1981 straight six manual 4x4 project

[1986F150Six]

Jonathan - The port on the carb only goes to something like 11" of vacuum, assuming your carb is like David's. And 11" isn't enough to pull the vacuum advance on fully, at least the way I think that one is set up.

So, I'd go to manifold vacuum ASAP. But, then you'll have more advance when cruising, so listen for pinging under part throttle. And if you have pinging then back off the vacuum advance by turning an allen wrench counter-clockwise (I think) a turn at a time until the pinging stops.

But I wouldn't play with the initial advance to quell the pinging if the engine is starting well with that timing. Too much initial causes the engine to kick back during starting, but if yours is happy where you have it then I'd leave it and work on the vacuum advance.

A simplistic, but not completely accurate, way of looking at the order of tuning is:

1: Initial advance. Dial in enough to get the engine to idle well but not enough to kick back in starting.

2: Centrifugal: In your case that's a given as David had that dizzy set up for his truck and that's a fairly close match to yours. But, what about EGR? There's a huge difference in the advance curve for with and without EGR, so what do you have? And, David, was the dizzy set up for EGR?

3: Vacuum: Dial in all the vacuum you can use w/o pinging at part throttle. Typically the most critical spot is your top gear at low RPM, but check it out to ensure you aren't pinging anywhere.

Gary, you posted this on 9/13/14:

We played with David's truck today to determine what his AFR is and what his timing is. First, we installed my AEM wideband meter and looked at the AFR:•Idle: Once warmed up it was about 12.5:1

•Cruise: At 62 where he ususally runs it was in the mid-15's on level ground, but climbing hills it got as high as 17.0 at one point.

•Power: Once the throttle was open it went as low as 11.5 but normally at about 12.0 - 12.5.

That said the carb, a 1970 YF carb off of an F350, is jetted just right. It really shouldn't be any leaner, but the truck runs well so it isn't too lean. And it certainly isn't rich.

Then we checked the timing. The initial timing was set at 18 degrees, which was getting good MPG but made the engine slightly hard to start sometimes. And, it pinged at full throttle, so the overall timing was too much.

As for the mechanical timing, at 1700 RPM where David cruises it was giving 10 more degrees advance. Then we checked the vacuum advance and found that it was starting to advance at 10" and was giving a total of 18 degrees 16" of vacuum, and at the 14" of vacuum the truck had at 62 MPH the advance was 12 degrees. So, total advance at 1700 was 18+10+12=40.

Then we turned the vacuum advance two turns clockwise, which made the vacuum start coming in at 8", gave the full advance of 18 degees advance at 14". Then we set the initial timing to 17 degrees, and the drive determined that it pinged both at part throttle as well as full throttle. So we put the initial timing at 14+, giving a total of 14+10+18 = 42 degrees at 1700 RPM. And the truck felt happier with that setting than it has.

[Gary Lewis]

Jonathan - The port on the carb only goes to something like 11" of vacuum, assuming your carb is like David's. And 11" isn't enough to pull the vacuum advance on fully, at least the way I think that one is set up.

So, I'd go to manifold vacuum ASAP. But, then you'll have more advance when cruising, so listen for pinging under part throttle. And if you have pinging then back off the vacuum advance by turning an allen wrench counter-clockwise (I think) a turn at a time until the pinging stops.

But I wouldn't play with the initial advance to quell the pinging if the engine is starting well with that timing. Too much initial causes the engine to kick back during starting, but if yours is happy where you have it then I'd leave it and work on the vacuum advance.

A simplistic, but not completely accurate, way of looking at the order of tuning is:

1: Initial advance. Dial in enough to get the engine to idle well but not enough to kick back in starting.

2: Centrifugal: In your case that's a given as David had that dizzy set up for his truck and that's a fairly close match to yours. But, what about EGR? There's a huge difference in the advance curve for with and without EGR, so what do you have? And, David, was the dizzy set up for EGR?

3: Vacuum: Dial in all the vacuum you can use w/o pinging at part throttle. Typically the most critical spot is your top gear at low RPM, but check it out to ensure you aren't pinging anywhere.

Gary, you posted this on 9/13/14:

We played with David's truck today to determine what his AFR is and what his timing is. First, we installed my AEM wideband meter and looked at the AFR:•Idle: Once warmed up it was about 12.5:1

•Cruise: At 62 where he ususally runs it was in the mid-15's on level ground, but climbing hills it got as high as 17.0 at one point.

•Power: Once the throttle was open it went as low as 11.5 but normally at about 12.0 - 12.5.

That said the carb, a 1970 YF carb off of an F350, is jetted just right. It really shouldn't be any leaner, but the truck runs well so it isn't too lean. And it certainly isn't rich.

Then we checked the timing. The initial timing was set at 18 degrees, which was getting good MPG but made the engine slightly hard to start sometimes. And, it pinged at full throttle, so the overall timing was too much.

As for the mechanical timing, at 1700 RPM where David cruises it was giving 10 more degrees advance. Then we checked the vacuum advance and found that it was starting to advance at 10" and was giving a total of 18 degrees 16" of vacuum, and at the 14" of vacuum the truck had at 62 MPH the advance was 12 degrees. So, total advance at 1700 was 18+10+12=40.

Then we turned the vacuum advance two turns clockwise, which made the vacuum start coming in at 8", gave the full advance of 18 degees advance at 14". Then we set the initial timing to 17 degrees, and the drive determined that it pinged both at part throttle as well as full throttle. So we put the initial timing at 14+, giving a total of 14+10+18 = 42 degrees at 1700 RPM. And the truck felt happier with that setting than it has.

Good find, David. But did you turn the vacuum advance after that?

[1986F150Six]

Good find, David. But did you turn the vacuum advance after that?

Yes. At each fill-up, I turned it clockwise 1 more turn until it was maxed out, so Jonathan could turn it counter clockwise several turns, if needed.

[Gary Lewis]

Yes. At each fill-up, I turned it clockwise 1 more turn until it was maxed out, so Jonathan could turn it counter clockwise several turns, if needed.

I think that the range is 18 degrees of advance across 6" of vacuum. And it was decreasing the cut-in point by 1" of vacuum for every turn.

We left it at 8", but I think you may have turned it two more turns. If so, it is coming in at 6" and gives the full 18* at 12" of vacuum. That may be too much for Jonathan's truck and, if so, he can back it off.

[Ford F834]

I think that the range is 18 degrees of advance across 6" of vacuum. And it was decreasing the cut-in point by 1" of vacuum for every turn.

We left it at 8", but I think you may have turned it two more turns. If so, it is coming in at 6" and gives the full 18* at 12" of vacuum. That may be too much for Jonathan's truck and, if so, he can back it off.

This '81 is a bitter onion...

First the good news. My initial test of the new distributor was on fairly flat ground and in a 45mph zone so I did not push it much above 50mph. Yesterday I drove the truck on the interstate and WOAH, the largest gains were at speeds and rpm's that I did not hit in the neighborhood. It feels like a whole different truck. It definitely sounds better at highway speeds and pulls stronger. I don't know how much of this is the altered timing curve from Performance Distributors, but I like the results!

When I reached Flafstaff at 6,000' altitude (up from 2,800' at home) the idle had dropped from ~650 down to 350-400 rpm and was at the stall point. I had to increase idle with the screw. I also tried manifold vacuum instead of venturi vacuum thinking the advance at idle might help the low idle. To my surprise I could not tell any difference between the two, whereas the old distributor would almost not run at all when hooked to manifold vacuum. I left it hooked to manifold vacuum, and when I returned to 2,800' the idle had a little stumble but not horrible.

I drove 300 miles on the first leg of the trip and the mpg calculation was 16.4 mpg. So it was about the same as what I have been getting for mountain driving at 70-75mph. I was running it pretty hard, and would surely be over 17 had I kept my speed down a bit. For what it's worth, when I made a dump run the scale said my curb weight was 4,480 lbs. That is with me out of the truck but a monster tool box on board.

I refueled for my return home, and about 70 miles into my trip I started loosing power. Not a full stall like before, but a pronounced (50%?) cut in power intermittently. I could feel it cutting out and kicking back in just as before. I don't know what to think. It seems like the problem is not fixed after all, but manifested itself a little differently this time. It acted up intermittently for about a half a mile and then ran fine the rest of the way home. I can be grateful that I wasn't stranded at night, but these kinds of problems are tough to troubleshoot. My next move, I believe, will be to drop the tank and have a look-see in case there is anything obvious going on in the tank.

[Gary Lewis]

This '81 is a bitter onion...

First the good news. My initial test of the new distributor was on fairly flat ground and in a 45mph zone so I did not push it much above 50mph. Yesterday I drove the truck on the interstate and WOAH, the largest gains were at speeds and rpm's that I did not hit in the neighborhood. It feels like a whole different truck. It definitely sounds better at highway speeds and pulls stronger. I don't know how much of this is the altered timing curve from Performance Distributors, but I like the results!

When I reached Flafstaff at 6,000' altitude (up from 2,800' at home) the idle had dropped from ~650 down to 350-400 rpm and was at the stall point. I had to increase idle with the screw. I also tried manifold vacuum instead of venturi vacuum thinking the advance at idle might help the low idle. To my surprise I could not tell any difference between the two, whereas the old distributor would almost not run at all when hooked to manifold vacuum. I left it hooked to manifold vacuum, and when I returned to 2,800' the idle had a little stumble but not horrible.

I drove 300 miles on the first leg of the trip and the mpg calculation was 16.4 mpg. So it was about the same as what I have been getting for mountain driving at 70-75mph. I was running it pretty hard, and would surely be over 17 had I kept my speed down a bit. For what it's worth, when I made a dump run the scale said my curb weight was 4,480 lbs. That is with me out of the truck but a monster tool box on board.

I refueled for my return home, and about 70 miles into my trip I started loosing power. Not a full stall like before, but a pronounced (50%?) cut in power intermittently. I could feel it cutting out and kicking back in just as before. I don't know what to think. It seems like the problem is not fixed after all, but manifested itself a little differently this time. It acted up intermittently for about a half a mile and then ran fine the rest of the way home. I can be grateful that I wasn't stranded at night, but these kinds of problems are tough to troubleshoot. My next move, I believe, will be to drop the tank and have a look-see in case there is anything obvious going on in the tank.

Bummer! It does sound like a fuel problem, so the tank approach is probably the next step. But, lots of work. Make sure you look at, if not replace, all hose sections as a vacuum leak in them causes all sorts of problems.

[Rembrant]

I drove 300 miles on the first leg of the trip and the mpg calculation was 16.4 mpg. So it was about the same as what I have been getting for mountain driving at 70-75mph. I was running it pretty hard, and would surely be over 17 had I kept my speed down a bit.

I'm no help with the current fuel problem, but I was curious about the 300/6 MPG. Kind of a random question, I know, but if all else was equal on a truck, would the 300/6 get noticeably better MPG than a 302? Or are they about the same, with simply different torque/power curves?

 

[Ford F834]

I drove 300 miles on the first leg of the trip and the mpg calculation was 16.4 mpg. So it was about the same as what I have been getting for mountain driving at 70-75mph. I was running it pretty hard, and would surely be over 17 had I kept my speed down a bit.

I'm no help with the current fuel problem, but I was curious about the 300/6 MPG. Kind of a random question, I know, but if all else was equal on a truck, would the 300/6 get noticeably better MPG than a 302? Or are they about the same, with simply different torque/power curves?

I have heard about good mpg results from both. For unloaded highway mpg (the usual yardstick for efficiency), I would expect similar results based on displacement. The advantage that the straight six has is torque from the long piston stroke. The 1,400 rpm torque peak makes it very good at handling tall gears and holding gear without downshifting. It also helps return good mpg while hauling. Like David says, it’s like a gasoline diesel, since it has many of the same characteristics. Ford’s fuel efficiency package was only offered with the straight six. My numbers are actually pretty low, but it is a taller heavier 4x4 and I have not spent any time on tuning it other that to get it running smoothly. Hopefully I can get it to around 18-ish. David gets mid 20’s but has the right truck for it 🙂

 

[Rembrant]

I have heard about good mpg results from both. For unloaded highway mpg (the usual yardstick for efficiency), I would expect similar results based on displacement. The advantage that the straight six has is torque from the long piston stroke. The 1,400 rpm torque peak makes it very good at handling tall gears and holding gear without downshifting. It also helps return good mpg while hauling. Like David says, it’s like a gasoline diesel, since it has many of the same characteristics. Ford’s fuel efficiency package was only offered with the straight six. My numbers are actually pretty low, but it is a taller heavier 4x4 and I have not spent any time on tuning it other that to get it running smoothly. Hopefully I can get it to around 18-ish. David gets mid 20’s but has the right truck for it 🙂

Ok, cool. That's more or less what I was thinking, but wanted to confirm.

I'm casually looking for another Bullnose, and I'm intrigued by the 300/6. When I was searching originally, before I bought the truck I have now, I specifically wanted a small block V8. Now that I have that out of my system, I'm thinking more along the lines of the 300/6 engine.

[Ford F834]

Ok, cool. That's more or less what I was thinking, but wanted to confirm.

I'm casually looking for another Bullnose, and I'm intrigued by the 300/6. When I was searching originally, before I bought the truck I have now, I specifically wanted a small block V8. Now that I have that out of my system, I'm thinking more along the lines of the 300/6 engine.

I am highly biased toward the straight sixes. I know they are not the answer for every occasion, but with each one I own I admire them a little bit more. My previous experiences have been with 4.10 geared F250 drive line trucks, and as such they are slow screamers (but strong). My current gearing is showing me a different side to this engine and I’m impressed! The close ratio and taller axle gearing is what I’ve been missing on my previous trucks.

Lots of folks talk about what a pleasure they are to work on, which is true. There is lots of space around and they are simple. But what’s even more awesome is when you open one up to rebuild it. I swear the block never wears out. The 240 that my dad and I did on his truck really surprised me. It was clattery, compression felt low (although we didn’t measure it) and it was starting to smoke. Odometer was not working, but it was a LOT after 34 years of daily driving. Turns out all it really needed was rings, valve guides/seals and lifters. The bores looked brand new. No ridge, all the cross hatching still visible and no wear that I could detect. Granted, my dad takes very good care of his vehicles, but the 300 that I rebuilt and put in my 1966 pickup looked the same way. It’s refreshing to not need a ridge cutter or wonder if it can be over bored enough to remove the wear. On the sixes I just had to hone the glaze and go.