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Discussion Starter #1
just found out not too long ago i have a 351m in my truck and not a 351w like i though...i had to change a bunch of parts i had put on the truck when i thought it was a W...just changed the plugs and now it seems to have a rough idle...so i'm figuring i have to adjust the timing since i timed it about a year ago with the old plus and the 351W parts on it...i don't have the catalyst sticker under the hood, so i need some info...can anyone tell me how many degrees btdc it needs to be, at what rpm, and do i need to plug any vacuum lines or disconnect anything?...thanks everyone....
 

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my 400 factorys setting is 6* btdc @ 500 rpm not sure if its the same or not. i have a 351m with the sticker under the hood on my other bronco but its at my buddys house or i would have checked that
 

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Dude, just put it where it runs the best. 10 may not be your engines sweet spot.


I'll agree that each engine seems to have it's own inherent differences and the sweet spot does vary from rig to rig, but I wouldn't necessarily say put it where it runs. Abiding by recommendations may help you find and later diagnose other problems. I mean hell, you don't just torque a bolt down when it's tightest, do you? Hell no, cuz you'll probably end up with alot of broken bolts. I hope you come close to the recommended torque specifications.
 

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I'll agree that each engine seems to have it's own inherent differences and the sweet spot does vary from rig to rig, but I wouldn't necessarily say put it where it runs. Abiding by recommendations may help you find and later diagnose other problems. I mean hell, you don't just torque a bolt down when it's tightest, do you? Hell no, cuz you'll probably end up with alot of broken bolts. I hope you come close to the recommended torque specifications.
Timing has nothing in common with a bolt (foolish to even compare the 2), timing is a variable you tune to peak performance - much like a dial on an older radio.

Timing light does nothing but confuses those that know little about timing and tuning. The only time a timing light would be of valuable is if you already had your engine running in the sweet spot and you had to remove the dizzy for what ever reason and you want to get it back at that exact proven location - and not bother with the 15mins of fine tuning it took you to get there.


You know pretty fast when you turn the dizzy in the wrong direction or too far - just as you do with that dial on the old radio.



I never use a timing light as its totally a waste of time.
 

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My example with the bolt was only to make the point many issues can arise when you don't follow specifications and/or recommendations, but apparently it was lost on you. What if you have a vacuum leak or a carb is maladjusted...you just temporarily masked those problems by going all willynilly with the distributor. Sure it sounds like it's running better, but you just masked other problems. The thing that is foolish is to advise anyone to tune by ear. Sure there are some guys out there that can actually do it...you may be one of them, I dunno...but I'd be willing to bet 99% of the folks out there that think they can tune by ear can't. Hell, I had a 351M in my Bronco that sounded better and ran better when it was outside specifications and bumped to about 20-22*BTDC. But on a stock engine, if it has to run there, that raises a red flag. Had I never had a light on there, or known what was recommended I wouldn't have known how far off it was. And like I said, it ran better and sounded better...but that very engine had a busted piston skirt on #6 and two other cylinders with zero compression. But according to your logic, I bumped the timing so it shoulda been fine, right? I guess I should become a mechanic now that I know the secret of fiddling with the dizzy can fix alot of problems.



BTW...wouldn't Ford's recommendation already be considered the sweetspot that you refer to? Ford seemed to have it running pretty well, so didn't they already do all the fine tuning...and just use a light and their numbers and you'll be golden?




To the OP...after thinking what exact 351W parts did you have on there that fit...and not only fit, but ran them for a year...and now think you need to take off? And I just realized you asked about plugging anything off...all you really need to plug off is the vacuum advance...so unplug the tube that should be routed to the carb and then plug the VA...I just use a golf tee.
 

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BTW...wouldn't Ford's recommendation already be considered the sweetspot that you refer to? Ford seemed to have it running pretty well, so didn't they already do all the fine tuning...and just use a light and their numbers and you'll be golden?
Not talking new truck here, (26 years old) what ever was the timing from factory isn't the time now and on top of that - timing lights can vary as well.

Again his truck is running, its not going to hurt him to take a little black marker to make where the dizzy is now and move it a little in one direction and a little in the other direction and see if any gains can be had., Your really over thinking this.
 

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I never use a timing light as its totally a waste of time.
That's how I timed my Bronco. :thumbup

600-800 RPMS/10 degrees

But feel your way, advance until it pings, then back down, till you get the idle you want.
 

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Not talking new truck here, what ever was the timing from factory isn't the time now and on top of that, timing lights vary as well.
Again...only reason a stock engine wouldn't fall in the stock recommendations is if there's a problem or it's not stock anymore. Maybe it's just me, but the only time I've had a stock engine not fall within stock recommendations is when the timing chain has more than 100k on it and is majorly stretched...which to me, is a problem. That said...maybe you know more than me about the rig in question and it's not stock...but I didn't see anything to lead me that direction. But even if he has a cam or something, there are typically starting points that come with...and if you're 10-15* out, that's not normal.
 

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Again...only reason a stock engine wouldn't fall in the stock recommendations is if there's a problem or it's not stock anymore. Maybe it's just me, but the only time I've had a stock engine not fall within stock recommendations is when the timing chain has more than 100k on it and is majorly stretched...which to me, is a problem. That said...maybe you know more than me about the rig in question and it's not stock...but I didn't see anything to lead me that direction. But even if he has a cam or something, there are typically starting points that come with...and if you're 10-15* out, that's not normal.
Guess I'm just more particular than you are on how my engine works as no two engines are the same. By the time you get your timing light out and hooked up I'll already have the engine working its best. :goodfinge
 

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Guess I'm just more particular than you are on how my engine works as no two engines are the same. By the time you get your timing light out and hooked up I'll already have the engine working its best. :goodfinge

HAHA...I hear ya. But I figure who would be more particular would be the other way around. I agree with you no two engines are the same, but I'd worry if I'm more than 5* off one way or the other and start looking for other problems. So the point I was trying to get across was with a light, you might be able to find other issues. No different than tuning a carb with a vacuum gauge or doing a leak down test with an actual gauge and not just an adapter to your air chuck. If you find it best to do it by ear...more power to you...but I highly doubt many folks have that capability.
 

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Discussion Starter #16
My example with the bolt was only to make the point many issues can arise when you don't follow specifications and/or recommendations, but apparently it was lost on you. What if you have a vacuum leak or a carb is maladjusted...you just temporarily masked those problems by going all willynilly with the distributor. Sure it sounds like it's running better, but you just masked other problems. The thing that is foolish is to advise anyone to tune by ear. Sure there are some guys out there that can actually do it...you may be one of them, I dunno...but I'd be willing to bet 99% of the folks out there that think they can tune by ear can't. Hell, I had a 351M in my Bronco that sounded better and ran better when it was outside specifications and bumped to about 20-22*BTDC. But on a stock engine, if it has to run there, that raises a red flag. Had I never had a light on there, or known what was recommended I wouldn't have known how far off it was. And like I said, it ran better and sounded better...but that very engine had a busted piston skirt on #6 and two other cylinders with zero compression. But according to your logic, I bumped the timing so it shoulda been fine, right? I guess I should become a mechanic now that I know the secret of fiddling with the dizzy can fix alot of problems.



BTW...wouldn't Ford's recommendation already be considered the sweetspot that you refer to? Ford seemed to have it running pretty well, so didn't they already do all the fine tuning...and just use a light and their numbers and you'll be golden?




To the OP...after thinking what exact 351W parts did you have on there that fit...and not only fit, but ran them for a year...and now think you need to take off? And I just realized you asked about plugging anything off...all you really need to plug off is the vacuum advance...so unplug the tube that should be routed to the carb and then plug the VA...I just use a golf tee.
i had plugs wires, cap, rotor, starter pcv valve on there from when i thought it was a 351W...i had to change the starter, and plugs for sure according to NAPA...the other things, according to NAPA could have been left on...but i changed them anyway...just in case...
 

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Discussion Starter #17
turns out the timing is fine...the problem was the plugs i put in were'nt pre gapped like NAPA said they were...they were set at .30 and not .40...runs fine after i gapped them right...

i still have the burning eyes from the exhaust smell, but it runs good...
 

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1982 was the last year for the M-block. You sure that is a 351M in your truck? Post a pic of your engine....
 

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turns out the timing is fine...the problem was the plugs i put in were'nt pre gapped like NAPA said they were...they were set at .30 and not .40...runs fine after i gapped them right...

i still have the burning eyes from the exhaust smell, but it runs good...
And that^^^...is exactly the point I was making. Turned out to be a misdiagnosis and timing was fine. Had he taken the advice of going all willynilly he would screwed up a perfectly timing setting and still had improperly indexed spark plugs.

1982 was the last year for the M-block. You sure that is a 351M in your truck? Post a pic of your engine....
Agreed...easy way to tell is to count the valve cover bolts. 8=351M, 6=351W.
 

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And that^^^...is exactly the point I was making. Turned out to be a misdiagnosis and timing was fine. Had he taken the advice of going all willynilly he would screwed up a perfectly timing setting and still had improperly indexed spark plugs.
LOL, your point was he should use a timing light, and we debated on the need to use a timing light to adjust the timing. And likely he could still gain from some tuning and adjustments in the timing department. I do agree though he should have checked everything over before hand - if it ran find before the changes, and bad after the changes than its unlikely that timing was an issue.
 
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