Been helping a friend to get his A running right but its stumped me. A few other people have tried but no-one can get it right. Its a 28 model A with a 32 carb and dizzy, stainless steel copies of the origional manifolds, free flowing zorst and a thomas head. It idles ok but wont pull or rev up properly. If you snap the throttle open it hesitates, splutters a little then eventually revs up. If you snap the throttle again before the engines settled back into idle it revs quite well. We've tried everything, all the usual timing/ignition checks, tweekign the carb, i even stripped the carb to check for dirt. Nothing seems to help, unless you run it on choke, then its fine. If on choke though you get the tell tale black puff from the zorst when you snap it open. Ive not driven it so not sure if it also pulls properly under load when on choke. The whole chokle thing suggests to me its too lean, but no amount of adjusting will get it right when off choke. It also sounds a bit harsh and poppy when at high revs, if we get it running a bit better it pops through the zorst. Any ideas? We've tried timing points carb settings (i assume that only effects idel though?) leads its got a new coil and condensor. Thanks.
Sounds like a lean mixture; if choking it straigtens it out. I don't know those carbs; but the settings you're talking about probably only affect the idle. Try to find the way the mixture is changed. Jets?
my 29 model A coupe all stock/ when i bought it the owner said the same thing was going on with this car and he was moving and wsnt going to try any more fixes, i spent alot of time checking things and after i took out the fuel line for the 3 rd time , i realized the line was going all the way into the petcock, the farrel on the gas line was installed way to far down on the line causing the line to dead end against the inside of the gas petcock on the firewall causing an extremely low fuel flow, only way it would run fine was on choke , the engine could draw enough fuel then, i would say at least rule that out sometimes it turns out to be the simplest thing, especially if it is runnig the other carb and he had to have made up a new fuel line there is no internall stop on the old petcocks, so it is possible to close off the fuel path with the tubing itself
Check the intake manifold gaskets. A leak here will cause a sympton that sounds like it is running lean. Sometimes the intake/exhaust manifolds (which bolt together) are not flat where they mount to the block which will cause an intake leak. Also, if you car has the vacuum windshield wiper still hooked up, check to make sure there isn't a leak anywhere in the lines. Also, remember the old rule that 90% of all fuel problems are electrical. Is your coil hooked up right-meaning the positive and negative leads going to the right place? Some condensors, even new ones are faulty-as are some new coils, so check this too. Keep us posted.
I'm not up on the real old carbs, but if it has an accelerator pump, I'd bet it's not functioning properly.
I will second this, I have run into this problem a few times. Sounds like what you have. Pull the manifolds and check the gaskets.--TV
I say vacuum leak if it idled badly. If it only does this when accelerateing I would say the carb jets are too small or the fuel passages in the ventury boosters are partly plugged up. when you close the choke you start to pull extra fuel from the IDLE circuit of the carb, not the high speed circuit. Either way, its still too lean.
Thanks folks, some good tips here, ill check them all. I did wonder about the carb jets but he says he's had it running well before, but it took him ages to get it running right. Then the head gasket blew and he's not been able to set it right again. I think its time to go back to the begining and pull everything off so we can e;iminate one thing at a time. Oh, no vac wipers and the carb is a fresh recon 32 carb.
Right, we checked the fuel line and the whole fuel delivery system is spot on. We swapped condensors about and checked every plug is firing properly with a nice healthy spark. We checked all the inlet manifold for leaks. I can find nothing wrong with it. We drove it about today, managed to get it pulling reasonably for a little bit but never as well as it should. If i advance it it sounds happy and revs up a little better but the exhaust starts randomly popping and it wont rev up high without sounding like it may explode. Retard it again and the exhaust shuts up and it sounds happy but picks up worse when you snap the throttle open and generally coughs and splutters. Im only adjusting timing a couple of degrees here, absolute maximum of 5 deg from the most advanced ive tried to the most retarded. Dont want to melt anything! How important is back pressure on these? Apparantly the last time it ran well it had more baffling. Other than that, all we can think is carb jets. When he had it running well befoe it picked up well and reved out properly with just a small stumble around 45mph. I dont know these carbs, which jets are which? Are they numered? Any guess what jet it should be reasonably happy with? Its a stock recon 32 carb. On the subject, whats the metal tube sleeve between the carb halves? Looks like it just restricts the flow
Ok, thoguht i'd let you know the outcome. I 'think' ive got this sorted now, hopefully without the rolling road expense. Last time he had it running it had a different, wrapped, baffle in the straight through exhaust. We wrapped the baffle with some wadding and now it seems alot better. Was raining so we couldnt take it for a spin to set the timing 100% but it deffinately seems alot happier now. I guess these engines are effected alot by backpressure.
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