[MikeB]

I have a 1970 Ford Torino GT with a 351C and 4 speed manual. I have done a lot of work on the engine (complete rebuild... balanced, new cam, head job, new 10.7:1 pistons, roller rockers, new demon 650cfm carb, plus more) and would be happy to provide specs if it helps. My problem is that on deceleration I am experiencing a lot of muffler 'pops'. Not backfiring, the car runs great, just muffler pops. I cannot for the life of me figure our what is the cause. I have adjusted the carb to no end. I suspect something with the valves or spark system, although all components are new, of high quality and workmanship. As you can read, this is very perplexing... any help or guidance appreciated, from one rodder to another.

 

[edcroozer]

HI, from my experiance with this type of problem I found it to be unspent fuel ending up inthe exhaust pipes and igniting. You will have to jet down or lean it out a bit to stop it. Take a plug reading, that will tell the whole story. Also recheck your timing. 99% of the time it`s a rich condition.

 

[MikeB]

Could it be leaking headers? I was told this may be the cause, and I do notice some small exhaust leaking from the headers (where mounted to the heads)???

 

[edcroozer]

Hi Mike, the header leak you speak of would sound more like ticking, it would not cause muffler rap on decelleration. without hearing it myself, you might try what I advised in the last posting.

 

[MikeB]

I really appreciate your help. One more go around if I may? The timing is about where it needs to be with this cam, or better stated where the car runs and takes gas the best. I have leaned out the carb pretty far (all four adjustment screws are between 1/2 and 1 1/4 turn out) or again, about where the car seems to run and idle best--although lean by most standards. As for the jets, I guess I just hesitate to change them as the carb is brand new and not really that big (650 cfm, vacuum secondary). This also was happening with the previous carb, a 600 cfm. Is your feeling that there is too much gas and thus, unburnt fuel igniting in the muffler? Or that the spark can't ignite such a rich mixture? Is there a way of testing this first?
Thanks!

 

[MikeB]

One other quick thought... (just in case it isn't the jets) Do you think it might be possible that the spark isn't correct... I replaced the stock pistons with 10.7:1 domed pistons, yet still use the stock recommeneded spark plugs. Might I need a hotter plug, or shorter/longer plug?

BTW I converted to an electronic ignition and am using an accel coil.

 

[novass]

The demon carb you speak of, is it a BG? If so a 650 flows 750cfm (don't belive me, email the company..I did.) But I do not think you are over carbed....As Ed said, if it were a header leak it would be a ticking sound (very anoying, and imbarasing)
I am also in the works of a new motor build...one thing I could never figure out (AND YOU MAY WANT TO LOOK INTO ALSO) is hot and cold spark plugs.
I belive you mention that you are using what was recomended..This is not always the case with a high compression motor.

I have a question for you....this muffler pop, dose it happen always? Or is it just after a hard throtle?
I have a 383 (9.5:1) and it runs fine. But if I open up the throttle all the way and then let off...I get the same thing. I like it.

 

[edcroozer]

MIKE, THE 4 CORNER IDLE SCREWS YOU HAVE BEEN ADJUSTING ARE FOR IDLE ONLY. THE METERING PLATE AND JETS ARE WHAT DETERMINES THE FUEL AMOUNT CONSUMED UNDER ACCELLERATION AND OFF IDLE OPPERATION. THEREFOR A JET CHANGE MAY BE THE ANSWER TO YOUR PROBLEM. JUMP DOWN 2 JET SIZES AT A TIME TIL THE PROBLEM IS FIXED, BE CAREFUL HERE YOU DON`T WANT A LEAN CONDITION EITHER. FIND OUT WHAT SPARK PLUGS ARE AVAILABLE START WITH THE MID RANGE PLUG, THEN COLD PLUG THEN HOT PLUG. EACH SET SHOULD SHOW YOU A DIFFERANCE IN PERFORMANCE. OF COURSE USE THE ONES WITH THE MOST GAIN.

[ August 24, 2001: Message edited by: edcroozer ]

 

[MikeB]

novass - it may not be leaky headers causing the pops, but there IS definately a leak there, as I can see smoke blowing back up the firewall when the engine is running. Also, the pops are very evident after a hard acceleration, but are also noteable during routine shifts, and if just revving the engine in neutral, although not as much as after a hard run.

edcroozer - I think first I will put an end to the leaking headers -- although no ticking sound is evident, there is definately a few leaks. I have always used the cheapy gaskets without rtv. I bought some of that copper rtv and will give it a shot first... needs to be done anyway. I suspect that will not fix the pops, and then plan changing the jets. Hopefully I can get the pops to stop here shortly... and will keep you posted.

Thanks for the help, and if you think of anything else, please let me know...

 

[MikeB]

OK... I got it. It was the wrong gasket on the headers! Ordered the correct gasket (351C 4B heads, got 351 2B heads) but was sent the wrong one, which has the same bolt pattern, and used it. I can't see much while bolting up the headers so I didn't catch it. Now have the correct gasket, with no leaking, and NO MUFFLER POPS!

 

[Stroke]

Prolly was the Ford Dust gettin inside.
I hear it's dangerous.

 

[whinny]

muahahaha

funny funny post.