts. The new bits were less than £100 so there is a way to go just yet.

My sonrecently purchased a late model resprayed expensive Stag from a very well known and respected specialist. Since his purchase he has had several things fail, and the lumenition module go phut. So he has a goodcoil and a new lumenition that I can swop over for a test if the above parts don't do the trick.

When I have done some tinkering I will report back. In the meantime any other suggestions are most welcome.

Thanks very much

Al

[Camo]

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It could be that the petrol is past its best, if its only done a few hundred miles per year over that last few years you really should drain all the pipes through, clean out the carb float chambers and then add fresh..... I have done this many times with new purchases, often sorts it out.

oh and welcome.....

Stuart

[al-stag]

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Reporting back:

Replaced diaphragms, and cleaned carb slides, also filled empty dashpots with oil, as there was no oil whatsoever there. Now burbles along like a dream. The diaphragms were a bit mishapen but were not porous as far as could be seen. Most of the time was spent wresting with phillips screw heads that had been b**d up, so new screws will be fitted shortly. The ignition bits can wait a bit as it isn't immediately necessary to fit them.

Went to look for the locking wheel nut removal tool (3 holes in the middle of a cylinder type), and its nowhere to be seen!

So thanks to one and all. I'll see those of you at the Benson Cafe when you meet up, but not this weekend because its going to be wet I think

Many thanks to one and all for the expert advice and the welcome to the forum.

Al

[DJT]

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al-stag wrote:

Replaced diaphragms, and cleaned carb slides, also filled empty dashpots with oil, as there was no oil whatsoever there. Now burbles along like a dream. The diaphragms were a bit mishapen but were not porous as far as could be seen. Most of the time was spent wresting with phillips screw heads that had been b**d up, so new screws will be fitted shortly. The ignition bits can wait a bit as it isn't immediately necessary to fit them.

Went to look for the locking wheel nut removal tool (3 holes in the middle of a cylinder type), and its nowhere to be seen!

Hi, Al.

Thanks for reporting back. Glad we were on the right track. Watch the dashpot oil. This is held in place by small o-rings at the bottom of the dashpots. These dry out and can leak the oil away. Replacement is a bit of a fiddle, but described in the repair manual.


As for the locking wheel nuts. These sound like the 'Tri-lock' type. They won one of those magazine product comparison tests a few years ago because they are very difficult to remove without the key.They have a hardened steel barrel that rotates on the outside, preventing them being turned by Mole grips or the proprietry locking wheel nut tool. I hope you can find the key. or at least the key number. Duplicates are available from the manufacturer. Let me know if you have the code andI will look out manufacturer contact details. I have these nuts on my car and bought a spare key a few years ago.

Dave

[al-stag]

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Panic over, the wheel nut thingy was in the ash tray, and me being a non smoker had failed to search there! An e-mail to the previous owner pointed me to it.

Took the wife out and s*ds law said it started misfiring a bit again. So it was back home and replace the HT leads, rotor arm and distributor cap. That seemed to sort it, but am ready for another stage if it resurfaces. I can swop out the coil and Lumenition with my son'sif necessary because he is away in his Audi for the weekend. I shall have to lethim have a drive to see if its now right up to scratch. Maybe I can service his carbs for a very small fee?

Am now browsing the Rimmer Bros catalogue to identify affordable replacements for various tatty bits. (stiff indicator switch, dodgy wiper switch, fuel cap lock that comes out with the key, collapsed drivers seat foametc!). Its surprising the small things you don't notice when you get carried away with a purchase. The wheels are alloy Mk II types I think, but the laquer has gone and they are pretty corroded. I think some paint stripper and elbow grease with wire wool and emery should do the trick.

Enjoying the tinkering, but a little frustrated with people reusing cr*p phillips screws. They willget changed!

Al

[Oldromola]

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al-stag wrote -

Its surprising the small things you don't notice when you get carried away with a purchase.

And some big things at the same time!

[jordo]

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I had sme problem with my petrol cap lock. I removed the origonal clip which is suposed to hold the lock in and replaced it with a larger external circlip. The lock stays in now and locks the cap fine.

Hope i'm not to late with this.