fuel problem nearly solved

[Mr 5]

ok so my running lean problem may nearly sorted....

ok,put a post up ages ago,saying the car runs lean after 10 seconds'ish on boost,like the carbs emptying too fast. changed and cleaned everything on fuel side....still no use.

now,iv checked pump voltage,constant 14volts,checked pressure,4psi idle, 4psi above boost pressure on boost....but still leaning out after 10seconds (car holds back and afr's rise from 12.1 to 14-15-16)

so guessing its a carb thing....but what do i need to do? stripped and cleaned it twice now,do i but a "group a" or a recon standard one ?

help!

[Markey Mark (BD)]

What size needle valve do you have in the carb mate?

[Brigsy]

What rpm does the afr go lean at, the ten seconds on boost means nothing to me

Grp a/another carb will not solve the problem, fix the one thats already fitted.

Sounds like the carb is emptying the bowl imo. If you are using a 2mm needle jet you will need to look at alternatives to fill the bowl, i.e from the bottom or upping the fuel pressure a psi or three.

Ive got this problem with the van, Ill be attempting to sort this soon.

[Rob@Backyardracing]

Are this thread https://www.rtoc.org/boards/showthread.php?t=5347

have you still not tried that needle as said

[Matt Cole]

What rpm does the afr go lean at, the ten seconds on boost means nothing to me

Grp a/another carb will not solve the problem, fix the one thats already fitted.

Sounds like the carb is emptying the bowl imo. If you are using a 2mm needle jet you will need to look at alternatives to fill the bowl, i.e from the bottom or upping the fuel pressure a psi or three.

Ive got this problem with the van, Ill be attempting to sort this soon.

Briggsy, throwing more pressure won't fill the bowl if the flow rate of the pump is in question. Plus it will just flood it when you when you dont want the extra fuel.

To contradict myself, if the pressure is at question or below par then it may work, but i would be looking at a better pump.

[Matt Cole]

Further to that i remember i was going to do a calculation on this, which i'll look into.

[Scoff]

I might be mis-reading matt, but more fuel pressure at the entry to the carb will indeed increase flow across the needle regardless of the pump. If the pump is not upto the job then you will not be able to increase the fuel pressure in the 1st place.

[markey b]

i have no knowlege in this subject, but i recall biggs had a similar prob with my car (when he had it) and when i got it it had an FSE fuel reg in the glovebox, got it fitted and setup and fuelling has been fine since

[Matt Cole]

I might be mis-reading matt, but more fuel pressure at the entry to the carb will indeed increase flow across the needle regardless of the pump. If the pump is not upto the job then you will not be able to increase the fuel pressure in the 1st place.

Aye Scoff, to clarify what i meant, if the pump flow rate is at question (the required fuel consumption l/s) or the fuel pressure isnt adequate then upping the pressure at the needed point (high rpm) may not make a difference.

[Scoff]

Aye Scoff, to clarify what i meant, if the pump flow rate is at question (the required fuel consumption l/s) or the fuel pressure isnt adequate then upping the pressure at the needed point (high rpm) may not make a difference.

Well, if you are able to increase the pressure then the pump must be working OK. In other words, if you can increase the pressure and measure an actual increase in pressure then you need not worry about the pump's flow ability. If it couldn't flow it then the pressure wouldn't have gone up in the 1st place

[Mr 5]

ok.... i have fitted a larger needle,2mm,which helped but didnt cure the problem.

brigsy,it doesnt happen at a certain rpm,only after 10seconds foot to the boards in any gear,in 5th at 50 mph the rpm is 2.5kish,by the time its got to 4k it leans out,but if i go from a standing start hard its the top end of 3rd it leans out,its always 10seconds..

i know its emptying the bowl since when i fitted the larger needle the time taken for it to run lean increased so larger needles filling the bowl faster.

dont want to have to up fuel pressure realy as i havent fitted or done anything to the car in 9months now so it has no need for more fuel? got RR'd last year in the same spec as it is now with no problems, yet now its going lean after 10seconds @ WOT?

the way i see it upping the pressure will only be hiding a problem,am i right?

also i bought a new pump from here,plus new fuel lines,filter,regulator,relay and needle shortly after all this started so all i can assume is the issue is the carb?

[Andrew Cooke]

have you removed the filter from the carb inlet?

[Mr 5]

have you removed the filter from the carb inlet?

yup yup

[Scoff]

Have you measured the pressure in the fuel line going to the carb ? You need to measure that and measure carb-top boost (not manifold pressure). There should be 4psi more fuel than carb top boost.

[Mr 5]

Have you measured the pressure in the fuel line going to the carb ? You need to measure that and measure carb-top boost (not manifold pressure). There should be 4psi more fuel than carb top boost.

yup yup, 4psi idle,+4psi on boost,carb top boost 18psi,fuel pressure 22psi constant

[Scoff]

yup yup, 4psi idle,+4psi on boost,carb top boost 18psi,fuel pressure 22psi constant

wierd, then I assume there must be something funny happening with the float or needle operation . maybe you could try a whole different carb-top section.

[Mr 5]

bought a cheap 2nd hand carb,cleaned it up and did just that,exact same problem still tho,am baffled!

[Mr 5]

ok....totally baffled....its fixed?!?!

last thing i did was take the pump out the tank to check the fuel pick up,which was clean,refited it,didnt use the car till yesterday and the problems dissapeared?

took it for a proper blast yesterday and no problem atall?

how? lol

[Brigsy]

Id be checking that wideband gauge of yours mate, might be reading wrong.

[Ashy]

ok....totally baffled....its fixed?!?!

last thing i did was take the pump out the tank to check the fuel pick up,which was clean,refited it,didnt use the car till yesterday and the problems dissapeared?

took it for a proper blast yesterday and no problem atall?

how? lol

More to the point, how did your pump get into the tank