JP91

So I've got my 300 slightly modified. It's got an offenhouser intake, 500 cfm 4 barrel, ported head, a comp mid range cam and the springs to go with it. I was told that the valve springs would help it turn the appropriate rpms. And it's never helped. My timing is close. It's maybe a degree or two but what else would make it not want to turn more rpms. Cuz it's only going to 2500 and at that point the cam has just started to kick in. Thanks for the help.

Scraptor

You had posted about this before, still having problems.
Ok have you

Checked that the throttle opens all the way?
Tried running it up 2500 in a higher gear then downshifting and staying on the throttle?
Checked compression, fuel pressure, and timing advance?
Checked the timing marks to make sure tdc on the balancer is tdc on the #1 piston.

Does it
Rev higher with the trans out of gear, or just not pull past 2500?
Does it just level out at that rpm, or is it popping or breaking up, hitching whatever.
Does it run okay off idle, have good throttle response or is it just lazy and dead.
Is it bogging or stumbling?
Are there any smart old hot rodders in your town that could help figure it out?

JP91

Throttle opens all the way. I found that out the hard way one night. If I down shift at 2500 it will pop and I'll kiss that motor goodbye. Compression and fuel pressure I haven't done but timing is maybe a degree or two off. Timing marks are correct. It won't pull past 2500. And it seems that once I messed with the timing it hurt it. Now it's wanting to not go to 2500. The motor starts to shake like its off balance at 2100. But before it would level out and hold there fine. No popping or anything. Good throttle response once the truck was warm. If you take off before it warms up it pops and wants to die. It bogs down in certain gears but I always thought that was just the ****ty trans. And there's a guy that builds engines for race cars close to me. He actually gonna build my motor when I get the money.
I greatly appreciate the help. I have posted about this before and you helped me out with it. I'm about to lose all my hair from pulling it out. Haha. Try to fix one thing and you've gotta fix 4 other things first.

Scraptor

This has me puzzling. I wonder if the valves are set too tight, meaning the rocker arms tightened down too much, and compressing the lifters too much so when rpm comes up, oil pressure comes up, the lifters pump up, and valves start hanging open,
The other thing i was thinking was lobes worn on the cam, because it seems to be getting worse, i had a dodge that ate two new cams in less than two months, how i found it the first time was the car became more and more undrivable, i blamed the carb, so i lifted the intake for a 4 barrel swap and could see the worn lobes. The second time it ate a cam when it started acting sick, I checked compression it was crazy high on two holes, two spark plugs were soaking wet with fuel, and one was nearly pure white, pulled the valve covers and watched the rockers with my timing light, you could see the slow ones.

I think i would pull the valve cover and check valve motion, with a timing light, the flashing will slow down the motion enough you should see it,if any valve aren t moving as much as the others, you could also check the lifter motion through the side covers.
If the cam seems okay, check the lifter preload.

Maybe all thats a wild goose chase, and its an ignition problem.

JP91

Well I was thinkin it was the rocker arms like you said. But when I changed headed the one on it was a studded head instead of the bolt type. So I bought brand new rocker arms and adjusted then like a Chevy. 0 lash and a 1/4 of a turn more. But it never helped. Then when we put the springs on the other day, the builder tightened them all the way down. He said they weren't adjustable. I know when I rebuilt the motor the cam looked fine. Nothing real bad I think one bearing was a little goofed up but nothing real serious. How would I check the lifter preload? But I'll try what you said about the rocker arms with the light. I really appreciate all this

Scraptor

The zero lash plus a quarter sounds about right for lash setting, and thats the same as lifter preload, turn the pushrods with your fingers, with the valve closed, when you start to get drag on the push rod, crank the nut a quarter turn tighter, which sounds like what you did.
I had a thought this morning, if you have a fast electric drill, you could test your ignition without running the motor, if you pull the distributor, and oil pump drive, you can chuck up the driveshaft in the drill, and spin it up to speed, you d want to disconnect the coil wire at the distributor, and ground it. If you can rig a tach where you can see it, you should be able to read the tach,and spin the dizzy with the drill, if its ignition, you might see the tach needle jumping, you need a drill that will turn at least 2000 rpm, which shouldn't be hard to find. Also if you can run the ignition like this you can pull a wide gap on the coil wire and watch the spark for highspeed breakdown.

Maybe you should join fordsix.com, those guys might have better ideas.

JP91

I joined it awhile back. I got to thinking last night if I have a vacuum line wrong on my carb. Idk if its just running in two instead of four. Only getting 250cfm instead of 500. I know both flaps are opening on the bottom. But the top idk about. Being a vacuum secondary I thought maybe the upper flap isn't opening. Cuz right now the carb is the carter afb or something like that, same thing as a edlebrock, 500 cfm 4 barrel carb with vac secondaries. I swapped out the choke to a manual one and all of the vacuum ports are closed off. (The three on the front.) but there is one that's like under where the choke box is and I've got a line going from it to the port for the secondaries. Im wondering if that is keeping the flap closed, from pulling a vacuum? Does that sound like it could be a problem?

Scraptor

One thing i know about those carbs, i don't know how they work. What i understand is the air doors work on engine demand but i don t undestand how.

JP91

Well the secondaries run off of vacuum, right? So wouldn't it want to open up at a lower rpm to be wide open at a higher rpm?