Gas/carb issue. Please Advise - PeachParts Mercedes-Benz Forum

Jason Bradley · #1 05-14-2002, 03:27 PM

My 'new to me' 1979 250T wagon with unleaded v6 runs, idles and starts fine. When I accelerate it will run fine for a few seconds then seem to bog down and stumble then roar back with the missing power. But, as I said, it idles fine. I have tightened down the carb and inspected it for obvious leaks ( none) . It seems as though there is some kind of fuel blockage but I can't see how it would idle and start fine then bog down only occasionally. Any basic tips or tricks would be welcomed. I am new to the world of Carbs. I have an old fuel injected land rover so I am used to wrenching and numerous unexplained strange occurences with electrics but this seems to be gas related and I would appreciate any advice or links to help me better understand and diagnose this problem.

Many Thanks,

Jason Bradley

stevebfl · #2 05-14-2002, 03:43 PM

Sounds like no spring pressure on the secondary air valve.

The back barrels on that carb are rather unique in operation. They are huge and upon openning they just put out the flame unless the device at the top (looking like a choke plate) has the proper resistance to movement. It acts like a choke letting vacuum develop below pulling fuel as the plate deflects far enough to add air.

With the engine off the plate should move freely with distinct spring pressure. If it binds the top of the carb must come off and the whole arrangement disassembled, cleaned, buffed, bent till the shaft goes through the necessary 3 points without binding. The tops are usually bowed and this causes the straigth shaft to bind. make sure the plates don't stick.

One way to determine if this is the problem is to tie the secondaries closed (they are not directly openned - they are openned with a spring and holding them just winds up the spring - no damage done) and see if this removes the bog. If so you will have to get the valves free and under proper tension and possibly adjust the arm that lifts the secondary metering rods (part of the secondary air flap movement. If you take it apart you will see the most valuable piece of plastic on a MB. It is the cam that drives the metering rods. It is not a separate part. It being missing/broken will cause the problem also (not lifting the rods as the air valve opens.

stevebfl · #3 05-14-2002, 03:46 PM

Sounds like no spring pressure on the secondary air valve.

The back barrels on that carb are rather unique in operation. They are huge and upon openning they just put out the flame unless the device at the top (looking like a choke plate) has the proper resistance to movement. It acts like a choke letting vacuum develop below pulling fuel as the plate deflects far enough to add air.

With the engine off the plate should move freely with distinct spring pressure. If it binds the top of the carb must come off and the whole arrangement disassembled, cleaned, buffed, bent till the shaft goes through the necessary 3 points without binding. The tops are usually bowed and this causes the straight shaft to bind. make sure the plates don't stick in the bore.

One way to determine if this is the problem is to tie the secondaries closed (they are not directly opened - they are opened with a spring and holding them just winds up the spring - no damage done) and see if this removes the bog. If so you will have to get the valves free and under proper tension and possibly adjust the arm that lifts the secondary metering rods (part of the secondary air flap movement). If you take it apart you will see the most valuable piece of plastic on a MB. It is the cam that drives the metering rods. It is not available as a separate part. It being missing/broken will cause the problem also (not lifting the rods as the air valve opens).

Jason Bradley · #4 05-14-2002, 04:12 PM

Thank you for your time and knowledge!! I recently tightened everything down on the carb ( all the screws and bolts) which most likely caused this issue. I have a gasket replacement kit to install soon so I will take it all apart and look for the things you mention. I understand this carb is prone to warpage.

Can you suggest a replacement carb or used part carb. I am worried that its grey market status will make finding the carb difficult in the states. Is there a carb rebuild kit from the factory I could order other than the gasket package ?

Thanks Again,

Jason

stevebfl · #5 05-14-2002, 07:20 PM

Individual parts are probably available from MB (with the exception of that cam). The carb is basically the same as the one used on 280 M110 cars up to 1976 (injected afterwards).

I can't suggest a replacement unless it would be from the 280 with some rejetting.

hs_300e · #6 05-15-2002, 12:26 AM

Try using carburettor cleaner. Spray it on all the moving parts with the air filter off and the engine running. If that doesn't cure the problem, then i guess you will have to take the carb apart and rebuild it.

I had the same problem on my old Mazda and using carb cleaner cured the problem.

Jason Bradley · #7 05-15-2002, 02:08 PM

http://www.geocities.com/johan01.geo/Weber/Sol2Webp1.htm

This shows how to convert from Solex 4bbl to a weber carb.

Thanks for all the help.

JB

autozen · #8 05-15-2002, 11:58 PM

JB,

You put the nails in your coffin when you tightened down that carb. You warped the air horn and caused the secondaries to malfunction. That is a moot point now. The solex which is basically an American Quadro Jet was, in my opinion, a piece of garbage. I would highly recommend the conversion to Webber. The only time I would disagree to a conversion would involve Zeniths. These carbs from the 60s and 70s are not well understand. People who say to get rid of them don't know how to set them up. Another impressive carb is the Stromberg 175 CD. It's the closest a carb will ever get to fuel injection, but unfortanately it is restricted to smaller engines.

Good luck,
Peter

Jason Bradley · #9 05-16-2002, 02:45 PM

I have cleaned and fiddled with it and it is running better. It bogs slightly at yield signs and under heavy pedal. The secondary or smaller barrel cover has no spring back, it stays where it is put but moves free and smooth by hand force. I don't know enough about it at this time to say more other than Thank You to everybody and any links you could send my way that might educate me more would be appreciated. I am waiting on a manual for it but the manual is in German and Ich haben fergessen mine deutsch!

JB
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