Stutter, threatens to stall when given a lot of gas

[TravelinLight]

The 75 FJ40 stutters and threatens to stall when it is given a lot of gas.
It will do it while standing still or driving.
It will idle fine and will slowly get up to speed fine but 2500+ RPM under a near-wide-open situation causes problems.
It has:
New gas tank
New fuel filter
New fuel pump, OEM
New TrollHole carb
Pertronix ignition
New plugs, wires, cap, rotor
New Remflex gasket
Intake manifold crack welded and epoxied
New air filter

After doing all this, the previous rough idle and backfiring has been solved but I'm still
left with the aforementioned problem.
Any thoughts?

 

[Splangy]

Intake manifold crack welded and epoxied

Where was the crack? You probably should have just gone with a replacement intake. Are you sure you don't have any more vacuum leaks?

Does it idle smooth or a little rough?

How's the timing?

 

[TravelinLight]

I don't know where the crack was as the mechanic fixed it.
It idles smooth.
After the pertronix ignition, the timing was changed from 7 all the way up past twelve with no change.

 

[Pighead]

X2 on double checking your timing, you had the dizzy out for the pertronix placement? Then doublecheck your carb linkage is hooked up correctly so that the accelerator pump moves when you hit the gas.

 

[TravelinLight]

I may have failed to explain in the previous post that the timing has been moved all over from 7 to above twelve and back with no change.
Wouldn't the accelerator pump not moving cause no acceleration at all?
Slow acceleration works on this vehicle just not fast acceleration.

 

[kurtnkegger]

Could it be he has a bad Vacuum valve gizmo that has gone bad, and is preventing the advance on the dizzy from catching quickly, and leaving all the work for the spinning weights?

 

[Splangy]

Slow acceleration works on this vehicle just not fast acceleration.

That sounds exactly like an accelerator pump problem. It's simple to check. Just work the carb linkage and see if fuel flows from the acclerator pump nozzle at the top of the primary.

Also, one other thing, is your mechanical advance working in your dizzy?

 

[RLMS]

Does the choke operate correctly?

Justin

 

[Pighead]

Wouldn't the accelerator pump not moving cause no acceleration at all?

No. The engine will accelerate very slowly without a functioning acc.pump...like yours.

 

[Trollhole]

Sounds like the secondary isn't opening up. PM sent.

 

[TravelinLight]

An updated description of the problem:

It backfires through the carb when it is at or near wide open regardless if it is opened up slowly or quickly.
Pulling the choke slightly eliminates the carb backfire but it still has hesitation and bucking.
Pulling choke halfway makes it run damn near perfect other than a high idle.
I take back what I said earlier about it idling perfectly. It actually surges a little bit.
Vac gauge read 17 and it goes down to 16 before going up to 19 when it surges.

Accelerator pump is squirting fuel.

 

[Splangy]

Sounds like you're running lean. Doublecheck for vacuum leaks.

 

[mcwinery]

X2 vacuum leak. I think I may have the same problem.

 

[kurtnkegger]

What is your idle set at? have you looked down the air horn to see if there is fuel from the primary? Just had this experience, and my idle was set too high....something to look at anyway...

 

[TravelinLight]

The idle is actually set around 850. It came back from the mechanic that way and I haven't had time to adjust it to ~650.
A high idle caused problems with your acceleration?

 

[Pin_Head]

It is lean at WOT. It could be a couple of things:

1. fuel pump not keeping up with demand. This sounds likely since it does it with no load too. Take a peek at the fuel level in the carb when it stumbles.
2. Power valve not opening. Not likely as it is a new carb, but maybe you used gasket cement on the base, blocking the vacuum port.
3. Wrong fuel pump (like running an early 2 line pump with a spacer) related to 1 above.
4. Wrong primary jet.

 

[TravelinLight]

Updated description of the 75 FJ40:

The idle has gotten worse. Here is a video of it running without choke:

YouTube - 75 FJ40 - Grumpy Idle Without Choke

With the choke pulled halfway out, the surging and slowing down is still present but not nearly as much.

It will accelerate without missing or backfiring through the carb when the choke is pulled halfway out.

I tried the paper clip test and the secondary isn't opening either.

Also, should I be able to see the secondary rod turn, thus opening the secondary butterfly when I give it WOT by moving the linkage with the engine running instead of having to use a paper clip and go for a ride?

 

[TravelinLight]

Here is a pic of the secondary:

and one of the primary:

The rings on the venturi look a bit bent and busted up compared to the original carb.

 

[Splangy]

It still sounds like you have a vacuum leak.

 

[TravelinLight]

Thank you, although I'm not sure how to go about finding it. I have sprayed carb cleaner all over the place with no result.