Big changes... How to properly set ignition timing...

[firenguitar303]

Hi All,

Wow, lots of good advice on this site. I'll get to posting on the introduction page soon, but here's my challenge...

1977 Fiat 124
- New Weber 34ADF
- New Pertronix MR-LS1
- New Pertronix 40,000 Coil
- New IAP 4-2-1 Header
- Custom middle exhaust pipe, essentially straight
- ANSA Muffler

The car is running really well, but I think my timing is a little off and I'm not sure exactly how to tweak it. I went through the Weber initial setup for mix and idle. I've tried different timing settings and adjustments, but between shifts and on decel I'll get some pops in the exhaust. Running rich? I changed the timing a bit and put in premium gas (not that I had detected any pinging) and the mileage between tankfuls went from 17MPG to 24MPG, so it's better. However, there still seems like hesitation coming off idle sometimes and again, the pops sometimes between shifts and also on decel.

My friends seem to think that I've leaned it out a bit with the straighter exhaust system, just not sure where to try and set the timing. My friends were also asking about the timing when at 2,500RPM and above. I looked yesterday and it was at about 32 degrees with it being about 5 at idle, I believe (timing light has an advance setting on it).

Any input is appreciated!

[azruss]

you can get a backfire on decel by pulling cold air into the exhaust port. this usually means an exhaust leak close to the head. Since you have modified your exhaust, it may be a design problem. anyhow check for a small leak at the manifold.

[firenguitar303]

Azruss, you may be on to something. Checked it a bit closer today and it is leaking right at the exhaust manifold. I probably burned up that gasket. Time to get another.

[firenguitar303]

Success! Leaky exhaust manifold gasket has fixed the issues!

1. No more excess noise from the engine compartment
2. No more backfires on deceleration
3. No more small pops on shifting.

Thanks!

[TulsaSpider]

Sweet! Didn't torque it down enough? How did the header fit?

[firenguitar303]

Hmmm. spoke too soon... A week later and I'm having exhaust leaks at the Exhaust Manifold again... Made another post for ideas to track that down...

[sptcoupe]

It doesn't take much of a misalignment between the exhaust ports and the header ports to cause an exhaust leak. If it is leaking at the same place, definitely check it out. Fastest way is to put the gasket up against the header and see how the holes line up.

I have run a number of engines with the 34 ADF. Not sure what other performce mods you have made, but try it with 10 BTDC and a total of 36 degrees advance. If you have not bumped compression or are running stock cams, the jetting in the ADF will typically be rich with the jets that come with the carb. Pops in the exhaust are also indicator of a rich mixture. Also check the float level, as the range it is set at when new is typically rich. You may solve your problem by simply adjusting the float, but that will depend on what other jets you are running.