engine and drivetrain Tii Rough Idle And Mixture Question

[classicman]

Hi

 

My car starts easily hot or cold, but I can't get her to idle nicely.  At 1100-1200rpm she's fine, if I try to get her below this she is unresponsive and then drops so low she wants to stall.  I've had her on a CO meter and she is set between the 2-3% band.  At 4,000rpm sh's at 5% although she starts smoking as though she's overfuelling.

 

If I drive her, she pulls well until about 4,500rpm and then she starts fluffing.  No backfiring.  If I keep the throttle floored, she wants to pull through but just can't.  I've gone through the KF set up and syncronisation procedure a dozen times to make sure all is correct.  Valve timing is correct and clearances right, in fact shes a little tappety.

 

I've gone through the ignition and replaced plugs, points, condenser, plug leads, coil.  Timing is right at 2,400rpm with the ball on the flywheel.  Points gap is 0.33mm to get the dwell angle in the correct range.  I'm pretty sure I've ruled out ignition.

 

What am I missing??

 

BTW, running 300deg cam, 39mm exhaust valves and 10:1 compression ratio on unleaded fuel.  Motor is completely fresh with new pistons rings and 0.5mm rebore.

[ray_]

You are running Alpina ITBs?

 

I'd start with getting the distributor recurved, and then an afr gauge. And also check the cold start cylinder actuation on the kf pump.

 

GL,

[lilmo]

Check/clean all screens & filters in the fuel system.  Start with the mesh one on the fuel pickup.

[thehackmechanic]

Search here for "tii" and "cam" or "kugelfischer" and "cam" and you'll see a long history of challenges getting the Kugelfischer system to run with a hot cam. By installing an air/fuel gauge, you'll be able to know if the loss of power at high RPM is due to leaning out, but I'm not aware of a quick and easy solution. Wes Ingram, I believe, sells a linkage that is purported to allow some degree of adjustability of the air/fuel curve by playing with the enrichment lever.

[bnam]

Classicman,

Have you checked for air-leaks?  Pump belt on correctly and not advanced/retarded?

Byas

[SydneyTii]

+1 on cleaning your screens in the fuel delivery path, dont forget the little one at the pump, I take it you have the correct fule filter i.e. the metal one? good luck, post what you find when you resolve it.

 

Cheers

Richard

[PaulTWinterton]

+1 on fuel delivery.

 

I had a similar situation, but not quite so bad.  Over 4500rpm the engine would starve.  My fuel filter in the tank was BLACK and OPAQUE.  Should be see-through.  A wonder it could deliver fuel at all.  Your idle issue may mean that it's even worse than mine was, not allowing enough fuel to even idle the car.  Check those screens.

 

It would be nice if it was that simple.  Your CO readings sound good.

[ray_]

Yep. A fuel pressure gauge is an excellent idea, in line with all the above...

[jireland2002]

After checking for blockage of fuel flow.  The NEXT thing you need to do is check the timing at full advance.  Probably something over 3200rpm.  You should be looking for 32-33 degrees at full advance.  If the timing is ok then it is probably lean at high speed do to the modifications.  You could wire the cold start injector to a switch and see if more fuel is the solution.  If it is then you get to have the pump redone.

[jgerock]

You are running Alpina ITBs?

 

I'd start with getting the distributor recurved, and then an afr gauge. And also check the cold start cylinder actuation on the kf pump.

 

GL,

+1 on Ray's comments (and others). Your signature indicates a 74tii with Alpina A4 spec.  Are you using a "regular" carb'd 2002 distributor, a 74tii distributor or something else?  If your distributor is worn out or has not been recurved for your modified engine, then you will not see the proper engine operation.  tii's should come alive above 3K RPM.

[classicman]

I have already replaced the in line fuel filter. I checked the filter in the tank this morning and it was black, but didn't look blocked. I cleaned it anyway. I also cleaned the filter at the pump - it too didn't look that bad.

I'm not running ITBs, still the std injection setup. I am running a thermostat that is 5deg colder than std due to high South African temperatures in summer.

I pulled #1 plug and it is black and wet - definitely looks more rich than lean......

Btw - std mechanical advance distributor with a new kit in it.

[classicman]

Checked fuel delivery back at the tank, and it is within spec.

[jgerock]

You said you checked the filter at the pump - which one?  There is the barrel-shaped one inside the bolt at the KF injection pump and there is a cone-shaped one at the inlet of the fuel pump.  The fact that your in-tank screen is black may indicate the next screen (at the fuel pump) could be partially blocked.  I have seen the fuel flow and pressure be OK at idle and revving while sitting still then drop during actual driving (under load).  

 

Here is the one on the inlet to the fuel pump

Notice how black and nasty this one was?

 

This is the one inside the KF pump inlet

[thehackmechanic]

Having had tiis with clogged screens (who hasn't?), my experience has been that the symptom is that the car literally feels like it's running out of gas as fuel delivery demands increase, whereas other KFish issues that lean out the mixture feel like... a lean mixture -- lack of power, backfiring when you step off the throttle.

[bnam]

Jim,

The pump on my Tii has 2 Cu washers on the inlet bolt.  I don't see that on the BMW parts diag.  Was it on yours?  Wondering if that is a one use only washer and what size I would need to replace it.

B