[Colin70TA]

Hey guys, I have been trying to chase down this problem for the last few months and I can’t figure it out. Not sure if it’s a engine or transmission issue.
Build is your normal stroked 400, ported e heads old faithful cam package. Intake is a ported HO, qjet for carb (done with cliffs parts/specs) and HEI distributor.

The problem, half the time the motor just doesn’t want to rev. If I hit it when I am rolling from 30-40 mph the car pulls very hard but from a stop or anything under or over that speed it almost feels like it has a throttle stop or running just on the primary’s. It spins the tires just as hard or harder at 30mph then from a stop.
From the 30-40 range it will pull to 80 nicely with no noticeable power loss of bog.

The transmission is the stock t400 with a 10” continental converter.
I took a friend for a ride and he really thought it might be the converter not allowing it to rev but does that make sense? I had my old 13 continental in there when I first put the build together this spring and it did the same thing from what I remember.

I checked my linkages a bunch of times to make sure nothing is binding and seems fine but this is the other thing. When I stomp on it from the 30mph roll and I let off it holds the rpms after and I have to blimp the throttle a few times to get it down. It does this every time after it pulls hard.

Anyways, hoping for some ideas or if anyone has experienced these symptoms in the past.

Thanks in advance! Colin

[JLMounce]

What's your fuel system? I'm assuming you can free-rev this engine to it's redline?

Considering this is happening most often from a stop or very slow speed, my thought is that your fuel system isn't up to the task. If you're still running a mechanical pump, it's likely that the system isn't able to pull fuel against your acceleration and you empty the fuel bowl around 3000 rpm.

[Joe's Garage]

It almost sounds like the choke flap is randomly getting pulled shut. That would also engage the choke's high idle feature when you let off, and keep the rpms up until you blip it and the fast idle cam drops back down.

Or that the little choke lockout lever is holding the secondary flaps shut.

I'd try wiring (or adjusting, if it's an integral choke) the choke flap all the way open and making sure the lockout is disengaged.

Second thought is that the gasket is somehow keeping the secondary butterflies from opening smoothly and/or holding them open a bit when you let off.

Good luck.

[JSchmitz]

I would look at the secondaries on the carb hanging up.

[surfsama]

Originally Posted by Joe's Garage

It almost sounds like the choke flap is randomly getting pulled shut. That would also engage the choke's high idle feature when you let off, and keep the rpms up until you blip it and the fast idle cam drops back down.

Or that the little choke lockout lever is holding the secondary flaps shut.

I'd try wiring (or adjusting, if it's an integral choke) the choke flap all the way open and making sure the lockout is disengaged.

Second thought is that the gasket is somehow keeping the secondary butterflies from opening smoothly and/or holding them open a bit when you let off.

Good luck.

This would be my guess too.
Have you looked into the carb (engine off) and had a friend push the accelerator all the way to verify WOT?
Also, check your transmission modulator.

[STEELCITYFIREBIRD]

Agree with last two responses ...very likely, the gas pedal will feel slightly stiffer if the secondary lockout is activated.

[JSchmitz]

Originally Posted by Colin70TA

When I stomp on it from the 30mph roll and I let off it holds the rpms after and I have to blimp the throttle a few times to get it down. It does this every time after it pulls hard.

If it were the choke lockout it wouldn't be holding open. I would check to make sure the butterflies aren't riding on the base gasket, etc. Check the air flap (and associated parts) and butterflies. Also, don't over-tighten the mounting bolts. Easy to cause throttle shaft binding.

[sdbob]

I had the air flap hang up only occasionally. Check to make sure its centered. I looked close and saw shiny rub marks.

[coonhunter70]

Sounds like its in a higher gear when leaving from a stop ??