Carbed ignition controlled by computer?

[BigElCat]

I have an 88 carbed Festiva. According to Haynes, the spark timing is controlled by the ECM as well as the carb jetting.

Can anyone explain this in more detail? Is the Haynes manual right?

My Suzuki Samurais have a feedback carb, but the ignition is not controlled by the ECM.

Haynes states that the spark timing is computer manipulated until the engine reaches operating temperature, and then the dizzy functions without computer assist. Or maybe I interpreted Haynes wrong.

An altitude compensator also influences spark timing, but it operates independent from the ECM.

My goal was to maximize the static (initial) advance using the 'power timing' technic. I don't want to battle the ECM though.

Power timing is where you keep advancing the timing until pre-detonation becomes a problem, and then back it off just enough to avoid the ping. It gives you free horsepower and increased efficiency.

[bravekozak]

stock Festiva carb

I could not tune the stock Festiva carb properly. It acted like it had a mind of it own.
Speeding up at idle and going down again at unexpected times. I still have a couple of them in mint condition on display in my museum.
Real carbs don't need computer control. No ECM. Just gas.

I upgraded first to a Weber, which was lots of fun.
Then to dual Hitachis.

http://www.bwbronze.com/festiva/

Recommendation: Buy a Weber + adapter + air filter from FMS.

[Festy46]

The only way the ECM could control the carbed distributor is if the ECM controls some of the vacuum advance that goes to the distributor. I never bothered checking it out. I pull both vacuum hoses off the distributor, advance the timing to compensate for them, and use only the internal centrifugal advance to give me the maximum advance.

Like Bravekozak said, dump the stock carb. I don't use the Weber though, too expensive. A 2 barrel carb for an early '80's Ford Escort with a 1.6L engine works fine for me and for about 1/4 the cost. I recently purchased a brand new Escort Carb on eBay for $50.00 including shipping.

[Hot_Wheels]

what about gas millage is it better or worse with a diffrent carb?

[Fordverde]

Depends on the jet sizes you put in. if you want the best economy then use an 82 for primary and 130 for secondary. If you want alittle more kick then use a 90 or 95 and a 150.

[m715]

I believe that what the Haynes is speaking of is actually the function of the ABCV stepper on the carb from what you are describing. About 80% of the time a stock carb has a problem, it has a vaccum hose off or cracked, a bad temp sensor, or a fouled O2 sensor. I don't see how the ECM is going to be involved in the spark advance as the two vaccum lines go to the carb base, and intake manifold directly. If you are looking for a little more kick out of your dist, look for a 1989 ATX that still has its installed. It will change the advance curve, and wakes one up quite nicely, thank you very much! I am using one of the FMS cams on a crate engine too. I like it! And, it didn't change the economy really at all! I am still getting 37 MPG with this crap fuel out there right now, with just a slight ping on the steepest hill on my commute.

Michael

[BigElCat]

If you are looking for a little more kick out of your dist, look for a 1989 ATX that still has its installed.

Michael

You're saying use the entire distributer out of a 1989 ATX? What's an ATX?

[worfdog]

ATX = auto trans. I bought one from FB71 about a month ago. have not installed it yet.

[m715]

You will be pleasantly surprised for no more work than is involved. It won't make a B6 out of it, but it does add zip to the acceleration with no economy penalty!
Also, I meant the post to say its ORIGINAL distributor. If it has been changed, it is likely to be a manual transaxle type (MTX) like you already have in your car. They had more spark advance in the 89 automatic cars to help give them a little extra kick to try and compensate for the low horsepower in the 89 cars only. Starting in 90, the fuel injection system was totally different, and the carburators went away for good. If I understand it correctly, the 90-93 FI setup was a better setup than the 89 with the computer controlling the spark advance instead of using manifold vaccum. Jim or Brian may be able to shed more light on the reason for the change possibly

Michael

[FB71]

the reason for the change is that vac/mech advance mechanisms are grossly inaccurate compared with computer controlled spark timing. Accurate timing is extremely important for emissions reasons. The change in the EFI system from '89 to '90 was not as drastic as some might think. Essentially, the systems are nearly identical, with the exception of ECM controlled timing being added in 1990. The injectors drivers, canister purge, air metering, and several other lesser systems are all direct carryovers.

[m715]

I guess then my question of the day would be then why the intake and vaccum connections etc were so different. I can't remember now, because it was a few years back, but we had an interesting time getting the bugs out to make a 91 engine work SMOOTHLY in an 89 ATX for another guy I work with. Maybe was just the difference in the intake because we had less vaccum fittings? Wish I could remember for certain......