Cutting out / running on

[leafie]

Hi,

Hope somebody can help, my newly acquired traveller is a 1968 with a 1098 cc engine and unleaded head, it was fitted with a marina carb by the last owner apparently to improve the throttle response.

A problem arose in that the plugs were getting blackened and causing a miss fire so a friend adjusted the mix to weaken it, new plugs, distributor cap, points and condenser were fitted. This has stopped the miss fire and the plugs no longer go black but the car sometimes cuts out when you come to a stop from anything over 25 mph. Also when hot it now runs on when you turn the ignition off. Other than this the engine runs perfectly. Can anybody help as this is driving me round the bend.

Leafie

[Willie]

Running on can often be cured by simply lowering the tickover
speed. Cutting out on deceleration is usually due to a weak mixture.
Your tickover speed probably increased when your friend adjusted
the mixture so it is likely that you can lower it. You can prove if
the cutting out is due to an overweak mixture by slightly pulling the
choke out when the problem starts. If this cures the problem then
enrich the mixture strength ONE FLAT AT A TIME until all is well.
only then should you re-set the tickover speed because adjusting
the mixture also alters the tickover.

[andrewsxt]

Trawling through distant memories it sounds like the timing might be out slightly or maybe a decoke is in order.
A minor guru will let you know soon.

[andrewsxt]

Sorry willie, must have been cross posting there, you are indeed one of the minor gurus i meant.

[Cam]

I'd say your mixture is out. This is probably due to having the wrong needle in the carb. Did you change the needle? or is it set up for a Marina 1275 engine?

If it's set up for a Marina engine and you have adjusted the mixture based on the plug colour there is a good chance that the 'running' area of the needle was too rich for 'normal' 1098 running so with you adjusting that then the idle and part throttle areas are now too weak. Overall you might have the 'correct' mixture, but if you have the wrong needle then different areas could be too rich/lean. Sounds very much like you have a lean tickover.

Which carb is it? HS4, HIF44?

[Willie]

Sorry, overlooked the fact that it has a Marina carb....about which
I know nothing.

[leafie]

Thanks for all the help

The carb was changed by the previous owner so I don’t know if he changed the needle.

Cam asked Which carb it is? HS4, HIF44?

How do I tell the difference between the two.

Thanks,

Leafie
[/quote]

[Cam]

One has a square base and the other has a little float bowl attached to the side. You can tell what 'bore' it is by removing the air filter and venturi and measuring across it's 'mouth'. If it's a HIF44 then it's way too big for a 1098cc engine.

Actually if I were you, I'd get hold of a good 2nd hand (or new if you are feeling flush) standard Minor carb and dump the Marina one!

[leafie]

Thanks Cam,

I will have a look in the daylight, but going away early tomorrow so I will have a look when I get back on Saturday. Problem with dumping the marina carb is the exhaust manifold was also changed to suite the carb.

Thanks,

Leafie.

[bmcecosse]

HiF = horizontal integral float - the square one ! And yes size 44 is too big for a 1098 unless you have modified the engine in other ways ? Ideal will be 38 mm carb from Mini 998 - and the needle in that will be better suited to your needs. Meantime - try richening the mix as suggested - but if it's HiF carb it is a screw at about 2 o'clock looking down on the carb from the front of the car. Screw in for rich and out for lean. Running on is often indicative of retarded ignition - so perhaps worth trying advancing that first. Generally advance it till it 'pinks' - then retard slightly till only the lightest/briefest of tinkles is heard on acceleration.

[Cam]

Personally I'd leave the ignition alone as the problem is likely to be carb related and you don't want to add another set of variables into the equation! Perhaps a quick check of the timing but get the carb sorted out first!

Leafy, is the entire exhaust system non-standard then? It all depends on what you want to do, but personally I'd change it all for standard parts and then at least you know where you are with things.

The existing carb can be made to work with a bit of mucking about though.

[leafie]

Thanks everybody,

The exhaust is a twin box stainless steel one with a larger bore, so changing all that could get expensive so I think making the existing carb work is a better bet. The fast idle is a cross screw head located at about 10 o'clock looking at the carb from the front of the car if this helps identify it ?

Thanks,
leafie

[Cam]

Actually you might MAKE some cash by selling the large bore exhaust and fitting a standard one. Mild steel system are only around £25+VAT with stainless being around £50+VAT.

But anyway, if you want to get the carb running sweetly then why not get the car rolling road tuned. Then they will fit the correct needle and tune her to perfection!

Incidently, if it's a HS4 or HIF38 then a AAM needle is a nice one. Can you take a couple of piccies of the carb, then we should be able to identify it for you.

[bmcecosse]

Fast idle screw is (almost) vertical and would be at 7 o'clock - it very obviously lifts the throttle. The mix screw is at ~ 2o'clock and comes in from the side. Maybe you have been using that to adjust the idle ? You can test the mix by getting the car up to full temperature - then lift the little pin at the font of the carb - just slightly - if it speeds up then too rich - if it slows down too lean. If nothing much happens then it's just right - which is highly unlikely. Also check you have some oil in the dashpot assembly - the black knurled nut on top of the carb.

[bigginger]

Thanks Cam,

I will have a look in the daylight, but going away early tomorrow so I will have a look when I get back on Saturday. Problem with dumping the marina carb is the exhaust manifold was also changed to suite the carb.

So there are two manifolds? I should't worry, I'd bet you can flog them for more than the cost of another carb. Whereabouts are you? I'd have thought you can probably pick up a standard carb/manifold pretty cheaply. If you can't, shout.

[Cam]

You can test the mix by getting the car up to full temperature - then lift the little pin at the font of the carb - just slightly - if it speeds up then too rich - if it slows down too lean. If nothing much happens then it's just right - which is highly unlikely. Also check you have some oil in the dashpot assembly - the black knurled nut on top of the carb.

Thing is though, that method will work even if you have a really bad needle in the carb. Then it can be undriveable afterwards. Best bet is to either swap the carb or get the right needle for the engine/carb combination. A lot of people fit carbs meaning well but end up with very poor results.

[Packedup]

Hi,

Hope somebody can help, my newly acquired traveller is a 1968 with a 1098 cc engine and unleaded head, it was fitted with a marina carb by the last owner apparently to improve the throttle response.

A problem arose in that the plugs were getting blackened and causing a miss fire so a friend adjusted the mix to weaken it, new plugs, distributor cap, points and condenser were fitted. This has stopped the miss fire and the plugs no longer go black but the car sometimes cuts out when you come to a stop from anything over 25 mph. Also when hot it now runs on when you turn the ignition off. Other than this the engine runs perfectly. Can anybody help as this is driving me round the bend.

Leafie

Too lean, timing out, air leak. They'd all cause running on and possible problems cutting out. Maybe burnt out valves would too.

If it was all OK before it was weakened, then most likely it's the carb setup that's the problem, or maybe the carb itself is worn (around the spindle is a good plae to get leaks/ wear).

Now your plugs aren't turning black, what colour are they? You want to be looking for a beigey tan-ny colour. If you're not too good at setting them by ear (which is quite easy with single carbs, a nightmare with twins IMO) I'd recommend getting a Colortune. You can check the mixture through the range with one of those too, although obviously not when it's under load (unless you are small enough to fit under the bonnet!).

But a 1098 is going to be totally "overcarbed" on a Marina HiF44, all top end and no bottom. I'd think the HS4 or HiF38 is going to be the better option, with preference going to the 38 (no worries with waxstats, flows a bit better, has a nicer throttle assembly). Look for a 998 Metro in the breakers, and remember to get the mounting and cable bits at the same time

[TerryG]

The Minor CTR in Brum sell recon HIF38s (I fitted one whth the correct needle as they told me what i needed for my engine) and a K&N pancake. Sounds great (Very anoing on a long drive though) and does make the engine rev more happily. Curiously it gets slightly better MPG too.

[Packedup]

HiFs flow better than the same size HS, have a bimetal "leaning device" which is far more reliable than nasty waxstats, have a nicer throttle linkage, and are less prone to spindle wear. Overall I think they're great But spare a thought for those stuck with the rubber capped Strombergs, luckily the Minor was never cursed with those abominations.

The K&N will be taking a fair amount of warm air in over the standard setup as the carb is right over the exhaust, which is bad for power but good in that the engine will warm up quicker. There's also going to be less aero drag (although quite how much of a part that plays at 3000rpm I don't know) than anything other than a brand new paper element (with large enough surface area too). I'd go for a free flow element inside a normal box myself given the choice, but the pancake is still a good buy as you only buy one, and just clean it every so often

[leafie]

Hi all,

Back from hols, carb is a HS4 FZX 1189 as fitted to the 1300 marina. Weakened the mixture until plugs are a light brown, still cuts out so turned two flats richer on the mix but still cuts out when lifting off the accelerator and coming to a stop. Met a retired Morris Mechanic on holiday he said the carb should work well. An MG Mechanic at the local garage down there said I would need a change of needle for a 1098 engine but he didn’t carry them. Any thoughts and is anybody running this carb without problems ?

Thanks,

Leafie.