engine bucks at low rpms

[catjim813]

All, What would cause my car to jerk and buck at low RPMS?  69 280 sl manual transmission.  Recent engine rebuild 123 ignition, new wires, and NGK plugs.  Could it be the fuel dampner     Replaced rubber hose on this section.  Injection pump?  Car runs well starts and idles well, also runs well on highway.  Cant seem to get this done. thanks for the help in the past.

[ctaylor738]

How about some background?  Did the problem start after you did the 123 and wires?  Or is it something you tried to fix with the new stuff?

[alchemist]

It sounds like timing problem. Do you have the right distributor? It could be an advanced versus retard issue. Try to disconnect the vacuum from the distributor and see if it improves.

[catjim813]

The bucking started after engine rebuild.  It does not do it all the time.  New wires and distributor were on the car before engine rebuild.  Car drove great but smoked at start up.  After rebuild no smoking but just not running as smooth as before. Injection pump seems ok, not sure if the fuel pump would cause this also. Waiting on snow to melt to get her out and work through this.  Plugs look good also in terms of light hazing on tips but I just cant get past this jerking.

[ctaylor738]

First, suggest a quick linkage tour.  Be sure that the throttle plate is closing all the way - you need to unhook the linkage and the spring and feel the "stickiness" when fully closed.  Adjust the stop if needed.  Now make sure that the pump lever is on its stop with the throttle at rest, and adjust the length as needed. 

Move the throttle and be sure that the levers on the throttle body and pump move at the exact same time.

Second, put a vacuum gauge on the port on the throttle body (or at the distributor end of the hose).  Start the engine and let it idle.  You should see vacuum like 15" of vacuum.  When you open the throttle, the vacuum should go to zero. 

[jameshoward]

+1 for a full run through of the linkage tour.

[billhon]

Please what is a 123 ignition? Is it an improvement  over the original. if you recommend this upgrade and get positive results what else needs to be upgraded at the same time? Thank you in advance for your answer.

[catjim813]

Thanks all, I will start with the linkage tour.   Any recommendations for a good tech person to do this in the Chattanooga Tennessee area?

[Garry]

Billhon,

Do a search on Petronix and 123 ignition systems on the forum and you will find a multitude of info on the electronic ignitions.

Garry

[Peter van Es]

Or go straight here: http://www.sl113.org/wiki/Electrical/ElectronicIgnitions