26 replies to this topic

[goat64]

Update:

 

I've changed old metal fuel pipes to new flexible fuel pipes with metal braiding. (I read somwehere that Vapour locking is not unusual in old cars run on modern unleaded wiyth metal fuel pipes in engine compartment).

Whilst  changing them, noticed that there was very free flow of petrol (under gravity) from tank to pump.

Old pipes were perished but still patent, no visible debris in them.

Not really surprising then that new pipes made NO difference - same problem of rough runnig as it warms up, tending to stall and no chance of restarting when hot.

The new pipes look good though, and I'm sure are less likely to leak / split in future than the old rubber connectors between metal pipes.

by the way, after some hours struggling to get new feed into pump, decided to remove crancase breather cannister from rear of engine block (it's only 1 13mm bolt) - much better access for my neanderthal hands.

 

Whilst poking around with air filter off, checked out float valve as suggested by midridge2.

All very clean, no debris, plastic float intact (no leak), needle valve moving very freely, float pivot allowing free mvt of float. I checked it when hot as well, in case of heat-dependent binding: no seizing of valve or pivot.

One thing: the manual suggests there should b 3.18-4.76mm celarance between lowest part of float (held upsiade down off-car and allowed to sit under gravity against tip of needle valve) and inside of lid of float chamber.  My gap seems more like 8mm, with no visible way of adjusting. The float is of the type with NO metal arm to bend, so the only way of adjusting float height is by changing depth of washers in the needle seating. Can't believe this is the cause, as the float chamber is 3/4 full of petrol, whether I open it cold or hot (i.e. when stalled). I could fidle around with washers in seating of needle valve, except I can't remove the pivot pin. I think it is just a tap-out job, isn't it? But it won't bude, and I don't want to hit it too hard and risk doing damage to the float / bending the pivot pin (both seem to be working fine).

 

So today when it was warmed up, I turned it off (after completing above checks) and tried restarting it. Very reluctant again, but it did start. - sounds like an old slow revving thuddy wide bore m/c engine when it fires initially, before firing up and allowing throttle use up to normal revs. It ran a bit rough for a while. I revved it (at approx the same revs levels as i would driving on teh road) for 1 min. It was still running a bit rough but didn't stall if i tickled the throttle. After turning off, it would not start again.

 

Whilst it was still hot, checked to see if good spark at HT lead end (where it connects to distributor cap) - great steady string spark, so I suspect coil is OK.

Checked for sparks at plug gaps - VERY DUBIOUS: weak spark, or not at all. Sometimes spark seemd to flop down sides of central insulator rather than jump gap. All plugs much the same. All plugs noted to be carbonised - i.e. dry carbon, no oil fouling and specifically no petrol smell - no hint of flooding.

 

I've checked all connections to distributor / coil / points (all are new). Checked cap and rotor arm - both new and look pristine, no tracking. Checked points gap - right where it should be (0.35mm), which is reassuring as I recently set it with dwell meter (51 degs) and haven't touched it since.

 

So, I fear we have at 2 problems, which is why it is proving so frustrating:

1) despite careful checking of ignition system before posting on here, there seems to be a heat-sensitive fault somewhere between HT lead from coil 9which is sparking reliably) and plugs. I find it hard to believe ALL HT leads to plugs have given up the ghost suddenly, and I can't see any shorting sparks when I examine HT leads carefully running the car in the dark. However, I will invest in new HT leads if I have to. Do you think dodgy HT leads to plugs would explain teh heat-sensitive ignition problem?

2) fuel delivery still an issue. I like te explanation of Mini Mad about relative fuel starvation when hot, except: plugs indicate running too rich , when it runs at all (carbonised rather than light grey). Also, when it is running (even if a bit rough) at normal temp, doing the piston-lifting-pin method of assessing fuel mix suggests exactly the right mix (revs rise slightly before falling back on lifting piston). However, I'm game for a challenge, so will open the fuel mix screw richer and try again.

 

I'll report back after starter spray / HT lead changes / fuel enrichment, but I'm on the point of giving up and asking my local friendly mechanic if he fancies taking it on. I hate giving up!

 

by the way, did anyone see my commet about wheezing?

 

By the way, did anyone see my comment about the wheezing noise:

"When the engine speed starts to die before it stalls (or I tap the accelerator to keep it alive, or pull the choke a bit out), there is an odd noise from the engine. The closest I can describe it is like a quiet asthmatic wheeze, but continuous. It seems to come from the alternator end of things, but I could be wrong. It goes away if I can pursuade the engine speed back up to normal idle.  Mean anything to anyone?"

 

Perhaps my mini is so old it has developed bronchitis?

 

Thanks again to all.

[goat64]

Forgot to mention re. "You might have a dud tank of petrol - maybe it is old petrol?"

 

Good thought.

 

It certainly was old petrol - 13 yrs old - but I flushed it all out and replaced with fresh unleaded with valvemaster as part of taking it of mothballs. I've got through 2 full tanks of fresh petrol since then, just running it on the drive and getting it up to MOT and back. The petrol in the pipes / float chamber is crystal clear - no debris. The only deposits I found anywhere was a light powdery bloom on the needle in the carb main chamber which polished off easily with a cloth and made no difference to the fault.

 

Thanks

 

Gautam

[midridge2]

A cheap
and easy think to do is again replace the condenser, there were a big batch of dodgy ones around.

[Wim Fournier]

I read all you wrote and understand that you don't think I'm right mentioning that the mixture is not good.

All right, follow your own way of thinking.

But in the end you will find out that there is an airleak in the intake track.

When you really think, you will understand that at low revs the quantity of fresh air that is entering via the leak is at its highist proportion compaired to the total amount of air entering. So at low revs you have the weakest mixture. Some times too weak for burning.

[goat64]

I read all you wrote and understand that you don't think I'm right mentioning that the mixture is not good.

All right, follow your own way of thinking.

But in the end you will find out that there is an airleak in the intake track.

When you really think, you will understand that at low revs the quantity of fresh air that is entering via the leak is at its highist proportion compaired to the total amount of air entering. So at low revs you have the weakest mixture. Some times too weak for burning.

I am ticking off things as I go, and on the to-do list is get some starter spray and check for intake leaks. The only reason I haven't yet is I haven't got any so trying things I can do 1st.  I'm still confused why lean mix would leave all the plugs carbonised. Anyway, will report back once tried.

Thanks for advice - I am very grateful.

Goat

[goat64]

"again replace the condenser, there were a big batch of dodgy ones around."

 

A cheap
and easy think to do is again replace the condenser, there were a big batch of dodgy ones around.

The condenser was replaced a few weeks ago to no avail. Is there any way of checking a condenser?  I seem to recall a similar ignition problem on my old renault 5 being fixed by a new condenser a few years back. That's why I changed this 1st. Like you said, a quick easy thing to (re-)try. Will let you know.

 

Thanks

 

Goat

[Wim Fournier]

 I'm still confused why lean mix would leave all the plugs carbonised.

Well, the mixture is only (very) week at low revs. Because -like I said- at low revs the proportion of inhaled air via the leak compaired to the amount of air that is sucked in via the carb itself is much higher. Compared to that amount of leak air is the amount of air coming via the carb itself at (wide) open throttle just a little bit.

When the throttle is almost closed the vacuum in the inlet manifold is much deeper than when the throttle is opened any further. So, at low revs there is coming in more leak air than with the throttle opened. At driving speed, there is almost no leak air and is the mixture almost rich. At low revs (throttle closed)  there is coming almost  no air past the venturi, so there is picked up very little fuel. The mixture is much too lean for burning.

Because the engine turns most of the time with the throttle open, the mixture is -most of the time- rich and carbonising the plugs. The few minutes with the throttle closed and too lean a mixture are not enough to burn that coal away from the plugs.

[goat64]

 I'm still confused why lean mix would leave all the plugs carbonised.

Well, the mixture is only (very) week at low revs. Because -like I said- at low revs the proportion of inhaled air via the leak compaired to the amount of air that is sucked in via the carb itself is much higher. Compared to that amount of leak air is the amount of air coming via the carb itself at (wide) open throttle just a little bit.

When the throttle is almost closed the vacuum in the inlet manifold is much deeper than when the throttle is opened any further. So, at low revs there is coming in more leak air than with the throttle opened. At driving speed, there is almost no leak air and is the mixture almost rich. At low revs (throttle closed)  there is coming almost  no air past the venturi, so there is picked up very little fuel. The mixture is much too lean for burning.

Because the engine turns most of the time with the throttle open, the mixture is -most of the time- rich and carbonising the plugs. The few minutes with the throttle closed and too lean a mixture are not enough to burn that coal away from the plugs.

Aha! That makes sense now.  I'll get some starter spray next time I'm in town and let you know if / where I find a leak.

Thanks

Goat

[goat64]

Very belated update on starting (and running) problems, and a question about the "pin lift" method fo fuel mixture setting.

 

renewed all the following:

coil

points (replaced with breakerless)

plugs and HT leads (3 of the 4 leads were suspect when resistance compared to a new one!!!)

tank (see other post re small to large fuel tank swap; original tank was full of rusty rubbish which very likely had found it's way further towards carb)

carb needle

 

I cleaned out all fuel lines, float chamber (loads of rusty gunk in bottom) and carb venturi / inlet chamber 9which were very clean aleady)

I checked timing (dynamic) it was OK.

Choke needed a bit of cable / cam adjustment, but not too far out of kilter.

Sprayed WD40 round inlet manifold when running - no suggestion of leak (no change in engine note / revs)

 

The new HT leads made a big difference to starting and running, and it's nice not to have to worry about petrol oozig into the boot / passenger compartment anymore, but I'm not convinced anything else from the above list made much difference.

 

I have tried setting fuel mix using "lifting pin" method numerous times at intervals, after each of the abovechanges to see if the mix was still matched to the latest tweak. Every time, I got this...

 

Even with fuel screw threaded up hard against the carb body (leaner and leaner) the lifting pin method still suggested itI was too rich (sustained increase in revs when lifting pin). Plugs very sooty very quickly after every cleaning, but not smelling of petrol. Engine not overheating at all, in fact block surprisingly cool (pump, hoses, rad all working fine)

 

In the end, I gave up and went back to old fashioned method (I have no gas analyser or colourtune plug).

I enriched the mixture 1-flat-at-a-time until it started to really drown (about 2.5 full turns open), then leaned it again until it passed maximum revs and started to drop slightly. This turned out to be around 1.5 full turns (9 "flats"). Now starts like a bomb, run sweet as a nut (apart from slight hiss from pinhole on exhaust clamp near ex manifold). Will now do 50mph happily (come on guys, it is only an 850 and its 45 yrs old. That's like 150 human years!)

 

I will check the plugs again after a few hundred iles, but to be honest, as long as it starts and runs reliably, I'm less fussed what the plugs look like.

 

So,anyone explain to me why the piston lift method has started to fail me? It always used to work OK.

 

I assume I have been trying to run it on vapour for the last few months with the fuel mix set on , well, nothing. I always understood that lean-run engines tend to overheat and have grey / glazed plugs (see photos in Haynes).  So any ideas why my engine block was on the cool side after 30-40 mins running (hesitantly) and why the plugs were so sooty so quikly.

 

Anyway, my lovely old 850 1976 mk3 is turning heads again out on the road, so I'm happy.

 

BW to all

 

Goat

Edited by goat64, 11 May 2021 - 03:31 PM.

[floormanager]

Hello Goat, I'm Paul, we bumped into each other a few weeks ago when we turned into the Plough at Plumpton.  I had the blue 68S.  Anyway, on Sunday, I saw your car drive past my house with learner plates on it.  I chased it to the junction and said hello to the lady and the young lad driving.  They said you'd got it running well now.  Lovely to see you Antique Gold 850 mini driving around.  Well jealous, such a nice genuine car.

 

In terms of lifting pins, I've not had much success with them.  You are only lifting the damper a really small amount, If you lift the pin all the way, you'll lift it more than necessary.  There's a post here

https://www.theminif...in-on-su-carbs/

 

All the best,

Paul

[goat64]

Hi Paul

 

Antique Gold is the official description. We call it "toddler poo". I must put a photo up on here, so members can enjoy the full nauseating effect.

 

Glad to hear I'm not the only one who has found the pin lift method for the SU carb a bit unreliable. I don't really uderstand how it would work anyway, but I'm happy doing it the "old fashioned" way, so will stick with that from now on.

 

Steer well clear of number 2 son with his "loser" plates on if you see him out and about. He's dangerous!  Actually, like most learner drivers, he's very careful and safe; I wouldn't tell him that though; not until he's passed his test.

 

Thanks for the link; very comprehensive.  I think I sort of did the basics (non pin lift method) myself by accident and it seems to be running sweetly now, so loathed to interfere again. Having said that, I may risk doing the full procedure as described again from scratch just to make sure it is as right as it can be.

 

Gives us a gentle "bib" when you see us out next.

 

BW

 

Goat

[DomCr250]

Very belated update on starting (and running) problems, and a question about the "pin lift" method fo fuel mixture setting.

 

renewed all the following:

coil

points (replaced with breakerless)

plugs and HT leads (3 of the 4 leads were suspect when resistance compared to a new one!!!)

tank (see other post re small to large fuel tank swap; original tank was full of rusty rubbish which very likely had found it's way further towards carb)

carb needle

 

I cleaned out all fuel lines, float chamber (loads of rusty gunk in bottom) and carb venturi / inlet chamber 9which were very clean aleady)

I checked timing (dynamic) it was OK.

Choke needed a bit of cable / cam adjustment, but not too far out of kilter.

Sprayed WD40 round inlet manifold when running - no suggestion of leak (no change in engine note / revs)

 

The new HT leads made a big difference to starting and running, and it's nice not to have to worry about petrol oozig into the boot / passenger compartment anymore, but I'm not convinced anything else from the above list made much difference.

 

I have tried setting fuel mix using "lifting pin" method numerous times at intervals, after each of the abovechanges to see if the mix was still matched to the latest tweak. Every time, I got this...

 

Even with fuel screw threaded up hard against the carb body (leaner and leaner) the lifting pin method still suggested itI was too rich (sustained increase in revs when lifting pin). Plugs very sooty very quickly after every cleaning, but not smelling of petrol. Engine not overheating at all, in fact block surprisingly cool (pump, hoses, rad all working fine)

 

In the end, I gave up and went back to old fashioned method (I have no gas analyser or colourtune plug).

I enriched the mixture 1-flat-at-a-time until it started to really drown (about 2.5 full turns open), then leaned it again until it passed maximum revs and started to drop slightly. This turned out to be around 1.5 full turns (9 "flats"). Now starts like a bomb, run sweet as a nut (apart from slight hiss from pinhole on exhaust clamp near ex manifold). Will now do 50mph happily (come on guys, it is only an 850 and its 45 yrs old. That's like 150 human years!)

 

I will check the plugs again after a few hundred iles, but to be honest, as long as it starts and runs reliably, I'm less fussed what the plugs look like.

 

So,anyone explain to me why the piston lift method has started to fail me? It always used to work OK.

 

I assume I have been trying to run it on vapour for the last few months with the fuel mix set on , well, nothing. I always understood that lean-run engines tend to overheat and have grey / glazed plugs (see photos in Haynes).  So any ideas why my engine block was on the cool side after 30-40 mins running (hesitantly) and why the plugs were so sooty so quikly.

 

Anyway, my lovely old 850 1976 mk3 is turning heads again out on the road, so I'm happy.

 

BW to all

 

Goat

I recon it was your condenser, just as Cooperman suggested.  I had exactly the same many years ago on my 1275GT.  A switch to electronic ignition is one of the best things you can do to any mini.