Technical What causes the engine to stall rather than idle?

[smart51]

The last couple of times I've been out, the engine will sometimes stall when coming to a stop instead of idling. Otherwise it runs well. What can cause that?

 

[the hobbler]

The last couple of times I've been out, the engine will sometimes stall when coming to a stop instead of idling. Otherwise it runs well. What can cause that?

A number of things can cause your problem----incorrect idle mixture (or even dirt in the idle jet), incorrect timing (should be 10 deg BTDC at idle) or incorrect tappet settings. Another possible cause is the spacer between the carburettor and the cylinder-head---these are known to warp and allow air in, which will then affect the fuel/air mixture.

 

[smart51]

I tracked the problem down to a partly blocked idle circuit in the carb. Taking the carb off and blasting its ports with carb cleaner left the residue shown in the photo. It swirls around in the liquid like powder, but is so fine that it doesn't feel like powder to your fingers. It's not much more than a year since I completely refurbed the carb. This gunk has built up in a couple of thousand miles. The filter in the carb is clean, so this stuff goes straight through it. Is there a good way to stop it?

 

[the hobbler]

I tracked the problem down to a partly blocked idle circuit in the carb. Taking the carb off and blasting its ports with carb cleaner left the residue shown in the photo. It swirls around in the liquid like powder, but is so fine that it doesn't feel like powder to your fingers. It's not much more than a year since I completely refurbed the carb. This gunk has built up in a couple of thousand miles. The filter in the carb is clean, so this stuff goes straight through it. Is there a good way to stop it?

View attachment 474660

Have you checked that the filter on the tank-unit is not damaged? It is the largest filter in the system. Whatever is the problem, do NOT be tempted to fit a filter between the pump and the carb as it is a dangerous place to fit one

 

[smart51]

The tank filter looks sound if quite brown in colour. It looks like it is crimped in place. Is it a replaceable filter or does the whole sender get done at once?

 

[the hobbler]

The tank filter looks sound if quite brown in colour. It looks like it is crimped in place. Is it a replaceable filter or does the whole sender get done at once?

To the best of my knowledge, the filter is NOT renewable as an individual item--it comes as part of the tank-unit. Whilst I concede that different manufacturers will come up with different coloured filters, the filter on my tank-unit more of a 'yellow' colour. It might be that the fuel contamination is coming from the tank which may need cleaning out. Most "Radiator repair" businesses can also clean (and repair) fuel tanks, so it might be a worthwhile "over-the-winter" project to remove the fuel tank (not a difficult job) and get it thoroughly cleaned internally