Mechanical advance

[tima01864]

Static advance 10 degrees
centrifugal advance 28 degrees +/- 2 deg
Air gap 0.012 0.016

[18Fiatsandcounting]

Static advance 10 degrees
centrifugal advance 28 degrees +/- 2 deg
Air gap 0.012 0.016

I'm not familiar with your specific engine, but this sounds about right.

I don't pay too much attention to static timing as I don't really care whether the engine is developing 8 HP or 9 HP at 850 rpm. 36 to 38 degrees of total advance are the maximum you want, and this is based on a calculation of the piston speed versus the speed of the combustion pressure rise. I believe it is a constant for all typical gasoline internal combustion engines, although there could be differences for exotic engines.

-Bryan

[tima01864]

I will mark off the degrees as we suggested with the compass. The cork cam gaskets are leaking, seeping, I have a set of rubber gaskets. Will try to sort all this out. I will install the OEM distributor while I am at it and check the timing marks on the cams.

[RRoller123]

That is really interesting about the cork, I am up over 200 miles on the new engine and have no leaks there at all. No sealant used.

Maybe try tightening them slightly? In steps, a little each day until the leak stops? But of course be careful, the aluminum cam boxes can easily crack.

Pete

[tima01864]

They were a little loose.
Have you tried adjusting the idle with the tps unhooked?
Too hot to drive the car, Early morning drives are the best in this heat

[RRoller123]

Yes, TPS is correct.

I just replaced the two throttle shaft seals, with the o-rings from MaxM. They fit perfectly!

The one under the TPS seemed pretty good, still pliable, but the one under the throttle spring was perished, rigid and cracked into pieces upon disassembly. About to take a drive and see if there is any difference. It would be unmetered air if it were leaking there, which is not good, causes lean. The narrow range O2 sensor can only make minor adjustments.

I also suspect the Charcoal Canister, it has a direct line to the plenum, as does the brake booster and fuel pressure regulator. Again, leaks there are unmetered air.

Lots to look at. It may be that I just have the ignition too far retarded, since I have been setting it at about 12, but that's with the throttle up around 1200-1500, which is the only range it will idle smoothly. It might be as simple as advancing the timing and then seeing if, by adjusting cable and idle screw, I can get the idle back down. Not sure. Vexing problem.

[tima01864]

With the TPS disconnected are you able to adjust the throttle/ Idle lower?

[RRoller123]

No, makes no difference. The TPS is normally closed (~2 ohms) when on idle, and goes open (~ infinity ohms) at any other position. When it is disconnected, it is like having the throttle at any open position, i.e it just tells the engine ECU that it is open and running at some speed other than idle. There is no proportionality and there is no WOT function either, although it is mentioned in some manuals. That is an error in the manuals. The TPS is either saying it is at idle, or that it is at some other unspecified speed. All this thing does is shut down the injectors to a minimum flow when the accelerator is backed off while driving, so that one doesn't get a backfire from too much fuel going out into the exhaust when you pull your foot off the pedal to shift, or brake, or whatever, while driving. But I will check it at the ECU connections tomorrow just to be sure, if I get a chance, we have 2 showings of the RV to do during the day.

More likely culprits are the AAV, the brake booster and charcoal canister lines, all 3 of which can be clamped off one at a time to see if that is where the excess air is coming from. It is possible that someone has gumpcukrussed the AFM bypass screw too, since the factory seal cap is missing. I will have to fiddle with that as well.

[tima01864]

I was looking at the AR website, Looking at the distributor sold for an 80-85 they state 22 degrees of advance on this unit, Proper for HC engine with FI. Can this be correct?

[RRoller123]

Starting from 10 would give 32 degrees total advance, seems reasonable?

[tima01864]

That does make sense now

[Nut124]

Sorry, late to the thread - Did you get this figured out?

I have been building a Fiat engine this summer and have dealt with just about all the issues you describe.

A Fiat twincam should easily pull hard past 6000rpm. Who built your engine?

Some suggestion below:

1. Cam spec sheets do not tell you anything about your installation. The only way to check is to use a cam degreeing wheel on the crank and use a piston stop plug to validate your true TDC marks. This is a pain but worth it.
2. Ignition timing: You will need a reliable TDC marker. Use a piston stop to validate your TDC timing marks. The other way is to remove the timing belt and use the crank "wobble method". Right around TDC, the crank turns easy in either direction about 5 deg or so with no timing belt. TDC is in the middle of that easy rotation. This is not as accurate as the piston stop.
Once you have a reliable timing mark, remove the vac advance tube from distributor and run the engine up in rpm while watching timing. The mech advance should move timing from about 10deg at idle to 36-38 at 4000rpm. If not, then there is something wrong with the mech timing advance. Check for dry grease under the advance fly weights. Timing at idle does not much matter as long as you have the 36-38 at 4000 and up.
If your vac advance is working, the engine should slow down when you disconnect the vac line at the distr.

Good Luck.

[tima01864]

I had two reputable FIAT mechanics build the engine and head, One for the cylinderhead a performance build and one for the bottom end with HC pistons. The engine runs strong, Much stronger pre build. Smooth with no vibration.
I used a drop indicator on #4 to confirm the marks at TDC in a CW rotation before mating the head, I used an Ottoco MLS head gasket from Allisons sold as .060 thick.
I have adjustable cam wheels to adjust timing to the cylinder builders timing marks.
I have a new distributor since the original was worn and would not hold the timing light steady at idle.
The limitation could be the FI system, This I have to investigate. Tho I am able to hold an idle at around 800RPM
Only thing un ordinary was the timing belt was very tight and the intake was a touch out of true and the belt did ride on the intake wheel fully.
My next step is to replace the intake cam wheel with an OEM cam wheel. At that stage I can recheck my timing