351M timing Issues

[RH428WF]

I have a 79 F-100 dent side with a 351 M. I was adjusting the 4 barrel as I was get crappy mpg. Got the truck running great then checked the timing. 28 degress BTDC. Should be at 6-8. Last year replaced the ignition mod, distributor, coil, and a complete tune up. Changed intake and carb this past summer. Buddy told me distributor needs to be turned back because of timing. Turned back distributor at TDC wires and cap good at number 1 with rotor button. Now cant get truck to start. Removed distributor and did it all over again multiple times dbl, and triple checked wires and cap, everything good. Still wont start. When trying to start spits fuel out of carb. VERY FRUSTRATED. After 8 hrs tried to kick it over and light it on fire, at least I wanted to. OH yeah this is my daily driver.

 

[5.0Flareside]

I have a 79 F-100 dent side with a 351 M. I was adjusting the 4 barrel as I was get crappy mpg. Got the truck running great then checked the timing. 28 degress BTDC. Should be at 6-8. Last year replaced the ignition mod, distributor, coil, and a complete tune up. Changed intake and carb this past summer. Buddy told me distributor needs to be turned back because of timing. Turned back distributor at TDC wires and cap good at number 1 with rotor button. Now cant get truck to start. Removed distributor and did it all over again multiple times dbl, and triple checked wires and cap, everything good. Still wont start. When trying to start spits fuel out of carb. VERY FRUSTRATED. After 8 hrs tried to kick it over and light it on fire, at least I wanted to. OH yeah this is my daily driver.

when you checked the timing you didnt pull off the vacuum advance did you?

the vacuum advance is a line coming from carb to distributor. as carb is pulling more vacuum (air/fuel) in the vacuum increases and allows the distributor to advance timing to help burn off the extra.

crank your engine over to TDC on #1 piston. Drop distributor in as close to dead on as you can with Rotor at #1 plug on distributor cap, and disconnect vacuum advance. fire truck up. check timing then and adjust as needed..

 

[RH428WF]

Not when I tried to start it. That was my first problem about 2 weeks ago had the vacuum advance line on the wrong side. Checked the timing after and thats when I saw it was at 28.

 

[RH428WF]

So your telling me it wont start with the line on?

 

[5.0Flareside]

So your telling me it wont start with the line on?

it will start with the line on.


when you adjusted the timing, you were adjusting it by the 28* number. when in reality if you didnt pull the advance vacuum line. the truck was probably at the 8* base timing. mark.

you have to adjust it with no vacuum advance going.

no you have your timing SO FAR off (to slow/retarded) it wont fire cause the plugs are firing WAY to late.. its just like if you dropped your distributor in 180* off..

 

[RH428WF]

That would be the reason that after I dropped the distributor back in at TDC with #1 piston, try to start then check again at TDC because it wont start. The rotor is at 180* from #1 piston at TDC.

 

[5.0Flareside]

exactly!!! your going to have to set that rotor as close to the #1 spot as possibly. may take a time or 2 to get it on the right tooth. and then adjust the timing to 8* btdc base timing, with the vacuum advance UNPLUGGED...

once you do that and plug the vacuum advance back in. you should have no issues unless you adjusted that carb way out of wack..

 

[LivingstonIPresume]

Man that sucks, I had literally the exact same issue. With mine it turned out the Issue was that the reluctor wheel had come loose and was causing timing issues, right after the carb was fixed the pin fully sheared and the engine jumped time. The guy who was showing me how to fix it said that he had seen the Gear drive pin sher and just spin but that was the first reluctor he had seen do that. That probably isn't what is happening to you but it sounded so close to my issue I thought you might check.

 

[Mil1ion]

One has to go by the sticker and calibration code for these engines.
There is not some magic number on these engines. EVERYTHING to do with tuning is dependent on the particulars of that specific engine,options and region.

What does the engine sticker say ?

These engines are timed with the Vacuum Hose to the vacuum advance Attached..not removed.

 

[Mil1ion]

More info.

How many miles on this engine ? The timing chain /gear system may be worn out.


a 4bbl carb on a stock 351M is just a waste of fuel.
4bbl's are great for fuel economy if you keep your foot OUT of the secondarie's
Once you open the secondarie's you may as well throw that fuel on the pavement.

The 351M is dog engine in stock form

 

[Mil1ion]

There are two times the piston hits TDC.
just before power stroke
and just after exhaust stroke


You need to verify TDC at top of power stroke but checking the position of piston after the intake valve just closed..(aka: end of compression stroke)

Check the 2 corresponding timing marks to see how close they are to each other

 

[Mil1ion]

you have to adjust it with no vacuum advance going.

IIRC,that concept was from years earlier

Some of these (1978-79+)engines are timed with the Vacuum Hose to the vacuum advance Attached.....not removed.

 

[LEB Ben]

More info.

How many miles on this engine ? The timing chain /gear system may be worn out.

That was my first thought.

IIRC,that concept was from years earlier

Some of these (1978-79+)engines are timed with the Vacuum Hose to the vacuum advance Attached.....not removed.

Interesting...any engine I've ever timed from the era, I've unplugged the advance.

 

[DNFXDLI]

Likewise Ben...I'm almost 100% sure that for setting initial timing the advance has to be removed.

 

[lostinfords]

what is timing? ..I thought you just moved the dist. until it ran smooth...been working for me for ages..every time my neighbor takes his 70 mach I to the shop and the play w/ the timing he always ask me to set it back up for him, one day I should see how close I get it set by ear vs. what it actually reads...

 

[5.0Flareside]

I learned from my dad to set it by ear. but have learned by gun is much better/accurate.

 

[GHoss]

I learned from my dad to set it by ear. but have learned by gun is much better/accurate.

True, I have a 400 with a straight up timing set and Edelbrock intake. I would set the timing with the vacuum line off at 12 to 14 degrees, it would not pass emissions. My Father in law, who has been working on nothing but these types of fords all his life, went out and set the timing by ear and BINGO it passed emissions! I checked it with a timing light and it read 19 degrees BTC. ????

 

[LEB Ben]

^^^Could be due to chain stretch and/or the the rubber on the balancer has been known to slip.

 

[Mil1ion]

People have to remember to first think about the moving parts wearing out,freshness of gasoline,vacuum advance seizing or diaphragm torn,altitude,special emissions conditions of engine locale

Mechanical settings have to be done and verified first,before any tuning adjustments

 

[vls]

These engines are timed with the Vacuum Hose to the vacuum advance Attached..not removed.[/QUOTE]

Now that's the first place anywhere that I've read that says timing on these engines (or any engine, for that matter) is with the vacuum advance connected. Haynes, Chilton, and numerous websites say to disconnect and plug the advance. Seems like timing would be dependent on vacuum, and at higher altitudes like mine, since vacuum is lower, timing would be even more retarded. But just the opposite is true. I have to advance my timing more up here (6000 ft) to get good performance. Pinging is not an issue at these altitudes.

On my stock 400, with timing set at 6 deg with the vacuum connected, idle is rougher and performance is terrible. When I set the timing without vacuum advance, and then reconnect it, idle is much smoother and acceleration is much better. Are you saying that in my case the timing gear/chain set has a problem? New one on me.