mercedes w115 200 1976 cuts out once hot after 5 mins starts again

[vam00sh]

hello
i registered here to get some help from you guys who seem to know everything about all mercs.
so 10 years ago my dad parked up hes 1976 mercedes 200 w115 with stromberg carb and we have been trying to get it going. so far we have changed all the things that we could possibly think of that cause it to cut out under load when hot. ( after 10 mins or so it starts again and then drives )
so far we have

changed water pump
changed fuel pump
changed thermostat
changed rotor arm and distributor cap
changed capacitor
changed the coil
changed spark plugs
drained all fuel and replaced with frsh

today i ordered a ballast resistor and coolant temperature sensor which i am hoping will fix it.
i am at wits end because after doing all this i dont want to take it to a mechanic the point was that we get it going. it runs so well now and i thought we fixed it but as soon as shes hot and you drive it a few hundred yards it cuts out. if anyone has any suggestions i would greatly appreciate it

 

[vam00sh]

hello
i registered here to get some help from you guys who seem to know everything about all mercs.
so 10 years ago my dad parked up hes 1976 mercedes 200 w115 with stromberg carb and we have been trying to get it going. so far we have changed all the things that we could possibly think of that cause it to cut out under load when hot. ( after 10 mins or so it starts again and then drives )
so far we have

changed water pump
changed fuel pump
changed thermostat
changed rotor arm and distributor cap
changed capacitor
changed the coil
changed spark plugs

today i ordered a ballast resistor and coolant temperature sensor which i am hoping will fix it.
i am at wits end because after doing all this i dont want to take it to a mechanic the point was that we get it going. it runs so well now and i thought we fixed it but as soon as shes hot and you drive it a few hundred yards it cuts out. if anyone has any suggestions i would greatly appreciate it

 

[vam00sh]

hello
i registered here to get some help from you guys who seem to know everything about all mercs.
so 10 years ago my dad parked up hes 1976 mercedes 200 w115 with stromberg carb and we have been trying to get it going. so far we have changed all the things that we could possibly think of that cause it to cut out under load when hot. ( after 10 mins or so it starts again and then drives )
so far we have

changed water pump
changed fuel pump
changed thermostat
changed rotor arm and distributor cap
changed capacitor
changed the coil
changed spark plugs

today i ordered a ballast resistor and coolant temperature sensor which i am hoping will fix it.
i am at wits end because after doing all this i dont want to take it to a mechanic the point was that we get it going. it runs so well now and i thought we fixed it but as soon as shes hot and you drive it a few hundred yards it cuts out. if anyone has any suggestions i would greatly appreciate it

 

[umblecumbuz]

It could be one of many things, and swapping parts in the hope of fixing the problem is often not the best way forward, but I can see your dilemma.

If a forty year old car has really been standing for a decade, have you tried draining the old fuel and refilling with fresh? That's a guess ... but others will come along when they read your post with more suggestions. Hope you fix it - lovely old cars.

 

[vam00sh]

It could be one of many things, and swapping parts in the hope of fixing the problem is often not the best way forward, but I can see your dilemma.

If a forty year old car has really been standing for a decade, have you tried draining the old fuel and refilling with fresh? That's a guess ... but others will come along when they read your post with more suggestions. Hope you fix it - lovely old cars.

yes we drained all the fuel and re did it... have been changing things one at a time like for like that fits with the symtoms ... also it was the only way i could try to work out what the problem is.... i did not see harm in fitting brand new bits as the thermostat was in bits and the spark plugs soiled etc

 

[LostKiwi]

A ballast resistor won't fix it. The way it works is that the resistor is bypassed at start time to provide a higher voltage to the coil and as soon as the key released it runs with the resistance in series. If it was the ballast it would fire then die as soon as the key released.
The temperature sensor also won't fix it as it's not used for anything to do with fuelling or ignition as far as I'm aware.

When it cuts out is it a clean cut out or does it misfire?

I'd probably be looking at the carburettor. Old fuel forms a sticky varnish that gums up the internals.

 

[John Laidlaw]

I’d be thinking carb too (god brings back memories), might be flooding so probably a complete strip and rebuild - needles, floats and such?

 

[LostKiwi]

I’d be thinking carb too (god brings back memories), might be flooding so probably a complete strip and rebuild - needles, floats and such?

That's what I was thinking.
Fuel as it gets old either forms a red dust that blocks jets or a nasty varnish that clogs everything. I'm sure the fuel bowl will bear evidence of one or the other. Likewise fuel filters. Fuel pump may also be in a sorry state - they use a rubber diaphragm which may not like having been left dry so long.

 

[Blobcat]

Hello & welcome,

I've combined all 3 of your threads so answers aren't duplicated

 

[vam00sh]

thank all of you so much... it starts and runs very smooth once hot it cuts out it may misfire then cut out but only when it is hot. initally it pulls fine and runs fine. we sprayed a carb cleaner into the fuel hose and air intake to try and clear it and my dad put engine oil into the carb. the fuel pump has been changed. so you guys think its the carb? as i have said it only cuts out when hot and under load then after a few minutes it starts up again. in between that 10 mins it turns over and seems like it wants to start but does not hence why i thought it is something electronic and temperature related once again thank you so much for all your help. so i guess i need to remove the carb and re build it ? or can anyone recommend someone somwhere i can send it off for a professional rebuild as i am a man who tinkers with cars and methodical but far from a professional
also i should add the car is petrol not diesel

 

[vam00sh]

That's what I was thinking.
Fuel as it gets old either forms a red dust that blocks jets or a nasty varnish that clogs everything. I'm sure the fuel bowl will bear evidence of one or the other. Likewise fuel filters. Fuel pump may also be in a sorry state - they use a rubber diaphragm which may not like having been left dry so long.

the fuel pump was changed and i fitted a inline fuel filter as i could not find one from the pump to the carb (would there possibly be one under the car? on the way to the fuel pump?) i just cant work out why it only cuts out once hot and under load. the car was running so so rough initially and all the things we have done have helped and it runs much much better now but we still can not use it as it cuts out. there is also a clunking from the rear but i was going to look into that once we can get it reliable and not cutting out lol

 

[LostKiwi]

If this is a 175CD constant depression carburettor undo the 3 or 4 screws holding the dashpot and remove. Check the condition of the rubber diaphragm - they're known to split with age.
You can also check the condition of the metering needle and jet. They should both be round without any obvious wear points though some shine is inevitable.

The metering unit should slide evenly and freely in the upper housing. Oil level should be no higher than the step where the metering unit is when the engine is off.
You'll see what I mean when you look. If the dashpot is too full of oil it will cause running issues when the throttle is opened especially when hot.

If all that checks out remove the carburettor and undo the screws holding the float chamber underneath the carburettor. Make sure it's spotless inside and that the float valve operates correctly.

 

[umblecumbuz]

If this was a later engine I would say crank position sensor.
Not sure if a 42 year old W115 had such a thing.

 

[LostKiwi]

If this was a later engine I would say crank position sensor.
Not sure if a 42 year old W115 had such a thing.

It's got a condenser (which means points...) Good old tech

 

[umblecumbuz]

From your comments in post 11, it sounds as though the fuel in the carburettor bowl runs out, causing the engine to stop. Then it slowly refills as you churn the starter and fires up again. That's another guess, but any port in a storm ...
I would suggest that engine oil as a damper in the carb is too high a viscosity, but I don't think that's the cause of your troubles.

 

[LostKiwi]

Engine oil in the damper is fine - Stromberg and SU carbs recommend it.
The purpose of the oil is to slow the rate of rise of the piston when the throttle opens giving a slightly rich mixture as manifold vacuum draws fuel past the needle. It's only an issue if over filled as the piston can't rise leading to oxygen starvation and excessive fuelling stalling the engine by flooding.

 

[umblecumbuz]

And we used to use diesel in our SU's!
... and fettle our own needles - and alter the return springs!
... and they always worked better when you used Brasso on the outsides (a sort of SU go-faster stripe)!

 

[LostKiwi]

And we used to use diesel in our SU's!
... and fettle our own needles - and alter the return springs!
... and they always worked better when you used Brasso on the outsides (a sort of SU go-faster stripe)!

Yeah I used to fettle needed and springs on the Dyno too.
Didn't have much option - a 1275 with twin HS6 carbs, a race cam (300 degrees duration, 95 degrees overlap), ported and chambered head and 12.5:1 compression doesn't have an off the shelf solution!
I later converted to a 45 DCOE for more flexibility...

 

[W115whydideye]

hello
i registered here to get some help from you guys who seem to know everything about all mercs.
so 10 years ago my dad parked up hes 1976 mercedes 200 w115 with stromberg carb and we have been trying to get it going. so far we have changed all the things that we could possibly think of that cause it to cut out under load when hot. ( after 10 mins or so it starts again and then drives )
so far we have

changed water pump
changed fuel pump
changed thermostat
changed rotor arm and distributor cap
changed capacitor
changed the coil
changed spark plugs
drained all fuel and replaced with frsh

today i ordered a ballast resistor and coolant temperature sensor which i am hoping will fix it.
i am at wits end because after doing all this i dont want to take it to a mechanic the point was that we get it going. it runs so well now and i thought we fixed it but as soon as shes hot and you drive it a few hundred yards it cuts out. if anyone has any suggestions i would greatly appreciate it

Hello Vam00sh- did you ever get to the bottom of this problem? I’ve just bought a 76 w115 that’s been stood for about 15 years and is having exactly the same problem!

 

[mattkh]

Hello Vam00sh- did you ever get to the bottom of this problem? I’ve just bought a 76 w115 that’s been stood for about 15 years and is having exactly the same problem!

Have you cleaned the connections to the ignition coil and checked the resistance..?