back fires only when motor is cold (within 1st 2 mins of startup tops). engine will backfire when the throttle is opened, throttle also seems to cut the engine out when opened and only resumes reving when you take your foot off, so to keep it running quick blips are needed. most backfiring occurs under the initiation of load. i have a 32/36 weber and an electronic dizzy (dont know what from), new leads, and plugs. timing is a little out but need to adjust dizzy to get right. and this arvo it backfired big and a puff of electrical smoke came out from under the dash, definetily electrical smoke, i checked the engine bay and was mint, but all electricals still work, lights, dash, radio, etc etc.
can anyone help pleeeeeeeeeeeeeeeeeeeeease
tahnks

sounds like u got a intermitent electrical problem, most likely cutting the 12volt supply to the coil on and off.. track down where that smoke came from its a good chance that wat ever is arcing/melting is wats wrong... probly around the igntion switch and fuse area.. or on another note your weber could be supplying too much fuel try leaner jets

One question, does it only backfire when cold, as that seems like the case from your message. If so, then there's not much wrong, most engines running carbs will backfire some when cold. From what I can remeber, these A series engines are prone to backfiring when cold...

Otherwise, there might be some dirt stuck in the carb somewhere, so that it only affects the cold start circuits/veins of the carb. Give it a nice clean-up, and it should be better...

It's backfiring when cold because the mixture is too lean & it's lean when it's cold because the manifold & other parts have not warmed up enough to convert the liquid droplets of fuel from the carb into a gas.

It's the gas that burns remember, not the liquid which essentially is passing through the cylinders unscathed.

The engine is cutting out when you stab the throttle because the accelerator pump isn't working, which is not uncommon.
When you stab the throttle you give the engine a gutfull of air, particularly through this bigger bore carb.

Unfortunately, the engine doesn't run on air, so it stops running, but when you close the throttle you re-establish a better airflow through the carb, it draws fuel from the discharge nozzle which makes its way to the cylinders & it runs again.
Is the choke function fully operational & correctly adjusted? My money say it isn't.

Sounds to me like you would benefit from the purchase of a carb overhaul kit & having it installed by someone who knows what he is doing. This should be followed up by a proper carb tune & rejetting as required as it seems to me that someone has fitted the first tired old carb that came along & expected it to work.

It won't

If you get smoke from the electrics, it won't be related to the carb in any way. [you do have a proper flame arresting air filter on it, don't you?] Electrical wiring smoke has a nasty acrid smell to it that takes your breath away, so you'll know it when you smell it.

only when cold, but, more violently than normal, you literally cant go anywhere. but will clean the carby thoroughly and go through the wiring to see any faults or burns.
thankyou for your help

how do you get to be so smart? are you from nasa or something? i'm upgrading to twin webers so old one will be out the door, but will look into it. cheers

Quote:Don't know about this being smart business, but paying attention to my apprentice masters & other tradesmen when I was first an apprentice mechanic didn't hurt & using a basic understanding of simple physics, a bit of experience, & a logical mind goes a long way.

Of course a little of the old Irish 'Blarney' helps to make it all sound smarter.

Oh yeah, I'm guessing that you also have extractors. [Just a guess]
If so, then the inlet manifold has no hot spot & the manifold does not warm up properly, which just makes the problem worse.

i would check the accelerator pump,its backfiring because it is to lean, u can try richening up the idle screw a little and get your timming right it all helps.
tommo

I keep backfiring too, not so much when I am cold, mainly after chilli burgers or pickled onions. I should probably retard my assigition, might stop those brown marks on my jocks too!