I forgot to tell you all that after 6 weeks of investigation the stumble has finally been solved.
The list at the bottom was where we were a while ago. Since then: * The magnetos and harness were bench tested and were OK. * A new carburettor was fitted and there was no change, so fortunately that was returned without cost. * Then the mags were removed again and stripped revealing one had an open circuit HT coil. That didn¹t solve it. * After that the rocker covers were removed and springs and valve lifts checked (all OK). * Then the exhausts were removed the right hand pipe had a cracked flange and a hole, but after repair no change. The whole affair was finding faults, raised hopes, then disappointment that the stumble persisted! My engineer had to start wearing a hat because his scalp was getting raw! Then, although it was serviceable and had bench tested just fine the harness was replaced. 95% of the stumble disappeared!!! Setting the idle jet correctly eliminated the rest. Not only has the stumble gone but now the engine runs smoother and it seems to fly a little faster too. Thank you everyone for your suggestions. It took 60 hours of labour but at least I¹ve had everything under the cowling except the engine itself thoroughly serviced! BR, Mike, airborne again! On 14/2/09 09:24, "Mike Willis" <[email protected]> wrote: > 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 > > [email protected] > www.ercoupe.co.uk > > Alon A2 Aircoupe > A-188 > G-HARY ________________ Alon A2 A-188 G-HARY www.ercoupe.co.uk
