i posted this over at the 1966 truck forums and it was sugested I repost it over here, so here it goes.

HI. Im hoping someone can point me in the right direction to go in.I have a 66 F100 which I purchased last September, it had a rebuilt 352 with a ford 2 bl carb and factory single exaust.Stock distro with points 3 on the tree manual steering and brakes and a overdrive trany.I bought it on tuesday and that sunday out for my first jaunt in it, It died and would not restart.I had to have it towed home. I found the carb was full of gunky looking stuff. So i pulled the fuel linecleaned it out, checked the Big fuel filter on the pump ,( it was clean )and installed a inline fuel filter. At the same time I bought a holley 500 cmf 2 bl ( new ) and a pertronics kit for the ing. I installed both and she fired up fine. i adjusted the carb per factory and all was well ( well not so well it was running rich) black smoak from the tail pipe.I leaned it out to # 69 Jets in stages from the # 73's that came with it stock and it seemed fine.I went on to install pw disk brakes, power steering, revamped the electrical system and repaired the overdrive. All with help from this forum. After that was done I had a dual flowmaster exaust installed running to the stock manifolds.At this point i ran out of funds.and at this point the weird things began.I took a trip and the gas milage was unbeleveabull But when I climed a tall hill it would pudder.I checked the plugs and they were way lean, So I up the jet size to #72's and it gave it more power and all was fine, for about a week, Then I pulled the plugs and they were still lean in fact not much change at all. so I uped the jets to # 74's, and all was well, well for about a week. I took a trip and got good milage and the pulgs were a very light tanish color and I thought all was good, Except When I finally pulled that hill agin and it still was a little breaking up under heavy load. I checked my plugs in a couple of days and they were white agin. So this time I uped the Jets to # 76's. Now every time I have upjeted I gain more power, I just pulled the plugs agin and darn it if they arnt still running whiteish, I went to the "Hill " and she pulled it fine but their is still a hint of breakup just a little now not as much. I tested the fuel pump and pull a steady 4 1/2 lb's of pressure.My vacume at Idle is 18 and I have no pings or overheats.It starts easy and runs fine But the plugs are bugging me.And their is one more thing. I notice after a run on the "Hill " the rpm dropes at the stop light From 750 down to 500.Then by the time I get to the next light it has raised back up to 750rpm. I'm not sure what to do now, Do I take it to a performance tuneup dyno type place and say here fix it, Do I keep trowing jets at it. Why is it taking such large jets and still running lean ? Do I have a fuel delevery problem ? Any clues would be helpfull, I dont know FE engines and I dont want to burn it up.I just want it to run right.

Thanks

 

Did you check that fuel pressure with the engine under a sustained load? Is the fuel level in the carb OK? I suspect a low fuel delivery problem. Try checking the fuel level after a pull up the hill, without letting it idle. Just shut it off at the top and check the sight plugs.
Also check all the fuel lines before the pump, especialy that short rubber one under the cab.

 

I agree with putt. It sounds like a fuel delivery problem. Check your oil, sometimes when a fuel pump goes it can leak gasoline into the crankcase.

Did you check your float level?

 

The float level is just at the botom of the site hole., this morning I checked the fuel filter and it was clean, on a lark ( I have been going to convert the distro but I havent got the softer springs yet.) disconected the vacume advance and pluged the inputs to the carb and distro, I went to work and it had the same RPM every time I came to a stop. I will put a fuel gauge on it and mon while I climb the hill, But I think maby the vacume advance mech is not returning to the same spot or maby sticking , this would make the timeing all over the place right ? will check both and get back to you.

Thanks for all the help

 

I have had a vac adv go bad that allowed the point plate to rest wherever it felt like. If you push the point plate toward the vac can, does it spring back to the same position? Is the point plate free to move if you unhook the vac adv arm from the plate?

 

Yea ! The distro was the problem, I checked the fuel pump pressure under load and it never wavered. I pulled the sending unit in the Gas tank and it looks like new inside all shiny metal, and the lines are the same. As I was going up "The hill " I run her up to 2,500 and stomped down on it. and Like all
She rose up on all four wheels and took off. At 60mpg I drop it into overdrive
and it still accelerated up to 70 and not wanting a ticket I backed off.I drove it a couple of days and found I was getting better gas milage ( I thought Ruh ro lean agin. so Today I checked the distro, and the person who owned it befor me ad put the lower tention springs in already. However I checked the timing at 3,000 rpm and it was around 42 BTDC, I lowered it to 36 BTDC ( it gets there at around 2,700 RPM ) and took it for a drive, It was less peppy off the line But After the run i checked my Sp Plugs and they were Dark Brown, almost to dark May need to down jet now ( am going to leave them in a week and recheck. I found my distro has a lot of slop in the Vacumn advance plate
so im goina need to secure that somehow. And i need to figure a way to limit the cent advance so I can run a bit more advance at idle. but man what a differance.

Thanks for the Ideas !

 

Under the point plate is the mech advance weights, springs etc. There is a two slot piece the springs fasten to, most of the time the limit post is in the long slot(more advance) Check by the ID stamped by the slot ie. 15L; 10L etc. The smaller the number the less advance it will allow. The vacuum plate should have a wave washer/spring holding it down to the point plate under slight tension.