So me and my dad have been trying to rebuild this 72 f100 that we picked up in late April. When we got it the motor was pretty well shot and burned oil rather badly. The first thing we did was pull the stock 360 out of it and took it to a machine shop recommended to us by our neighbor (Has had a dozen or so motors through this shop with good luck on all of them) They tore the motor down and found that the heads were cracked and that most everything inside was pretty well worn out. So they started the rebuilding process to create a 390 out of the stock 360. They did everything top to bottom boring honing you name it. Once we finally got the motor back and everything installed back into the truck we got it running and followed the machinist's break-in procedures. The truck has run for about a total of 40-50 minutes at this point. It seemed like we had to advance somewhere in the neighborhood of 22-25 degrees BTDC(as indicated by the balancer) to get it to even run. We have had it running multiple times and now were trying to get it adjusted to where it would idle (would run good revved up but not near idle). It does not seem as though it wants to turn over at this point (have spark - not sure on fuel). Does anyone have base settings for the mastercraft 2 barrel that came on those trucks in 72? We have put a new distributor cap and wires on and have made sure that we have spark at approximately 0 on the balancer on the number one plug wire. Any suggestions would be greatly appreciated.

 

To get it well tuned you will probably need a vacuum gauge, this helps you determine if it's rich or lean at idle. But it sounds like you are not at that point yet. So it was running, but not idling, and now it won't start at all? One suggestion I have is to check your fuel filter, I know the engine is all new & fresh but these old gas tanks have a tendency to be full of rust and clog the filters pretty quickly.

 

I'd verify TDC using a piston stop and reset the distributor. Note the timing pointer against the balancer... is it accurate? If not, the balancer could have slipped and that's what is giving a false timing reading. Either that or whomever set the timing chain lined it up incorrectly. Lightly mark TDC on the balancer otherwise..... now use 2 x pi x r to figure out the measurement of one degree of timing and mark 6 BTDC and 10 BTDC, respectively.

Second, rebuilding the carb requires setting the float level and then the idle mixture screws 2 to 2.5 turns out from bottomed (gently!). Set the cold choke at 1/8-inch from closed..... use a 1/8-inch drill bit on the forward wide of the choke horn. Of course, don't drop the bit! The instructions on base settings are in the rebuild instructions or a repair manual.

Verify the firing order and then fire it up with a tachometer, vacuum gauge, and timing light at the ready. Tune it.

 

Thanks for the quick response everyone. I will be trying some of the suggestions in the morning. Would I be ahead to rebuild the carb? I haven't yet and I suppose that could be causing some issues? I will certainly get a vacuum gauge and find tdc on #1 again and check the balancer against that. The way we did it before was to have one of us put our thumb over the plug hole on 1 and then turn it over till it puffed air. We then used a plastic straw and hand turned the motor back and forth until we found tdc. Is that an accurate way to find the position of the piston? Thanks again everyone.

 

Have to ask. What oil did the machinist recommend for break in procedure?

 

Welcome to FTE. Got pics of your project?

 

Basic start settings are:
1. Lightly seat the mixture screws and then back out 1.5 turns.
2. Adjust Idle speed screw until it contacts the tab and then go an additional 1.5 turns.

Rebuilding the carb is a great idea. Use the Ford kit and not the repro stuff. The gaskets in the repro stuff are not right.

My first thought is you have a vacuum leak. Did you use new gaskets for the carb mount? (one above and one below the spacer)

 

I believe the stuff was a 5w30 race oil (br30 brand) that all the guys who dirt track race around here use for break-in/racing. I bought the oil from them in the amount they wanted me to put in. It's full on the dipstick as well.

 

Yes I have new gaskets above and below. I do know that while it would run and may still run (was running low on battery and possibly flooded last night) it doesn't want to idle. The truck ran good when it got wound up around 3 or 4 thousand rpm. The engine builders break in guide said to get it started and then let it run at 3-4 thousand rpm for 30 minutes and fluctuate the speed up and down. We got the thirty minutes in two days ago and then went and bought a timing light hoping to start tuning yesterday. When we removed the vaccum advance off the distributor and plugged it with a golf tee as per the chilton repair manual it would not start at all.

 

1968/76 F100/350 360/390 use the same cylinder heads and engine block. The bore (4.05") is the same, the stroke is different: 360 = 3.50" ~ 390 = 3.78."

All it takes to convert a 360 to a 390, is to install the 390's crank, rods and pistons, everything else is the same.

 

Hey Bubba, Welcome to FTE!

I also agree with the above advice. A vacuum gauge is a must for engine diagnostics. I screwed up years ago when I had my Y block rebuilt - threw a junkbox carb and distributor on. It ran but not very well. This was a big mistake. If an engine needs a rebuild it's guaranteed the distributor itself is shot, too.

20+ degrees initial timing seems unlikely, the starter would kickback. A slipped damper outer ring will cause a lot of confusion setting timing. A vacuum gauge works slick to set initial timing, no light required and the damper markings can be ignored. Damper will need replaced or rebuilt in this instance though. Vacuum gauge also excellent for carburetor tuning. Carbs can be rebuilt but there are some wear items that are overlooked or beyond the average mechanic to repair. Throttle plate shaft wears and the bores will get egg shaped and present a vacuum leak, impossible to tune right. Make sure it's a serviceable core to begin with. These can be drilled and bushings installed.

 

I don't honestly know what initial is set at. When it runs long enough for us to get a light on in we are somewhere in the neighborhood of 3k rpms. Is 20' of advance unreasonable at that speed? Also how would you set initial with a vacuum gauge.

 

. Right maybe I confused that in the original post. They put all new parts in and machined the block because they were worn not just because they were building it into a 390. The motor had best we can guess 111000 miles (5 place odometer) on it and had a nice ring ridge. Also both heads were cracked so they got new cores and machined and put hardened seats in them.

 

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Update: my neighbor who's good with hotrods finally had a chance to come and look at it. He said vacuum and everything else looks fine but that I'm definitely running out of fuel - have to keep pumping it to keep it running. Said timing seems in the neighborhood just by listening. And that the fuel pump is definitely getting good pressure to the carb because when we took that line off fuel came squirting out from the fuel pump side.