Brought to you in part by:

Great deals on auto restoration supplies!

.


JC Whitney clearance center!

  Mustangsandmore Forums
  Ford Racing
  Popping sound...?

Post New Topic  Post A Reply
profile | register | preferences | faq | search

next newest topic | next oldest topic
Author Topic:   Popping sound...?
MrXerox
Gearhead

Posts: 348
From: Oklahoma City, Oklahoma
Registered: Nov 2000

posted 08-03-2001 12:14 AM     Click Here to See the Profile for MrXerox   Click Here to Email MrXerox     Edit/Delete Message   Reply w/Quote
I am experiencing a backfire type sound coming from the passenger side tailpipe of my 351C. It only seems to do this until it gets good and warmed up and then goes away? Please note it is a brand new motor with 61 miles on it so far. It has a solid roller cam in it and I believe it needs to have the lash set on it again since it has been running now. Could this be causing this? It is very intermittent but is only coming from the right side...I am sure the carb needs some major adjustments as well but I just wanted to rack up around 200 miles or so on her untill I start messing with the fine tuning...

IP: Logged

jkilroy
Gearhead

Posts: 1808
From: Vicksburg, MS
Registered: Dec 99

posted 08-03-2001 07:50 AM     Click Here to See the Profile for jkilroy   Click Here to Email jkilroy     Edit/Delete Message   Reply w/Quote
I think you are probably onto it. Pop off the valve covers, do the hot lash bit and check for bent pushrods, broken inner springs, that kind of thing.

------------------
Jay Kilroy
68' Fastback GT 390
"No such thing as a cam thats too big"

IP: Logged

Mark
Journeyman

Posts: 1
From: N.E. Ohio
Registered: Apr 2002

posted 08-03-2001 11:08 AM     Click Here to See the Profile for Mark   Click Here to Email Mark     Edit/Delete Message   Reply w/Quote

I would definatly be checking valve clearances. And I would do it before starting it again.

I would then start it with the 'running adjustment' valve covers on and look for a hanging valve.

It could be something as little as a bad cap, wire or plug.

But I would check the valve train ASAP because 1) mechanical valve trains should be checked after (or even during) their initial firing, things settle in and clearances can change alot, and 2) A valve train is a terribal thing to waste.

Whatever it is, sounds like it's specific to one cylinder.

IP: Logged

MrXerox
Gearhead

Posts: 348
From: Oklahoma City, Oklahoma
Registered: Nov 2000

posted 08-03-2001 04:20 PM     Click Here to See the Profile for MrXerox   Click Here to Email MrXerox     Edit/Delete Message   Reply w/Quote
So I should let the motor warm up all the way and then set the lash on the valves or just set them cold now that they have a few miles on em? The specs on the cam call for .020, is there any harm in setting them at .015? Sorry for the newbie questions, this is the first non-girlyman cam I have ever had

IP: Logged

steve'66
Gearhead

Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000

posted 08-03-2001 04:27 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Lash should be set with the engine warmed up to operating temp. If you set them cold they will be loose after the engine warms up. You want the valves set perfectly, but being tight (as long as you're above Zero lash)or loose shouldn't cause the popping. It's probably an ignition problem, or the jetting is way off. Are the plug wires running parallel with each other on that side? What do the plugs look like? Are there any carbon tracks inside the cap? How's the tailpipe look? Good luck.

SteveW

[This message has been edited by steve'66 (edited 08-03-2001).]

IP: Logged

Doc
Gearhead

Posts: 466
From: Redwood City, Ca. USA
Registered: Jan 2001

posted 08-03-2001 11:05 PM     Click Here to See the Profile for Doc   Click Here to Email Doc     Edit/Delete Message   Reply w/Quote
Lash tightens as it gets hot so if it were lash it would get worse when warm. I had a 390 that ran like doo doo because the cap wiring was laced wrong but it did it hot and cold. I think it's so rich it's firing some raw fuel in the pipe and as it gets hot enough to burn all the gas the pop goes away.

IP: Logged

steve'66
Gearhead

Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000

posted 08-03-2001 11:53 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Larry,

I may be wrong but I think it's too lean. And it may have a vac leak on the right side, either a pcv or power brake hose/booster. The warmer the engine gets the leaner the mix can be and run ok. Right? I'm also pretty sure when I set the valves on the new 351w cold, they loosened up after the break-in(when warm). That could have just been the cam/lifter breakin that loosened the clearances.

SteveW

IP: Logged

Doc
Gearhead

Posts: 466
From: Redwood City, Ca. USA
Registered: Jan 2001

posted 08-04-2001 12:35 AM     Click Here to See the Profile for Doc   Click Here to Email Doc     Edit/Delete Message   Reply w/Quote
Ok! I'll go for a vacumme leak or lean or both and yes valve train gear gets set and wears in a bit on break-in so loosens in most cases but the old rule of thumb for stock street stuff was +.002 for a cold setting and were generally very close when hot. I wasn't implying the valve shouldn't be run and the valve train shouldn't be checked very closly. On rollers I set them cold +.002 then again when she warms up and after every run, test drive or pull. To quote Mark "a valve train is a terrible thing to waste" . Your advise to look at the plugs will probably reveal the offending cylinder .

IP: Logged

steve'66
Gearhead

Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000

posted 08-04-2001 12:41 AM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Thanks Doc,

That's good info! I appreciate it, as I haven't set the valves cold since the initial build.

SteveW

IP: Logged

MrXerox
Gearhead

Posts: 348
From: Oklahoma City, Oklahoma
Registered: Nov 2000

posted 08-04-2001 12:33 PM     Click Here to See the Profile for MrXerox   Click Here to Email MrXerox     Edit/Delete Message   Reply w/Quote
I think you guys are correct...I hooked up my Edelbrock air/fuel monitor and it reads as if my motor is running too lean. I have an 850DP with 80's in the front and 84's in the back...should I switch these around? It looks like the mixture is about right when I start it up but then the meter leans out as it warms up to the point that no leds are even lit up on the guage. However, when i give it some throttle the leds light up to about the correct range so I must be at least close...?

IP: Logged

Mark
Journeyman

Posts: 1
From: N.E. Ohio
Registered: Apr 2002

posted 08-04-2001 01:03 PM     Click Here to See the Profile for Mark   Click Here to Email Mark     Edit/Delete Message   Reply w/Quote

I would set them cold (just to make sure everything has clearance), then run the engine to temp and reset.

I've seen hydraulic valve trains where the intake valve wore to zero lash (propane fueled). They would cause a popping on startup and while cold because of the intake remaining slightly open. Compression was being pumped back into the intake and sometimes the flame would travle past the valve. Either way it was a dead cylinder till till the engine(s) got warm.

Then I have seen exhaust valves cause backfiring for both too much and not enough clearance.

In extreme 'no lash' I have seen exhaust valves held open. During combustion (what combustion there is) the pressure goes straight out the valve.

In less extreme cases the popping is the exhaust valve opening too soon in the power stroke. The cylinder pressure hasn't dropped 'enough' and the valve opens against high pressure.

Too much lash and the valve opens late in the power stroke when cylinder pressures are climbing. The slug nears it's bottom most position and slows but the combustion gasses are still expanding, pressure climbs and the valve opens. Pop!


Then theres the possability the valve event are so mistimed by impropre lash that the cyllinder just isnt pumping air.


How important is lash?

My 920 Virago (V-Twin scooter) was having real problems idling. The problem had been getting worse for miles and years. I figured it was the "junk" hitachi carbs and the fact that I rode her hard. I mean, Real Hard.

One day while adjusting the valves I had the test gauge (0.0005" indicator) home to check the rim run out.

I set the clearance with a feeler gauge then set the indicator up to measure the actual lash travel. Thousanths off. WTF??

Rocker faces and valve stems had worn and I was measuring the high points. Bummer.

I set "lash" to "measured travel" on all cylinders. Idle returned as did low speed running, torque and throttle response.


So, valve lash is a pretty important part of an engines operation. There is a temptation to think a few thousanths of an inch doesn't mean much when the valve travles hundreds of thousanths of an inch.

Those few thousanths mean one helluvalot.

IP: Logged

MrXerox
Gearhead

Posts: 348
From: Oklahoma City, Oklahoma
Registered: Nov 2000

posted 08-04-2001 08:31 PM     Click Here to See the Profile for MrXerox   Click Here to Email MrXerox     Edit/Delete Message   Reply w/Quote
Update:
I adjusted the valve lash while motor was at operating temperature (some of them were WAY lose) Also, I switched the jets around so that I had the 84's in the front and the 80's in the back and it seems to like it better than before. By the air/fuel meter it is running around 13 or 14:1 at idle on startup (good) and then dropped back past 15:1 (too lean) after 5 minutes of running or so....It is still making that popping sound from the tailpipe. It also seems to be running about 1200rpm at idle and I cant seem to adjust it to idle at a decent speed. Could it be that this 850DP is just too big of a carb for this engine? Please note this motor has ALL brand new high-end parts in it so I doubt it is wires, distributor, etc...

Stumped,
Sean.

IP: Logged

SteveLaRiviere
Administrator

Posts: 43151
From: Saco, Maine
Registered: May 99

posted 08-04-2001 08:33 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
What do the plugs look like?

------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L DOHC
Ford. The closer you look, the better WE look!

IP: Logged

All times are ET (US)

next newest topic | next oldest topic

Administrative Options: Close Topic | Archive/Move | Delete Topic
Post New Topic  Post A Reply
Hop to:

Contact Us | Mustangsandmore Front Page

Copyright 2005, Steve LaRiviere. All Rights Reserved.


Ultimate Bulletin Board 5.47d

Amazon Honor System Click Here to Pay Learn More

[Build a free Mustangsandmore.ws Home Page!]

[Posting Pictures]

[About M&M][Acronyms][Calendar][Chat][Classifieds] [Members' Pics]

[M&M Conventions] [M&M Mug Shots]

[ Mustangsandmore.com Bookstore] [ Smokin' Fords] [Tech Articles]