Switching a 3.2 Motronic to Carbs, Where's 'Myth-Busters' when you need them.... Options

[RiqueMar]

My Dad is exploring the possibility of a converting a 3.2 Motronic engine to Carbs. However, the problem is that the distributer is different. The only option seems to be to recurve the distributer. However, we have heard rumors that if you can find a distributer off a 2.7, you're set?


Any truth in this? Personal experiences?

[Mark Henry]

I know you can't do it on a 3.0 because it spins backwards.

About the only other option is a megajolt jr. or MS system or an after market crankfire system.

(If it works I have a 2.7 bosch dizzy.)

[Brian_Boss]

The only option seems to be to recurve the distributer.

There is not really anything to recurve in a stock motronic dizzy. It does not control spark timing. There are no points. All it does is send the spark to the right cylinder. There is an advance mechanism but it only serves to keep the rotor pointing at the terminal in the cap as the spark is advanced by the ECU. The timing is completely controlled by the ECU based on a programmed advance curve and input from the flywheel position sensor.

[RiqueMar]

I know you can't do it on a 3.0 because it spins backwards.

About the only other option is a megajolt jr. or MS system or an after market crankfire system.

(If it works I have a 2.7 bosch dizzy.)

Exactly, the direction is different, which I believe matches that of a 2.7. Hmm, if I find that it is simple as that, I'll def keep that in mind

The only option seems to be to recurve the distributer.

There is not really anything to recurve in a stock motronic dizzy. It does not control spark timing. There are no points. All it does is send the spark to the right cylinder. There is an advance mechanism but it only serves to keep the rotor pointing at the terminal in the cap as the spark is advanced by the ECU. The timing is completely controlled by the ECU based on a programmed advance curve and input from the flywheel position sensor.

Yes, but when switching to a carbed engine, wouldnt you need a conventional distributor?

[GeorgeRud]

It sounds like you'd be taking a step backwards to go from Motronic to carbs. Unless you're doing some other modifications to the cams, pistons, etc., the carbed engine will not run as well as the Motronic engine.

[championgt1]

(IMG:style_emoticons/default/agree.gif) Why would you want to change to carbs?

[eitnurg]

BTDT. The 2.7 distributor has way too much advance (about 35deg all-in) and should be re-curved to max 25-28deg (see http://www.911chips.com/ignition.htm for the 3.2 advance curve). You can run it unmodified, with the timing backed off but this means it runs way too retarded at idle: you get a terrible off-idle bog on acceleration (which the carbs just add to) until the revs rise and the advance mechanism catches up. Alternatively a locked distributor and something like a MSD timing computer works well - until it breaks.
The "direction of spin" issue is lost in the mists of time. These days I have trouble remembering what I had for lunch yesterday.
Otherwise concur with what's already been said: if the Motronic is set up & running, leave it be.

[RiqueMar]

(IMG:style_emoticons/default/agree.gif) Why would you want to change to carbs?

Yes, it is, in a way a 'step-backward', but its also rather nostalgic, which is what he wants.

[SirAndy]

its also rather nostalgic

Ah yes, the good old days of clogged idle jets, flooded bowls, non-existing cold start, out of sync running and crappy gas mileage ...


Those were the days!
(IMG:style_emoticons/default/biggrin.gif) Andy

[RiqueMar]

its also rather nostalgic

Ah yes, the good old days of clogged idle jets, flooded bowls, non-existing cold start, out of sync running and crappy gas mileage ...


Those were the days!
(IMG:style_emoticons/default/biggrin.gif) Andy

But they sound sooooooooo cool! (IMG:style_emoticons/default/aktion035.gif)

[siverson]

> But they sound sooooooooo cool

Not when they have "clogged idle jets, flooded bowls, non-existing cold start, out of sync running and crappy gas mileage". (IMG:style_emoticons/default/smile.gif)

I agree, stick with the Motronic.

-Steve

[IronHillRestorations]

The only way to go would be with new PMO carbs. They are made differently and don't have the same problems the Webers have with idle jets getting stopped up.

I'm with the other guys though, your Dad needs to drive a 914 with a 3.2 Motronic engine. Reach in turn the key, no snappity-pop-pop, no "look how fast I can change fouled plugs", modern FI.

[BigD9146gt]

Not sure what your dad has on the motor already, but that mass-air flow conversion and chip help with some power, and with the cone filter you can hear more of the air going in... Dansk sport exhaust and that noise will provide more than enough nostalgia.

If you must go carb'd, PMO. If you want supa nostalgia, PMO EFI stacks and stand alone setup. That will give you tingle in the most desirable of places.... just not the wallet area. That will feel more like pins and needles dead leg feeling.

[sean_v8_914]

I would use EFI on every engine if I could afford it

[Cupomeat]

(IMG:style_emoticons/default/agree.gif)
Stick with the FI, the car is nostalgic enough.

[Eddie914]

I have a 3.2 with Webers. I wanted Motronic but the induction was sold from the wrecked 911 before I showed up to buy the 3.2.

As long as the fuel is kept free of water it runs great. A few pumps of the accelerator on cool mornings and it fires right up. It sounds and looks nostalgic too.

I'm running the same distributor (and carbs) that came off the 2.7 that KABLAMMOED in my conversion 914-6. The PO did the conversion so I am not absolutely sure what distributor it's running. It still has points, Permatune CDI, Black Bosch coil and mechanical rev limiter (6700 rpm ditributor rotor).

I will look to see what numbers are on the distributor. I am gone for the weekend so I will look next week.

Cheers,

Eddie

[MoveQik]

(IMG:style_emoticons/default/agree.gif)
Stick with the FI, the car is nostalgic enough.

I agree. Been from sea level up to 11k feet and everywhere in between. Car starts and runs perfect with a simple turn of the key. (IMG:style_emoticons/default/biggrin.gif)

[RiqueMar]

I have a 3.2 with Webers. I wanted Motronic but the induction was sold from the wrecked 911 before I showed up to buy the 3.2.

As long as the fuel is kept free of water it runs great. A few pumps of the accelerator on cool mornings and it fires right up. It sounds and looks nostalgic too.

I'm running the same distributor (and carbs) that came off the 2.7 that KABLAMMOED in my conversion 914-6. The PO did the conversion so I am not absolutely sure what distributor it's running. It still has points, Permatune CDI, Black Bosch coil and mechanical rev limiter (6700 rpm ditributor rotor).

I will look to see what numbers are on the distributor. I am gone for the weekend so I will look next week.

Cheers,

Eddie

Eddie,

Thanks for the input, please let me know all that information, it is greatly appreciated. Clearly, there's not alot of info on the subject.

[naro914]

We went from a carbed 2.7 to a motronic 3.2 in Huey and I would rather walk everywhere than go back. It is soooo nice to just jump in, turn the key, and go. No coughing, no backfiring, no clogged jets....

Granted, Papa Smurf has PMO carbs, but it's highly modified and there is no FI to make it work right.

If you build an engine for carbs (correct cam profile, compression, etc) I think it comes out great. But if you just retrofit FI with Carbs, it may not work as nice.

[Mark Henry]

If you build an engine for carbs (correct cam profile, compression, etc) I think it comes out great. But if you just retrofit FI with Carbs, it may not work as nice.

(IMG:style_emoticons/default/agree.gif) And that is your answer,
I don't agree with all the detractors of carbs (and that coming from a SDS FI guy) but sticking a set of carbs on a FI engine will never give you the result you want.