BMW doesn't start after standing still long time.

Tim Schoon

Tim Schoon

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Hi all,
My name is Tim Schoon and together with my dad I have restored a BMW 3.0Cs from 1973. I started working on it when I was about 5 years old and we finished it 10 years later when I turned 15. Now 2 years later we are still enjoying the luxurious ride we get from this beautiful car. However these 2 years were not without trouble as you might expect ;). We have driven it from Holland to England without any issues however after this trip we wanted to go for a ride again but it wasn't as smooth as before. we did some investigation and came to the conclusion that it was the carburettors that were not synchronised. Sent it of to a specialist which sorted the issue.
Now just 2 weeks ago we wanted to drive it for the last time and make it winter ready before we leave it stored for the winter. However we didn't get far, at first. The car had been standing still for about 6 weeks and didn't want to start with the shook on. the only thing we could think of at the time was to add a little brake cleaner and directly it fired up without problem. we drove it around to charge the battery again and it ran amazing.

My dad had to wait for me about 30 min on a parking lot and he said that the petrol smell was pretty strong. On the way back the car started to drive a little worse again, again we had this shocking while driving.

Our thoughts are that the fact that it doesn't start is potentialy that the carburattors don't get enough petrol and the flow of petrol into the carburators is to little?( after standing still for long time? would there be a small leak somwhere? can that leak cause the car to smell of petrol when standing still? and while driving doesn't get enough petrol either??)

those are our thoughts, however we are clueless apart from these ideas.

thanks for helping in advance

Tim Schoon
 
My CS is also hard to start if it has been sitting for a few weeks. Instead of cranking the engine for a long time to pump fuel into the empty carburetors, I open the air filter a spray some starting fluid into the carburetors. It then starts instantly, and after a little more cranking will stay running.
 
My car does the same as Mark's and i also prime it after it sits a long time. This doesn't explain the rough driving though so i would probably start by looking for vacuum leaks.
 
If you think gasoline is not getting to the carburetors from sitting so long you can install a one way check valve into the fuel line
 
teahead said:
Does that help w/evaporated gas in the float bowls?
Click to expand...
Obviously not, but fuel doesn't evaporate that fast. My GMC truck has a faulty check valve in the fuel pump and I have to "prime" it before starting by turning the ignition on and off a few times. Not sure how it would work with bowls, I can't remember how they're configured..
 
It helps keep fuel from draining back to the tank so that next time you crank it doesnt have to suck fuel from the tank, only from the check valve. If the fuel bowls are low it will fill them quicker and get the engine started with less cranking.


teahead said:
Does that help w/evaporated gas in the float bowls?
Click to expand...
 
I've found that age is a significant factor in diagnosing this problem. After I got older I found that it was harder to start after sitting for a long time...
 
ther is not enough information in. your post,

you did not mentioned how far did the restoration went as to the carbs or engine or ingnition elements

it is relevant to konw your setup in detail
 
i do not know what is the shook ?
“weeks and didn't want to start with the shook on”
do you mean the choke ?

do you really know how to start the car ? how the choke is engaged ?
which carbs do you have ?
 
if you made sucha long trip without issues most likely the car was correctly restored, but it seems strange that you did not noticed the need for a synchro since the begining

as stevehose mentioned it is a good thing to install an antireturn valve and a clear fuel filter too, for a prize you might install a manometer too, this way you will be able to check if the pump works correcly, presssure should be 0,21 to 0,25 bar

antireturn valve will help, and the clear filter will let you see the fuel present

in principle this setup will avoid any problem in starting the car after a long time
 
Hello, I have the original Zenith carbs in my e9 and to cure the same problem I put in an electric fuel pump. Problem solved. Very easy to install.
 
Stevehose said:
If you think gasoline is not getting to the carburetors from sitting so long you can install a one way check valve into the fuel line
Click to expand...

Hi Steve,

This is exactly what I did but the problem remained exactly the same. Car starts perfect after standing stil for a few days but if it stands for a month or longer I have to crank it for quite some time before she wil start-up. Maybe my fuel pump also is up for renewal?
 
Philippe db said:
Hi Steve,

This is exactly what I did but the problem remained exactly the same. Car starts perfect after standing stil for a few days but if it stands for a month or longer I have to crank it for quite some time before she wil start-up. Maybe my fuel pump also is up for renewal?
Click to expand...
It sounds like some of the gas is getting past the one way valve. It may be only a tiny bit but over a month, since the carbs are much higher than the gas tank, gravity takes over and slowly drains all the gas back in the tank. The mechanical pump only works when the motor cranks so, unless you have an electrical pump, this does not sound surprising to me.
 
Thanks for the info Bo, makes perfect sense.

As long as the battery is strong enough and I'm able to crank the engine for 15seconds everything returns back to normal. All part of the fun. The cars that start on the first push of the button under all circumstance we drive everyday.
 
dang said:
My car does the same as Mark's and i also prime it after it sits a long time. This doesn't explain the rough driving though so i would probably start by looking for vacuum leaks.
Click to expand...

These are all very savvy responses. Here are the dumb things I've done or overlooked which corrected starting problems. Vacuum leaks fixed my similar issue--old hoses replaced, including one particularly dumb move on my part unknowingly knocking old hose to coil loose every time I removed the filter cover, but I did learn PO had installed wrong size hose. Rigged and soon to be replaced old positive battery cable with cracks, etc. Replaced cracked fuel line T-splitter. At others' suggestion, I add a second fuel filter after doing anything with fuel lines or tank, and that has trapped more junk than I thought. You and your dad seem far more knowledgeable than me, but just in case.
 
Same issue here with my CS.

Sat since 88, unseized the mechanical fuel pump and primed the fuel system and ran fine when i started it once every fortnight or so.

Left it for about 4 months and same issue, i usually just disconnect the fuel filter and use a small vacuum pump to fill the fuel filter up from the tank, then stick some petrol down the carbs.
 
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