Hi All

I have a funny backfire on the aks400 - under load occasionally it stutters then backfires through the carb - anyone know whats the likely cause...air leak from the carb to the manifold?....intake gaskets into the cylinders?...poor timing?

Check for mechanical problems- ie gaskets, missing manifold nuts cracked insulator etc
Ignition timing
Too lean -blocked jets, float levels, fuel pump or pipe issues

and what ignition? possible condensor failure.

Hi Sean

Its got 123 and I've done a quite a few miles and not noticed any pinking so would err away from lean mixture but will go through your list - cheers!

?
Pinking can occur without the mixture being weak, as evidenced by the 'restored' 2CV I've been sorting out for the best part of this week.
Hardly surprising that it had melted a plug, with over 50* total ignition advance.
Valve clearances of 0.01 to 0.05mm didn't help with the way it ran either.

While fitting a new section of rubber hose to the tank (just one of the tasks which had been ignored during the rebuild), I found that the nylon fuel pipe had been kinked so much that it would have been restricting fuel supply under WOT conditions.

Anyway, as Sean has suggested, I'd agree that insufficient fuel supply under conditions of high demand could explain the intermittent nature of the problem with your van.

Ken
( Fed up with these shiny 'restored' cars, where 99% of the input has been on the bodywork or the interior, with as little time as possible spent on the mechanical aspects.
Although that work often has to be done again, so it might have been better left as it was... )

Re the carb insulator block which can crack, you can spray WD 40 round it with the engine running if it improves or you get white smoke from the exhaust ( takes quite a good squirt ) then there is a leak, also check how tight the carb mounting nuts are, theses can work loose or may have been left a little slack by someone as they are awkward to get at with out the cranked tool made for the job.

funny you say that, my jets needed a clear out on my way home at quarter to one this morning.. then i went out to get some strings for my banjo and it would bang and pop from the exhause when de-throttling..?

Neil
If its the timing its more likley to be retarded than advanced so perhaps that's why there is no pinking.

Rebel
l are you on a proper exhaust or some sort of custom job? Yours could be too rich , too advanced or leaky manifold. But a bit of crackle on the over run on straight through pipes is usually what you aim for.

Chris has the ecas 2>1 on his van, same as what i have on mine and i notice a a little pop on the let off from around 3k down to 2k also! not from higher up the revs though!

Looks like the carb was a little loose on the manifold - tightened it up and it hasnt banged since.......

joe is right, 2>1 normal swan and torpedo, timing has been a right issue, but its bang in. went back to points, back onto 123, new carb on standard jets this time, even replaced a dodgy head, i have a small leak at the swanneck but ive not had an issue for hthe last couple months til the other day