73 2.8 rsr, 74 3.0 rsr

[Propain]

The cars in question are authentic 73 2.8 RSR, and 74 3.0 RSR. As I'm sure you know both feature twin plugs, and mechanical fuel injection. Both cars have developed a similar problem.

The cars "break up" and sound very rough between 4-5k RPM, and they have little to no power at these RPM. The issue is mostly at part throttle.

At full throttle, and taking the cars up to 8k and then shifting drops the revs in the next gear beyond this rough patch (past 5k), and they run, and pull strong.

The 2.8 problem is much more pronounced, and has gotten worse, to the point where there is almost no power before 5k revs, and it is very rough. There is also a bit more smoke than usual coming out of both cars.

I would be very grateful if you could help point me in a direction to start investigating. The shop where these cars are looked after is very far away, and I would love to be able to pin point the problem with out having to send them away, as I do not trust them with just anyone. Could you possibly propose areas to investigate. I have very little experience with these twin plug cars.

additional info: both of these cars do not have a rev limiter, or red line on the tach. It is possible that each car was pushed beyond there 8k redline (maybe 9k max, but unlikely they went that far) and definitely not more than once, I do not know if this is relevant.

Thanks in advance for any help you may be able to provide, and for contributing to the well being of such incredible cars.

[Yellow491]

What dizzies are you running,bosch or marrelli,points or pickup etc,timing out.
If they are pulling well over 5 to 8,i doubt they have been overeved.
Extra smoke could be fueling,are they proper rsr pumps.
What is the belt tension like on the pump,they can jump a tooth.
Lots of variables,do you know any one who knows whats what on them,it could save you a lot of time,if not check the basics first.
Hope this helps.

[Propain]

Thanks for the reply. Dizzies are the original Bosch. Both cars are absolutely original 73,74 spec RSRs with the exception of a full cage, and some modern recaros in the 3.0. Original everything, including glass, and matching engines. I hope that you are right about them not having been overreved, anyone else care to chime in?

[72targa]

There are many potential things to look at. That said, one simple thing to look at has been mentioned. I remember an experience with the one '74 RSR I've been involved with that had what turned out to be an unknown issue with the mechanical fuel injection belt. It "looked" fine but the car ran inconsistently as you describe. To make a long story short, at an event, the belt broke. Once it was replaced, it was like magic! The car transformed into a beast. Good luck with your analysis.

[Mike_Moore]

These are both very specialised engines to set up and what you describe sounds like pretty typical RSR (mfi) mechanical fuel injection pump problems.

The RSR injection pumps are the heart of these engines and the space cams inside are designed to start to give their maximum fuelling at around that
4-5000rpm figure you mention, and under that the cars can be notoriously lumpy. They do need to be set up by somebody who knows what they are
doing, ideally by using the proper Bosch test flow equipment to ensure that the pump itself is functioning correctly.

Once the pump has been set it's best to then put it back on the engine out of the car and run it up on an engine dyno to set the idle and main racks in
conjunction with your ignition and cam timing to optimise the power delivery of the motor.

All very time consuming and expensive to do if you use the right people but those are very special cars you have there, and if they are originals it has
to be done right.

Hope that helps.

[RSTarga]

Some of the space cams in the pumps tend to show wear. It usually manifests itself in that rev range where there is a step.

[uai]

I'd start with a wideband 02 sensor and check the Lambda (Air/fuel ratio for US) and Ignition.

[Yellow491]

Just to add if both are playing up around the same time,check the common link,the fuel also.
If you suspect overev,have a leak down carried out,not a big job,but i suspect they have not at this stage.
They also sound terrible with no load at 4500 ish,with the rsr cams etc.
Even changing the exhaust,they need to be tuned to what ever exhaust or fully open you are running.
Where are you,we may be able to point you to some proper experts.
Good luck.

[Propain]

The 2.8 is having its pump sent out, and rebuilt in Germany, it was found to be the source of the problem. After driving around in the 3.0, we decided the fuel mixture was running rich, and after looking at the throttle linkage, the left side linkage was much stiffer than the right side. They are now equaled out.

The car is now in great running order. She sounds sooo good, and pulls hard from much earlier in the rev range. Hopefully when the rebuilt pump is back the 2.8 will be the beast it was before this problem started.

Thanks for all of your help, with your pointers we were able to approach a competent technician and start finding solutions.

[Yellow491]

Well done
Just make sure the 2.8 is done properly,i have been there with experts!
A friend had a pump sent to germany and back 3 times before it was right.
Enjoy the cars,they are the best.