backfire thru the exhaust

[FreakinFord]

HI
i live in the Netherlands and i have a 1971 Ford F100 2 wheeler with a 302 cdi engine

whenever i slow down the engine backfires thru the exhaust !!
what's wrong here ??

Thanks
john

[BigRedTruck]

I have the same problem on sudden acceleration.....guy at the shop said something about the fuel pump being involved other than that not much.

[68F250]

You may have an exhaust leak somewhere from the exhaust manifolds on back to the muffler(s).

Another possibility is your carb. is running way too rich but I think you'd be able to smell that.

Are there many Ford trucks in the Netherlands?

Barry

[oldschoolrods]

Probably a fuel pump, can't keep up with the demand for fuel.

[FORDification]

Backfiring is often caused by mis-adjusted timing as well...or flucuations in the timing caused by a very loose timing chain.

[FreakinFord]

Thanks guys !!

so i have to check (1) the timing and/or timing chain, (2) the fuelpump (i was looking on replacing that anyway) and (3) the exhaust manifolds or (4) the carb.

any tips or instructions for getting the job done ??
i guess for the timming thing i have to bring it to the shop ?

how bad is this backfiring, can it cause damage or is it just annoying ??

for Barry: not so many Ford trucks around here... (not many trucks at all, as a matter of fact)... mostly Chrevolet or Dodge (the "W 200"... old ones from the armed forces in Germany)..
and the ones you see are mostly new ones (F150, Ram that kinda things)
i almost weekly look at all the adds.. this year i saw about 5 or 6 pre '80 Fords trucks for sale.

Belgium however is another story.. trucks are more common there.

John

[muchtomydelight]

Do the simple things first.

Odds are that your ehxaust donuts are cracked or missing or loose. Look at where the manifold is attached to the pipe. If they are loose, tighten them up.

Then check ignition timing. It should be 6-8* BTDC with the vacuume line removed and plugged. Unless it is below 0*, I don't think that this is your problem.

I doubt that its the carb or the fuel pump, as fuel demands are minimal when you are slowing down. If the carb were running that rich, a popping exhaust would be the least of your worries.

The next thing to check is the timing chain. On a windsor engine (maybe FEs too?), you can remove the fuel pump and push the chain with your finger or screwdriver and see how loose it is. Anything more than about a half an inch in deflection is unacceptable, and the timing set will need to be replaced.

[jor]

John,
It sounds as though you might not know how to time your engine. Buy a timing light and it will come with directions. It's not hard. You disconnect from the distributor the little vacuum line that goes from your carburetor to the distributor vacuum advance (looks like a little flying saucer) and plug it with a golf tee or a bolt or something. Then, loosen the bolt that locks down the distributor (not too loose, just loose enough to move the distributor by twisting it). Attach your timing light pickup wire to number one cylinder. On our FE engines, it's the first one on the right side (pax side). Attach the red and black wires to your battery and start the engine. Point the light at the harmonic balancer (the front of the crankshaft) and see which mark is being shown by the flashing timing light. As you (actually it really takes two people) turn the distributor, the mark will change. You want to set it at 8 degrees or so before top dead center or whatever you book recommends. When you get it right, tighten down the distributor and put the vacuum line back on and off you go. I find it helpful to rub chalk on the timing marks so I can see them better with the light (old eyes). Good luck.
jor

[FreakinFord]

muchtomydelight and jor, thanks guys... you made it sound easy and do-able.. i'm on it !!!

John

[muchtomydelight]

i marked my balancer with white out. My bet is still on the loose exhaust somewhere.

[willowbilly3]

Modern day points tend to have soft rubbing blocks which wear out prematurely causing the points gap to close. When the points start closing or loosing gap it will pop on deceleration.

[NM5K]

The 6 banger pop!!!! I know it well from my buddies 74 truck with a 240...
I've seen this happen on his a few times for two reasons, I think already listed... #1 of course, make sure the timing is right, and also the advance operation. But I have seen flaky carbs cause this also. They run too rich, and expel unburned gas into the exhaust, where it eventually explodes. I've seen this blow mufflers off... So if the timing checks don't fix it, do a careful check of the carb to make sure it's not too rich. MK

[willowbilly3]

If you have an engine with air injection that pops on deceleration it usually means the divertor valve isn't working.

[NM5K]

His also mainly did it on decel, but I don't think his has air..Not sure...But I don't think the 74 did. Anyway, his did that on his last carb which was acting up quite a bit. When he replaced the carb, the pop was gone. But his truck has also done it due to timing problems also. His is real LOUD!!!!!! when it does it.
Like someone next to you blew a 12 gauge in your ear. Anyone close to you usually jumps 3 ft in the air, including me...
On the other hand, so far my 300 has never done that once...Even with the carb acting up. But my timing has never been off... MK