intermittent misfire/fuel starvation

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stu60
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intermittent misfire/fuel starvation

Post by stu60 »

Help! has anyone any ideas on what to try next.

Rover V8, Holley carb, Edelbrock inlet manifold, electronic Lucas distributor (type that drives oil pump)

New rebuilt engine installed which sounds and runs sweetly (bar fault below), didn't have this issue before new engine fitted.

Symptoms
car runs sweetly 90% of time but has happened twice now when on motorway after 10 minutes at constant throttle opening i start to lose power, feels like fuel starvation or could be ignition/misfire. Feels like car might die but then comes back on song and doesn't repeat. has only happened on motorway at 3000 rpm, as soon as drive through fault it runs perfectly again.

might be coincidence but both times i think i refuelled 10 minutes or so before fault with super unleaded. Also the car is set to run quite rich to get it to run smoothly from cold but once warm the tickover is a little high at 1000-1100 rpm

Car difficult to restart when hot

Cures already tried between first and second occurrence
- new coil fitted
- new distributor amplifier module fitted
- definitely felt smoother after fittings these two items & restarting not a problem (so thought i had cured it)

Latest thoughts
- fuel pump? the pump has always been noisy from day one (noticeable loud whirring noise as it primes, can't hear once engine running but probably making this noise always. is this normal?
- bad earth somewhere (I have checked everything i can see in engine bay)
- fuel starvation due to heat evaporation but then why would it cure itself?
- Holley carb not suited to 4.0 Rover V8 (was on vitesse 3.5 previously), i've read Edelbrock/Weber is better?

All suggestions gratefully received!

thanks Stuart
stu60
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Re: intermittent misfire/fuel starvation

Post by stu60 »

hi
just had another thought i have a Malpassi filter king fuel pressure regulator fitted. do you think this might need adjusting to take account of new engine being slightly larger at 4.0 vs 3.5?

but surely i would see a problem under normal acceleration on the road?
stuart
Jerryedmans
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Re: intermittent misfire/fuel starvation

Post by Jerryedmans »

A couple if thoughts. Does it have a choke? If no choke cable, have you double checked the Choke plates in carb are open? I had issue when first starting my rebuilt engine and as I had air filter in I did not realise choke plate had licked closed. Started great when coke and then bogged down as it warmed up. Second thoughts - vacuum in fuel tank? Is the breather open and working? Filter King is a strong possibility. It was first thing that got adjusted when I took car to John Sleath rolling road for tuning. Next is to make sure jets in carbs are adequate but doubt that would be intermittent. Good luck.
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peterc
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Re: intermittent misfire/fuel starvation

Post by peterc »

I have only had that issue once and it appeared to be a loose connection on the distributor amplifier.
Peter C
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