Got my MFI engine running

[dhamilto]

Gents, after a couple of years of sitting on the garage floor I just re-installed my 73' 911T MFI engine. It was plenty smoky to begin with and would not idle but after following the MFI tuning guidance on this site I have it idling smoothly and the smoke has cleared. I will tell you what I did, and then I have a couple of questions which I hope the experts can help with..

Removed towers and cleaned, cleaned throttle bodies with carb cleaner, set stops, set rods so that levers are rested on stops, set fuel pump rod to 114mm (was one turn out), removed and soaked air bypass screws in carb cleaner then cleaned and oiled them (all three on left side where extremely stiff; they now all move smoothly), cleaned out air bypasses, screwed them all the way in and then back 2.5 turns. Idles nicely Have ordered an air flow synchroniser to fine tune later...

What confuses me is that it idles at around 850rpm at startup, but then increases (to 1000) when the engine is warm. I expected it to start high and then fall. My questions are: is it supposed to do this? The target 900rpm value is for hot engine right?

Also, my air box does not have the warm-up regulator / housing. I have seen other 72/73 MFI engines without it fitted; can anyone tell me what it does, how it works and where the pipe goes after it goes down through the tinware? Do I need to obtain one of these for proper operation?

Hope someone can help!

Best wishes, Dean

[RSTarga]

You don't need the warmup piece unless you live some place very cold. the tube hooks up to your left heat exchanger.
Is your hand throttle all the way down after start up? It's the lever between your seats for cold startup and should be pushed down as engine speeds up. Or just blip the throttle and push down completely.

[tobluforu]

Do you have the double preheater hose attached to the pump and the steam hose connected to the HE? Also, make sure all the rods are adjusted after car is fully warmed up/heat soaked. Did you clean the thermostat? Yes, you want 900, give or take after car is warm. If timing and everthing else is in order, this where the synch will come into place. Unless the TB's are rebuilt its almost impossible to hope that setting the air screws 2.5 turns out and having the TB stops set just right will equal perfect idling, if so they would not have the air screws. Once you get it to idle at 900, raise to 3000 rpm and adjust airscrews again.
One other thing, unscrew the round device on top of the pump and make sure it has the right amount of shims which I think is three???
You do not need the warm up regulator.
Good luck and your on your way, now the pros can chime in.

[Flieger]

You are quibbling over 850-1000 rpm?! Don't worry about it! My car's throttle bodies are warn so that messes with any low-mid rang tuning. The headers also mean I cannot run a thermostat so I have a screw to hold the thermostat in the fully warm position. If you do not do that, then the engine runs way too rich.

My motor runs fine in the mid to high rpm range though.

[dhamilto]

Thanks guys, my hand throttle lever has never worked and it never really occured to me until now that maybe it is needed for cold start no matter what the outside temperature?? So, what I think I need to do now is get the hand throttle working and set it up to give ~1100rpm when fully on (cold)? Then lever down and set the idle to 900 when warm? I received an air flow synchronizer this morning and will use it to equalize the airflow while setting idle.

Forgot to mention: while idling (hot or cold), the speed drops if I push the pump rod indicating too rich. The spark plugs are also black indicating rich. Will check the operation of the thermostate with a heat gun. assuming that moves ok, should I go straight for the screw through the fan and make it leaner?? Out of interest, I just ordered one of those Gunson's Colortune devices that allows you to see the colour of the flame through the spark plug hole. I will use this to check/adjust the mixture. Compression guage is on the way too. My fuel pressure measures a bit low to the pump ~7psi if the cheap gauge is to be believed (manual says 11.8 +-3).

tobluforu: I dont know what 'the double preheater hose attached to the pump' is. The only hose attached to the pump (apart from fuel) is the inch-ish diameter hose from left HE to side of fuel pump thermostat...

Thanks for all comments! Best wishes, Dean (now back in UK, not PA)

2000 996 C4 tip S cab black with dead engine
1986 944 auto seal grey 210,000 miles
1973 911T 2.4MFI targa blue metallic code 334 under restoration

[daepp]

dhamilto:
I have a 72 MFI.
Re: The warmup piece on the airbox - makes no difference as far as I can tell whether it's on or off - I just keep it as it's original. I does get in the way for adjusting the points.
Re: Cold start lever - I use this always on cold starts, regardless of ambient temps. But I think all it does is pull on the accelerator cable. And to that end, that is a weak spot. white nylon piece attaches the lever to the cable and ofter breaks. Not hard to replace. Mine broke, and now I always "assist" the lever by pressing on the gas pedal as I pull up on the lever. Then crank, and sweet HC goodness and flat six songs begin!

[tobluforu]

Originally Posted by dhamilto

Thanks guys, my hand throttle lever has never worked and it never really occured to me until now that maybe it is needed for cold start no matter what the outside temperature?? So, what I think I need to do now is get the hand throttle working and set it up to give ~1100rpm when fully on (cold)? Then lever down and set the idle to 900 when warm? I received an air flow synchronizer this morning and will use it to equalize the airflow while setting idle.

Forgot to mention: while idling (hot or cold), the speed drops if I push the pump rod indicating too rich. The spark plugs are also black indicating rich. Will check the operation of the thermostate with a heat gun. assuming that moves ok, should I go straight for the screw through the fan and make it leaner?? Out of interest, I just ordered one of those Gunson's Colortune devices that allows you to see the colour of the flame through the spark plug hole. I will use this to check/adjust the mixture. Compression guage is on the way too. My fuel pressure measures a bit low to the pump ~7psi if the cheap gauge is to be believed (manual says 11.8 +-3).

tobluforu: I dont know what 'the double preheater hose attached to the pump' is. The only hose attached to the pump (apart from fuel) is the inch-ish diameter hose from left HE to side of fuel pump thermostat...

Thanks for all comments! Best wishes, Dean (now back in UK, not PA)

2000 996 C4 tip S cab black with dead engine
1986 944 auto seal grey 210,000 miles
1973 911T 2.4MFI targa blue metallic code 334 under restoration

That's the hose I'm referring to, but there is an inner and an outer hose. Does you rpm transducer/speed switch work, if not this can cause black plugs.