Yeah, we discussed the cleaned? plugs before. I agree it's gonna be difficult to get an accurate reading with those. On the plus side, the car is running much better now. Probably due to the floats now being set more accurately than they were. 
 [mention=28721]jalexquijano[/mention] Did someone try to readjust the floats after they came back from Ztherapy?

Mark do you think that valve adjustment effects he initial issue "popping exhaust".
Also for FYI I finished installing a Zstory full exhaust system and took it to a Dyno with out tuning it at all. Carbs were so lean we added 1.25 turn while it was warming up just to get it below 14:1. Then backed it off .25 after the first run. Final run was 11.71:1 so probably could lean it out some more. Definitely would rather run rich. That change took out a light backfire on deceleration.


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 From the beginning his plugs were sooty, Ignition didn't seem to be the problem so mixture had to be the culprit. The popping started with the new exhaust. Something about the old smaller exhaust prevented the popping even with a rich mixture. How many turns down did you end up with yours and how accurate do you think the float levels are?

1 hour ago, Mark Maras said:

 Yeah, we discussed the cleaned? plugs before. I agree it's gonna be difficult to get an accurate reading with those. On the plus side, the car is running much better now. Probably due to the floats now being set more accurately than they were. 

 @jalexquijano Did someone try to readjust the floats after they came back from Ztherapy?

Im not sure. My car sat for 4 months without having the engine crank while it been restored and paint. However, when they try to start the engine they argued that the floats were stucked and had to open the bowls.

  I can understand opening the float bowls if they thought the floats were stuck. Can't imagine why they would have adjusted them. Oh well, it's better now. Keep us posted on how it's running.

11 hours ago, 7tooZ said:

Mark do you think that valve adjustment effects he initial issue "popping exhaust".
Also for FYI I finished installing a Zstory full exhaust system and took it to a Dyno with out tuning it at all. Carbs were so lean we added 1.25 turn while it was warming up just to get it below 14:1. Then backed it off .25 after the first run. Final run was 11.71:1 so probably could lean it out some more. Definitely would rather run rich. That change took out a light backfire on deceleration.


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What exahust do you have? I used to have the stock exhaust with a resonator in the middle and a dynomax muffler at the end as per the pictures attached. It had no deceleration backfire even with a 4 turn clockwise ( 4 turns left) when releasing the gas pedal in 2nd and 3rd gear. My cam is a Schneider 274F as my car engine has been modified to 2.6L by PO. After installing the MSA Premium Stock exhaust for stock manifold i am experiencing lots of popping when releasing the gas pedal on 2nd and 3rd geat. PO also eliminate smog pump and all emission crap.

http://schneidercams.com/274FL6.aspx

Timing is set at 11 BTDC.

Any clues? I will verify all the flange gaskets once again as i still suspect a leak between the manifold to the downpipe. I felt some hot air blowing at that union last week. Maybe i can drop some wáter and soap in that área to verify. Anyone????

 

Would a more restrictive muffler provide better back pressure? My msa premium exhaust is very free flowing, although I get no popping with my 2.4L and original cam on my 72


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This is what i have on my engine. I guess since you have the original camshaft and the original engine you are not experiencing any pop. I also noticed some hot air leaking from the union between the manifold to the downpipe. Could fixing this solve the decel popping?

Looks like there's a hole in the weld where the rusty old stock tailpipe meets the new muffler. That's the worst welding I ever saw. Sorry if you welded it yourself. Whoever did it should practice a lot on some old parts before welding for a customer.

I noticed my truck backfiring through the tail pipe after a small hole rusted out in the header about 10 inches from the exhaust port. Cause and effect maybe, but I don't understand t how a hole in a header would cause backfire.

The popping is from unburned fuel igniting inside the exhaust pipe.

If oxygen gets into the exhaust pipe through:

1. too much cam overlap during over run

2. poor valve adjustment

3. burned exhaust valve

4. holes in the exhaust system

5. too big an exhaust pipe and reversion

then the oxygen will ignite the fuel and cause the popping.

 

The other possible causes are:

1. retarded timing igniting the fuel when the exhaust valve is partially opened

2. too rich a carb setting sending unburned excess fuel out with the exhaust gas.

Edited June 27, 20177 yr by 240260280

 Perfect explanation, as usual. Thanks for adding the other possible causes.

Well the two last options have not solved my decel backfire. Im at 11 btdc and had already tested lowering to 2.5 turns in the past and the problem persists.

Edited June 27, 20177 yr by jalexquijano

11 minutes ago, jalexquijano said:

Well the two last options have not solved my decel backfire. Im at 11 btdc and had already tested lowering to 2.5 turns in the past and the problem persists.

 Two down, and five to go.