3.5 V8 on carbs loosing all power at 2k rpm when hot, 3k when not

Well, this seems to be a theme at the moment...

My problem is the following: I took the old lady to Tunesia, already on her way down she had issues when hittin 2-3 k rpm when hot, e.g. stop and go traffic in plain sunlight. That usually went away when the arbs got enough air flow to cool down a bit. Now in the desert she started too loose all power roughly at 2.5k. It feels like working against an engine brake, idling I can ref her to 5k with no issues, I cannot keep the revs up so, they drop back to just shy of 3k.

Before going to the desert I changed the mixture as it seemed to be tad on the lean side. I'll try that agin maybe.

Anything else I can check? The fuel pump died as well, during diagnostics (if I measured right), she only got aroung 7 to 8 V. Maybe that os part of the peoblem. Tonigjt we gonna see a friendly mechanic to check the spark plugs. Anything else to look at?

Temperature was manageable, never got above half of the temp gauge, oil temp never got above one thord of the gauge. The carbs are running **** hot so.

Any hints to get to around 110ish on a motorway woupd be great, the way back means crossing Tunesia, Italy and over the alps.

Otger than that, she got me up all the dines I never would have considered possible in general.

Coil overheating?...fuel evaporation?...

The fuel pump voltage could be a fault in the wiring.
Had this on my EFi. Fuel pump stopped. Powered off a battery the pump was fine.
Fuse intact.
Checked voltage at the wiring loom connector to the fuel pump plug.
Digital meter showed battery voltage.
Bit of head scratching & tested the same point with a test bulb. Nothing, not even a glimmer.
Turned out to be corrosion in the loom wire a couple of inches from the plug.
Enough strands still there for the meter to show, but not enough to pass the current required to run the pump.

So, we made it out of the desert, alive and not on tue back of a recover truck, we did some very mild offroading today.

What is realized: The engine is comparatively cool, the carbs almost melted the snorkel tube. First thing I did was getting rid of the snorkel, that did wonders! I hit 6k rpm this morning idling, and kept her there. So, all good. At least I thought.

I think it is evaporating fuel. When you turn of the engine, and start again the fuel pump is running dry for more than 30 seconds. Today it was over 45° C air temp, the wind was hotter. The engine worked fine again this evening, after cooling down and at 37° air temp. After 20 km or so she acted up again, this time at close to 3k rpm. So my preferred theory is overheated carbs and evaporating fuel plus a hot coil (thanks shippers!). I know she has some mass contact problems (one of the things I couldn't get done earlier), so I wont rule out a less than optimal power supply to the pump. And the ignition could use some love as well.

Good news is, I get up mountains without turning into a traffic risk, the engine isn't overheating and oil pressure is constant.

One question so, is it normal that the fuel pump isn't working when directly connected to the battery? The pump is new, so the wiring should be ok. The existing wiring of the pump, through ignition lock and all that, is something to do very soon so.

Oh, and I'll replace the fuel return line. She has two bents that are new.

hef19898 said:

One question so, is it normal that the fuel pump isn't working when directly connected to the battery? The pump is new, so the wiring should be ok. The existing wiring of the pump, through ignition lock and all that, is something to do very soon so.

Click to expand...

If an electric pump is directly attached to a battery - pos & neg - then it should run until disconnected from the battery.

hef19898 said:

Oh, and I'll replace the fuel return line. She has two bents that are new.

Click to expand...

The fuel return is not just for pressure its to cool the fuel...

Ratae said:

If an electric pump is directly attached to a battery - pos & neg - then it should run until disconnected from the battery.

Click to expand...

Earth problem?...

Earth problem, I think so... This damn facet pump also has all of one wire, which goes to the relay of this very interesting transistor ignition someone ripped out of a Jag XK8. Other than that the pump is screwed to the chassis, same front inner wing the battery earth attached to. The pump kicks in as soon as the ignition light is on... Did I mention already that the wiring is a nightmare?

Shippers said:

The fuel return is not just for pressure its to cool the fuel...

Click to expand...

THAT would explain a lot...

hef19898 said:

Earth problem, I think so... This damn facet pump also has all of one wire, which goes to the relay of this very interesting transistor ignition someone ripped out of a Jag XK8. Other than that the pump is screwed to the chassis, same front inner wing the battery earth attached to. The pump kicks in as soon as the ignition light is on... Did I mention already that the wiring is a nightmare?

Click to expand...

The facet pump that was on my 101 V8 had rubber mounts which means you have to earth it seperatly...Iv'e changed it to a different pump but still earthed it seperatly it only needs a lead under the bolt down bracket to chassis so thats 2 wires attached to pump...

I have to check that... She's running for now, no idea why but I wont challenge her on that!