ok, i've been battling an issue with my vehicle for some time, it runs great up to about 5100 rpm, then the engine looses power, no misfires are felt unless i stay on the throttle and try to go higher, as soon as i shift into next gear i get all of my power back, best way to describe it to me, it feels like a modern car feels like when you hit the redline. I've checked fuel pressure while doing it, i'm showing steady 8 psi at the carb, my timing is set at 34 degrees at 3k rpm, about 10 degrees initial, i've tried running +/- 4 degrees of that with no change, I've ran two different carbs, a 670 holley with vac secondaries, and now current is 750 holley with mechanical secondaries, car has more power down low with the 750 but acts the same after 5k. I'm running 93 octane fuel, i've tried octane boost which didn't do anything. I've checked compression yesterday was between 165-180 on all of the cylinders. my cam (specs below) should be good up to 6400, intake should be good to 6500. so i'm out of ideas. tomorow i will bring a dial indicator home and check cam lift to make sure my cam is not wiped out. only thing that worries me is that it seems like i have alot of crank case pressure at idle, my pcv valve is working and i got strong vac at the valve.
Floating the valves... Over rich condition... Ignition timing is not up to par... What is telling you you have excessive crank case pressure???
What balancer are you using? Stock? Was it a Maverick engine you started with? Ford used 3 sets of timing marks, most aftermarket balancers usually only come with 2 of the sets, and that's where it gets weird, the stock Maverick engines had the timing pointer, in the position to be used with the 3rd. If that makes any sense....When I first rebuilt my engine, it kinda ran the same way, I had the timing waaaay off, but it ran and idled fine....
If you are going to 5100 then it starts, I'd strongly suspect the valves. Stock valves? Cam? If you shift and it runs fine til 5100 again, then when you shift the valves are working again, til 5100.
engine very far from stock, engine and cam specs are in my signiture, the block is from 79 granada i've been told, ignition is full msd minus the wires, i've tried two different ignition boxes also, i can free rev the engine to 7k in neutral no problem, balancer is aftermarket. tomorow i will check the TDC and make sure i'm using the right pointer. on the crankcase pressure, if i take off the breather and put my hand over the hole seems like there is bit more then normal, hard to describe.
Sorry, at my age I don't read well. I'm assuming you changed the valve springs. I see you run at 8 psi. I run a Holley 750 HP at 7psi and go to 7200. So the fuel delivery should not be a problem unless the filter is bad between the pressure reg and the carb. I lost over a second in the 1/4 one time. Changed a lot of things only to find the foam in the fuel cell had deteriorated and clogged the filter. I had cleaned the lines up to the reg. Hope you find it.
Sounds like valve float to me too. You might try running it with a vacuum gauge and compare it under load when it's breaking up to when you free rev it. Another possibility is spark plug gap or plugs themselves. Some fuel additives leave a conductive coating on the porcelain and can cause similar symptoms to what you're describing. I would pull one after an acceleration run to see what it looks like.
Sounds like you may have to much lifter preload my old 306 done like that till I set the hydralic cam with a .002 feeler gauge
Agreed. My Pontiac would do the same, I set it to zero lash (no pre-load) and it pulled hard till it ran out of go.
i work on briggs motors constantly because they do this often and it sounds like valve float or weak springs. just adjust the valves like others mentioned.
adjusted the right side of the engine tonight, found out which timing mark i'm supposed to use (i think i was on the right one, but not sure) valves were a bit tight, so backed the adjusters out to 0 lash, tomorow will do the left side and take it for a spin
