Can someone point me in the right direction - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

gumby01 · 07-07-2003, 06:46

I own a 1974 ZG Fairlane & am getting nothing but grief, I have just spent a load of cash fixing the gearbox/diff & rear shocks. Now the old girl has developed the nasty habit of backfiring through the carbie, noone knows what is wrong I have 6 different opinions.
Does any one know what is wrong?
The motor is a 302 Cleve with a 465 c.f.m Holley.

TopGhia · 07-07-2003, 13:32

Timing is out, water in the fuel, or most likely a sticking inlet valve.

Get a bottle of Redex (do they still make it?) or some other upper cyl cleaner/lube (the stuff you usually put in the petrol tank) then get hold of a mate, warm the car up, take the air cleaner off and get your mate to dribble the stuff straight out of the bottle into the carby.

You will be in the car keeping the revs up as it will want to stall out. Give it a good rev and try to use the whole bottle. Stop pouring when it starts to choke. Tell him to do this at arms length, you don't want a backfire if he's looking down the carb.

May work, makes shitloads of smoke and looks real impressive, but an old remedy for sticking valves.

Let us know how you get on.

gumby01 · 07-12-2003, 22:22

My girl is still no good, when the throttle opens up to about 1/2 way to 3/4 she goes boom out of the carb, even if she is warmed up. She idles well and drives well low down, but give her a hit and flames or smoke come popping out.

TopGhia · 07-12-2003, 23:14

Well you probably have a lean condition in the carby.

Check all these. :)

Hesitation, stalling, stumbling, flatspot, or deadspot during acceleration: Backfiring or spitback up through carb.
1) Vacuum leak. 1) Check for vacuum leak & fix it.
2) Ignition timing retarded too far. 2) Reset timing.
3) Accelerator pump nozzle has dirt in it. 3) Clean out the nozzle tip.
4) Accelerator pump cup swollen up from contact with bad gas or chemicals. 4) Replace the pump cup.
5) Economizer jet too small or partly blocked. 5) Clean out economizer jet & check the size.
6) Choke pull-off open too far. 6) Adjust the pull-off tighter.
7) Secondary throttle plates not closing all the way. 7) Fix it.
8) Vacuum hoses hooked up wrong. 8) Connect up right. Be especially careful of the EGR & Dist. connections: sometimes the pipe locations are reversed
9) Idle jet partly blocked with dirt. 9) Clean out the jet & any other dirt that is in there.
10) Distributor timing not advancing properly. (worn breaker plate, worn shaft, pin hole in diaphram, crack in hose, etc.) 10) Check distributor and all related systems carefully. Replace defective parts.
Hesitation, deadspot or stalling that only seems to occur after the first mile of warmup. 1) Defective electric assist on choke 1) Replace it.
2) Defective accelerator pump (low output). 2) Replace it.
3) Float level setting very low. 3) Adjust to factory specs.
4) Bad ignition condenser. 4) Replace it.
5) Plugged heat crossever system in manifold. 5) Inspect and clean passages in the intake manifold and heads. Test heat riser valve, replace if defective.
6) Defective source of hot air up to the carburetor. 6) Check and replace as necessary: heat shroud duct, temperature sensor, vacuum door moter, manifold vacuum supply.
7) Defective thermal switch. 7) Check all thermal switches, especially those connected with the distributor, EGR, & vacuum motors in the air cleaner housing.

Thats most causes, your carby may need pulling down.

Have fun.

gumby01 · 07-13-2003, 00:29

It doesn't seem to be a carby problem I have just taken off the 465 and put a 600 on, it still does the same thing only louder with more flame. I am now lacking a eyebrow. The timing only just got done about a week ago.

gumby01 · 07-13-2003, 00:37

It backfires whether it is cold or warm , more when it is cold but this is expected, it only happens when throttle is past halfway.

svo347 · 07-13-2003, 01:02

Backfiring normally occurs because of a timing fault....Whats it drive like down low? ok or does it just play up when your up high in the revs..?
check the points & then the coil, it could be the secondary stage of the circuit.
Does it idle ok.... other things to look at would be a manifold leak.

TopGhia · 07-13-2003, 01:19

Plug wires in correct order?

gumby01 · 07-13-2003, 01:27

It idles fine and drives down low fine, wouldn't the plugs being in the wrong order affect it the idle as well??

mongrelEB · 07-13-2003, 01:41

Yes they would. If somebody else did the timing, I suggest you do it yourself.
Mark where the dizzy is, then loosen it and twist until the motor runs at its fastest idle. This is roughly the correct timing - at least good enough to drive with.
Does it still backfire?

The other possibility is vacuum advance on the dizzy - do you get vacuum at the solenoid while the motor's on?