Backfire

[pedro]

Got a slight problem. Engine (2ltr Pinto) not at all happy - did a bit of investigating and found a split in the advance/retard vacuum hose. Fixed that but now have a backfire and stuttering at about 3,000 rpm. Don't think its fuel. Could the loss of vacuum caused a longer term problem. Candidates seem to be a condenser and/or points but somebody suggested valves. It is a leaded head but I am conscientious about putting in an additive. Any ideas please 

['The Gaffer']

If you only noticed the backfire after replacing the vacuum hose, maybe the engine was previously timed with the leak and therefore needs re timing?

[paintman]

My Pinto will runs well with or without the vacumm pipe attached.....know a few people which don't bother with it!

[Ace Fettler]

Be handy to know what carburation you are running?

[YellaBelly]

I'd be very suprised if the valves are an issue through using unleaded fuel. Even if you didn't put additive in, apparently it will take a very long time before the valves would be damaged by running hot especially as most kits tend to do relatively low mileage.

I'm also using a 2l Pinto on points, and I've only recently got it started so it's not yet running properly, but I have had a couple of pops and bangs from the carbs, and I haven't yet had it ticking over on it's own which I think is either an air leak or more likely just timing/setup.

[Denzle]

To start, do a process of elimination starting with the timing.....points...condenser....coil....plugs, leads & cap.

If its still there then go to the carbs.

It sounds to me like a plug possibly breaking down under load, or a cracked distributor cap or lead.  Ford caps were well know for sparking across the cap for no particular reason and creating a popping sound as you decribe..

In the dark you can sometimes see the faint blue streaks of electric jumping across the cap.  But it has to be very dark to see them.

Warm the cap over a cooker flame, protect the carbon brush in the centre,then give a light spray of WD 40 inside and out.  Then clean off the coke from inside the cap terminals.   Do this first after checking the timing.  Let it dry well before refitting.

If none of these have cured it, put a compression tester down each bore, turn the engine over and check the comression on each cylinder.  But I dont think this is your problem as this would be a regular missfire and not a pop.

Come back if you have no success....     Denzle....

[paintman]

Be handy to know what carburation you are running?

I got a Weber DGAV twin choke with a pointless electronic distributer running from a Ford module.

Mine pops all the time on the overrun......I quite like it but it does not back fire!!

   Tony

[Quarrycars]

Have you tried disconnecting the vac advance again and see if the problem goes away?  Vac adv usually helps the fuel mileage a bit and may help light throttle drivability; if it is connected to manifold vacuum then it will affect the idle.  One of the problems I have seen is loose or cracked wires to the distributor base plate causing running problems as the advance operates.

Good tip from Denzle about letting the WD40 dry before refitting the cap, the stuff is flammable and I have blown a cap off after spraying it , and this one was screwed on!

[pedro]

Thanks all for your advice. Found one of the leads had a problem so hope to be back on the road this weekend

[Denzle]

Thanks all for your advice. Found one of the leads had a problem so hope to be back on the road this weekend

Just glad we could all help........