Thread: Tuning engine.

Confirm Ignition timing.

Originally Posted by Gippslander

I am having issues with our 3.5 V8, (Series 3 Stage1 ) it runs smoothly when I run it stationary but when I take off it is smooth low down and then Boggs down as I accelerate almost stopping. If I push the throttle to the floor it hesitates then gradually picks up, if I hold it around 3/4 throttle it will maintain revs but the moment I relax the throttle it fails again. I have checked the electrics because it feels like the key is turned off and on but can’t see anything wrong.
i have checked the fuel level in the carbies plus raised and lowered the needles to see if that will help nothing seems to change its response. I have also put an exhaust gas analyser on it and driven out the highway and it showed rich mixture through the gear changes and lean at 80 kilometres an hour in top gear.
I removed the fuel return line and checked the flow, it is a new pump but it didn’t seem to be flowing very well so I changed it for a spare I had. It flowed better but still didn’t fix the problem has anyone had this issue before or does anyone have any ideas what I should do next, every time I play with petrol engines I realise why I became a diesel mechanic.
Gippy

Hi Gippy, I am not familiar with the V8, but I had some similar problems like this in my 2.25 petrol. After checking through the fuel lines I couldn’t put my finger on the issue. I ended up tracing it to the screw mounting the condensor inside the dizzy being a bit loose, essentially causing a bad earth. An easy check anyways…

Cheers, Matt

Any ignition shortcoming can cause this sort of effect - from plug gaps to incorrect points adjustment, to automatic advance not working properly, or sick coil or condenser, and definitely ignition timing.

It could be a fuel problem, what sort of carbies are on the motor. It sounds like the accelerator pump isn't working or a diaphragm problem.

Ian
Bittern

Hi Mate, Im assuming they are twin Strombergs?? I just rebuilt my stage one V8, and put a kit through both carbys, have you pulled the needles out to check for imperfections? Needle and seats are hard to come by, but you can typically clean them up, also check the dash pots are holding oil, there is an O ring at the bottom of the plunger.
What ignition timing are you running? Im still on a points dizzy while I wait for a new Bosch electric one, but have found 10dbtdc is working well, check the vacuum advance is working and not a cracked/blocked vacuum line..good luck

Thanks to all for the ideas so far I have found fuel pressure issues even though it was a new pump. I checked vacuum advance and it was faulty so I have changed the distributor for another one both are electronic units but different types so I had to change the wiring to suit the new one. I had a day away from it and plan to go through the fuel system again today, I have rebuilt both carburettors installing new diaphrams, needle and seats plus new “O” rings in dash pots they are CD 175 Strombergs. I am not sure what running timing is as I don’t have a timing light I have set static timing at 6 degrees BTDC and adjusted when running to the smoothest condition at idle without vacuum advance connected.
I will let you know results after today hopefully it will get sorted I need to get it in for a roadworthy this week if possible.
Again thanks for the advice.
As an afterthought does anyone know if the Series 3 Stage 1 V8 had a restricted orifice/valve in the return line to tank like the Range Rover Classic

I am still trying to get this car to run properly I have changed the fuel pump, installed what I believe are fuel atomisers/defuser plates inboard of the carburettors and a restricted valve in the return line to help the pump keep fuel up to the carburettors. To no avail I can drive the ok if I accelerate slowly maintaining engine vacuum but if I accelerate quickly I loose vacuum and the car dies. I am nearly calling defeat and have now decided it may be something to do with the main jets and needles, We have managed to get the car roadworthy and it is now club registered. I have attached a photo of what I believe are defusers which I think are designed to assist in the fuel atomisation process has anyone seen these before.
CB4A6D4E-7E7E-4FA2-9BA2-43F68E37685D.jpg

G'day,

I would connect a vacuum gauge to the inlet manifold and see what you have at idle and acceleration. The gauge will tell you if the ignition timing is retarded at idle. Also can detect leaking valves and leaks in the inlet circuit. A good gauge to have in the toolbox!.

Chris