newbie MFI questions

[knapmann]

Hmm, not having much success.

I removed all the linkages again. reset all the butterflies to 3/4 turn past stuck closed. all air bypasss screws at 2.5 turns. I started it, and it idled ok around 600, i adjusted all the air bypass screws to give me flow reading of 6 on the sync whilst the engine was warming up. One thing I learned it that it takes ages to get to temp, and as it warms the idle rises, when it was pretty warm around 140 it was idling happily around 900 for around 10 mins this was after about 25mins of idling, I thought "great its sorted". But the temp kept slowly rising, over the next 5 mins the temp started to hit 180 and the idle really started to rise quickly, it started to do the microswitch hunting because the switch was pressed in like at idle but the revs were climbing above 1600-1700 or so. I hadnt touched anything since balancing the bypass screws 20 mins earlier. Now it was properly hot I had to get the idle down to something sensible so I screwed in the bypass screws. Even with all the bypass screws fully closed and the sync reading 4 on all cylinder (much lower than Ive ever had it yesterday) it was still revving at 1200. There was nothing else I could do to lower the air flow other than close up the butterflies and even with them closed by 1/2 turn each (now only 1/4 turn open) the idle was still high. I gave up at this point and turned it off I thought maybe thats as good as I'll get it. I adjusted all the linkages and re-installed them. Which took 20 mins where the engine (thermostat) was cooling. When I restarted the car just to see if it would re-start like when i turned it off, I just got black smoke and crappy revs and it died, clearly now that the thermostat cooled down a bit and mixture went richer the now fully closed bypass screws and butterflies are way to restricting.


I can only think there is air getting in past the butterfly shafts or that there is a timing problem. The spindle shafts have been re-bushed though at some point and there appears to be very little wear/play in them, I can just about feel a tiny bit of movement but I would have thought that it must be normal to feel a tiny bit of movement. Part of the problem is that I dont know what has been done and when.

At least I know my microswitch set up works with the hunting test.

I think my next move is to check and set the timing, to date I have assumed that its all ok and set correctly...

[inaglasshouse]

With the butterflies shut and the idle bleed screws fully closed, that seems like an awful lot of air flowing. So...

Are the butterflies sealing? What do they look like? It's possible to have little movement in the spindles but still a terrible seal... full refurb involves fabricating a new bore sleeve, not just doing the spindle bearings.
Does it definitely need 1/4 turn on the butterfly stops to move them away from stuck closed and prevent binding?
Are all the butterflies the same, or do you have one errant one?
Air leak from elsewhere (gaskets)?

Timing definitely needs checking regardless.

[inaglasshouse]

Sorry, not been paying attention - is the car drivable? If so I'd be tempted to put the air bleed screws back to 2.5 turns, check the timing and advance, then forget about idle for the moment and see how it's working hot at proper revs and under load.

[knapmann]

Sorry, not been paying attention - is the car drivable? If so I'd be tempted to put the air bleed screws back to 2.5 turns, check the timing and advance, then forget about idle for the moment and see how it's working hot at proper revs and under load.

No the car is in bits, I think my next move is to check the timing and go from there. I'd also like to get the injectors tested if I can find a place to do it just to rule out of the many unknowns I have.

[knapmann]

I’ve forgotten the exact spec of your engine but here’s another picture for you. All Porsche, all 1960’s, all different spec.




I think it’s wise to check that all the linkage is the matching spec for your set up before you go adjusting things especially the pump. You can easily get lost and end up going round in circles. You may well have the correct set up in which case all this is irrelevant.

Regards
Mike

Ive given more thought to this... surely the only crank that matters is the crossbar which activates the TBs and pump in unison. Bell crank and gearbox crank do nothing other than affect the amount of travel in the pedal to turn the crossbar, which although of some importance is irrelevant to engine running, (as long as the pedal is not holding the throttle open and is achieving WOT). I have a 69 pump and crossbar so should be fine, but as the spec for pump rod length is 114mm across the board i assume crossbars are interchangeable unless the TB pivot point changed year to year... which wouldnt surprise me in the least come to think of it!