400i bucking / jerking at low load and rpm

Check your distributor advance. Is it sticky? Advance should increase smoothly from idle to 5000 RPM.
Ken

 

That's more because carburettors just can't work well below that value . 2% CO is already the "standard fudge up" for K-Jet systems as the F spec is usually more like 0.8%-1.2% CO at idle on the K/KE-Jet models. If 4% CO at idle "fixes" your runability issue, you are just masking some other issue that you haven't identified yet -- JMO. Good Hunting!

 

Esben
I had sticky advance mechanism just before a 5-day rally. We had to get home on a flat bed. In an hour or so, I got cap off and squirted some lube down inside, wiggled rotor around. It ran like a top for the 5-day rally.
Afterward, I sent distributor to Dave North in NJ who rebuilds them. He has an ad in FCA magazine. He replaced top and bottom bearings, lower seal, and then set up weights and springs on a distributor "dyno". He gave me the advance curve results. Car ran perfectly once reinstalled and idle advance set.
You could do my first action to see if you are on the right track.
Ken

 

Before removing the distributor (that's a painfull task!), as suggested by ken, just remove the cap, and the rotor "finger", then check that the wick inside the hollow of main shaft is filled with oil. If it is dry just lube the wick and the spread some oil on the cams.

Once all is thourougly lubed, you can wiggle the distributor rotor. As the main shaft will be locked by the camshaft, if you move the rotor, the only thing that will bulge will be the cams of the distributor. So you will feel the resistance of the springs while the cams are "opening". You can gently actuate the cams till they feel smooth again.

Sorry for the so-so english. I hope you get the idea...

 

As far as adjusting the distributor, that's not such a straightforward task:

1) aside from the poor accessibility,
2) the distributor is located in an extreemly hot area, so the heat plays its toll on the bearing and the seals. In other words if you remove it, just replace all these.
3) Additionnaly the shape of the distributor is not compatible with most distributor tester, so even if you find someone who has access to a Sun or Alen tester, you will need the specific adapter that allows to mount the distributor on the testing machine.

So you'd better be sure your distributor is the culprit : test the advance with a timing light first, and check the temperature of all the exhausts (you may have a few missing cylinders).

 

Something light like 3-in-1 oil.

 

Good day Esben,

Firstly, do not mix up the springs, pins, or the very thin washers that might be present underneath the "pin" or inside the pin's cylinder. All of these items contribute to the distributor's advance curve and can be specific to each weight. Secondly, be very careful withe the plastic bushing (the advance weight rests against this bushing) that is affixed to the center shaft. This bushing has a specific outer diameter which sets the maximum possible travel of the advance weight (and effective distributor advance). All of these parts are no longer available. If any are damaged/lost then one many need to either send the distributor to someone that knows and has spare parts... or one must buy a used/replacement distributor... or be resourceful enough to make new parts made including springs with various spring rates.

Lastly, ensure you check the inside portion of the "cup" that the pins rub against. You will note that one pin (on each advance weight) is in contact with the cup at all times, whereas, the 2nd pin will only contact the cup once the distributor has advanced sufficiently. Because the "pins" do contact/rub the surface, then can cause the surface to wear and at times creating a groove/pocket that prevents the pin from freely sliding across the surface. Attached is a picture of what can happen... which happened on my 512BB. What it manifests is an inconsistent advance curve which can become "stuck". In my case, slowly changing the idle speed... like casual driving, which cause engine running issues, the distributor was not advancing or retarding like it was supposed to. Fast idle changes would have enough momentum to allow the pin to transverse the worn pocket. It took a while to discover this and was only found after I ruled out all other possibilities and spent time on my distributor machine where I noted the inconsistent advance curve.

To ensure that this does not happen, ensure that the inner cup is greased so as to minimize the pin head friction against the inner cup. In my case, I have to weld up the divot, then machine the surface, and then treat the surface to minimize friction/wear.

Cheers,

Sam

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Good day Esben,

Sounds good. I suspected that many of the items I mentioned you would have looked at... but the worn "divot" on the inner cup was a new one for me and so I wanted to highlight this. I am still confused as to how it could have worn such a defined area... and only on one side? It is an odd one and threw me for a loop for a sometime, as I never looked at this area so closely and at the right angle that made the issue stand out.

As for the programmable MSD box... sure, this could certainly work. In fact, I started work on a design that would allow one to retrofit these distributors to be used with "regular" (non programmable) MSD and other electronic modules, but with a fully programmable advance (via Laptop or Smartphone). My approach is somewhat unique and does not require any permanent modifications to the existing equipment ... and to the naked eye would look totally OEM (assuming one maintained the original electronic ignition module that had its guts upgraded to a newer device). I had hoped to have my design a bit farther along, but alas, one work project has consumed a lot of my time... Hopefully I can get back to work on what I am thinking, as if so, then dealing with the original advance mechanism could be gone. I will create a thread on all of this, once I am further along.

Cheers,

Sam

 

In one of your posts, you said it was almost out of the adjustment range of the slot or something similar. I was thinking that all depends on how the distributor was installed. Now you figured it out. Great perseverance and using good logic to solve a 400i issue!! You will need both in the long run with the car!!
Ken

 

Esben
One of the things I did to make life easier working on the 400i was to make a couple of a D-size copies of the electrical wiring diagram. I used it FREQUENTLY for troubleshooting! Staples, Kinkos etc. can make the large copies. Keep up the good work.
Ken