newbie MFI questions

[knapmann]

Im looking at setting up my engine for running.

1) Ive read all about the 114mm pump rod setting. I have set the rod accordingly and connected it to the crossbar. I have also set the crossbar to throttle body rods at 149.5mm as I have also read, however they are too short, in order to make the connection at 149.5mm i have to turn the cross bar and thus open up the MFI pump off its stop. My question is, do I set the 2x crossbar to TB rods at 149.5mm even if it lifts the pump arm off its stop or do I extend the rods so that the pump arm is on its stop as well as the TB's.

My assumption is that with the TB's at idle against their stops the linkage should be set so as to have the MFI pump against its stop also... in my case this would require the TB to cross bar rods to be more like 153mm (quite different to the 149.5 given)

2) Main and Idle mixture adjustments... I havent touched these on my pump but the plugs I took from the engine were very black suggesting rich running. Is there a "default" setting for these? e.g. 12 clicks clockwise from the hard stop... or something like that, it would be good to know where on the spectrum my pump is set before I dive in changing things. It could be set very rich, very lean or anything for all I know.

[210bhp]

Have you got the correct cross bar and bell crank for your engine? There is more than one type of bell crank which might explain your difficulty.

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Regards
Mike

[inaglasshouse]

My question is, do I set the 2x crossbar to TB rods at 149.5mm even if it lifts the pump arm off its stop or do I extend the rods so that the pump arm is on its stop as well as the TB's.
My assumption is that with the TB's at idle against their stops the linkage should be set so as to have the MFI pump against its stop also...

Your assumption is correct. Set the pump-crossbar rod to the prescribed length, and adjust the closed position of all the butterflies.
After that set all other rods to be correct for the entire set up to be on its closed stops.
Crossbar to middle butterfly rod lengths do sound wrong... basic question, apologies, but are those butterflies definitely adjusted to be closed?

[hot66]

assume everything is else with the engine is spot on yes ?

Set the pump to cross bar linkage length as CMA ( check measure adjust )

keep all other rods disconnected

start engine and with it at temp, and assuming throttle plates are fully shut, set the airflow screws on the throttle bodies ( as shown in CMA ) so they have matching airflow and tickover is as desired

now refit and adjust the linkages between each butterfly on the throttle bodies making sure no butterfly moves off its stop

now fit rhd crossbar to throttle body linkage , again makeng sure its length is adjusted so it doesn't move the throttle butterflys ( this should be similar length to as CMA states but dont worry if it isnt at this stage if youre just trying to get things running )

in theory the LHS ( when looking from the rear of the car ) linkage when fitted should be similar length to the RHS ( CMA gives the tolerance ) .. but bear in mind the end of the cross bar has a slight adjustment too so this might need to be reset.

All that as a starting point should get you pretty close

ONly after all that is done should you then think about MFI pump adjustments ( dont just go adjusting it randomly ... tweek a little at a time and then retest )

MFI cars like to run rich so dont expect plugs like a modern FI car especially if its been ticking over a lot

[hot66]

after saying all that .. my cross bar to throttle linkage lengths are 149mm

[knapmann]

Have you got the correct cross bar and bell crank for your engine? There is more than one type of bell crank which might explain your difficulty.


Regards
Mike

Hi Mike I wasnt aware of differences with these but it appears that I have the 1969 crossbar (lever arm is flat and not ridged) and bell crank (different to both the ones you pictured).

[210bhp]

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

[Cortina]

Agghhhh - Neil , Don't touch the pump at this stage (you may never have to ?). Rich running was only because it had been started and run numerous times to show people like me .... it had never been driven (as in on the road) - so simply forget about plug colour - it's not relevant !

I would be VERY surprised if all the linkages etc are not the correct "mixture / combination"

cheers
Alan

[210bhp]

There you go, I’m talking bunkum. But it was just a thought.

Regards
Mike

[Cortina]

There you go, I’m talking bunkum. But it was just a thought.

Regards
Mike

Don't think so Mike - just remember the ASSUME rule .... if in doubt (which there is) - check and re-check ..................
(mean while back to 928 underseal ................)

[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

I have a lot to check, the number of differences year on year model to model is unreal, seems like they never left anything alone! Figuring out what I should have will be the hard bit, '69 only no doubt...

Neil

[knapmann]

OK so I fired her up, eventually. At first it just wouldnt go but I figured out the fuel pump wasnt spinning, it was clogged up with crap. Are fuel pumps always noisy? It is at least as loud as the buzz from the CDI unit.

Heres what I did. Fired it up with all the linkages disconnected, including the gas pedal, TBs, pump the lot. The butterflies were set to whatever Paul left them at. The air correction screws were all set at 2.25 turns. The idle was around 500-600, and very lumpy as you would expect when this low. This is what I did.

1) There was a decent amount of variation in air flow reading across the cylinders from ~6 to 10 on my STE sync, the one i think everyone uses. I used my sync to raise the flow from the lower reading cylinders to match the highest one which was reading 10 by adjusting the buttterfly idle stops (not the air bypass screws). The idle went really high around 1800, having balanced them I lowered all the idle stops by 1 flow reading on the sync at a time, i.e. to 9 then 8 then to 7 and the idle was around 1100, still a bit high.

2) I went to lower the butterfly idle stops further to 6 but when I try I am half way through doing so (3 or 4 of the 6 stops adjusted) and suddenly the idle drops by 500 rpm to 600 and it goes all lumpy like where I started. It'll be very quick, I will have adjusted 3 or 4 stops down to 6 flow on the sych then when I adjust the next stop down the revs will die straight away

3) After repeating this a few times I left it at 7 and 1100rpm.

4) I manually activated each butterfly and heard a rise in RPM which told me all 6 cylinders are firing OK. I also nudged the pump rod at both 1100RPM and 600RPM settings and the revs died both times which tells me that I dont have a lean fuel issue. I felt for hot air from the thermostat outlet, the flow was very weak so I removed the pipe itself from the inlet side, here the flow of warm air was more perceptible but not like a hair dryer which is what I was expecting, is this normal? CMA shows a thermostat cleaning procedure which I have not done. I have checked the pump timing and pressed in the shaft on the back side of the pump to make sure it moves as it should.

So at the moment I can have it running quite nicely at 1100-1200 or slow and lumpy at 600 and im not sure why. heres my thoughts and questions

a) should you set the idle by adjusting & balancing the air flow using the stop screws or the air bypass screws, I have read different opinions on this, I followed Lee Rices article and set the bypass screws all the same then balanced the flow with the butterfly stops.
b) there might be a timing issue, I havent looked at or touched the timing
c) there could be an injector issue, i have no idea on their functionality (how reliable are they? is there a go-to UK based place to send them for testing?)
d) there could be a pump issue possbly around the difference in the idle circuit and the main circuit, I have read that there are 2 circuits both with mixture adjustments, and that the idle circuite operates at <1000rpm. Maybe my engine is operating ok on the main circuit above 1000rpm but when it switches to below 1000 on the idle circuit there is an issue that makes it drop significantly

tomorow I will do the hunting test on the microswitch/rpm transducer system, clean out the thermostat maybe and lubricate the dizzy.

[inaglasshouse]

Progress!

A couple of thoughts:
1) Condition of throttle bodies? If they are worn, the butterflies are never going to seal properly, and idle and part-throttle are always going to be a bit of a lottery as the spindles wobble around in their holes.

a) should you set the idle by adjusting & balancing the air flow using the stop screws or the air bypass screws, I have read different opinions on this, I followed Lee Rices article and set the bypass screws all the same then balanced the flow with the butterfly stops.

2) Personally I set the stop screws to "fully closed then back a tiny bit so the butterflies aren't jammed" with engine not running. Then adjust idle balance using the bleed screws. From memory that's the CMA way, although I agree the Lee Rice articles are also very useful. With that done, and bleed screws set at the same starting point (2.5 turns out, or thereabouts) there shouldn't be huge variation in flow between cylinders. Unless the TBs, or something else, are leaking air. Or there's a different problem (compression etc).

BTW personally I wouldn't go too far on optimising idle initially. It's running, good start. Better to sort out the fuelling and timing at working revs, then come back to the idle later.
The main rack adjustment on the MFI pump has much more effect than the idle adjustment, so definitely needs setting up for normal running before attempting any fine tuning of the idle mixture at the pump.
Stating the obvious, all bets are off until it's fully warmed up so the enrichment from the pushrod "thermostat" connected to the warm air hose is no longer in play. When cold, that system is having a large effect on the fuelling, and there's not much point aiming for perfection in that enriched state.

[hot66]

Use the bleed screws not the butterfly stops. Have the butterfly’s set so they are closed as CMA states. There should be no reason not to use the air bleed screws and if they have no effect they need cleaning out.

When the engine is cold you control idle with the hand throttle anyway and as above, then enrichment systems are in play. Massive difference in idle running between a cold mfi and a fully at temp mfi

[knapmann]

thanks both, I think I will try again today and instead follow the air bleed route and see how that goes.