74 Tagra Full throttle cutting out????

[ARCSinAK]

Hi-

I have been struggling with a problem of my 2.7 cutting out and full throttle at the top of the RMH range, under load. Had a retired 911 mechanic friend of mine come over to day, we started with checking csi full pressure cold and it was to spec. We changed the ignition set up by installing an extra distributor with pertronic magnetic ignition, re-set timing, ETC. The engine seem to run smoother at idle and drivers fine until you pin the throttle, if you gradually accelerate she pulls strong. IF you apply full throttle the motor cuts out around 4G. if you back off from full throttle it pulls. Any thoughts on the cause would be appreciated.


Plugs wires are new factory insulated buru. I don't have points now, but that had no change on the symptoms. New cap. Haven't changed the plugs yet..... I'm I dealing with a lack of fuel at fuel throttle? Ignition? Stumpped.

I need to add that this car had been for years running with out a CDI box. I installed a MSD 6A, followed directions, watched a video of a install on a 911 ETC could not get it to start with the MSD, went back to the set up that was in the 911 when I took ownership which was ignition switch hot wire to coil and white wire to the -1 side of coil.

At times the cutting out problem had all but disappeared, but it's back with a vengeance, frustrating when she runs well until you apply full throttle. All of the trouble shooting today did nothing to change this issue.

[Bigtoe32067]

Fuel pump. Check pressure and volume. I would bet volume is under spec.
You already eliminated the ignition system so there really isn’t much else.
Tony

[ARCSinAK]

Pressure tested to spec. How does one check volume?

[timmy2]

Which coil are you using? Could be failing.
One for Kettering or a CDI type?
You need a Kettering compatible one the way you are wired.
Need one for MSD if using MSD.

[ARCSinAK]

The cutting out issue was present before I tried the MSD set up but would come and go.
Never got the MSD to fire
I have a MSD Blaster 2 Coil with the MSD AL

Switched back to original Blue coil and it ran with the Pertronix but still had the cutting out issue.

Used this wiring set up. But did not run the MSD 12V hot wire to the starter, just to fuse block in the engine bay. Plan to run a wire this weekend, but you would think it would still fire......

[ARCSinAK]

Changed fuel filter, no change.

[speedster911]

have you tested FP hot?

I sent my 74 FP to Peter George to rebuild, Initial tests (cold) everything was in spec / good fuel flow and pressure. After 30 minutes of testing FP ran excessively hot and was not within spec.

Fellow pelican recommended Peter George and I was very satisfied with his communication, knowledge and final product.

[30westrob]

I would check resistance of your plug wire ends. Rob

[kltarga72]

MSD needs to be wired to the starter motor, thats why they use heavy gauge wire for the power connections. Larger diameter wire allows for larger current draw.

Engine compartment fuse block
1. fan pass compartment 16A
2. fan engine compartment 25A
3. rear window heating 25A

I suggest reinstalling MSD and follow directions carefully.

[ARCSinAK]

Thank you for the advice.
This issue was present before the attempted MSD installation.
It seems to happen straight away when the engines under load at full throttle.
Took it for a drive after I changed the filter. Under acceleration it pull strong until I hit 3/4 full throttle then stumbles, Boggs and cut out as soon as you lift the symptoms go away.

Not sure the it happens after full pump is hot because it will occur straight away.

I will keep the investigation going

[ARCSinAK]

Update, I emptied tank by disconnecting the rear line before the fuel accumulator, seems as though there was plenty of volume. I wanted to check the screen in the swirl pot, which I changed when I re-furbished the tank, thought it may have been restricting fuel flow, it was clean. Still having the issue on hard acceleration ........

Wondering what would be the next system to check. Still running on the coil with out a CDI, but the strange part is this has been a intermittent issue.....not sure whether it fuel or ignition based. She seems to run fine until I am at 3/4 + throttle under hard acceleration.

[Bigtoe32067]

I had the same issue once and it was the ground strap. To look at it it was fine but it was actually in two pieces so under heavy load and engine flex it would pull apart and misfire like crazy until you let off and the two ends would go back together and then it’d be fine again