back fire or misfire or something else

BIG MIKE

BIG MIKE

Senior Member
My flatty backfires Right on the start when you push starter button. Would that be Crossed wires? it Idles nice but when under a load it backfires like a sharp bang. thanks BIG MIKE
 
like 51 merc said , possible sticking valve, dribble 8 oz or so of mmo down the carb, and then put 5 or 6 oz in ten gallons of gas, run car for 100 miles or so, see it that cures the problem
 
Need way more info. Check all the ignition wires to make sure they are correct on both ends . Check plugs to make sure you don't have any fouled. Check supply voltage to coil (6v or 12v) or less if you have a ballast resister in line . Also, does it do it all the time or just cold or just hot ? Did you change anything recently and this started ? As they say, most ignition problems are fuel and most fuel problems are ignition. Is this a worn engine ? rebuilt ? low miles etc etc ?
To have any chance of doing an internet diagnosis you need to give as much info as possible. From there I would bet you will get good help and be directed to check certain things as a process of elimination.

We will wait for your reply with info :D
 
I put in New plugs new wires new rotor new electrode caps new points Plugs are gaped correctly, I put mmo in all the time, its just i turn on starting ign, push button and Bang , but after warm up she idles fine when I drive her out it stats banging again , Its in a (Tank Mk 2 Bren Gun Carrier) my engine .
 
I wonder where it leaks from I never see any leaks, maybe ill give it a cleaning now that vehicles done for the season , thanks
 
BIG MIKE said:
I wonder where it leaks from I never see any leaks, maybe ill give it a cleaning now that vehicles done for the season , thanks
Click to expand...

If it leaks internally you are not going to see it, but it still takes something like an open valve to ignite it.
 
Still as soon as I push starter button , Bang (backfire) runs smooth on idle , But when I push gas pedel it starts running uneven rough etc batt Good Gen Charging oil psi Good , new plugs wires condensor rotor electro caps , and it still bangs
 
Could the miss fire be from a Vacuum leak? or not enough fuel? i have a Gas reg on at 3 1/2 PSI? should it be more? would Engine Constantly miss fire if Wires were crossed? just asking that ?
 
If it didn't backfire before the tune-up, it is most likely a result of the tune-up. If your points are set incorrectly it will affect timing, advanced or retarded. If it is backfiring through the carb your timing may be too far advanced, if tailpipe too far retarded. Check that plug wires are not crossed. Did you get a good cap and rotor? ( I bought one from MACS and the rotor will move more than .100" on shaft, can't time that out) It could be any number of things but that's not how the smart money is betting.

1932 V8 had it right, please provide more info, type engine/ distributor, etc.
 
I would definitely check your firing order first for a crossed wire. Did this problem start after you did the wires, plugs, etc...? It would idle fine sitting there, but run poorly under a load. flatheads don't run a lot of fuel pressure, 2-4 lbs max. On a single carb, I'd say closer to 2-3lbs. If it started after the work, it has to be something you did during that process.
 
Hey Big Mike, welcome back!! Where have you been hiding?? Are you sure someone is not lobbing mortars near you? ;);)
What carburetor and distributor are you actually running? I think I have seen pictures of the engine setup in this tank before, or maybe it was another tank you own, but maybe a couple pics added here would refresh my memory, and allow others to see it as well. Actually, as someone else already mentioned, with all the things you have just added or changed doing a tuneup, something you have done is most likely the problem. Some of my best guesses would be.... a couple spark plug wires in the wrong place, either at distributor inner cap, or at the plugs, points not set correctly, timing not set correcrly, bad capacitor, low voltage to coil, loose/intermittent connection of coil wire, and/or loose wire terminations at the wire wound coil resistor, etc., etc. This is all guess work, but may be things to check out. Keep plugging away, you will find the problem. Good luck!
 
all this stuff started after i took off the Govenor , it acts like a 2" riser now its a 34 flathead old helmet style dist, ill check my wires again for the 3rd time,
 
youi know after xmass ill take a vid of it , the vehicle only goes out 6 times a year in parades or reenactments sometimes at car show static displays and when i take her out i only go less than 7mph i think this past year i only did less that 15 miles LOl, im just sick of listening to the banging under a load going up a hill
 
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