1971 280SL Only idles fine with timing at 55 degrees BTC !

[CoreyJ]

Just recently had the MFI pump rebuilt, new electronic distributor, plugs & wire set, fuel injectors cleaned and tested - and the only way the engine runs good at idle is with the timing at 55 degrees BTC, not what should be 5 to 0 degrees. All our alignment marks are correct on the pump, valves have been adjusted/
How could the timing be off so much? Slowly give it the gas and it starts backfiring through the intake. Any thoughts?

[Benz Dr.]

Is the vacuum line from your brake booster tight?

[stickandrudderman]

Always confirm the basics first.
Remove No. 1 plug and find TDC by inserting a rod or screw driver in through the plug hole and resting it on top of the piston. Then rotate the engine by hand (easier with all plugs removed) to find the highest point. Then confirm that your timing pointer is aligned with zero on the crankshaft pulley.
On more than one occasion I have come across a pulley that has been forced on to the crank in the wrong location.

[ja17]

Make sure your using the correct timing scale. Some engines have two scales and they are off set about 40 degrees.

[CoreyJ]

I'm still at it. Noticed with the engine running if you pull #3 or #6 plug wire it hardly makes any change. Have strong spark, cleaned and tested fuel injectors, rebuild MFI pump, and all cylinders compression in the 140psi range. If timing set at 5 degrees it won't even run.

[mrfatboy]

Did the FIP get installed at the correct 20 degrees ATDC and not 180 degree off?

See the tech manual or "toothpick method" for info.

[Pawel66]

Have you checked what Benz Dr., stickandrudderman and ja17 advised to check?
Have you just installed 123 distributor perhaps or you have the original one?

[CoreyJ]

We do believe we have the timing correctly set and this is how it ran when the original distributor was installed prior to installing the 123 distributor. We are now checking fuel delivery to the MFI pump. This has the smaller fuel pump with the bypass hose. Question: We would like to do a flow volume test to determine if the flow is in spec. What quantity of fuel should we get for a given amount of time? I've heard like 1 quart in 20 seconds - we get no where near that. Also, where is the "overflow valve without gas hole" on the MFI pump? Many thanks!!

[Pawel66]

That is why I asked if you switched to 123. When installing the 123 it is easy to set it up 60degrees wrong when you follow instructions. I would try to turn it ca 60deg until the other green light lights up (or the same second time, I do not remember). I am surprised the engine started, mine did not want to start. took us a while to set it right. Check when which cylinder fires.

I suggest you check it. Of course I may be wrong, I am not a mechanic.

Look at the posts about it, Members wrote about it.