Just set the timing on my 71 360 FE, factory sticker says 6BTC but….. when I set it at 6BTC it barely wants to stay running. Seems to run best at around 3 BTC. But even at 3BTC there’s a slight misfire at idol and gets worse when just out of acceleration then goes away after RPMs are up. I did put a Protronix igniter and coil in the distributor. Any ideas….?? I’m at a loss… any helps appreciated!!

thank you!

 

Use a piston stop and confirm that your timing marks are correct. The outer ring of the damper may have slipped which will give you a false timing. The 390's seem to run pretty well at 12 degrees at idle so your numbers seem off. Make sure that when you set the base timing that the vacuum advance is not plugged in. After setting the base timing to 12, reconnect the vacuum advance. Although the vacuum may have been connected to the ported vacuum on the carb, it will likely run better if you connect it to full manifold vacuum. When you connect the vacuum line, the timing should advance. If it doesn't, the canister may be damaged/leaking. Check the mechanical advance mechanism in the distributor to ensure that it springs forward and snaps back and check for any side to side play. Petronix units may not work well if there is excessive radial/side-to-side play in the distributor shaft so make sure the shaft side-play is minimal. Last, make sure you bypass the pink resistor wire and provide the Pertronix with a full 12 volts.

 

Thanks, good call on the resistor wiring, I made that correction. Regarding the vacuum advance I have to disagree with running it off the manifold, my experience in doing that makes the engine run horribly, runs best off the port of the carb. Timing Still wants to be at 3 BTC, must be something else going on. BTW it’s a 360 not a 390. Thanks for the help!

 

Each motor is different where some like manifold and others ported.
Only what to know is to try each one and see what works for that motor.
Dave ----

 

Thanks makes sense. Another data point to ponder….Motor runs terribly rough when slightly accelerated in neutral and drive, basically the vacuum off the port is increasing thus causing the timing to advance and causing the truck to run very rough misfire etc. Seems like the timing is advancing too quickly but when you get above 1000 rpm it’s back to running smooth.

Any ideas? Do I need to retard the timing a bit more to the vacuum advance doesn’t advance too quickly when accelerating?

 

It sounds like you may have an adjustable vacuum advance. They are adjusted by inserting an allen wrench in the inlet. Turn clockwise to reduce the amount of advance. It still seems to me that your damper has slipped giving you false timing numbers (TDC incorrect) or that your mechanical advance is not working correctly - a broken advance spring, for example. I would use a piston stop to confirm true TDC and then carefully check the mechanical and vacuum advance.

 

I am not so sure it is the amount / limit but when the vacuum starts to pull in.

I am sure on my 300 six (numbers are just saying) I could start to have vacuum pull timing in at say 5 HG and adjust so it would pull in at 10 HG.
It still gives the same amount / total only changes when it starts as the vacuum has to over come the spring pressure before it can move.

To limit the amount of timing the vacuum can add you would need to limit the stroke of the vacuum advance and I dont know of a easy way to do this?
You could limit the mechanical advance by placing a short hose over the stop to bring total timing with vacuum down where it needs to be.
I need to do that to my 300 as I am getting some pinging at high throttle and adjusting the vacuum advance dose not help.
I also dont want to back off base timing is it starts good right where it is so I need to limit the mechanical to stop it.
Dave ----

 

On two of my FE's, the screw that you access through the inlet tube restricts the amount/distance that the vacuum arm pulls. The one on my Cobra replica would back out over time giving me almost 20 degrees at cruise and it would start bucking and missing. I'd turn it in and back out a few turns to get it back to 8 to 10 degrees of advance. Easy enough to check, try a few different allen wrenches and see if you find the screw and turn it in. I would sure fix that over reducing the base timing so far that it won't accelerate. Overly retarded timing will also potentially cause overheating problems. Find top dead center, verify the mechanical advance, measure the actual vacuum advance at idle by plugging and unplugging the hose into the full manifold vacuum port and then adjust/replace parts as necessary. When the conservative factory base timing is about 6 and most people are able to run quite well at 12, having to drop the timing to 3 degrees to get it to idle indicates something isn't right. Yes, all engines are different, but I don't know of an FE that has to run 3 degrees base timing to run. Find out what's wrong and fix it.

 

Vacuum advance canister is not adjustable. Took it apart and there’s no place of an Allen wrench. Either way, i disconnected the vacuum hose from the carb and canister and plugged both (carb port and canister port) truck runs much better coming off idle. No more hesitation or missing. I’m guessing the canister was advancing the timing too much too fast off idle, now it’s unable to do that since the canister isn’t receiving any vacuum. Thanks all for the help, I’ll keep playing with it until it’s right.