220s hard starting - PeachParts Mercedes-Benz Forum

peter c · #1 07-12-2006, 05:23 PM

I have a 1957 220s that starts cold perfectly and re-starts hot perfectly but if the engine is hot and the car is left for 15 minutes or more it is very difficult to start. anyone have any ideas ?

300SDog · #2 07-13-2006, 01:18 AM

Sounds like carburetor vapor lock where fuel vaporizes in the system and prevents normal flow. Heat shields, even tin foil insulating the carbs from exhaust manifold heat can help. I believe thats a low pressure fuel pump on the primitive 220S, might want to check the diaphragm for small cracks. Also keep the glass bowl fuel filter clean. Basically a question of fuel vaporizing in fuel lines and carb passages too, thats what you are fighting.

peter c · #3 07-13-2006, 11:16 AM

thanks for the info. I will check the fuel pump first.

sokoloff · #4 07-13-2006, 12:38 PM

I think if it starts easily cold and hot, then it's not your fuel pump I wouldn't think. I'd look to the carbs/heat risers. These cars are notorious for being hard to start after they haven't been started for a week or so. The fuel in the bowls evaporates and it takes a long time to prime them again. That's not your problem.

Might find something here too - http://www.mbzponton.org/ or join our ponton discussion group. We've got over 500 owners there with a great knowledge base - http://autos.groups.yahoo.com/group/ponton/

Len
'59 220S Cabriolet

300SDog · #5 07-13-2006, 02:00 PM

Sokoloff, are you saying that MB had butterfly heat riser valves directing exhaust directly under the carbs even as far back as 1957? Jeeze yeah, gotta hammer those valves into position that does not roast the carbs and cause vapor lock when fuel turns to fumes inside the carbs and fuel lines. Slam those butterfly heat risers with a hammer so NONE of the exhaust fumes roast the carbs, thats what I'd do.

Dunno why MB bothered with those ridiculous heat riser valves at all (maybe fuel freezes to ice as it flows into carburetor float bowls at wintertime in Germany?). Those crummy rust-prone heat riser valves are a curse to the Vintage MB, says me. Downright dangerous for later model Zenith carbs, roasting and destroying them by warping em out of shape.

sokoloff · #6 07-13-2006, 03:02 PM

Yep, they had spring/weight loaded heat risers on the pontons. Often they are rusted in place, but can be freed up to work properly. Parts to fix them are still available too. See them here - http://www.mbzponton.org/valueadded/other/heatriser.htm

Len

peter c · #7 07-14-2006, 01:12 PM

Heat risers are free and should be working ok. The only way it will start is if I put the peddle to the floor and crank it for a while. This gennerally indicates a flooded condition but with a hot engine sitting for over an hour one would think any excess fuel would evaporate by then. If it is left to sit for several hours it will start right up. Vapor lock or flooded ?

barry123400 · #8 07-28-2006, 01:31 PM

To separate vapour lock from flooded just pour a very small amount of gas in the carbs when you know it is going to be hard to start.

Mark DiSilvestro · #9 07-28-2006, 05:52 PM

I believe it's a flooding condition that occurs on a hot engine after it's been parked for between several minutes and a half hour, especially on a hot day. I've seen it reported on 220 Ponton engines with the dual compound Solex carbs and also experienced it on my '60 Fintail, which has the same carbs. I suspect that gas may be percolating from the vents or main jets of the hot carbs, then dribbling down the throat to pool in the intake manifold. I also suspect that todays reformulated gas exascerbates this problem and that the compound Solexes are more prone to this condition, as I haven't heard of this problem with the Zeniths.
In this situation, I wouldn't try to dump in extra gas for a 'test', as this would probably flood it permanently. I've resigned myself to 'clear the flood' by flooring the gas pedal when it happens.

I've also experiencd the other no-start condition after the car has sat for several days, which I believe IS due to the gas evaporating. So far I haven't had to prime my Fintail.

Happy Motoring, Mark

t walgamuth · #10 07-28-2006, 08:03 PM

you didnt say but is the engine spinning over fast?

if not you might just have a bad ground.

tom w

Mark DiSilvestro · #11 07-28-2006, 10:31 PM

In my case, the starter spins normally.

Happy Motoring, Mark

peter c · #12 08-04-2006, 03:09 PM

I have already done several tests and it is definitely a flooded condition. After discussing this problem with several carb experts including a few in Germany, all seem to agree this condition is a design flaw in the solex carb. I was told when the fuel in the carb bowl is hot enough to percolate it runs into the throat of the carb via the bowl vent which is located in the thoat area. I find it hard to beleive that every 220s or every solex carb has this problem. I am working with a local carb guy to try and solve this problem. I will be sure to post my results.

sokoloff · #13 08-04-2006, 05:19 PM

No, it is not a problem with all or even many 220S's that I've heard of. Are your carbs due for a rebuild? Is the float level correct, etc.?

Len
'59 220S Cabriolet

peter c · #14 08-07-2006, 04:33 PM

Carbs were rebuilt about 4 years ago to try and solve this problem. The problem did not improve. Float level should be OK as the car idles and runs perfectly.

sokoloff · #15 08-07-2006, 05:14 PM

See message #4 above. Ask on our ponton discussion group. Someone there more knowledgeable than I ought to be able to help.

Len