I have an 82 f250 w/ 400/C6. I'm having trouble getting the engine to run right with the timing in spec. The factory decal says 3 degres BTDC. That alone seems weird. almost everything i've read says 6 degrese. Anyway, it's on the calibration sticker as well as the emissions decal...3 degreese. So if i set it there, the engine runs like crap. Doesn't idle well, shakes, misses etc. Now, keep in mind i'm trying to maintain the emissions controls on this engine. If i advance the timeing to about 10 - 12 degrese, the idle smooths way out. I can get it to idle great at the 600rpm spec. It still misses a little bit, but not bad at all. I have rebuilt the carb, and the mix screws are set at 2 turns out. I have tried playing with them a little bit, but no luck. With the timing at 3 degrese my vac guage shows about 17. When i advance the timing i can get a steady 21. I'm really frustrated, because i have gone over and over everything. I'm sure i have no vac leaks. Any ideas what i am doing wrong, or what could be off? Is it possible for the timing marks to be wrong? Is there another way to measure timing to check the marks?

 

Did you remember to time the engine with the vacuum line to the distributor disconnected and plugged like the instructions state?

 

I think that "3" is actually an 8, maybe? I've never heard of 3 degrees before on any of the years. I have my initial timing set at 10 degrees on my stock 400 in the '79 and my Hi-Perf 400 in my '53. Set it where it is smooth and gives you good vacuum. Just make sure it doesn't ping when you get on the gas pedal. Your elevation has a little bit to do with it as well when you set the timing. There should be a few more guys that will chime in here before too long. Good Luck!

EDIT** I stand corrected, there is a timing of 3 degrees listed for a 400 in my Chiltons. However, it lists other 400's for that year and they are at 6 degrees. I have no idea why so many different listings. Interesting...

 

Well, it's definitily 3 degrees. It is listed in two places, one on the valve cover and the other on the emissions sticker. Yes, the vac advance is disconnected and plugged. I'm not sure why there are different listings either, as i have the chiltons manual too. Could this be related to the emissions system? My air diverter valve is not working right, so i have the air pump belt off the pulley. When it's connected I get backfires on deceleration. Maybe the air pump has to be hooked up for it to run right at 3 degrees? I don't see why, but i could be wrong. Any other ideas?

 

you might check one thing i ran into several years ago the vacume advance arm had came loose and allowed the pickup to turn was saying in time but in reality was not also have seen the roll pin on the distributer strip. same results

 

I did loose the roll pin on the distrubutor. it's good now...but the rotor wasn't spinning at all when the engine turned over. that was last year's problem. With the vac advance disconnected for initial timing, would the arm still be a problem? Could you explain a little further as to exactily what I am looking for? Thanks!

 

you have an e clip that holds the arm on to the pickup if the e clip pops off the pickup coil or stater as some call it can move anyway it wants to allowing the timing to be off. the arm is what holds the pickup coil in place,also dont rule the roll pin totaly out i have seen the roll pin brake and the rotor still turn, that one was a good one i was just a kid then

 

Is your vacuum advance hooked to manifold or ported vacuum, and does it even work at all? Typically, a vacuum advance needs to be hooked to ported vacuum, BUT, I have seen factory setups where the sticker calls for a very low initial timing setting (like yours), but the advance is hooked to manifold vacuum. So, on these engines, you set the timing with the advance disconnected like you would for any other engine, but the advance pulls it much higher after you hook it back up.

For example, I have a 351W in a '77 LTD and the timing calls for 4 degrees BTDC. But the vacuum advance came hooked up to manifold vacuum from the factory, so at idle, it's really idling at around 20 I'd guess. This just means the timing curve drops from idle in my case. It's a different way of doing it from what I'm used to, but it seems to work well, and my motto is "if it ain't broke, don't fix it."

My point is, keep the timing at 3 with everything disconnected like the sticker says, but hook the advance to manifold vacuum afterwards and see if that corrects it. A lot of people will say this is not correct, and I agree, it's not the way I'd choose to set up an engine, but I've seen it done on late 70's\early 80's smog motors and an '82 400 is a prime candidate.

 

Actually I like to run my engines using manifold vacuum for the advance. But the distributor has to be set up right with all of the RPM dependent advance in the mechanical advance.

 

Set it at 10-12 where it runs the best ( 3 degrees is retarded, literally ) And when you go in for emissions, set it back to the sticker specs.

 

Well, the vac diagram under the hood says it's ported. I'll double check how it's set up though. Thanks for the help!

 

OK...did a little research. The vac advance is hooked up to the ported vac port through 2 vaccum control valves. One valve is for when the engine is cold, it applies manifold vaccum to the advance to help engine warm up. The second is an extended idle control. This valve applies manifold vaccum to the advance if the engine coolant reaches a certain temp to help the engine cool down. So once the engine is warmed up, but not overheating the advance has ported vac to it. I do know that the advance works, as i tested it with a vac pump. When i apply vac to it, the engine speeds up. I guess that means it works...lol.

 

That information and analysis is correct.

Both of those functions may be in the same vacuum switch assy.

 

Thanks for the confirmation...2 seperate switch assy's though. So I guess i'm back to the beginning...3 degrese timing and a crappy running engine .

 

I have a f-250 4x4 with a 400 ,what do you mean by ported and what are these vacume controle valves .My vacume advance is hooked right into the carburator.And for the timing I just turned the dist untill it idled good, but I dont have alot of power.