slow increase of rpm

[mauro12]

Hi guys! i hope you can help me! i have a 250sl 1967 with zf 5 speed manual, i didnt use the car for almost 2 years and after i decided to bring it back to life so i sent the fuel injectors to clean by ultra sound and the car right now is going pretty good. The only thing i cannot improve is that when i go over 4,000rpm the car seems to feel bad and the rpm goes up very slow. What do you think can be the problem? is the injection pump which needs to be overhauled? Apart from this the car is fantastic, no problem at all. I hope you can give me some advice.  Thank you

[Benz Dr.]

The list is too long for me to cover everything but start with the basics and move forward from there. Start with ignition, fuel delivery and throttle linkage. There is a lot info here on the site.

[ranchomerced]

Check that the fuel rack will move completely forward. On the front of the pump there is a cap that covers a plunger inside the pump. Put a 5mm bolt in it and push it in and pull it out. make sure its not sticking.

[mdsalemi]

Start with the ignition...though our fuel systems are "injected" I always remember the quip from an old service manual I once had for an MG, where they stated "Carburettor is a French word meaning 'It's the electrical system, stupid!' "

At 4,000 RPM your moving parts are screaming along and you are asking a lot of the distributor, points, plugs, wires, etc. Might be something as simple as dirty wires causing electrical breakdown...been there and done that on other cars...

[BaronYoungman]

could be fuel pump that has a worn armature or bushes that will not spin fast enough to keep up with the fuel demand.
 just another thing to check Bob

[mauro12]

I checked all linkages and changed all ball socket and cleaned the throttle body but the car still suffer after 5000rpm. It is like I have to keep pushing the accelerator but the rpm indicator is still not increasing. Any suggestion?

[ja17]

First make sure that your linkage is opening all the way when the pedal is pressed all the way down. Check at the intake venture, that it is opening all the way. Try a fresh set of spark plugs.

[Tyler S]

Check that the distributer mechanical, and vacuum advance/retard is functioning correctly. Also check the vacuum line to it. A simple test on a 250sl or any with an 051 distributer is to disconnect the vacuum line at the throttle body for the vacuum advance. If the vacuum retard/advance is functioning, The RPM should rise when disconnecting the line at idle.

[Bonnyboy]

My advance/retard mechanism in the distributor lot a retaining bolt and I had a similar issue - check from underneath (mirror on a stick would work) to make sure you have two bolts holding the advance/retard.    I discovered I only had one after I took the distributor out and then had to redo the timing. 

[mauro12]

I think I didn’t understand well what you meant. Have you had the same problem as me and you solved in this way?

[mauro12]

I just tried today and when I accelerate in 2 gear ,it is like the power finish at 4500rpm. I don’t know if is an electrical problem ( distributor or my electronic ignition which is old now) or maybe spark plug wires. Any ideas? The linkages are all correct with new ball socket, throttle body is cleaned, air filter is new and fuel injectors are cleaned with good spray.

[Tyler S]

Mauro, Do you have access to a timing light to check the timing at 3000 rpm?
It should be about 35-38 deg advanced.

[mauro12]

I don’t know but I can ask my mechanic to do for me. Do you think is this the problem? What I have to do?

[Tyler S]

It is a good start to check. Along with dwell. Have your Mechanic check the timing at idle. Then raise the rpm to above 3000. The timing should advance to 35-38 degrees BTDC
Since the car has been sitting for so long you may also want to rule out an intake or exhaust restriction. (Air filter, plugged exhaust-critters like to build nests in strange places)

(Always start with the basics. Engines need 4 main things to work properly. Spark, Fuel, Air and Compression. Eliminate each one as a potential culpret one at a time and you will eventually get to the root of your problem)