Dear Harry, Kevin, Robert and Rich, Thanks for your replies and suggestions.
I should add that: * Idle mixture setting was the first thing my engineer tried * The float is fine and not leaking, and the fuel level inside the chamber is correct * The carb. has now effectively been rebuilt (twice!) * All of the inlet tubes were checked for leaks when the carb. was off and were fine * I can¹t remember the exact idle rpm but I think it is around 600 and certainly not much higher Sorry, my engineer has been through everything obvious and not so obvious and I have been wondering if there was some Ercoupe peculiarity that might give us a clue. He has a long knowledge of Ercoupes and is a very competent engineer, but also a very frustrated one at the moment!!! Me, I¹m just spending money much faster than if I was flying, and that ain¹t cheap over here in the UK! Best regards, Mike On 14/2/09 15:49, "Harry L. Francis" <[email protected]> wrote: > HI Mike, > > Intersting, we thinnk of a stumble on STromberg Carbs often due to too lean > an idle misture....or partially stopped up idle circuit........ BUT in Marvel > carbs, this dhouldnever happen due to the use of an acceleration > pump.....always RICH when going from idle higher RPMs... Oerhaps the idle > circuit is set too rich, due to idle speed set at 1000.. Idle should be ~ > 650-700 rpm...and idle mic\xture set at those speeds with warm engine. If the > idle speed is set too high RPMs, then the main metering begins to > work......Now adjusting the idle mixture at the higher engine speeds, may up > set the change-over mixture, causing the stumble. > > Another potential is excess fuel from the accelerater pump, causing the rich > mixture stumble. > > Fly Safe - Have Fun > > Harry Francis > N93530 > > Good Luck > > --- On Sat, 2/14/09, Mike Willis <[email protected]> wrote: >> From: Mike Willis <[email protected]> >> Subject: [ercoupe-tech] Throttle stumble >> To: "[email protected]" <[email protected]> >> Date: Saturday, February 14, 2009, 4:24 AM >> >> Hi guys, >> >> As previously mentioned I¹ve been experiencing a throttle stumble that seems >> to be getting progressively worse. This is on my Alon A2 with a C90 and MA3 >> carburettor. 6 months ago there was nothing apparently wrong. >> >> The main time it is exhibited is at take-off, when advancing the throttle, >> albeit slowly to avoid a rich cut, still results in a stumble. It ticks over >> at 1,000 no problem, and once above 1,500 it runs smoothly. If you advance >> it very slowly it is OK, with carb heat on it doesn¹t happen either. It is >> exactly the same running on each of the magnetos. >> >> It therefore appears to be a carb. problem with maybe a fault in the >> accelerator pump or a leaky manifold gasket. >> >> A strip down revealed >> * a little bit of dirt in the float chamber >> * a leaky inlet manifold gasket on no. 3 cylinder >> * a very small slit in the accelerator pump washer >> * a corroded main jet packing washer. >> >> In addition the >> * needle valve has been replaced >> * the primer system checked >> * the fuel flow measured from the pump (10+ USG/hour) >> * the float level checked >> * the jet size is correct >> * ignition timing is correct >> * new set of plugs fitted >> * magneto earthing checked >> * cylinder compressions seem fine >> >> And guess what, no change! It is exactly the same. >> >> If anything the engine seems to run rich and lumpy and fuel consumption is a >> little on the high side. >> >> The next plan is to get all the cowlings off again and start checking the >> mags and harness. >> >> Anything else we have missed? >> >> Best regards, >> >> Mike >> >> m...@ercoupe. co.uk >> www.ercoupe. co.uk >> >> Alon A2 Aircoupe >> A-188 >> G-HARY [email protected] www.ercoupe.co.uk Alon A2 Aircoupe A-188 G-HARY --
