Hey guys,

84 TA, 355, CC Qjet, 700R4.

The trouble I'm having is if I hammer on it from a stoplight/stop/anywhere and get the RPM's 3500+ quickly, the car starts to stutter and miss, similar to the effect of hitting a rev limiter.

Under steady/normal acceleration, the car will run strong all the way 4500rpm before it starts to do the same.

Downshifting to pass on the freeway has the issues as well at around 4500rpm.

Car runs smooth as can be driving around, starting, stopping, in traffic, until I start getting the RPM's up.

In-tank fuel pump is 5 years old. No issues from it that I can tell, it got me from Salt Lake to LA and Back.

Fuel pressure is a steady 5-5.5 psi, any higher and the gaskets on the carb start to get "wet".


Plugs, Plug Wires, Cap, Coil, rotor are about 2 years old and ignition module are is 15 months old. Factory original distributor.

I'm just looking for thoughts/ideas on where to look. Could it be the Distributor might have finally gave up on me?

Any thoughts/ideas are welcome. Thanks!

 

I should add that it's not throwing any codes and the timing is set to 7* BTDC.

 

Still running the paper fuel filter in the inlet fitting? When was the last time it was changed? Diagnosed a Q-Jet fed elcamino recently. Car would idle and cruise fine. Within a couple of seconds off WOT acceleration it would start bucking and surging badly. The filter had fallen apart and the metal end piece was lodged into the fuel inlet of the carb, blocking a large portion of the flow. Replaced the fuel filter and it pulled strong past 5,500 rpm.

Also bought a parts house mechanical store pump recently that literally made it through engine break-in and died halfway down the street.

 

Fuel delivery.

The fuel filter suggestion is spot on. That's where I'd start too.

Change it out and let us know.

 

Remember that a stock QJet nose-filter passes fuel from the inside out. If you take it out it will look "clean" because all the dirt is on the inside. Don't go by appearance.

 

I have an inline filter before the mallory regulator. Can I simply remove the qjet nose filter?

 

I pulled the fuel filter completely as I'm running an inline filter in front of my fuel pressure regulator.

This fixed 80% of the stumble I had under hard acceleration.

Now occasionally I still get the stumble from a hard launch at 4500rpm+, but not all the time. Where I run into problem is when the car shifts, it seems to stumble from the moment it tries to shift, through the shift and into the next gear, almost like it is having a hard time recovering (acting like it did before with the inlet filter in place).

Should I bump up the fuel pressure from to 6psi or is there some place else I should look first?

Fuel delivery is from an electric 255lph in-tank pump with mallory regulator set at 5-5.5psi.

 

Has this carb ever been rebuilt? Reason I ask is some of the rebuilder inlet valves SUCK. They are very tiny. Built a dualjet recently and ended up using the OEM inlet valve seat where the float needle valve sits. The hole drilled in the OEM part was 2x the diameter of the cheap GP Sorensen kit.

 

It was rebuilt by Cliff Ruggles at http://www.cliffshighperformance.com/

I would think he'd have covered that part.

 

Took it up on the freeway last night and on some on and off-ramps. From a dead stop, ran hard to 5000+ when it shifted and didn't stutter at all through the gears on several stops-starts this way.

Afterwords when I was driving home, 40mph on the street, slowed to take a corner, rounded the corner and hammered it down from 20mph, and it stuttered/choked it's way from 2500RPM until I let off the gas at 45 (30mph zone). Backed off, hit a stop light. Hammered it off the stop light and it ran fine again. So now I'm just confused.

 

You need to get a fuel pressure gague on it. Something you can read from the driver's seat. You'll chase your tail forever until you figure out under what conditions you get proper fuel pressure. Revving quickly through the lower gears (especially coming off a corner where the pump can suck air if the tank is low) is much more stressful on the fuel system than hitting it from a highway roll.

 

Any suggestions on how to run a fuel pressure gauge into the cockpit?

 

Have you actually checked the fuel pressure with a gauge, and when was the last time you changed the inline filter? You could have too much pressure now, or possibly the inline filter could be clogged.

 

Just buy a remote gague kit and hook it up close to the carb inlet. Snake the copper or plastic tube to the gague, which you (temporarily!) duck tape to the outside of the windshield. It only take a run or two and you'll know if the fuel system isn't keeping up.

I never permanent mount my FP gagues. Just too dangerous if something happens to the line. And the "isolators" that are recommended for interior mounting the gague can get flaky and unreliable over time.

 

carbs like 7 lbs of fuel pressure.you could be starving for fuel. which is what it sounds like to me

 

when i push the pressure over 6, I get fuel seepage out of the gaskets in the carb.

 

The gauge I currently have is installed on the regulator port. I can't check it while driving, but it's a simple matter of popping the hood to make sure the pump is working properly.