Suddenly leans off

[Nayls]

Just had my 5 on the rollers but had to abort two runs 1st run was aborted due to the top rad hose popping off,
2nd was aborted due to the car running lean all of a sudden

the boost is only set at 17psi (manifold),the boost had reached it's limit & the afr's were good (about 11.7) but then all of a sudden the afr's rise up to nearly 14.

cant be the bowl emptying as it's not making a lot of power.

carb spec is:
main 120
a/c .9
1st std
2nd 1.4
vanturi 25mm

any ideas what to check 1st?

was thinking of trying a slightly bigger a/c?

[James5]

What gear and rpm was it @?

[UNICRONICUS]

Wouldn't a bigger air corrector lean it out more though? Also don't overlook the possibly that your AFR sensor could be faulty...

[Nayls]

What gear and rpm was it @?

4th
just reaching 5000rpm

[Nayls]

Wouldn't a bigger air corrector lean it out more though? Also don't overlook the possibly that your AFR sensor could be faulty...

doh! sorry i meant main!

[UNICRONICUS]

Ah, nice. Flat out in 4th at those revs could mean that the bowl is emptying due to a few things:

1. FPR isn't doing it's job properly
2. Fuel pump can't supply enough fuel quickly enough
3. The needle valve isn't opening properly or perhaps the hole needs to be drilled out slightly larger
4. The main jet could go up a tad, perhaps to a 130 main?

To name but a few

[Mart]

cant be the bowl emptying as it's not making a lot of power

I'd stick a pressure gauge on the carb fuel inlet & see what's what @ w.o.t before rubbishing off that idea...

[Nayls]

I'd stick a pressure gauge on the carb fuel inlet & see what's what @ w.o.t before rubbishing off that idea...

i want to do that,but you cant have the gauge in the car for safety reasons,or is such a gauge available now?

[James5]

Could be worth trying a bigger needle jet.

Only other thing is to possibly enlarge the main jet to a 125.
As your 2nd stage is already enlarged to 1.4
FPR?

[Nayls]

what i dont understand is why it goes so suddenly? when it does it it's not getting any extra boost,it fuels the 17psi for a bit but leans as the revs rise.

[Nayls]

Could be worth trying a bigger needle jet.

Only other thing is to possibly enlarge the main jet to a 125.
As your 2nd stage is already enlarged to 1.4
FPR?

did you have one of them mate? needle?

[Mart]

i want to do that,but you cant have the gauge in the car for safety reasons,or is such a gauge available now?

You drive a gtt - There is no such word as safety

I used to use a normal boost gauge.

J.D

[Nayls]

You drive a gtt - There is no such word as safety

I used to use a normal boost gauge.

J.D

in the car? or taped to the window?

[Mart]

In the car. You think I'm crazy!?

[TommyB]

fuel pump, i had this trouble.

[Nayls]

In the car. You think I'm crazy!?

errrrr.......... just a little!

[Mart]

Fwiw, imho, unless you're running crazy amount of advance and/or high comp', that's a bit too rich for 17psi map anyway. Should be able to lean off another half a point easily there without any det' being present.

[Nayls]

Fwiw, imho, unless you're running crazy amount of advance and/or high comp', that's a bit too rich for 17psi map anyway. Should be able to lean off another half a point easily there without any det' being present.

Fook that!! i'l turn the boost up instead!

[Mart]

errrrr.......... just a little!

If you're that worried, see if you can borrow a Spa gauge or the such like then, whereby the sensor stays in the engine bay.

Any pressure gauge, whether it be for air/boost, oil, water, fuel, should be a sealed unit, and at the end of the day 17psi of pressure is 17psi of pressure regardless if it's air or liquid.

[Mart]

Fook that!! i'l turn the boost up instead!

Not if the float chamber's already emptying

[Dave Reed]

i want to do that,but you cant have the gauge in the car for safety reasons,or is such a gauge available now?

If you don't want to do the same as Mart , then SPA do a electronic fuel pressure gauge, it isn't cheap tho.....

[Dave Reed]

If you're that worried, see if you can borrow a Spa gauge or the such like then, whereby the sensor stays in the engine bay.

Any pressure gauge, whether it be for air/boost, oil, water, fuel, should be a sealed unit, and at the end of the day 17psi of pressure is 17psi of pressure regardless if it's air or liquid.

aaaaa you beat me to it......

[Nayls]

If you're that worried, see if you can borrow a Spa gauge or the such like then, whereby the sensor stays in the engine bay.

Any pressure gauge, whether it be for air/boost, oil, water, fuel, should be a sealed unit, and at the end of the day 17psi of pressure is 17psi of pressure regardless if it's air or liquid.

do they 'spa gauge' have a memory function then? im not on the rr now so would'nt be able to watch it.

[Mart]

Yep, you can recall max/min limits, but you'd only need to glance at the gauge real-time to register the fuel pressure you're getting at w.o.t

Seems an expensive outlay to me when an analogue gauge will equally do the trick.

[Nayls]

Yep, you can recall max/min limits, but you'd only need to glance at the gauge real-time to register the fuel pressure you're getting at w.o.t

Seems an expensive outlay to me when an analogue gauge will equally do the trick.

very true!

might aswell get a mate to sit in the passenger side & hold the gauge out the window & check it,just to rule it out.

would be nice to know the fuel pressure all the time though.

[Andrew Cooke]

would be nice to know the fuel pressure all the time though.

weirdo

[Nayls]

weirdo

why!?

[Rob@Backyardracing]

In the car. You think I'm crazy!?

Blah, tie wap to wiper arm and go for blast....take fuse out on wipers tho just incase you switch them on.... what i do anyway

[Adey aka Ewok]

would be nice to know the fuel pressure all the time though.

its easy, if its running correct ure fuel pressure raises as a constant, and its always 2.5-3psi more than ure boost pressure, 17psi carb top should be 20psi of fuel

[Rob@Backyardracing]

its easy, if its running correct ure fuel pressure raises as a constant, and its always 2.5-3psi more than ure boost pressure, 17psi carb top should be 20psi of fuel

2.5-3 is a bit low.. normally around 4ish.

[Adey aka Ewok]

3 diff cars ive checked have been this, all the same guage tho

[Ross99]

gary why do i think that tommorrow i'll be sitting in your car holding a gauge out the window!

why out the window i'm lost or is it best i dont know seems i'm holding it?

[James5]

did you have one of them mate? needle?

Got a 1.9 that seals.

The others are bigger than 2.0 and not sure if they seal properly. If you want the 1.9 pm your address and I will stick in the post matey

[Nayls]

its easy, if its running correct ure fuel pressure raises as a constant, and its always 2.5-3psi more than ure boost pressure, 17psi carb top should be 20psi of fuel

im well aware of what it should be!

im just saying if it was safe to have one in the car it would be nice,i could then rule it out straight away.

[Nayls]

gary why do i think that tommorrow i'll be sitting in your car holding a gauge out the window!

why out the window i'm lost or is it best i dont know seems i'm holding it?

course it will be you! you're my partner in crime!!

you can hold it in front of you if you like? if the hose pop's off & blows fuel in ya face though,dont blame me!

[Ross99]

lol thought they'd be a catch bodge and bodge back in business again then i take it.