Maestro 1.3 carb question

[threelitre]

Hi All!

As you might know, I have a Maestro 1.3, which has the manual choke version of the HIF carburetor - and no ECU of course. I have not yet managed to get a good idle from the car, and assume, since the car has been standing for 3 years before I got it, that dismantling and cleaning the carb may help.
But I do have 2 good (and clean) carbs from models with electronic control. These differ not only in having the stepper motor and the fuel cut of switch, but also in having a device to control the mixture on part/full-throttle (lean-rich). Could I expect any difference when replacing the electronic choke on one of these carbs with the manual one? Like running a little weaker mixture and still getting no pinking or lean-burn hesistation on pickup or the like...

Regards,
Alexander

[G Force]

Hello there. I would say your best bet is to clean and overhaul your original carb rather than graft the manual choke onto one of your electronic choke spares.

I dont see any advantage fuel economy wise, I think the part throttle weakening device you are refering to is the vacuum switch, which only operates whilst on choke, and is prone to failure due to the diaphragm splitting thus causing heavy fuel consumption under all conditions.

If you have overhauled and cleaned the original carb already and still have poor idle. Check the valve clearances 0.014" cold, check for air leaks, faulty igntion ht components, firing order 1342, distributor vacuum unit diaphragm. Try adjusting fuel mixture at idle, turn mixture screw anti clock wise till engine stumbles, then very slowly clockwise untill engine runs smoothest, repeat a few times so as not to screw too far clockwise.

cheers gary :)

[threelitre]

Originally posted by G Force
I dont see any advantage fuel economy wise, I think the part throttle weakening device you are refering to is the vacuum switch, which only operates whilst on choke, and is prone to failure due to the diaphragm splitting thus causing heavy fuel consumption under all conditions.

Ok, I'll dive a little deaper in the operation of that vacuum switch. I thought yt to be working all the time.

If you have overhauled and cleaned the original carb already and still have poor idle. Check the valve clearances 0.014" cold, check for air leaks, faulty igntion ht components, firing order 1342, distributor vacuum unit diaphragm. Try adjusting fuel mixture at idle, turn mixture screw anti clock wise till engine stumbles, then very slowly clockwise untill engine runs smoothest, repeat a few times so as not to screw too far clockwise.

cheers gary :)

This is all done, except stripping the carb. I've had it on CO2-figures of 0.8 up to 2.5, and the idle is never really satisfying. I also find that it could do a little bit better on picking up when the throttle is opened. But I can only compare to the LE, whch behaves better, and most of all smoother. Otherwise I can't complain. The car is fast and economical, its' mainly the idle... BTW, the idle is only a bit rough, since you entionend errors like wrong firing order - this would be really lumpy :)

Cheers,

Alexander

[G Force]

no vacuum switch only in use whilst choke is on. ;)

you could try setting valve clearences when hot, tappets just a couple of thou on the tight side has big effect on idle quality. co can go up to 3%.

ps old hle had really smooth idle, i think had a different cam.

cheers gary :)

[MGTurbo]

Originally posted by G Force
no vacuum switch only in use whilst choke is on. ;)




cheers gary :)

Please explain to me how a vacuum controlled switch only operates when the choke is on??? It works all the time (until it fails) meant to give extra enrichement upon initial acceleration (although the carb damper does the same job)

The ORFCO is ECU controlled, when engine revs drop below a certain rpm it operates to save fuel, help with emissions etc. IMO, both devices were crap, that is why all late 1.6/2.0 Montego's ran without them.

A lumpy idle could be caused by failed choke seals. There is only one seal fitted to manual choke carbs, 2 on the stepper motor of electronic carbs. They shrink with age, allowing neat fuel past at idle, and worth changing for new. STD seal size, BSO13, obtain them in viton, otherwise they will swell.

You could also look into your ignition timing. If this is set too retarded or too advanced this can cause a lumpy idle, as can simple things like vacuum leaks.

Gareth

[G Force]

Originally posted by MGTurbo
Please explain to me how a vacuum controlled switch only operates when the choke is on??? It works all the time (until it fails) meant to give extra enrichement upon initial acceleration (although the carb damper does the same job)

The ORFCO is ECU controlled, when engine revs drop below a certain rpm it operates to save fuel, help with emissions etc. IMO, both devices were crap, that is why all late 1.6/2.0 Montego's ran without them.



Gareth. The vacuum switch only provides acceleration enrichment whilst the choke is operating because quite simply what it does is bleed air into the rotary choke.

It works like this, vacuum is applied to 1 side of the diaphragm in the switch from the manifold side of the carburetor throttle butterfly. The 2 connections that connect to the carburetor via short rubber pipes, one is connected to the atmospheric side of the carburetor the other connects to the outer chamber of the rotary choke, the 2 tubes are then connected via an air bleed restrictor in the switch body itself. When manifold pressure is low the diaphragm is lifted allowing both pipes to be connected via a larger air bleed restrictor in the switch port that leads to the choke chamber, causing a large amount of air to mix with the fuel around the choke valve. Then when accelerating manifold pressure is high the diaphragm is pushed by spring pressure closing off the port in the switch that leads to the atmospheric side of the carburetor, when the switch is closed only a small amount of air can bleed into the rotary choke through the small restrictor in the switch, causing the fuel mixture to become richer. Once the choke is closed then no fuel passes through it hence the vacuum switch no longer has an effect on fuel mixture.

On later models with electronically controlled ignition and carburation. The vacuum switch was not required because the acceleration enrichment whilst the choke was operating, was provided by the ecu indexing additional stepper motor steps in response to high manifold pressure.

I am sorry my explanation is a bit long winded but you sounded like someone who might be interested.

Cheers Gary ;)

[threelitre]

Thanks for all the aanswers guys!

Again, everything (apart the carb, which I did not dismantle) is OK and fine. When I got the car the ignition was set to 8 BTC, and I changed it to 12 as it shoould be, but the only noticable difference was at high revs, which I hardly use (OK, goes right up to 6000 now without hesitation). I don't think that there are any seals wrong in the carb, but I assume it can do with some cleaning. But probably the idle is OK like it is - I tried to achive the smooth tickover of the LE engine... So this would probably not be possible anyway :(

Yes, the LE has a different cam, with no overlap, so that it runs out of breath at high revs, but is picking up better and noticable smooth on low revs. So the note on setting the valve clearances on a hot angine ames to the same area: enlarging the valve clearance and thus reducing the overlap. I might gain a little improvement on idling and also a little improvement on part throttle economy here. But I also will have higher stressed valves and seats (higher closing speed) and a little loss in peak power, probably not noticeable for me.

But Gary's description how the vacuum switch works does make perfect sense to me (I didn't find a description like that in Rover's workshop manual). It also explains why the LE with the electronic choke always seemed to use less choke (less rich mixture) then my manual choke car (all settings correct!). The vacuum switch leans out the mixture for cruising or idling, and then switches of when load is sensed (via difference between pressures in inlet tract/carb) - similar to me using less choke when rolling on a straigh road, but applying a little more when pulling away from traffic lights. So towards fuel consumption on mainly short drives the work of the vacuum switch should be noticeable (more then the fuel cut off that is also missing on my later car). But that's a good reason for me to try and fit it...

It wouldn't help smoothing out my generally rough idling. But as said it's not _that_ rough, when looking at the running engine it hardly moves or rocks as it would do when I disconnect one ignition lead :)

So I will be going to try and clean my carb, redo all the settings (trying to get it run lean in general, it recently delivered 45mpg when driving about 60-70mph) and will see... But the next move could well be the adaption of the HIF44E to manual choke ;)

Regards,
Alexander

[MaestroMatt]

Gareth's suggestion of changing the seals on the auto-carb is a worthy one. Try it before you switch to manual choke as it will cost very little and take 5 minutes to do. It made a profound difference to the idling of my car - it is silky smooth now.

[threelitre]

Originally posted by MaestroMatt
Gareth's suggestion of changing the seals on the auto-carb is a worthy one. Try it before you switch to manual choke as it will cost very little and take 5 minutes to do. It made a profound difference to the idling of my car - it is silky smooth now.

Erm, I don't have an auto-choke - and it wouldn't make sense to fit it without an ECU and wiring and... :)

Alexander

[MaestroMatt]

That'll teach me to not read posts properly before replying!

Anyway, I wasn't talking to you - I was talking to, er, everyone who does have an auto choke fitted ;)

[MGTurbo]

Originally posted by threelitre
Erm, I don't have an auto-choke - and it wouldn't make sense to fit it without an ECU and wiring and... :)

Alexander

You still have a seal on the choke shaft which performs the same function as it would if it were an auto choke. As they are the same material, given time and age, it will shrink, and cause lumpy running when cold. When the choke is working properly on manual and auto choke carbs, the idle should be smooth, even from cold, but with a higher idle until warmed, at which point you'll either push your choke back in, or let the stepper motor do its stuff. Many cars i come across make 'hunting' noise caused by being over-rich. although this can often be caused by the owner leaving the choke on too long... I'm glad i've got my ECU... In fact, as a case example to prove how well it works, i went outside last night to start the turbo up after two weeks, it was sub-zero outside, started first time and idle sat at 1100rpm :)

Gareth

[threelitre]

Originally posted by MGTurbo
You still have a seal on the choke shaft which performs the same function as it would if it were an auto choke. As they are the same material, given time and age, it will shrink, and cause lumpy running when cold.

Well, it's idling nice when cold :) It is only rough when warmed up and it idles at aboout 800rpm... But I'll take that carb apart anayway, so I'll just replace all the seals.

Many cars i come across make 'hunting' noise caused by being over-rich. although this can often be caused by the owner leaving the choke on too long...

I am more on th opposite and try alwasy to use the least possible amount of choke with the car running well. That means more choke in the city as when going on the motorway directly. And this leads me to think about fitting a carb with that vacuum switch.

I'm glad i've got my ECU... In fact, as a case example to prove how well it works, i went outside last night to start the turbo up after two weeks, it was sub-zero outside, started first time and idle sat at 1100rpm :)

I must say, that I would have preferred a Maestro with automatic choke - I liked it on my old LE. And it worked well, when the electric connection was fine... It's not that I am not used to drive cars with manual choke ;)

Alexander

[SimonR]

Originally posted by MGTurbo
There is only one seal fitted to manual choke carbs, 2 on the stepper motor of electronic carbs. They shrink with age, allowing neat fuel past at idle, and worth changing for new. STD seal size, BSO13, obtain them in viton, otherwise they will swell.

Gareth - I've found out where I can buy the Viton seals from but there is no BS013 listed. Was that a type-o (I saw 103 and 301)?

Many thanks

Simon R.

[Simon]

I've got a pack of 5 ordinary O rings for the stepper motor from the dealers so you can have a couple if you are interested, Simon.

I tried to get my stepper motor off the carb on my car but there are 2 problems, firstly that of access being as there is now a whacking great big PAS reservoir sitting in the way! Easy to solve, but secondly the stepper motor bolts are on very tight and, because they have crosshead screws I'm afraid of mangling up the screw heads.

So, have any of you got any good advice for stepper motor removal and are new bolts available, preferably with different heads - if so where from?

My 1.6 Maestro starts from cold but won't idle until the temp gauge moves and I'm getting fed up with constant restarts!

[SimonR]

Originally posted by Simon
I've got a pack of 5 ordinary O rings for the stepper motor from the dealers so you can have a couple if you are interested, Simon.
Thanks Simon I'll happily take you up on that offer. Tell you what, shall I swap them for a Maestro Technical guide CD that I made for you last year and haven't sent yet...?!

I tried to get my stepper motor off the carb on my car but the stepper motor bolts are on very tight and, because they have crosshead screws I'm afraid of mangling up the screw heads.

So, have any of you got any good advice for stepper motor removal and are new bolts available, preferably with different heads - if so where from?
I had exactly this problem when I was working on F153's engine in November. Those screws are a real pain in the backside. I used an electric drill/screwdriver thing with exactly the right pozidrive screwdriver bit on the slowest speed. I found that pushing really hard against the screw head and very gently squeezing the trigger got all but one shifted. The third one I had to saw off the head and then use mulgrips to twist it. When I put salvaged replacements back in I coated the threads in copper grease to prevent the problem in the future. I'll be very glad of that when it comes to changing the 'o' rings again!

My 1.6 Maestro starts from cold but won't idle until the temp gauge moves and I'm getting fed up with constant restarts!
Huh, tell me about it! F153 is exactly the same. It's soooo annoying when in queues of traffic and there's always that slightly dodgy moment when it takes a little longer than normal to restart and you think it's not going to! I wonder if the Haynes plug gap setting is correct - could it be this that's causing part of the problem?

Actually, while we are on the subject, I have noticed a really weird thing with the engine management while it's cold: habbitually I start the car with the clutch depressed but this causes an even worse cold idle/cut out problem - the engine will cut out three or four times before I've even left the drive. However if I remember and start up without depressing the clutch, the car seems to start quicker (usually about 2 cranks) and runs much better, cutting out less. Odd isn't it?

[G Force]

Originally posted by F153JUE
Actually, while we are on the subject, I have noticed a really weird thing with the engine management while it's cold: habbitually I start the car with the clutch depressed but this causes an even worse cold idle/cut out problem - the engine will cut out three or four times before I've even left the drive. However if I remember and start up without depressing the clutch, the car seems to start quicker (usually about 2 cranks) and runs much better, cutting out less. Odd isn't it?

Hi this one could be down to worn crankshaft thrust washers causing excess crank end float, which puts extra load on the engine with the clutch pressed. It may have been caused in part by your bad habit, putting load on the thrust washers before they are properly lubricated. PS don’t know what Haynes say the plug gaps for a 1.3 should be but .035in is correct or .040in for a 1.6.

Cheers Gary
:)

[SimonR]

Originally posted by G Force
Hi this one could be down to worn crankshaft thrust washers causing excess crank end float, which puts extra load on the engine with the clutch pressed. It may have been caused in part by your bad habit, putting load on the thrust washers before they are properly lubricated. PS don’t know what Haynes say the plug gaps for a 1.3 should be but .035in is correct or .040in for a 1.6.

Cheers Gary
:)

Hi there Gary, that's interesting - I though it was *good* for the engine to have less load on it when it started. What's the reasoning to have the cluth engaged?

Also I hope nothing's worn in the engine - it's only done 2,600 miles!

Thanks for those feelerguage settings - I'll make sure my plugs are as you say.

So you reckon in future I should start the engine with the clutch engaged...?

[Simon]

I've always started cars including my own with the clutch pedal down without any problem. However, it might be that you have got a rogue engine. You could try and see if the crankshaft pulley moves when you depress the clutch, if so - problems...
Triumph Heralds and Spitfires suffer with this problem notoriously. I've never heard it on a Maestro or Montego though.

BTW Simon, I went across to Ledbury on Saturday. Wow!

[E_T_V]

Another possibility is that the clutch cable is interfering with the throttle cable (they are often zip tied together in the engine bay). If this is the case it can confuse the ECU (if fitted with auto choke) as it thinks you are trying to give it some gas when in fact you aren't. Not sure if the 1.3's are fitted with a throttle switch on the pedal, but if it is check that this isn't being activated when you depress the clutch.

[G Force]

Originally posted by F153JUE
Hi there Gary, that's interesting - I though it was *good* for the engine to have less load on it when it started. What's the reasoning to have the cluth engaged?



I dont know exactly where the pressing the clutch down before cranking is a good thing came from, but i do know that it is something often done by truck drivers which is probably advantageous in their case, as trucks have massive gearboxs with heavy oil in them and do need a lot of effort to turn them when cold, but they also have massive crankshafts and thrust washers and slower cranking speeds so making them more robust.

You can sort of tell if you have a lot of crank end float by watching the front pulley whilst some one presses down the clutch but you realy need to push the crankshaft in towards the gear box first. I also hope that your engine is ok and at such a low milage I doubt that you will have contributed any towards any wear that may or may not be their, I was just thinking if it had had a long lifetime of starting in the manner you do may have been an explaination for worn thrust washers. Personnally as for pressing the clutch to start I would not do it

Cheers Gary:)

[E_T_V]

Yes that is right, pressing the clutch removes load from the engine when starting it so it is more likely to start and be less drain on the battery. It is much more applicable to big diesels with huge gearboxes and thick oil as you said however it might make a little difference to our cars on a really cold morning. I never worry about such things, I think it is more likely to be a cable fouling problem in this case.

[F690OTF(RIP)]

It also means that unless your clutch cable's broken or become detached you can guarantee that the car isn't going to lurch forward when you crank the engine.

[SimonR]

Thanks for the ideas chaps - I'll take a look at the cables and see what's gong on there. From now on I'll start the engine with the clutch engaged which, TBH I was doing anyway as it starts and runs a lot better.

I'll let you know how I get on!