adjustment on 77 Carb to avoid mild lean

E

emrliquidlife

True Classic
Hey guys,

Got Ivan Cotton's 77 X here and we are replacing the spark plugs. Old plugs indicate that the 1 and 4 cylinders are running mildly lean, and the 2 and 3 cyclinders are a good. Is there any adjustment on his carb that we can tweak to avoid the lean condition?

Thanks,

Ed
 
Stock Carb?

You should really put a larger Carb on that car with the cam shaft that is installed.

However, increasing the main jet size will richen the mixture. The needle screw is only for the idle mixture.

TonyK

Grimsby Ontario Canada.
 
His car is actually a stock 1.3L

Putting some new plugs on the car made it zing.

I'll let him chime in if he wants.

When/if we pull the jet, will it have a number on it?

Ed
 
Jet size

The jet number will be marked on it as the bottom of the emulsion tube. Not sure of what number would be on it, but let us say it is 115 with 175 on the top for air correction. You have 2 choices here. Increase the main jet by 5 or 10 but leave the air correction on the top alone or decrease the air correction by 10 or 20 and leave the main alone. Both will give you a richer mixture.

All Fiats are under carbed, so a bigger carb with a non progressive linkage ( meaning both barrels open at the same time) will give better performance. The engine needs to breath a bit better than stock, regardless if it is a 1300 or not.

TonyK.

Grimsby Ontario Canada.
 
Thanks Tony. My experience with stock Fiats is nonexistant. My car is FI.

He currently has all of the smog equipment on. Would there be a benefit to removing anything?

I need to get him to vent the stock aircleaner.

Ed
 
Smog stuff.

Anything that you can do to help the engine breath is a help. 77's didn't have a Cat unless they were in California. Fiat used a converter with a bunch of loose ceramic beads rather than a matrix in the exhaust flow. Removing the Cat and the Air pump would be of benifit. Adjusting the timing a bit more advance will also help give the car a bit more snap. The problem is that the carb has very small barrels. Just installing a bigger Carb make a big difference on the bottom end. These cars are high rev. type engines that the standard cam limits their breathing due to the short duration and over lap. Yet with a bigger carb with even the stock cam, off the line starts are surprizing quick.

TonyK

Grimsby Ontario Canada.
 
Desmog the '77?

He currently has all of the smog equipment on. Would there be a benefit to removing anything?
Click to expand...

The bolt-on smog equipment on a 49-state 74-78 doesn't really hurt performance all that much. There's the parasitic load of the smog pump, but that's not enormous. There's the vacuum retard, which hurts gas mileage and driveability a bit, but it only matters at part-throtle and idle. The crankcase vent system and evaporative emissions controls are basically free except for the tiny amount of weight they add.

Desmogging these cars does have two advantages:
  • It cleans up the engine compartment no end, and makes working on the car way way easier.
  • Getting rid of the vacuum retard improves part-throttle drivability, fuel economy, and makes it a lot easier to get the timing and idle settings right.

Now, the non-bolt-on stuff that there's for smog control, the lower compression and less aggressive cam compared with European spec... that probably hurts a lot more.
 
Desmogged

Yesterday morning I took my 128 Wagon in for it's first smog since I have owned it. Passed with results well below state averages, which always seems easy to do with a car that everything functions on.

My list of things to do when I got home:
Remove air pump, belt & mount so I can do the first engine service (had a broken timing belt & bent valves when I purchased it)
Plug air injection system at check valve, seal off all remaining air injection components so they will not rot before next need for them.
Set timing to 10 degrees advanced at idle with vacuum retard hose off.
Replace converter with test pipe.

At a minimum reset the ignition timing if you want a 1300 to be driveable.

Once I get all the rest of the car's issues delt with I will of course reinstall of the stuff before I drive it.
Chris Obert
 
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