72 MGB Morning Sickness

[Hal Beers]

Won't start first thing in the AM. Turn on key, pump strokes once or twice. Crank engine but no start. Fires but quits cold in about 2 sec. Obvious fuel starvation. Detached fuel line at fwd SU and proved pump good by output measure at carbs. Attached bicycle pump to carb fuel inlet and pumped twice to pressurize carbs. Fuel bubbles visible at piston bases. Reattached fuel line, cranked and engine started immediately. Runs, starts and pulls fine all day. Next AM, same thing, same cure. Have changed original needle-seat float valves to ball-type from Moss with no change. Any ideas?

[PositronicRay]

Have you tried choking manually? i.e. hand over the air intake while cranking.

When you turn the ignition on you should here the SU pump run for a few seconds and then cut out once it's pressurised.

Edited by PositronicRay on Monday 23 February 08:38

[Hal Beers]

Have primed with raw fuel, both carbs, runs 2 seconds and quits. Have used cockpit choke, no help. Pump strokes only once or twice when ignition first turned on, as though the float bowls were already full. The bicycle pump trick works every time. My symptoms don't yet make complete sense. E.g. Yesterday no start as usual, drained one float chamber by loosening fwd float chamber cover [HIF SUs], did nothing else [no bicycle pump], turned on ign and pump stroked about 5-10 times to fill the empty chamber, engine started right up. Stuck float I guess, but both carbs at the same time every tiime??

[kev b]

You might try tapping the float bowls firmly whilst priming and seeing if the pump works for longer in case both float valves are sticking.

I assume you have made sure the chokes actually work when you pull the dash knob.

[Hal Beers]

In this Northern California climate my engine has never required use of the choke to start. By test and parts replacement I have ruled out the pump and the float valves. My current working theory is that due to an accumulation of some kind of gummy foreign matter, BOTH COLD PISTONS ARE STUCK ALL THE WAY DOWN first thing in the AM, not rising off their seatings when the engine is cranked, leaning the mixture to the point that a cold engine won't start and run. The pistons must come off their seating surface a little to enrich the mixture. If the pistons don't come off their seating, the resulting mixture is at its leanest and a cold start is unlikely. Later in the day, after running some and with the sun up, the pistons are warm and moving freely and thus the engine starts and runs fine. This squares with the fact that the bicycle pump trick works with a COLD ENGINE because one of the things it's doing is RAISING THE PISTONS OFF THEIR SEATS. This AM the first thing I did was to raise both pistons briefly using the pushbuttons that are in the carbs for that purpose and then let both pistons drop. The engine then started promptly and normally, and idled smoothly from the first. Later, with a warm engine idling nicely, I forced both pistons down on to their seating. The engine all but died due to the very lean mixture. When I released the pistons they rose slightly, as expected, the mixture was enriched and the idle returned to normal.

Proof positive will be to catch the cold engine refusing to start and then raising the pistons briefly to break the sticky, doing nothing elst to the mill. I'd bet it will then start just fine.

If that happens, the obvious cure will be to thoroughly clean pistons, chambers, carb inlet passages, jet faces and needles to get rid of whatever foreign matter is causing the sticky, and it would probably be a good idea to flush out the entire fuel system including the tank. But before I do that, I want to catch the rascal in the act.

[kev b]

I did not realise you were in California, do you have ethanol in your fuel? It seems to play havoc with any motor left unused for more than a few weeks.

Even here in the UK, with just a little ethanol added to some brands of fuel, I have seen motorbike carbs need stripping and ultrasonic cleaning to remove the gunge produced when hygroscopic ethanol combines with moisture.

Anyway it sounds like you will soon have the problem sorted, if not, send me a ticket and I'll have a look at it for you.

[Hal Beers]

Well, so much for my high-blown theories. Sure enough, no start this AM as usual. Lifted the pistons per plan, hit the key and....no start. Drat! The bicycle pump trick worked again thank God but the mystery still is unsolved. My 'sticking pistons' idea was bs, I guess. Realizing I needed to understand SUs better, I found this excellent discussion

http://www.zparts.com/zptech/articles/mal_land/ml_...

According to this fellow, the pistons don't move during a start thus enriching the mixture, not leaning it. Goodbye Sticking Piston Theory.

Because the bicycle pump trick works every time I am now going to assume the jets become blocked after a long layoff and cool temperatures, the air blast from the bicycle pump opens them and the engine runs. So the next plan is to attempt a start and if no start stop right there and pull the carbs. Then, very carefully disasseble them and check the jet inlets for blockage of any kind.

If I find crud, 'good news, bad news'. Good news: Cause found. Bad news: Where is it coming from and how to eliminate it?

More when I know it.

[PositronicRay]

Your bicycle pump thing is surely just flooding the carbs enabling it to fire. I used to "tickle" motorbike carbs for the same effect.

I still think the problem is choking, even in a warm climate, if you have a the carbs set up correctly (not too rich) you can need a little choke to help it fire.

Have you checked the choke or tried manually choking?

[Hal Beers]

PositronicRay:

Thanks for listening and trying to help. But regarding your 'choke' suggestion...

1. Over the many, many years I have owned and maintained this car, in this climate my engine has seldom, virtually never, needed choke of any sort to start.

2. The choke feature is known to work. I have applied it to a warm, running engine. The engine runs roughly, belches black smoke and the idle speeds up. Choking the cold engine from the cockpit has not helped with my present difficulties.

3. I haven't touched the carb setup, mixture or linkage, over the history of this symptom.

4. This problem came on gradually a few months back, intermittently at first and then, with no change to the system setup, consistently every AM.

5. The suggestion that the bicycle pump is simply flooding the carbs is opposed by the fact that priming through the carbs with squirts of raw gas causes only a few seconds, two or three at the most, of running and then the mill dies of fuel starvation.

6. No, I have not tried the manual choke idea primarily because I'm alone working on this car. Now it is time to try it if for no other reason than to possibly rule out the 'needs more choke' theory. I will enlist the aid of another geezer who lives down the street. The downside of that will be that he is an unstoppable storyteller and I will have to invest about an hour listening to irrelevancies for 30 seconds of useful help.

Just this morning the engine failed to start again but rather than dismantling the carbs as I had planned I kept at it because the engine ran a second or two on an early try. I did not use the choke at all. It showed more and more signs of life as I continued to give it short bursts of cranking. Eventually it staggered into normal operation. One way to interpret that is that I had gradually cleared the morning crud from the jets until the thing sprang into life. But that's just a theory, like Darwin's Evolution.

[Geordie MGmike]

Hal,
It sounds like both the floats are set incorrectly/sticking, holding the valves closed!
If I interpret your symptoms correctly I come up with the following;

1, at first switch on the pump strokes 1 or 2 times which only restores the line pressure
2, Runs for a couple of seconds whilst using what fuel is left in the jet until it leans out and stops
3, Bicycle pump adds pressure and forces the float(s) down and opens the valve(s)
4, as you continue to crank the engine the vibration causes one or both floats to drop and allows the fuel in
5, engine starts (possibly on two cyls) and shakes the other one free
6, removing one carb base causes the float to move (? not sure about this one) allowing the fuel to reach a critical height to start the engine.

Proving this is going to be a little difficult! But you could try giving the carb's a bit of a tap (or use a big hammer ) before starting the first time in the morning.

Best of...

[Hal Beers]

GeordieMGmike...

Arguing against the 'misadjusted float' theory is the fact that after running beautifully for years, this symptom began out of the blue while the SUs still had the original needles and seats installed. Thinking like you = sticking needle valves [smart man!] I replaced them with aftermarket ball-closure [Grose Jet] valves. No change in behavior.

Also thinking like you [smarter still] I early on gave the float chambers a few smart raps. No sound of the pump filling empty chambers and no change in behavior. Furthermore, if the floats were set incorrectly, how to explain that once I get the thing to run in the AM it starts and runs like a champ all day, until wakeup time tomorrow.

But please keep thinking. This thing will yield its secrets some day and then we'll all be embarrassed at how simple it was. Especially me.

[nta16]

have a look at the John Twist vid on needle and seats below if you've not already seen it plus about dampers and oil

232 MG Carburetter Needles and Seats (odd sizes) - http://www.youtube.com/watch?v=pVX_JClyeDQ&lis...

(needle & seat comparison) 222 MG SU Carburetters: Setting the Float Height - http://www.youtube.com/watch?v=82YNx-RkGNI&lis...

41 Matching SU Air Pistons - http://www.youtube.com/watch?v=IfU47Oqq9wA

(first part needles and seats, springs and carb oil) 123 MG Carburetors & Doors –
http://www.youtube.com/watch?v=v9QI3NlvwiY&fea...

[Hal Beers]

Latest news flash: This morning I planned to pull the carbs for a close inspection as I mentioned a couple of days ago. I was ready to go ahead with that plan regardless of whether the engine started or not, simply so that I could rule out serious carburetor contamination and crud as the root of my issues. I hoped that the thing would refuse to start so I could catch it redhanded. No such luck. The bloody thing fired right up! [I'm beginning to talk like a ruddy Brit, God forbid!]

But off they came, per the plan. I disassembled them both finding nothing of note in the way of crud, but I did discover evidence of my poor workmanship of the distant past. Both floats were quite a bit out of adjustment, both set to permit a lot more fuel into the float bowls than the book calls for. The height adjustment per the book is 0.04 +/- 0.02" between the machined surface of the float chamber and a spot on the float [look it up in your shop manual for the HIF SUs] Mine were more like 1/8 - 1/4" lower than that, a setting that would result in much more fuel in the bowl and they were different from each other. Deplorable. I have no idea how they ever got that way but I'm the one who must have done it years ago. Nobody else has ever seen the inside of my carbs. I'm surprised that the thing ran as well as it has for decades with the floats set to that level. But, it has. The alert reader would ask why I didn't catch the misadjustment when I replaced the original needles and seats with the Grose Jet units a little while back. The answer is that I stupidly neglected to even check them at the time, assuming the Grose valves were drop-in replacements and how could anything be amiss? Nobody's perfect.

I also checked the several and various ports and passages the HIFs have for emission control, finding nothing out of the ordinary. They all were open and functioning.

So I put everything back together, turned on the key, heard the pump filling both bowls, and then hit 'Start'. The thing lit off and ran smoothly immediately, like it has for many years. I now will run it to warm it up and check the mixture adjustments now that the floats are in spec. Then I'll wait until tomorrow AM to see what if anything I have improved.

Bottom line: I discovered the floats but their misadjustment has existed for a long, long time so that can't have been the cause of my recent difficulties.

One last thing. There is a short run of rubber fuel line in the engine compartment, from the steel delivery tube near the left fender through an in-line fuel filter and on to the carburetors, plus a short length of the same stuff between the carbs. Just to say I've ruled that out too, I replaced both sections and the filter. Neither rubber section was deteriorating internally, I cut them to check, and the filter was wide open to the breath test. No smoking gun there, sorry to say.

Stay tuned.

[nta16]

Hal Beers said:

[I'm beginning to talk like a ruddy Brit, God forbid!]

you should be so lucky

Hal Beers said:

The answer is that I stupidly neglected to even check them at the time, assuming the Grose valves were drop-in replacements and how could anything be amiss?

it's great that you're reporting back and even telling of you making the same mistakes that many of us often make, such as assuming instead of checking (never assume as it makes an 'ass' out of 'u' and 'me')

another saying is "when all else fails check the bleeding obvious"

Hal Beers said:

Nobody's perfect.

true, unlike many you know this and recognise and accept it in yourself so you already have a good start on sorting this car problem

Hal Beers said:

Stay tuned.

keep going and reporting as it's all useful info


for others a John Twist video of setting the floats - 222 MG SU Carburetters: Setting the Float Height (needle & seat comparison) - http://www.youtube.com/watch?v=82YNx-RkGNI&lis...

[Geordie MGmike]

Hal Beers said:

Bottom line: I discovered the floats but their misadjustment has existed for a long, long time so that can't have been the cause of my recent difficulties.

Stay tuned.

Agreed, having badly set floats could have been compensated for by setting the jet either side of the normal expected number of turns on the mixture screw.

Now we know there's plenty of fuel at the jet and there doesn't appear to be an electrical problem, so what else could cause it not to fire? To much air would do it..

Have you got the carb butterflies with the POPIT valves that are designed the open on overrun? Perhaps one or both are sticking open allowing too much air in the system for the limited amount of fuel being sucked out of the jet. There again I would expect the addition of some manual choke would help, but who knows with the good ol' B

[Hal Beers]

Well, no cure today. This AM I hit the starter and, again, no start. All that effort with the carbs was for naught. The bicycle pump trick worked as usual, so at least I have wheels for the day.

The mantra is 'air, fuel, ignition'. We have air. I do have the poppet valve anti-runon throttle plates so maybe too much air has been suggested but why then IMMEDIATELY after the first start of the day all is well? How about ignition? Same question. Just to be sure, and before the bicycle pump trick, I pulled the plugs and checked to see that they are all firing. They are. Just leaves fuel, right?

It helps me to write things down. The knowns so far seem to be:

1. Long layoffs, i.e. many hours such as overnight, are definitely bad about 90% of the time. In the past two or three weeks I have achieved a normal AM start only 2 or 3 times.
2. Cool i.e. ambient engine and carb temperature MAY be bad. E.g, a few nights ago, after the car had sat outside in cool weather for hours, it refused to start, the only time that has happened except in my own garage. The bicycle pump, which I carry with me always now, got me going. Was it the layoff? Was it the temperature? Both?
3. Raw fuel squirted into the carb inlets does not achieve a start. Never.
4. Pressurizing the float chambers to cause fuel to emerge from the jets achieves a start every time. Always, no exceptions.
4a. After that start, no further problems all day except for #2.
5. I believe the float bowls are full in the AM based on having drained them once after failing to start and the fact that the pump strokes only once or twice before a non-start. [See #7]
5a. After draining a float bowl and securing it, the engine started immediately!
6. The fuel pump is known to be good. It delivers a plentiful flow. I do not know its output pressure but it supplies everything the engine needs once I get the mill to run.
7. The pump will fill an empty float bowl, and when the bowl is full the pump stops, exactly as expected. E.g. I ran the pump until it filled the bowls and stopped, removed the fuel line at the forward carb, plugged it with a drill bit and ran the engine for 90 seconds at 1500RPM with only the fuel in the bowls before it died. As it died it ran for a few seconds on only one carb so I know what that sounds and feels like. When I reattached the line the pump refilled the bowls in about 5 seconds and stopped pumping.

I am reluctantly focusing again [still] on the carburetors, looking for a phenomenon that affects them BOTH after a long layoff. I guess I will have to strip them both to their constituant parts, examine them more closely, clean them meticulously and hope for the best.

How about some of you smart guys suggest a perceptive test or two that will help me draw a better bead on the likely culprit[s]? E.g. I could have shut the engine down half way during the test described in #7 and tried a restart to prove that the engine would/would not start with only 1/2 a bowlfull of fuel. Keep in mind that I already have ruled out faulty choke behavior by warm-engine test. The choke function is alive, causing rough running, black smoke and increased idle speed.

[Hal Beers]

As I looked at my list of 'knowns' I concluded that one potential cause that fits all the data is blockage of both jets by some mysterious goo that loosens when the bicycle pump does its thing, somehow stays out of the way during the day, but then reappears [congeals?] overnight to create at least partial blockage of the jets the next morning. I have no smoking gun for the origin of the mystery goo but a bad tank of gas, perhaps more than one, could do the trick.

I further reasoned that the bicycle pump doesn't have the oomph to blow the jets permanently clear with the metering needle taking up cross sectional area at the face of the jet but does at least clear the jet enough that the engine runs. So this AM I approached the day with a new plan. Whether or not the engine started [it did] I intended to remove the domes and pistons and flush out the jets with the metering needles out of the way.

With the domes, pistons and metering needles off, the bicycle pump attached to the fuel inlet pipe and rags draped over the engine to catch fuel, I pressurized the float chambers. A stream of fuel emerged from each jet, of course. [Have you ever been surprised by your baby boy while changing his diaper? If so, you get the picture.] Interestingly, they were different in quantity and arc range at first. I pumped until the bowls were emptied and only air was coming from the jets. Then I twice more filled the bowls and emptied them. By the third interation the streams of fuel were looking much more the same in quantity and length of arc. I think I have now flushed the jets as well as I can and to do better will require replacement of the jets. Not quite ready to do that yet.

With the domes and pistons handy, I cleaned them thoroughly and gave them each Mr. Twist's 'drop test', which is also described in the MG Shop Manual. My pistons each took 7-8 seconds to fall per the procedure. The book says 4-6 is the spec for my HIF-4s. Close enough, I guess, especially when the book's alternative is to replace both the domes and the pistons, which I am NOT going to do.

With everything back in place, the engine lit off like it always had until this mysterious malady struck. Now we wait and see.

[nta16]

presumably you also - "Using a petrol-moistened cloth, clean the inside bore of the suction chamber and the two diameters of the piston." - and - "Lightly oil the piston rod only" - (as per SU booklet)

did you also try, as per JT vid, using "90 weight gear oil" for dampening(?) (I have, all year round, and find the action from its use to be very smooth and bear in mind it can get fairly cold over here in winter)

[Hal Beers]

Yes, I did give the bores and piston diameters a good cleaning, they needed it badly, and used WD40 on the piston rod for the test.

As for dampener oil, I've been using engine oil, 30wt, forever with satisfactory results. Fact is, I so seldom check the dampener that I'm sure I've run hundreds of hours with no oil whatever in the piston rod and can't say I've noticed a difference. But if Mr. Twist says 90wt gear oil, I might give it a try. What's the worst that can happen?

However, others like SU itself say differently, http://sucarb.co.uk/technical-hif-type-carburetter... and my original 43-year-old MGB Handbook, pg. 51, says explicitly in bold, 'Under no circumstances should heavy-bodied lubricant be used'. Anyway, they've got 30wt in them now, the engine is running splendidly, and I have no complaints about the dampeners.

[Expatloon]

Unless you deliberately drain the dashpots they can never be empty, there is nowhere for the oil to go.

People who say they have to continually top up are probably overfilling and expelling the excess the first time the drive the car afterwards - and so they top it up again !

The level is supposed to be just above the top of the piston but in reality if you feel resistance when you replace the piston then that means there is enough oil in there for the damper to perform it's function.

I think your problem is to do with the choking on the HIF and more likely the linkages or rather than actual carbs themselves, are you sure the cable is pulling fully