Need help: 1973 Carrera RS MFI stutter

[JESchrager]

Long time owner, dead stock 1973 RS, starts well, runs well. Has strange intermittent stutter. Especially bad when cold, it starts to buck at about 3,500 RPM under hard throttle. If you push very gently on the throttle, you can avoid the stutter. No tach weirdness, so we think it is not the CD box, which is an original CD, as is the coil and distributor. Plugs look normal. I am thinking about the MFI system, but I have had many MFI cars and never seen this problem before. Thanks, Jim Schrager, South Bend, IN.

[edmayo]

Anything been done to the car since it last ran correctly?

[gulf908]

Hi Jim

low back pressure muffler ?

cheers
Dennis

[jim schrager]

Anything been done to the car since it last ran correctly?

Good question. This stutter started years ago, then went away (yes, I know it is weird), then came back, and now is worse than ever even though the car is still drivable. Went it appeared, we had done nothing to the car to cause it. It was completely rebuilt prior to my ownership and has about 13K kilos since the rebuild. Plugs always look good, no smoke, no funny noises, starts easily, makes excellent power. Thanks, Jim S.

[jim schrager]

Muffler sounds stock and has no apparent corrosion. The fact the stutter appears at times and then goes away makes me think whatever is causing this is not itself a hardware issue. Thanks, Jim S.

[HughH]

Have the injectors been checked for spray pattern / cleaned recently? Any chance that a dodgy injector or two caused by lack of use or maybe even the fuel type being used that causes a miss under load but then cleans itself up mostly at other times?

[RSTarga]

Has everything been checked as per the CMA booklet? Distributor giving proper advance etc.

[csbush]

bad gas? How old is the gas in the tank?

[69Sman]

Check the rotor....

[JESchrager]

Thanks for all these ideas. Car ran perfectly before stutter started, and after stuttered appeared. This leads me to believe it is something intermittent. We have not checked the injectors. We will do that, but the stutter is like someone shut off the engine for a moment. Today we will again hook in a known-good CD box and maybe another coil. All looks good on the MFI adjustments given how well it ran before the stutter and how well it runs when the stutter does not occur--for periods of months at a time. So that brings us the gas. This car is in the Midwest and goes out once a month or more during good weather--but probably about one tank of gas a year. So it has old and new gas. I use only Shell. The gas does not smell bad and the engine is not running rich, and no blue smoke. Temps are just below the mid-range on the temp gauge. I will try a new rotor, that is a new one on me. I was also thinking of a new set of points. Thanks again, keep those ideas coming. Best, Jim S.