Chevy High Performance
Click here to find out more!

Engine and exhaust backfire, stalling - intermittent.

Chevy High Performance
1 |  2 |  Next   | Last 
Item Posts    Sort Order

Engine and exhaust backfire, stalling - intermittent.

reinventingben reinventingben
New User | Posts: 7 | Joined: 05/12
Posted: 05/23/12
05:34 PM

Hi all. New to the site and fairly new to being this involved in wrenching on the car. I've learned a considerable amount from the site, so just a quick thank you to all that contribute.

Engine is a '69 350 in a '62 Bel Air. Edelbrock 1406, Mallory distributor w/ vacuum advance.

I recently rebuilt the carb, verified timing (8 BTDC), dropped the tank to verify no blockage issues as I thought maybe something was up with fuel delivery.

Car idles fine. If I let it warm up a bit it runs perfectly. It seems my problems arise as the engine temp increases and if I turn the motor on and off frequently (stopping at stores and such). The backfires, in both locations, are extremely intermittent. It just runs so unreliably. And, in stop and go traffic, the engine temp rises quickly. I've changed the thermostat and verified fluids. Is there a way to help the car run cooler, even in AZ summers? Might this be vapor lock?

Any help is really appreciated. Acquiring the tools is fun, but expensive. My next purchase is a fuel pressure tester as maybe my pressure is low? Causing a lean mixture under load?

Thank you for your time.  

waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 05/24/12
02:39 AM

in a 62 belair..   how do you have the power to the ignition system handled???  do you still have the bypass circuit from the starter solenoid installed..    the ignition switches break the power connection to the ignition coil wire when the key is in the cranking position..   as you release the key.. the power from the starter R terminal drops out .. sometimes before the ignition switch contacts close..  this momentary drop out can be like the UPS driver turning the key off then back on and sending a massive backfire through the exhaust..    monitor the primary voltage with a test light on the positive side of the coil..    if it drops out when you release the key from the cranking position. that could cause the backfiring..

fuel pressure testers are cheep... for testing mechanical fuel pumps...   it measures 15 PSI and 30 inches of vacuum.. so you can test the suction side of the pump also..   should be able to pull over 23 inches of vacuum and hold it..

Image 13809

there is a cheep easy to do test that also needs to be done..   the free flow pump test..

cold engine.. disconnect the power to the coil so there is NO chance of any spark being created..

disconnect the fuel line at the carb..,   extend it with a section of fuel hose into a clean clear 2 or 3 liter plastic bottle...  have somebody crank the engine while you watch the pulses of fuel into the bottle..   each pulse should be the nice and full.. equal...  not diminishing..

this proves the fuel system is not restricted...

find a magnet.. hold it next to the bottom of the bottle of gasoline after the test.. is anything attracted to it???

rust or red dust in the fuel system can hold the fuel pump check valves off their seat.. causing vapor lock type issues...

clogged fuel filters inline and clogged strainers in the fuel tank can also cause vapor lock.. as the fuel pump can create lots of suction..   if its having a hard time pulling fuel up because of a restriction. the lowered pressure drops the boiling point of the fuel even farther and it changes to vapor at the wrong time.. the fuel pump cannot pump expanding vapor..  

but wait.. this could be the cause of the overheating problem..  as the fuel level drops in the carb.. the air fuel ratio goes lean.. this causes the engine to over heat...

perhaps the fuel pressure tester above is the wrong one for your application. if you want a dash mounted gauge..   the full flow test is an important..

magnets in the tank help.. big strong magnet like from a car speaker stuck to the bottom will also work..  just don't ever pull them off..

this is rusty fuel in a white plastic pan..  


so.. lean air fuel to do fuel issues can cause the engine to overheat...

how about more cooling fan blade count. or width..  there are different width blades to move more air..  

reinventingben reinventingben
New User | Posts: 7 | Joined: 05/12
Posted: 05/24/12
06:16 AM

Wayne! Thank you for your time, sir. Later today I will take a closer look at the ignition system and then perform the free flow test as well. I still have the tank dropped and it was clean as a whistle. I also didn't find any sort of pick up filter. I also suspect the fuel filter is wrong. I had a friend run for parts and just assumed it was correct. I was making a list of parts to buy last night and Autozone shows a much smaller filter. Would a larger filter account for improper flow? I also noticed that the original line feeding the carb is a larger diameter than the fuel line coming from the tank. Should this be the same size?

I am planning to invest in a dash mounted guage... It is a stock fuel pump. Any benefit in upgrading to an aftermarket pump?

Again, thank you. I feel a little less frustrated now.


waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 05/24/12
09:03 AM

i like bigger fuel injection style filters..   if you can hide them...

if the tank is out..     find some magnets and drop them in .. away from the sending unit so it does not grab the float arm and attempt to hold it down...

they can just live there and protect the system..  try to get supermagnets... much stronger.. keeps the rust attached during fuel slosh..

there should be a strainer in the tank on the end of the sending unit .. this helps keep the fuel line full of fuel also..

they are available in 5/16 and in 3/8...   i will have to find the numbers.. they are in a different computer..  if you have a ford dealer.. sometimes they have them in stock..  lasts ones i got were about 8 bucks each..   ouch.. but worth it..
i looked around.. found this decent priced version over at classic industries

Correct replacement of the original fuel tank float strainer used to help keep contaminants in the fuel tank from entering into the fuel lines. This will keep dirt and other elements from clogging or entering the carburetor. This part attaches directly to the fuel tank sending unit.
classicindustries Part Number: # G6979
Part Number: # K404
there are several variations on these.. so check the catalogs..  other suppliers have them also.

Spectra Premium/Fuel Tank Sending Unit

Part Number: FG89B
Application: With return line
Convertible, Sedan or hardtop
Notes: Includes fuel sender, float and strainer

Spectra Premium/Fuel Tank Sending Unit
Part Number: FG89A
Application: Without return line
Convertible, Sedan or hardtop
Notes: Includes fuel sender, float and strainer

radiator cooling fan motors, the perm magnet starters, some heater fans have really strong curved magnets.. along with power window motors from newer cars.. sometimes.. easy to extract.. sometimes not..    starter rebuilders might be a source for broken super magnet parts..

you can also since you have the tank out.. pick up a universal speedometer cable core.. and shove that through the fuel lines..  if you have blown them out and both ends are disconnected..     once you get it in far enough and have thick palmed gloves on..  you can hook a variable speed drill to the end.. have the friend keep the cable tight with the drill motor while allowing it to feed in by it turning in the proper direction..  then flush the lines properly..   think of a plumbing snake..  

pepsi1 pepsi1
Guru | Posts: 1718 | Joined: 09/11
Posted: 05/24/12
11:38 AM

Wayne is one of the sharpest guys in our forum.

Just one thing you have an older fuel system, make sure your fuel cap is vented. Sometime the heat from the ground will heat the tank and force fuel to become pressurized in the tank, and push it passed the needle and seat in the carb. Allowing raw fuel to get passed and when you restart the engine a cylinder or 2 will foul for a split second. and then when it gets ignition you get that bang...

I am just adding my 2 cents, because over the years I have had problems such as yours, and what fixes them can be a multitude of things. Then when it goes away what was it that worked?

Try this: If you haven't already. I always let the engine run for a couple minutes after stopping before shutting it off equalize. Especially if I've had the A/C running. Now with aluminum heads its definetly worth 2 minutes of idle fuel. I shut all the accessories off let the engine idle for a couple minutes.

Just make sure all your fuel lines are not close to the ground, to pick up heat from the tarmac. Then also anything close to engine heat will make fuel boil in that area. If you can insulate all the fuel lines with cheap plumbers insulation. If that works then use some nice insulation...its not a easy cure, again only my 2 cents


reinventingben reinventingben
New User | Posts: 7 | Joined: 05/12
Posted: 06/21/12
07:20 PM

Hi All,

Its been awhile, but finally found the time to start digging around....

I have come across a slow stretch in work, so decided I would attempt my first rebuild on a motor.

After fiddling with all the much appreciated suggestions I noticed something very peculiar: the radiator remained under pressure LONG after the car had been shut off. Like days. A little research suggested a head gasket leak. I have long wondered what has been done to the motor as far as upgrades go, so it has given me an excuse to tear it down. I've wanted to spice up the engine bay anyway, so with it empty tis the time.

Since I haven't yet purchased the equipment necessary to fully pull the engine, I have been pulling off what I can. I am down to the block on the top end.


Top of the pistons are BLACK? Any reason to worry?

Bottom side of intake manifold in one section is BLACK. Worry?

Passageways in the cylinder heads were clogged with gunk, which I suspect may build up normally over a given period of time. On the back end, 7 and 8, there is a build up of a white chalky substance in what I'm guessing is the coolant passage ways. Worry?

I have been taking photos, so I can post them if you guys think they will be helpful.

Plan on making some upgrades while I'm "in there." Def a water pump, new headers, camshaft?, new pistons if it needs to be bored.

Thank you guys. I am really new to this depth of work, but am excited.  

waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/21/12
09:19 PM

cooling system holding pressure for a LONG time is perfect...

there is a lot of issues with older chevy motors .. sometimes they can be fixed.. sometimes overhauls...


i like to figure out the issues before i tear it down..

let me relate a story my boss told me about a trip to baja in a 62 GMC 3-71 diesel C20.  they passed a family on the way south with a 63 impala with the engine spread all over the side of the highway..  no way to help.. but on the trip north.. the family was still there..  working franticly under the hood..  this time they stopped.. after rebuilding the engine.. the car still would not start..  merle and doug had probably 60 years of auto repair knowledge between them.. the points were burned out..  they had installed new ones at the beginning of their trip.. but had neglected to clean the grease off the contact faces.. so they burned again.. 5 minutes and the engine was running..  they tore the complete engine apart and it still did not start..

bad valve guides..  recessed valve seats from the lack of lead... excess crud along the bottom of the valve springs..  causing oil to build up over the  top of the guides and being sucked down the guide building up massive amounts on the back side of the valves..

post your photos to photobucket..  then after saving them.. hover your cursor over the thumbnail image..  a menu will drop down.. click on the 4th link down..  paste that link here and it will show up...  

reinventingben reinventingben
New User | Posts: 7 | Joined: 05/12
Posted: 06/22/12
08:19 AM

Thanks for your time, Wayne.

When i say pressure in the rad, I mean like when I open the cap it sprays! This was after a few days sitting in the shade. I was under the assumption maybe the engine was leaking compression into the radiator?

Here are the pics. There are quite a few.










waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/22/12
11:53 AM

as for the Black carbon under the Intake..    thats NOT a LOT... a lot is when it FILLS the lifter valley and you have to pry the intake off as its holding it down..

the white stuff is aluminum corrosion from either straight water or coolant that has never been changed and has gone acidic...  or somebody put old style radiator fast flush in it and did not wash it out completely....  

the corrosion is going to be a problem as its DEEP...   you are going to need to get in with a dremel tool and carve it all out till you get to bare shiny aluminum..  then you have a choice of epoxy or have it welded up and the intake carefully resurfaced...  i have FIXED lots of corroded through .. yep where water is squirting up intakes by carving away the corrosion to stop it..  and filling with JB WELD.. then using a a long board sander to smooth the surface level..  please... only attempt ONE side at a time.. as you have to have the side you are working on LEVEL for the epoxy to not flow out..  level as in machined surface UP...   i have also drilled with a variable speed drill set to almost a crawl.. with double ended 1/8" drill bits from the body supply store.. so it does not break off ..

do you have a 5 way painter tool.. and a 180 grit diamond file to sharpen it to a razor edge with NO BURRS..  drag the edge of the painters tool along the diamond file side to side on the tapered side to create a smooth perfect edge.. then a SINGLE stroke with the flat side flat against the file to remove any curl from the edge..  this allows you to totally scrape the aluminum intake surface and the various cylinder head and block surfaces without a single scratch.. you will have to resharpen it several times .. if you see a scrape.. stop and resharpen..  

Hyde 6 In 1  

waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/22/12
12:36 PM

this head the right hand cylinder was not firing properly

this head.. second from the left was not firing properly...

can you climb in..  put a hose on the fuel line and a plug in the end.. slowly rotate the engine a quarter turn of the crank at a time and examine the lifters if they rise the same amount..

or with some carb cleaner sprayed on them.. and a thin flat screw driver to wedge into the snap ring groove without destroying the lifter... work it up and down while you spray it to wash the varnish off.. till it comes all the way up and out..   please TAKE ONLY ONE out at a time...

make sure the lifter is not concave on the bottom.. it should be fairly smooth.. no big gouges out of it where it would show a cam lobe going flat..  please.. replace it into the exact same hole you took it out of...  mix ups WILL CAUSE a ruined cam 2 weeks after start up...  been there ..

do you have a LOT of miles on the heads...   do you have a decent machine shop.. where they could do a valve job on YOUR HEADS...  if you decide to go that way..   hopefully they will use a valve spring compressor .. not a hammer and socket to take them apart..  that always bends the head of the valve as it strikes the work bench at an angle..

lets look at the distributer cap and wires...    

do you have a digital volt meter.. set it to 200K ohms..   200,000 ohms..   measure the individual wires while still plugged into the cap.. from the inside terminal in the cap to the terminal in the boot at the spark plug..  the display on the digital volt meter should be less than the length of the wire in inches..    a 24" wire should show less than 24 on the meter.. 12 to 18.. spark plug wires are 1,000 ohms per inch MAX..    look at the inside of the cap for cracks.. for carbon tracking..   if you find a wire or two that are not reading.. anything. you have found a major issue..  

reinventingben reinventingben
New User | Posts: 7 | Joined: 05/12
Posted: 06/23/12
02:28 PM

Hi Wayne,

Just so we're clear, I know zero about this motor other than what I am currently learning. This vehicle almost fell in my lap and has since become a passion. Also, outside of routine maintenance and a few DIY jobs, I am a COMPLETE novice when it comes to motors. Please don't dumb down for me. I just wanted you to know my level of ability and why rebuilding this motor has piqued my interest.

I pulled the lifters - one by one - they look perfect, as far as I can tell. They are aftermarket hydraulics - Crane 99377. Since I have not yet pulled the cam I have no idea whats in there. I need to make a trip for a harmonic balancer puller.

I will test the wires this evening with my volt meter and respond with the results.

Upon pulling things apart and being under the vehicle a bit more more than I've ever been I have noticed the trans is leaking. The motor is completely covered in old oil around all the usual places, which is another reason I'd like to redo the entire thing. I plan on taking my time and making some real progress with this motor.

Again, I want to thank you for all your time and willingness to help. With Google and and this forum I would certainly be in a bigger mess.

So now I'm trying to school myself on certain things - compression, camshaft upgrades, piston upgrades, etc. Any good sites you can refer me to?

Cheers and enjoy the weekend!

This is my baby, by the way.

IMG 0069  

waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/23/12
03:22 PM

those look like 993 casting number heads....  most people use those for boat anchors.. but they worked on millions of chevy motors just fine..   if you wanted more power then you had to change up..

can you grab the stamped in numbers off the front of the passenger head block surface.. just in front of where the head gasket is...  post them...  so the block can be identified..

how far do you want to go...   how thick is your wallet..

a great swap at this point in time.. would be a set of vortech heads.. a matching vortec carb type intake..    there are a LOT of options on cams...

new cap and rotor for the mallory.. please figure out the model number to get the proper cap and rotor..

this is the most active forum on the cars side of the many magazines here..

there are SO many cams and different ways to build a small block chevy...

you will also want to examine the tops of the pistons around the edges.. while installed..  to verify there is no piston damage .. no grooves in the cylinder walls when you rotate the crank and inspect the walls..

what you are seem to be asking for is a site with all the knowledge of years of experience in one spot on every subject..  

reinventingben reinventingben
New User | Posts: 7 | Joined: 05/12
Posted: 06/23/12
08:42 PM

They are 993 heads. I am def considering upgrading. I have been looking around for some deals.

3970010 1969 4BBL 350. v063wm I learned: June 30th 255HP & prob installed in a C20.

I did replace the cap and rotor about three months ago when all the problems first started to arise, along with the plugs, wires and coil.

When I first got the car I noticed the water inlet was a bit warped because it was slowly leaking coolant. I replaced it and everything seemed OK.

Cylinder walls: they look and feel clean except for the very top 1/4". Most of them seems to feel a bit rough and have a black discoloration. Farther down they look and feel completely smooth.

And no sir, I wasn't asking for one comprehensive site to teach me everything. I was just wondering if you had any references to point me towards that might give me a bump in understanding. Have no fear throw out your wisdom and I am unwavering in my energy to decipher it. I totally appreciate you and your time. Paycheck Friday = books and tools.

Thank you, boss man.  

waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/23/12
09:17 PM

there are probably 30 automotive magazines on this site... each one has a tech section and hundreds of articles on engine and almost every other subject about cars..

the intake needs work... if you are going to REUSE it..

the heads need to be examined..  put the spark plugs back in.. lay them with the chamber flat..  spray or pour some gas or solvent into the chamber..  see if it leaks into the intake or exhaust ports..

this is normally done with a hand vacuum pump.. with a rubber faced adaptor to cover the ports to see if the valve seats are holding..    a big version made from some clear plastic with a rubber seal around the outside is probably better..  just more work to create..

when you mention that the problems started a few months ago when you changed the cap and rotor/ wires..   that leads me to look toward them...   mixed up spark plug wire positions.. crack in the cap..  not fully inserted into the cap..    not fully seated at the spark plugs..

since i cannot tell which cylinders 3 on one side.. 4th on the other.. what cylinders were those on the engine...   just tell me if the #3 head or the #4 head has a sending unit between the spark plugs .. as usually Only one head will have it. usually the left head..   the right side  head will have a pipe plug with a square drive..

the distributer cap layout did not survive the anti spam machine.. it undid all the spacing .. end edit  

pepsi1 pepsi1
Guru | Posts: 1718 | Joined: 09/11
Posted: 06/24/12
02:23 AM

( will get you all the books you will ever need.Start with a basic tear-down book and rebuild. It will tell you how to look for worn out and/or broken parts. Don't be afraid to ask questions.

Sitting in the driver's seat. That is considered the left side.
So on the left side (driver's side) you have cylinders from the front..
#1 #3 #5 #7...Passenger side...#2 #4 #6 #8.

The parts you've shown are nothing out of the ordinary. Have the block pressure tested. Like Wayne said throw the 993 cylinder heads in the garbage. Don't even bring them to the machine shop to get torn down. (Put that money toward good heads)!

JUST A LITTLE FYI: As long as your buying tools buy an electric etcher. Mark all your parts with a number some way you will be able to identify your parts when you get them back from the machine shop...You can use a metal stamp set. I don't like using them as I think they are a little harsh hitting the connecting rod cap or the main bearing cap. You can fracture a cap and not know it. (THATS MY 2 CENTS ONLY).

How ever you mark them you will know your getting your parts back. After you get all your parts back from the machine shop, and the diagnosis is in then you can start purchasing your new parts.Until then don't worry about that. But I can't stress this enough, mark your parts.

Another FYI: When you said your engine was in a C-20 truck. You may have good bottom end parts.I.E. crank,pistons, etc. I've seen machine shops take those good parts and replace them with a lesser part then yours. If you know whay I mean...,When you get your Crankshaft out,,give us the part number from them. It's easy enough to find out what it is. When your ready for parts we can figure those out also. Of course it depends on your budget, as always....
Thanks Bob  

1 |  2 |  Next   | Last