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Rover V8 lumpy running, low fuel pressure?

Rover V8 lumpy running, low fuel pressure?

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Discussion

sweatyfox

Original Poster:

2 posts

2 months

Thursday 10th August
quotequote all
Hi all,

I’ve been having some running issues with my car with either fueling or ignition.

When started the other days it was lumpy and missing. Decided to go for a drive and it was still missing a few minutes later I had total loss of power and engine cut.

I tried to start it and nothing at all, didn’t even try to fire.

After about 20 minutes it fired up and I was able to get back home but still running lumpy.

Have since been out for another drive, again running lumpy and at one point was total power loss and then kicked back in with a jolt.

It seems to be running ok at tickover but haven’t been back out since.

The car setup is a Rover 3.5 V8, running Twin 1.75” SU carbs, low pressure Facet fuel pump. Has always run fine until this week.

I have tested the fuel pump and output pressure was 6psi.
The fuel regulator output pressure tested at 0psi. Nothing showed up on the gauge, but when you put the pipe into a bucket fuel flows pretty well, just no significant pressure.

Is this likely to cause problems?

Or should twin 1.75” SU carbs definitely have a positive fuel pressure of around 3psi?

Thanks in Advance,

Sweatyfox

stevieturbo

12,647 posts

169 months

Thursday 10th August
quotequote all
Fuel...air...spark.

Confirm all is well there, and on all cylinders and at correct times.

Compression test.

Steve_D

11,177 posts

180 months

Thursday 10th August
quotequote all
Next time it cuts out check to see if there is fuel in the carb.

Does your engine use an ignition amplifier? (normally on the side of the dizzy but may be on the bulkhead or on a bracket with the coil.
These can fail with a misfire then die completely when it gets hot. Normal reason is someone has fitted it without heat transfer paste on its mounting face so it overheats.

Steve

sweatyfox

Original Poster:

2 posts

2 months

Saturday 12th August
quotequote all
Thanks for your replies.

The car doesn’t have an ignition amplifier (its Installed in a kit car) so just down to the basics, dizzy, coil and ballast resistor.

Do you think that no measurable fuel pressure from the regulator could be causing the problem?

Do SU carbs work best under pressure?

Thanks.

Mignon

217 posts

11 months

Saturday 12th August
quotequote all
Pressure is simply the result of flow against a restriction. If there's no restriction then there's no pressure regardless of how high flow is. Carbs don't require any minimum pressure as long as they get enough flow, they simply can't cope with too much pressure which might hold the float chamber needle valves open. Maybe just try removing the pressure regulator and see what happens as this may be blocked somehow. The carbs should cope directly from a 6 psi Facet pump.
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stevieturbo

12,647 posts

169 months

Saturday 12th August
quotequote all
sweatyfox said:
Thanks for your replies.

The car doesn’t have an ignition amplifier (its Installed in a kit car) so just down to the basics, dizzy, coil and ballast resistor.

Do you think that no measurable fuel pressure from the regulator could be causing the problem?

Do SU carbs work best under pressure?

Thanks.
Cant comment on all SU's but any Metro turbo ones I used, the needle valve would rarely seat above 5psi or so anyway.

But you should have some measurable pressure in the line if the pump is to be capable of running the engine under load ( electric or mechanical pump ? )
Because most of the time it should be pumping against the almost closed needle valves.

And again...Fuel, air, spark, compression test.