1.7L running rough in the mid RPMs, Potential Causes of rough running (MIDS) Options

[scwade]

I have a 1971 1.7L (with big bore kit) running FI. I'm having some odd behavior between 4,000-4,300 RPM. It runs rough at that RPM regardless of gears/speed.

I've checked timing at 3,500 (fine).
I've swapped spark plugs (bosh) // got rid of some pre-detination ping, but still have the roughness (cutting out)
I've put in 91 octane (best I can get here in CA)

Still happens.

PS - it idles rough as well. When I remove the "retardation" line it idles fine. I've not tried to run it full boar with no retardation though.

Any ideas?

Scott

[scwade]

Thanks Brad and all. I think we've got it. I didn't get the electronic points as there is no one in my area that had them. I'm in Santa Clarita (LA area) as opposed to Santa Clara (Bay Area). I'll order them this week.

Valves needed adusting....I found one valve a .0025 - pretty tight. Many others were between .004 and .008, half were at .006 (as they should be). so tweaking those helped tremendously. (I'm replacing the nuts and screws next time as one is cross threaded, but it was close to .006 already). I have a new new dizzy, but left the old one in, and we are running much much better now. I'll replace the points in them both to see how they run, then I'll add electronic points to one and have a quick switch for racing and normal driving.

The jerking at 4000+ is GONE! I also noticed that the ("temp new bad dizzy") caused the RPM guage to jump all over the place. After reading all your input, I suspect the points were no good on that one, and probably could be replaced on my current dizzy. So when I try again I'll go for the bosch points.

Still idles rough (and stalls), but I'm guessing its due to the big bore kit. loosening the idle screw didn't do too much (Even though I adjusted the switch per rennlist). I guess if I get ambitious I'll see about adjusting the MPS to increase the idle only. Or maybe that was in the FI...I'll have to read that rennlist again.

I wen't with the first notch, then the 2nd notch. I think the second timing notch is the way to go, but I'll test them both again with new points.

Regardless, I think I'm past the dizzy headache. Now I want to tweak the spark plugs. Should I go bosch platinum "4233", or NGK BPR6ES?

Thanks again guys.

s