Misfire that gets progressively worse until stall

[jhv8]

Hi everyone I hope someone has seen this before and can point me in the right direction.
I’m running a SD1 Rover V8 215cu/3.5ltr in my Healey and this year when I brought it out of winter retirement it developed a strange problem.
It’s running an Edelbroke 500 CFM performer (1404) AVS carb on a Offenhauser dual plane manifold with a road race Hurricane high lift cam.
It uses the original SD1 opus contactless dizzy, coil and ignition amplifier module.

When I first got it back on the road it drove OK but under hard acceleration up near the top of it’s rev band it would hesitate, slight misfire.
This got worse over a couple of weeks until it would lose power altogether and stall completely once you had used any hard acceleration.
The car would then not start unless you left it alone for 5 – 10 minutes and then it would start and you could get ½ mile or so with the power going bit by bit until it stalls altogether and you then have to wait and repeat the process until you can get home.
If you start the car you can leave it idling forever, you can even rev it, the fault only happens after acceleration under load.

I pulled all the spark plugs and they show good fueling (very light brown colouration the same on all thought it might be the coil or pack breaking down so because of limited time I booked it in to an auto electrician.
They originally said yes it was the ignition amplifier module that was the fault and they replaced this and the coil, just to be sure. I didn’t hear any more from them so I rang and asked when I could have the car back and they said it still had a slight misfire hesitation when the throttle was really tramped on.
I went down there to take it out for a check just to make sure they weren’t confusing the slight dip you get when you floor the throttle (carb is really big for the engine) and I got ½ mile when the car did the same thing as I had taken it in for (even with the new module and coil).

They don’t seem to know what wrong with it and I’m a bit concerned leaving it with them.

I would have thought it was fuel but the carb seems to have fuel going to it OK and I can hear the fuel pump clicking away.
I installed a fuel filter between the pump and fuel tank a couple of years ago to stop crap going through the fuel lines and it is transparent so you can see the fuel moving. I’ve completely filled the tank since the car was put back on the road so I’m thinking it’s not bad fuel.
I’m really stumped

Anyone seen this symptom before or have a clue what’s wrong?


Thanks in advance for any replies.

Rob

[katanaman]

the opus never was very reliable so I would go for changing this if you can get hold of another one to even test it. It could be the sensor inside the dizzy that is failing with heat. Definitely sounds like something isn't playing when it gets hot and the dizzy is the most likely in my mind. Cant see it being carb icing at this time of year and if it was fuel starvation it wouldn't need to be left for 5 to start. Its a well proven combination carb wise so I cant really see it being fuel vapourisation either especially again as the weather isnt particularly hot.

[ian.stewart]

Does it pop and backfire a bit when the engine is slowing down, sounds a bit like fiel starvation, I had a really strange problem not dissimilar the car would run one day, then like a bag of poo the next, even refusing to start at all on a couple of occasions, turned out to be a cardboard seal from the lid of a fuel addative being sucked onto the fuel pickup pipe,
Have you set the fuel pressure too low, or is the pump not up to the job, I there is a blockage in the tank this can kill a vane type pump.

[jhv8]

Thanks guys, it would appear your both right.
The amplifier was starting to fail, but the main problem is that the car is very old (40+) and leaving it garaged through the winter is not helping so the fuel tank has gone rusty inside and under heavy acceleration the pick up in the tank is clogging with crap. When you stop and wait the crap eventually falls back off the pick up and your good to go again.
What threw me was the transparant filter I had between pump and tank was showing clear fuel.

Thanks


Rob