308 not running smoothly at cruising speed

Could somebody help me out on the following issue.

I have owned a '78 US spec. 308GTS for 2 years now and am currently facing the problem that it is not running smoothly at cruising speed. It is very hesitant and it feels as if not all cylinders are adding to the power. However as soon as I touch the acceleratorpedal it is pulling like hell up until over 7500 RPM. Also at idle it is running smoothly.

- The car is US spec. but with airpumps and retarded breakerpoints removed. So I am running on 1 set of breakerpoints per distributor. Timing is set at 7 BTDC
- Oil / Oilfilter / petrolfilter / airfilter / sparkplugs / timingbelts + bearings where replaced last year less than 1000 miles ago(by myself). Car was running fine after that.
- Ditributor caps / rotor / sparkplug cables / extensions look OK
- I checked timing which was OK
- I checked the sparkplugs visually and with timing light with running engine, both were OK
- I checked the airflow through the carburetors and synchronized them with the help of a WEBER synchrometer
- With the help of a CO meter I adjusted the mixture screws on the carburetors

All the above did not help.

Is there anybody out there that has some tips and tricks to solve the problem.
If not I will bring it to a specialist but I rather have a try myself before.

Regards,
Ronald Koers, The Netherlands
Image Unavailable, Please Login
Image Unavailable, Please Login