Fuel starvation help!
Discussion
I am running a 1380 ford crossflow in a trackday seven. All the usual p+p head, l+b, hot cam etc using a webber 32dgv downdraft. At trackdays I am getting bad fuel starvation coming out of right hand corners.
I am about to fit a facet fuel pump and have already raised the float heights.
Any ideas chaps?
Studog
I am about to fit a facet fuel pump and have already raised the float heights.
Any ideas chaps?
Studog
Hmmmm.
If it's only on right handers it could be the petrol tank fuel pick-up point. Where is it on your car? If it's on the right then as you turn right (as it's a track day car I suspect you're going for it a bit) then the fuel will be slopping to the left of the tank.
Maybe worth changing the tank for one with internal baffles and/or a central pick up.
An easy test is to try the car with a full tank. That way there is no room for fuel to clear the pick up.
I may be way off the mark here but it certainly sounds the most likely problem based on what you've said so far. Let me know by email (I'm not regularly on this forum)
If it's only on right handers it could be the petrol tank fuel pick-up point. Where is it on your car? If it's on the right then as you turn right (as it's a track day car I suspect you're going for it a bit) then the fuel will be slopping to the left of the tank.
Maybe worth changing the tank for one with internal baffles and/or a central pick up.
An easy test is to try the car with a full tank. That way there is no room for fuel to clear the pick up.
I may be way off the mark here but it certainly sounds the most likely problem based on what you've said so far. Let me know by email (I'm not regularly on this forum)
Cheers for the comments guys. Unfortunately not quite that easy as the tank is foam filled and has central pickup.
Have now fitted high pressure pump and raised the float level all to no avail. The problem only occurs when I get to full throttle, in a staight line it is fine. Pain eh, any ideas?
Have now fitted high pressure pump and raised the float level all to no avail. The problem only occurs when I get to full throttle, in a staight line it is fine. Pain eh, any ideas?
Hmmm
Only on exiting right handers and only at full throttle !! Certainly sounds like fuel starvation.
A few things that might be worth considering...
Is there anything that could block the tank vent under these conditions?
Is there anything under the bonnet that could block airflow (loose sound deadening material etc)
Is there a fault with the carb? Can it be turned 180 degrees on the manifold? (I'm not familiar with this set up). This would prove the carb was OK as the fault would likely appear on left handers.
Could it be electrical? Maybe something's moving under cornering Gs and the extra engine movement due to full throttle is pulling at the LT/HT leads ??
Not an easy one to find unfortunately. I would be tempted to put float heights back to standard and try one thing at a time if I were you.
Good luck and let me know how it goes.
TTFN
Plipton
Only on exiting right handers and only at full throttle !! Certainly sounds like fuel starvation.
A few things that might be worth considering...
Is there anything that could block the tank vent under these conditions?
Is there anything under the bonnet that could block airflow (loose sound deadening material etc)
Is there a fault with the carb? Can it be turned 180 degrees on the manifold? (I'm not familiar with this set up). This would prove the carb was OK as the fault would likely appear on left handers.
Could it be electrical? Maybe something's moving under cornering Gs and the extra engine movement due to full throttle is pulling at the LT/HT leads ??
Not an easy one to find unfortunately. I would be tempted to put float heights back to standard and try one thing at a time if I were you.
Good luck and let me know how it goes.
TTFN
Plipton
I had the same problem on my Rover V8-powered Westfield which has a fuel cell with a pickup in the right rear.
I know of two solutions, and have implemented the easier but less robust. That solution trys to prevent air from entering the fuel line. I mounted two one-way check valves on opposite sides of an empty food can sitting in the foam on the bottom of the fuel cell. The diameter of the can is just less than the fill port of the fuel cell. The valves were fixed to the can inside the fuel cell -- ship in a bottle style. The fuel pickup line draws from inside the can. I just got back from the track and it worked fine.
The more robust approach uses two fuel pumps. The first pumps from the fuel tank into the bottom of a "surge pot." A connection at the top of the pot lets fuel, and occasionally air, return to the fuel tank. A third connection, 1/4 of the way up the side of the pot (to avoid picking up crud), feeds a second pump which supplys the carb with fuel but never air.
I hope this is understandable and useful.
I know of two solutions, and have implemented the easier but less robust. That solution trys to prevent air from entering the fuel line. I mounted two one-way check valves on opposite sides of an empty food can sitting in the foam on the bottom of the fuel cell. The diameter of the can is just less than the fill port of the fuel cell. The valves were fixed to the can inside the fuel cell -- ship in a bottle style. The fuel pickup line draws from inside the can. I just got back from the track and it worked fine.
The more robust approach uses two fuel pumps. The first pumps from the fuel tank into the bottom of a "surge pot." A connection at the top of the pot lets fuel, and occasionally air, return to the fuel tank. A third connection, 1/4 of the way up the side of the pot (to avoid picking up crud), feeds a second pump which supplys the carb with fuel but never air.
I hope this is understandable and useful.
studog said: Cheers for the comments guys. Unfortunately not quite that easy as the tank is foam filled and has central pickup.
Have now fitted high pressure pump and raised the float level all to no avail. The problem only occurs when I get to full throttle, in a staight line it is fine. Pain eh, any ideas?
Not had any experience of those carbs, but I know some types don't like running at an angle. For example I've seen Hollys with the float jammed open under acceleration pumping neat fuel up through the air filter and over the windscreen! SUs are specially designed to be tolerant of high lateral G. Would it be possible to test the carbs at different angles and check the float is working properly? If its sensitive in one direction, you may find that mounting the carb at a slight angle is just enough to make the difference.
Hope this helps,
Peter Humphries (and a green V8S)
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