Just wanted to see if anyone might have some specific info on this setup, if you have the same or similar setup, what you might be running in yours. I do not have major problems, just want it dialed in right.
1970 F-100, 2wd, T85 O/D tranny. fresh built 390 (2000 mi on it) that is stock with 485/511 lift cam and 1:7 rockers. Cast 4 bbl intake. Dual exhaust. It is healthy but not a monster by any means. Everything is new and tuned up the best I can get it. Plugs at .035, points at .017 with 28 dwell, timing at 6 deg before. I have 20.5 hg of vacuum at idle that is set at 650 rpm.

New Holley 600 p/n 80457SA and runs good out of the box but wonder if it could be better and so that's where this thread comes in!

This particular issue is that it is a bit sluggish at low rpm acceleration, like when it is in 3rd gear or 3rd gear OD and I am cruising and I hit the
pedal to speed up some it is just kind of blehh. Not flooring it, but just a moderate acceleration. I can feel the engine fluttering and seemingly struggling and I don't know if it's getting too much gas or not enough. Or if it's just the way it is. I don't have any stumbles or hesitations, just blehh. The carb comes with #65 jets, a #31 pump nozzle and 6.5 power valve. So, I wonder, do I need to up the jet size a couple notches, up the power valve number so it comes in sooner (because of the vacuum reading I have) or do nothing. Not really sure at this point. Thanks

Dan

 

I'd try scooting the initial timing up to around 12° or so, and then w/ vac advance disconnected and plugged see what your total timing maxes out at.

When timing is good reconnect vac advance, make sure float level is good and dial in idle mixture for best vacuum. Make sure accelerator pump squirt is adequate. Check plugs for jetting. The jets will affect cruise manifold vacuum too, check engine vacuum at different speeds, have to rig up vacuum gauge in cabin. About 2 points below the lowest cruise vacuum observed is a good size for PV for your altitude.

Everything affects manifold vacuum - ignition timing, jet size, and so on so try not to change too many things at once. It's a PITA tuning distributors and carburetors but well worth it when you're done!!

 

Agreed, bump that timing up. As much as your fuel quality will take. It shouldn't rattle with 10-12* initial. A good aftermarket distributor is much easier to adjust total and vacuum timing, but with what you have it should be fine just giving it a touch more initial.

Don't re-jet it. Likely is just fine for what you are doing with it.

Power valve, it should have 6.5 in it(stock). If you have a vacuum gauge, attach it so you can read it while driving. If it goes below 6.5 inches when trying to accelerate then it is adding the needed fuel. That is what that number means, it opens at that point.

In 3rd or OD, you likely don't have enough motor to make it accelerate any more then it can right now at whatever speed you were at.

 

You did not say what you are cruising at when putting your foot into it.
Plus you did not say what your gearing was out back.

I'm running a 5sd o/d with 411 out back with 32.5" tall tires. an at 60mph I'm taching 1bout 1,900 with a 390 with 428 crank 0.30 over a mild cam 8.7 compression ratio to burn the cheap regular gas 600cfm Timing at 10atc: Headers with some head clean up an port smoothing some what.


Mine at the speed vacuum up 15-16 is only good at a slower increases then like at 70mph which where it will start to pulling pretty good but you have to remember your in some low rpm's below your engine even starting to get into it's power band while on o/d these are for speed hwy upper speed limits type cruising. So bottom line you may be expecting more Getty up go an not even starting to get into the cams power band.
An my trucks wt. is well over 6000lbs 4wd f250
Orich

 

Wow, you're pulling 17" of vac at 70mph? That's amazing. And 15.7 cruise AFR, is that right?

 

Oh no Tedster9
The lower left under dash gauge is not what your thinking, that's for my on board air pressure 157psi. My 02 gauge can't be seen to read as it's next to my temp gauge has a white face second photo..

If any has noticed in the lower photo that my foot is not on the gas pedal well, I was on the freeway with the Cruise control on level road.

Orich

 

I agree about bumping the timing. I'm running 20* initial and 38* total. Sounds like you have a vacuum guage so set your base timing until you get the highest vacuum reading and then check your total to see where its at.

 

Ok Rich, that's a smooth runnin' mochine ya got there.

One thing that I've been experimenting with is the power valve. Once the jet size gets sorted out. 6.5 is "standard" but with a stockish engine that draws high vacuum, bumping it up higher can improve throttle response.

Rich, what size PV do you run with your setup? Is it safe to assume it's a high one like 10.5? I believe the general idea is to size it a couple points below the lowest average cruise manifold vacuum observed. In other words want it responsive for enrichment when we push the go pedal, but otherwise closed.

If we run too high a PV value and run into a steady headwind, or drive higher in elevation etc the PV, engine manifold sinks and PV will tend to open and stay open. This will kill any economy, foul plugs etc.

 

'


That added stroke of that 428 crank(410ci) really helps with low end torque. Nothing like a stock 390 would have.

 

Hey all, sorry for the delay in responding but we had so much to do since posting so I want to follow up with you. Thanks so much for all the replies. Let me start with the timing. I have only owned the truck a few months and when I got it the PO had the timing set at about 12 degrees I believe and the thing rattled pretty bad, especially at high speed and under a load. So I backed it back down to about 5 degrees and went from there and even now it is just shy of 6 degrees. Only because that is what I understood the original specifications to be for this truck and engine. 6 degrees. But I do agree, my gut tells me me that bumping it up to 10 or 12 would in theory solve some of my problems but I am afraid of spark knock and don't want to ruin this motor. But, since I have owned it I replaced plugs and wires which weren't all gapped just right and they weren't all torqued the same either from the PO. Also, the carb that was on it was junk, so I put the new holley on it and have set the float to Holley specs. New fuel pump and filter. I also put a new Duralast Gold dizzy on it at set it to where I mentioned and am running ported advance to it.
Also, Agreed. I need (want) to run a line so I can watch the vac gage in the cab when I am driving, I think that will help answer some of my questions too so I will try and do that today. So, IDK maybe some of the junk that was on it was causing the spark knock and it may take more timing now after the tune-up, but I'm not sure because even still at 6 degrees if I don't run high octane gas in it it will ping under a load.
Orich, I have 3.50 gears in the truck and when I say cruising, I guess I mean any speed where I am just "cruising" down the road at a constant speed. anywhere from 30 to 70 mph.
I also agree that it may not need more jet because the new plugs have about 500 miles on them and they are clean, like almost no deposits on them. Even if I did re jet I can't imagine needing much more than a size 67 or 69. What do you all think? Thanks again

Dan

PS, I don't think I can adjust the advance curve on that new dizzy, does anyone know?

 

That's what you'll want to look into, your total timing (vac advance disconnected and plugged) and see where it tops out at. Usually 34 or 36 degrees for V8 is in the ballpark. Usually any distributor can be adjusted internally, some more of a PITA than others. This allows for more initial advance without running into ping on the other end.

 

What dizzy are you using now oem or aftermarket.
Lower rpm driving if your pinging sounds like you need to reset the vacuum advance from coming in to much. Most Vacuum advances can be adjusted through the hose nipple with like a 1/8" allen wrench turning clock wise locks it out more. But get your timing set an if pinging lockout the advance more this kind of do a little like 1/4 turn then test drive looking for the that sweet spot.

 

[QUOTE=Tedster9;16907716]Ok Rich, that's a smooth runnin' mochine ya got there.

One thing that I've been experimenting with is the power valve. Once the jet size gets sorted out. 6.5 is "standard" but with a stockish engine that draws high vacuum, bumping it up higher can improve throttle response.

Rich, what size PV do you run with your setup? Is it safe to assume it's a high one like 10.5? I believe the general idea is to size it a couple points below the lowest average cruise manifold vacuum observed. In other words want it responsive for enrichment when we push the go pedal, but otherwise closed.

Ted~9
I was just running 6.5 and had to change to a littler heavier spring to keep the holley sec from opening up .

But now changing over to Holley Efi Terminator setup so hopefully in a couple days I'll be firing it up for the first time. The weather has only let me working on it as been cold & rainy so got will see how the weather hold out the past sunny days..

Orich

 

Orich, it is a new Duralast Gold distributor. I don't believe it's a reman. Also, I put my vac gage in the cab yesterday and it only drops down to like 8 to 10 under moderate acceleration, it only goes lower if I mash it, and then it doesn't stay there that long. Also when I let off the gas, the vacuum jumps up to 25-30 for a few seconds then back to roughly 21, which is what I'm idling at 21. I think I may try about an 8.5 power valve. One thing I don't understand is why I can't advance my timing any more than I have it. Everyone else seems to get away with it, but mine will rattle. Could it be the way the cam was degreed in by the shop that built the engine? It was professionally rebuilt. Thanks

Dan

 

Sorry tedster, I missed your post just now. So then are you saying that if I can back off the advance curve, that I should be able to have more initial timing? thanks