Fast idle and cutting out

[kingsea99]

Evening

I took the seven out on Friday, the hottest day of the year and had a couple of what i think must be related issues.  Engine is a 1.6 crossflow, electric fuel pump and filter king regulator installed adjacent to the pedal box.

Car started and ran fine with idle at about 800-900 rpm as normal.  On startup i could hear the electric fuel pump clicking and then slowing as it came up to pressure.  Normally this is the only time I hear the pump.

During the drive with the car up to temp I intermittently started to hear the fuel pump and noticed that at idle the revs had increased to 1200 at idle.  Headed for home and pump was audible more and more and the car started to misfire. 

With the bonnet off all looked ok and I could see some fuel in the filter king, but the car wouldnt start and the pump continued to click as if trying to come up to pressure.

After 15 mins I tried again, the pump quietened, car started and I got home.

I have checked for air leaks and fuel leaks and there are none, tank has fuel, put a gauge on the filter king and get a steady 3psi, car starts and now idles back at 800rpm so i am a bit stuck.

Could it be that the filter king got too hot?  Not sure how that would account for the fast idle though or indeed the lack of fuel pressure

Sean

[elie boone]

Maybe a combo of things, like a sticky throttle cable but the bowl of the filter king should be full so it could also be a problem of venting the tank ?

[kingsea99]

Checked the throttle cable and didnt appear to be sticking, and also removed filler cap to see if it was a venting issue - will keep working through the options

[Roger King]

It's impossible to answer this with any certainty, but it sounds like a fuel supply problem; the rise in revs at idle may mean that your mixture screws are set too rich and the fuel supply problem is actually correcting this. Causes could be - faulty pump or wiring, fuel line blockage, non venting filler cap, stuck float or needle valve, dirty filter in the carburettor, foreign matter in the fuel tank - and I'm sure there are many others.

Years ago we had a 7 race car that would test out perfectly each time on the rolling road or even on the real road, but at every race it would misfire after a couple of laps. It would always run perfectly a few minutes later. We tried everything we could think of and eventually changed the tank which solved it. It turned out to be some rubber-like debris that was larger than the bore of the fuel pick up, but would every now and then get sucked up and almost completely block it; once the fuel pump was turned off it would drop back to the bottom of the tank and the problem went away.

[kingsea99]

It is very odd.  The fuel pump sounds like it is unable to draw fuel from the tank (the pump is adjacent) so something within the tank may be a possibility.  The car has a caterham filler (the flat aero type) - are these vented?  The fact I still had the issue with the filler cap removed may rule out venting as the problem.

 

[elie boone]

I would start and disconnect the fuel pump, and make sure the suction line is free without blockage, you should be able to blow the line trough by mouth. if that is ok i would test your fuel pump if it delivers what it should and if that is ok test the pressure fuel line  there is no blockage by disconnecting the carb and see how much fuel is coming thru.

[Bricol]

To second the blocked fuel pipe idea - my Dolomite Sprint used to do the same - fast idle and cut out, but restart after a while.   the restart seemed to coincide with hitting the carbs with anything to hand - I remember a traffic cone being used onces, much to the amusement of some school boys passing by . . . turned out to be flakes of rust in the tank - every little while, a larger flake would block the end of the pick up pipe . . . falling off after a while when the pressure dropped.

[kingsea99]

I will strip off the hoses and give them a check and run the pump into a container to ensure its ok.  May also order up a new facet  filter (even though the current one is only 6 months old)