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Ideas please

After much messing my sprint engined car runs like a dream (mostly)

However immediately after a bend or a roundabout a get a few seconds spluttering, presumably fuel starvation, back off the throttle and it clears and all back to normal, it revs easily towards the red line and off we go again.

I have a clean filter and float chambers so it’s not liking like grot in the system.

Any ideas??

Thanks in advance

S

Daft question.

Does this occur equally when exiting a left or right hand bend? Is the hesitation immediate or a few seconds afterwards?

What pump are you using?
Check wiring for bad connections or broken wires
And check the run of all fuel hoses.

Hi, not sure if the sprint engine has the same arrangement as the 8 valve but the standard TR7 mechanical fuel pump has an integral mesh filter located between the upper and lower part of the pump. This catches rust/sediment from the fuel tank which can build up to quite a degree if the tank is old. From memory there is a single screw on the top of the pump body that allows you to remove the top and hence take out the filter and clean it. Worth a look as the picture shows what I found on one of my cars.
Rich.

Sorry I should have mentioned I’m using an electric pump mounted near the outlet of the tank.

There seems to be plenty of pressure.

This miss is exiting the corner to be honest I’m not sure if it’s left or eight, I will investigate further.

I am going to swap the fuel filter as the ones I bought seem small compared with the usual but don’t seem restrictive. Plus once the hesitation is over it revs like a dream and feels pretty quick

Ok quick test drive later, and carbs tweaked a little, I can confirm it’s turning both ways, I also have 7/8ths of a tank of fuel on board

I can’t see any lose or chaffed wiring...

Does your electric pump have an integral filter? Tank rust can be a very fine dense powder and can move around with the cornering and acceleration forces blocking the flow.

I had this issue with my V8. I had no idea there was an integral filter to protect the pump until I opened it up.

It could be flooding, rather than fuel starvation. You say you have "plenty" of fuel pressure, but is it plenty or too much? SUs do not like much over 2 PSI fuel pressure, & the same applies to Weber & Solex carbs.

I once drove a Brabham Cosworth F2 with DCOE Webers. The owners mechanics, having melted a hole in a piston in the past insisted on running 3 PSI fuel pressure. After any moderate time on the over run, or braking it gave time for the thing to flood, & it took over a second of spluttering to clear.

Do you ever get a smell of petrol after such an occurrence?

Hasbeen

Carburettor Fuel bowl float levels correctly adjusted? Needle valves free of wear ridges. No stiction in the mechanisms? It's been a while since I've had to maintain SU carbs.

While the problems you mention are usual, excess fuel pressure, very common with generic after market electric pumps will cause flooding.

What is your fuel pressure? If over 2.2 PSI it will cause some minor problems with any SU no matter how good it's condition.

If over 3 PSI the problems will be bad. If you have overflow from the float bowl to the charcoal canister, check it for petrol.

Hasbeen

The flooding is an interesting shout, I have a flow regulator somewhere, I’ll plumb it in along with clean filters and see what happens

Thanks for all your input, much appreciated. I’ll report back ASAP

What electric pump are you using? There are all sorts out there that give too high a pressure for SU carbs.

I had trouble with pressure regulators on the 7. I don't know why, unless it is that they don't like small fuel flows. We used them totally successfully on Cosworth Ford, & Repco Brabham F1 & F2 engines, but at about 8 miles to the gallon they were using a lot of fuel.

I tried a couple on the 7 with a new mechanical that was over pressure, & causing flooding. They would occasionally simply cut the fuel supply completely for no reason I could find.

I switched to a New Zealand sourced electric pump, [similar to the SU pump], rated at 1.5 to 2.5 PSI. It has so far been successful, about 4 years now. It is installed low down in the engine bay, which probably keeps it's pressure a bit below it's peak capability.

The 4.6L TR8 has a common rail injection system, controlled by a Haltech computer as used in Oz V8 super cars. As I have been too slack to build a serge bottle system for it, it suffers from starvation when turning right with the fuel level below half. I have decided to try the Holly carb fuel mat system, claimed to supply fuel as long as there is a cup or two in the tank.

I'll report this when I have done it.

Hasbeen

So.... I got waylaid by a footwell puddle!

I have fitted a pressure regulator, cleaned the fuel lines and filters from back to front with no joy.

It’s still hesitating badly out of bends and is on more than a third throttle. It runs great and will rev well on light throttle openings. I checked the servo vacuum and that seems well.

I bought a colourtune to see if I could narrow it down a little.

Cylinder 1 I get a white flame which I can’t make blue however I richen the mix.

2 is yellowish suggesting a bit rich, both are fed by the front carb, I assume.

3 and 4 are nice and deep blue

I took out the plugs and 2 is sooty the rest look reasonable, I swapped it out for a new plug and went for a run and it’s sooty again.

All the gaps are good

I checked to dizzy cap and was surprised to find it and the body look like the attached!

What’s going on, any thoughts?

Think you are on the SU carbs, what oil is in the dashpots? If the pistons are lifting too quickly that can cause hesitation.