72 MGB Morning Sickness
Discussion
I'm not a big fan of WD40 for use on anything much and think (don't know) SU meant to use light oil (no pun intended) to "lightly oil piston rod only" - '3-In-One Multi-Purpose Oil' the makers (WD40 company) state “is SAE 17, it is quite a fine oil.” whereas the ‘3-in-ONE Motor Oil’ (blue label) is equivalent to SAE 20, some owners use either as dashpot oil too
for the dashpots most over here go for 20w/50 engine oil but which oil to use and to fill to what level varies depending on which book you read and whose opinion you want to take
I too go with if you can feel suction as you pull the rod up then there's enough oil in the dashpot
30 weight engine oil overlaps 80 and 85 gear oil so not the big difference in thickness as you and some others might think (see chart below) and if I don't find 90 weight gear oil too thick for a British winter I'm sure you wont in your winters, whether you'd need to adjust your carb settings for the difference I don't know but as you're adjusting anyway
for the dashpots most over here go for 20w/50 engine oil but which oil to use and to fill to what level varies depending on which book you read and whose opinion you want to take
I too go with if you can feel suction as you pull the rod up then there's enough oil in the dashpot
30 weight engine oil overlaps 80 and 85 gear oil so not the big difference in thickness as you and some others might think (see chart below) and if I don't find 90 weight gear oil too thick for a British winter I'm sure you wont in your winters, whether you'd need to adjust your carb settings for the difference I don't know but as you're adjusting anyway
Thanks for all the free advice and especially interesting was the lubricant chart. I was unaware that 'gear oil' viscosity range had a correlation to 'engine oil'. Since 30wt is in the viscosity neighborhood of 80-85wt gear oil and the dashpot action is considerable, I intend to continue to use it.
The good news is that the engine is back to normal, meaning Morning Sickness is gone, at least for now. It starts readily under all the conditions prevailing here in Northern California, morning, noon and night, hot or cold, and no choking is required, just has been the case for decades.
The bad news is that I have no solid understanding why. The ONLY overt actions I ever took, aside from the bicycle pump trick, was to replace rubber fuel lines and the inline filter, open and clean the float chambers, adjust the float levels, replace the original float needle valves and flush the jets as I described a few days ago. Notice I never touched the 'starter' valve, aka the choke. None of those actions revealed a smoking gun. Not even the jet flush because the next morning the engine again refused to start even using the choke. However, the morning after that I used the choke again and the engine started instantly. It has ever since without the aid of the choke, just as I had been experiencing lo these many years.
Some of you continue to focus on the choke function and rigging. I haven't touched the choke setup and it is known to be correctly rigged and functioning. Nor have I adjusted the mixture screws, even when disassembling the floats and removing the jets, which all can be accomplished without disturbing the mixture scews.
So, I'm left perplexed as to 'why' but for now I going to declare victory and wait to see if my luck holds.
The good news is that the engine is back to normal, meaning Morning Sickness is gone, at least for now. It starts readily under all the conditions prevailing here in Northern California, morning, noon and night, hot or cold, and no choking is required, just has been the case for decades.
The bad news is that I have no solid understanding why. The ONLY overt actions I ever took, aside from the bicycle pump trick, was to replace rubber fuel lines and the inline filter, open and clean the float chambers, adjust the float levels, replace the original float needle valves and flush the jets as I described a few days ago. Notice I never touched the 'starter' valve, aka the choke. None of those actions revealed a smoking gun. Not even the jet flush because the next morning the engine again refused to start even using the choke. However, the morning after that I used the choke again and the engine started instantly. It has ever since without the aid of the choke, just as I had been experiencing lo these many years.
Some of you continue to focus on the choke function and rigging. I haven't touched the choke setup and it is known to be correctly rigged and functioning. Nor have I adjusted the mixture screws, even when disassembling the floats and removing the jets, which all can be accomplished without disturbing the mixture scews.
So, I'm left perplexed as to 'why' but for now I going to declare victory and wait to see if my luck holds.
PositronicRay: Yes, I am running a little rich and have been told the exhaust does smell a bit like fuel, which is the stuff you call petrol. Years ago I carefully set up the carbs per the Shop Manual and found the result to be lean. So lean the engine staggered at hiway speeds. So, in small increments I richened the mixtures until it smoothed out. It didn't take much and it's been there ever since. At the time California required that I smog check the car. Even rich as it was it passed easily. Since the result was a smooth running machine that started easily and passed smog check, I figured I had a good solution. Mileage is OK, I get about 20mpg around town, 23 on long stretches. What's your experience?
By the way, I installed an overdrive transmission a few years ago. It greatly improved the driving comfort at hiway speeds but did nothing for fuel economy. Nor should it. Overdrive or not, it takes the same BHP, thus gph, to move the car at 65mph. Any savings would come from a tiny reduction in friction HP, not noticeable in the big scheme of things.
By the way, I installed an overdrive transmission a few years ago. It greatly improved the driving comfort at hiway speeds but did nothing for fuel economy. Nor should it. Overdrive or not, it takes the same BHP, thus gph, to move the car at 65mph. Any savings would come from a tiny reduction in friction HP, not noticeable in the big scheme of things.
You're fuel consumption sounds a little low my 1275 was getting 35mpg (imperial) on a run (approx 28mpg US)it's often about the roads and driving style however.
The overdrive should help I would have thought, certainly makes it a nicer car on the motorway.
I would give it a service, ignition, tappets and then have another go @ setting up the carbs.
I've never got on with those colortune things so rely on the book way of setting up SUs. It can be a bit of a fiddle but a with a little practice and once it's right the engine runs so much better.
If everything is worn it makes it much harder. Often in the UK people take them to an expert with a rolling road, once set up don't touch the buggers.
When I do the timing I only use the book figures as a guideline, fuel is different now and things get worn. I advance the ignition till it pinks (3rd gear 2k revs and accelerate up a hill) then back it off a bit.
No point touching the carbs until everything else is spot on.
I would reckon to always use the choke for a cold start, even when the ambient temp was 20 C. If the car has already been run that day and been left baking in the sun I could get away without choke.
The overdrive should help I would have thought, certainly makes it a nicer car on the motorway.
I would give it a service, ignition, tappets and then have another go @ setting up the carbs.
I've never got on with those colortune things so rely on the book way of setting up SUs. It can be a bit of a fiddle but a with a little practice and once it's right the engine runs so much better.
If everything is worn it makes it much harder. Often in the UK people take them to an expert with a rolling road, once set up don't touch the buggers.
When I do the timing I only use the book figures as a guideline, fuel is different now and things get worn. I advance the ignition till it pinks (3rd gear 2k revs and accelerate up a hill) then back it off a bit.
No point touching the carbs until everything else is spot on.
I would reckon to always use the choke for a cold start, even when the ambient temp was 20 C. If the car has already been run that day and been left baking in the sun I could get away without choke.
Edited by PositronicRay on Friday 6th March 17:38
It's been over a month since I last checked in about my MGB Morning Sickness. What's been happening over that time is a long story which I won't relate. The short form is that I have been trying a lot of things with no real solution found. Until now.
HIF pistons, perhaps uniquely, have a tiny plastic button inserted into the bottom of the piston. My 43-year-old buttons had worn to nothing, virtually flush with the piston face. I replaced them, $8,50 from Mr. Joe Curto, http://joecurto.com. The new buttons project 0.030" from the piston face and serve to hold the piston face off the bridge when everything is at rest and, presumably, during a start.. It seems that's important, otherwise why is the button there? My engine's starting behavior immediately changed. For several days now I have been able to reliably start the engine first thing in the morning, sometimes without using the choke but always if the choke function is used. The bicycle pump is no longer needed but I'm carrying it in the car just in case. I'm calling this a solution without knowing exactly what is happening or why. Can anybody shed light on why these buttons are there and how they make a difference during the starting event? I have a theory but I'll let the rest of you weigh in with yours.
Take a look at Mr. Solihull's posting at http://www.mg-cars.net/mgb-technical-bbs/hif-carb-... [May not be available on your server] Scroll down to the next-to-last entry to see a sketch of the HIF bridge and portings. The sketch accurately shows my '72 carburetors.
HIF pistons, perhaps uniquely, have a tiny plastic button inserted into the bottom of the piston. My 43-year-old buttons had worn to nothing, virtually flush with the piston face. I replaced them, $8,50 from Mr. Joe Curto, http://joecurto.com. The new buttons project 0.030" from the piston face and serve to hold the piston face off the bridge when everything is at rest and, presumably, during a start.. It seems that's important, otherwise why is the button there? My engine's starting behavior immediately changed. For several days now I have been able to reliably start the engine first thing in the morning, sometimes without using the choke but always if the choke function is used. The bicycle pump is no longer needed but I'm carrying it in the car just in case. I'm calling this a solution without knowing exactly what is happening or why. Can anybody shed light on why these buttons are there and how they make a difference during the starting event? I have a theory but I'll let the rest of you weigh in with yours.
Take a look at Mr. Solihull's posting at http://www.mg-cars.net/mgb-technical-bbs/hif-carb-... [May not be available on your server] Scroll down to the next-to-last entry to see a sketch of the HIF bridge and portings. The sketch accurately shows my '72 carburetors.
If the link I provided in the last entry for a picture of my '72 HIF pistons and bridge areas doesn't work for you, try mg-cars.net, click on MG, click on MGB Technical, click on HIF carb setting, scroll down to the next-to-last entry. As for the latest news, I am finding that use of the choke is now necessary in the morning, but at least the engine starts and runs smoothly. It also seems that a little attention to mixture tuning is now called for with the installation of the little buttons. I will do that next and see how, if at all, the starting behavior is affected..
Several days have passed since I installed new buttons and the results are good. With full choke on the first start of the day the engine lights off 100% of the time and for the rest of the day no choke is needed. That is a real change in cold starting behavior and I think I'm done with this issue. But what accounts for the change?
Here's my explanation of my starting issues and the role the buttons play in mitigating them. First I'll describe how I understand the SU carbs to work in general. In particular I visualize the carb in very low air flow such as when starting. If you can poke a hole in this explanation, go ahead.
1. As air flows across the bridge the piston is caused to rise [or fall] to maintain a constant, pre-established pressure at the bridge, or venturi section. 'Constant depression', so-called. That pre-established pressure is determined by the spring in the dome which is balanced by the difference of venturi pressure and ambient pressure acting across the piston, venturi pressure on top, ambient below.
2. There must be sufficient air flowing over the bridge, thus lowering venturi pressure, to cause fuel to flow past the needle and into the carb throat.
3. If the piston is resting flat and tight on the bridge, air flow area does not exist, air will not flow between the bridge and the piston face, the necessary 'constant depression' conditions will not be established and fuel will not be drawn from the jet and into the carb throat.
4. At constant engine RPM [thus constant air flow rate] raising the piston manually will weaken the mixture, not richen it, because the 'depression' pressure is increased due to a larger venturi area having been created between the piston face and the bridge surface. When the depression pressure is increased, fuel flow will decrease, weakening the mixture.
5. So, to establish correct fuel/air mixture ratio for starting, a] there must be SOME venturi area created for air to flow and fuel to be drawn from the jet, but b] too much area will so weaken the resulting mixture that it will not ignite. It is necessary for some venturi area to exist at the bridge but not too much. The buttons do that job at very low air flow.
6. With my old buttons worn to nothing, insufficient venturi area at the bridge prevented the necessary 'depression' to exist during a low-air-flow event like cranking at starting revs. Sufficient fuel did not flow from the jet and the mixture was too weak to ignite UNTIL a generous prime was provided [the bicycle pump]. The prime allowed the engine to spin however briefly. Once the engine began to spin a lot more air flowed past the bridge, pressure at the bridge was reduced [aka 'depression'], the piston was raised to establish the correct depression pressure, fuel was drawm from the jet and normal carburetion occurred. After the first start of the day a warm engine would start on a weaker mixture, or sufficient residual fuel/air mixture remained in the manifold to permit a start for at least a few turns until the carbs began to function. A dead-cold engine required such a rich mixture to start that not even the starting valves were sufficient without the contribution of the main jet, which was lacking due to worn buttons.
7. With the buttons in place, the pistons are now raised 0.030" off the bridge, sufficient venturi area exists to allow normal carburetion, and with a little choke to finish the job the engine now starts reliably.
8. The fact that this problem came on gradually over months is consistent with worn/wearing buttons. It doesn't take much lift of the piston off the bridge to allow a start but as my buttons wore to nothing, eventually no lift was happening and a cold start was not possible.
I'll stick with this explanation until someone refutes it or the car develops Morning Sickness again.
Here's my explanation of my starting issues and the role the buttons play in mitigating them. First I'll describe how I understand the SU carbs to work in general. In particular I visualize the carb in very low air flow such as when starting. If you can poke a hole in this explanation, go ahead.
1. As air flows across the bridge the piston is caused to rise [or fall] to maintain a constant, pre-established pressure at the bridge, or venturi section. 'Constant depression', so-called. That pre-established pressure is determined by the spring in the dome which is balanced by the difference of venturi pressure and ambient pressure acting across the piston, venturi pressure on top, ambient below.
2. There must be sufficient air flowing over the bridge, thus lowering venturi pressure, to cause fuel to flow past the needle and into the carb throat.
3. If the piston is resting flat and tight on the bridge, air flow area does not exist, air will not flow between the bridge and the piston face, the necessary 'constant depression' conditions will not be established and fuel will not be drawn from the jet and into the carb throat.
4. At constant engine RPM [thus constant air flow rate] raising the piston manually will weaken the mixture, not richen it, because the 'depression' pressure is increased due to a larger venturi area having been created between the piston face and the bridge surface. When the depression pressure is increased, fuel flow will decrease, weakening the mixture.
5. So, to establish correct fuel/air mixture ratio for starting, a] there must be SOME venturi area created for air to flow and fuel to be drawn from the jet, but b] too much area will so weaken the resulting mixture that it will not ignite. It is necessary for some venturi area to exist at the bridge but not too much. The buttons do that job at very low air flow.
6. With my old buttons worn to nothing, insufficient venturi area at the bridge prevented the necessary 'depression' to exist during a low-air-flow event like cranking at starting revs. Sufficient fuel did not flow from the jet and the mixture was too weak to ignite UNTIL a generous prime was provided [the bicycle pump]. The prime allowed the engine to spin however briefly. Once the engine began to spin a lot more air flowed past the bridge, pressure at the bridge was reduced [aka 'depression'], the piston was raised to establish the correct depression pressure, fuel was drawm from the jet and normal carburetion occurred. After the first start of the day a warm engine would start on a weaker mixture, or sufficient residual fuel/air mixture remained in the manifold to permit a start for at least a few turns until the carbs began to function. A dead-cold engine required such a rich mixture to start that not even the starting valves were sufficient without the contribution of the main jet, which was lacking due to worn buttons.
7. With the buttons in place, the pistons are now raised 0.030" off the bridge, sufficient venturi area exists to allow normal carburetion, and with a little choke to finish the job the engine now starts reliably.
8. The fact that this problem came on gradually over months is consistent with worn/wearing buttons. It doesn't take much lift of the piston off the bridge to allow a start but as my buttons wore to nothing, eventually no lift was happening and a cold start was not possible.
I'll stick with this explanation until someone refutes it or the car develops Morning Sickness again.
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