I actually posted this under the 1967 - 1972 F-100 & Larger F-Series Trucks forum, but realize this may be more appropriate
A couple of months ago I bought my '67 (F100 w/352 & manual 3 speed tranny) and since then I've done all the basic stuff, like oil change, new PCV valve, spark plug wires, belt, fuel filter, fresh oil in the oil bath filter and finally installed a new radiator. The truck is running pretty well except that I feel it may be lacking a little bit of power. I realize it's an old truck and it has over 130k miles on it so I'm not really sure how much umph the old girl should have. AND, it's missing it's muffler so possibly that is contributing.
The truck was built in Michigan and lived it's life in Nebraska, just on the edge of Colorado. Now, the truck lives in Denver at 5,000 feet and my first thought in the "lack of umph" was likely a re-jet of the carbs for the altitude. But I began to think, I have no idea when the truck had last been properly timed and adjusted.
I think I'm a little out of my knowledge level as I have no experience with adjusting the timing on an auto with 4 wheels, and screwing up could mean an un-drivable truck. I am wondering if there's anyone on this forum in the Denver'ish area that might be willing to help me do this right? Maybe it's already "right", but knowing 100% would be awesome. There is a shop across the street that could probably do it, but I'd like to learn how myself and plus I'd know it was done right.
I could pay in beer, lunch, satisfaction of imparting your knowledge to me, extreme gratification???
You are correct Amy, altitude is huge on tuning. Once you rise above 2000ft the difference in air density is approx 4% for every 1000ft so here in Denver timing and fuel needs to be compensated for at about 20% thinner air.
I'm at 6500ft. I advance my base timing between 4 to 8(10 on my wife's jeep).
You didn't list the carb or jet size but power valves in the carbs are HUGELY effected. Example: a stock mc2150 for a 302 or 300 usually has a 10.5" pv(but can be any size). At altitude with stock base timing vacuum can be as low as 12" and just the slightest throttle throttle drops the vacuum and your power valve opens prematurely costing you power and fuel economy.
Two things you should look at, a vacuum gauge and a air/fuel gauge.
If you hook the vac gauge up to the manifold you will have what your motor pulls for vac. If you loosen the distributor and slightly advance it you will be able to watch your vac level rise(make sure any vac advance to the distributed is capped while doing this). A timing light is good to see where you start to where you stop on advancement. When adjusting you will see vac rise then start to fluctuate and fall, this is your max vac point. I have heard people say to back off up to 2" vac but this doesn't give the best performance up here. I back off no more than .5" myself.
Air/fuel gauges cost $15 to $40 and a 1-wire O2 sensor is about $18. To accurately see what the air/fuel mix is a gauge must be used. A wide-band O2 setup is optimum but will set you back $250-$500 depending on setup. I just went with a simple setup but it works.
I recently set my wife's 4.2 jeep up(not a ford but vacuum is vacuum regardless of the gas engine), as it was horrible on mileage and down on performance. It got about 11.3mpg.
By setting the timing by vacuum and installing the correct jets and power valve I have been able to not only greatly increase the power but fuel economy is now just under 20mpg at 19.7.
Hope this helps.
Thank you this is GREAT information. I did buy a timing light and have advanced the timing using it and what a difference that made! Wow, much more responsive! I do also have a vacuum gauge which I was going to use to dial in the carbs. I will definitely be taking note of the timing using your method with the vac gauge.