MFI/ tune-up problem

[Peter Frans]

Ok,

After a rebuild on my engine I was not satisfied with the way in ran; it had a flat spots in accelerating and a uneven idle. I decided to have my MFI pump rebuild.
After refitting I now have great difficulties getting above 3000 rpm under load ( when reving the engine in standstill it not apparant). All is fine until 3000 after which it starts to buck and backfire. After getting it past 4500 it goes again.

Today checked valve clearence, timing, dwell, replaced plug wires without any result. I am now suspecting the distributor or a wrong rebuild on the mfi pump.

I am in for suggestions to solve this.

Peter
1970 S

[lsolon]

Did you read this and follow it?: http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm
Check everthing

[GIBSON]

Peter,
Yes, check the distributor (points, advance etc.) Then I'd check:
1. Rod length from pump rack to cross bar, it's critical. Be sure that is exactly in spec.
2. Set all stops on the individual throttle bodies, make sure they are even with no pre-load. Take off the individual rods and be sure they connect with no tension or pre-load. In my experience, these two areas cause most of the hesitation/flat spots in MFI.
3. Be sure your pump is timed correctly with the engine. Who rebuilt it? If it was Gus at Pacific the pump is right
4. Check your idle and mid-range adjustments on the pump. A few clicks the wrong way can cause flat-spots and just poor performance.
Ideally, get your car on a CO meter and see set the pump to perform best with real feedback.
I have the best luck with these problems by just starting from scratch with all the settings, take nothing for granted and measure everything. If you are patient and the T-bodies are basically intact (i.e. no worn throttle shafts which screw-up idle) you should be able to get it working well.

Bruce Herrmann
73911S