So I've had my '73 F-100 since I was 15 years old, it was my grandpa's truck and I was happy to have it. The only modification I've had done to it was an upgrade from a 360 to a 390 when I was still a teenager b/c back then I knew that bigger must be better...

Since the upgrade/rebuild (about 12 years now) the motor will occasionally go tic tic tic for the better part of 10 min with a cold start, not all of the time, but enough to be annoying. The major downside is the power lags at highway speeds. The motor is nice and strung until about 70 mph, at which point any pressing of the accelerator causes a huge clunking noise and the power bottoms out, like surging only in the other direction, I don't think it's fuel starved and I've tried higher octanes to no avail. Once this power diving starts it doesn't stop until the motor cools down. When it's cold I can power up hills at 80 mph, but once this the "problem" shows up it's constant.

Any advice on this anti-surging and ticking would be much appreciated, it's frustrating having tons of power, but not being able to use it b/c I can't even hit the gas.

Thanks!

 

Sounds like two separate problems. To start with, have you kept the oil changed? The ticking sounds like lifters. Frequent oil changes will prevent this. You need to clean out the crankcase. People have many different solutions for cleaning out the crankcase, some of them risky to your engine health.

A safe way is to change the oil and use one of the oils designed for Diesel engines. These oils have LOTS of detergents for dispersing diesel soot. They also are certified for gas engines. Examples are chevron Delo, Mobil delvac. Get the engine hot and pull the drain plug and filter and let it drain a long time. Those last few drops are the sludgiest. Do this every few hundred miles until the noise goes away.

It sounds like the noise you're hearing at 70 is actually the engine starving for gas. It sure sounds like you have a high speed fuel delivery problem. Make sure the tank is venting, the filter and lines are clear and check the float level. Also make sure the needle and seat are clear and flowing well.

Hope this helps.

 

Agree with all the above.. On the weak at speed I'll just add check/replace the rubber fuel line sections. With time and alcohol they get dry and brittle or soggy with fuel. Cracks can let air in and spoil the fun and soggy lines can get sucked shut by the fuel pump. I chased this problem for a while on a '78 and a few feet of rubber hose fixed it.

 

I've had that high speed/ engine hot/ under load fuel starving thing happen on a lot of different old engines ever since I got my first one. Try running a bottle of octane booster/fuel system cleaner. Will work.