Sudden back firing issue when starting when engine warm

[guys72Mach1]

Lots of good tips to help me narrow this down, I appreciate it guys. Looks like it's going to be a busy this weekend trouble shooting. I did start it a couple of time yesterday, starts right up when cold no issues, after it's warm same thing, have to crank it over several times then on second try starts right up, no back fires this time though. Took it for a short drive ran like a bat our of hell, no issues, to busy at work to do more with it until this weekend.

- Starts fine cold every time

- Runs great once started

- Warm engine requires cranking several times doesn't start, then starts right up on second cranking attempt

- At times back fires out of drivers side exhaust upon warm start up.

I have a long list of recommendations that'll I go down the list doing this weekend to see if I can resolve it without having to leave it with the strangers at a repair shop.

(Warm engine requires cranking several times doesn't start, then starts right up on second cranking attempt)

This is when you need to try the WOT(wide open throttle). If you hold your foot to the floor and crank it and it fires right up, then you know it's is being flooded.

If that changes nothing, then I would move on from the carb.

The one side backfire is odd.

As Wolverine said after he moved the ladies in the red dresses out of the way, put his stogy on the ashtry and sipped some scotch, maybe a valve is torqued improperly and not closing all they way.

Those should be no more then 22ft lbs, and you should be able to just spin the pushrod with your fingers after it's torqued down with both valves closed.

Let us know, we are all interested in the solution. Although, I'm sure you are more intersted in it then us!

 

[Jim and Jutta]

.

(Warm engine requires cranking several times doesn't start, then starts right up on second cranking attempt)

This is when you need to try the WOT(wide open throttle). If you hold your foot to the floor and crank it and it fires right up, then you know it's is being flooded.

If that changes nothing, then I would move on from the carb.

I failed to mention I did try your recommendation yesterday with a warm engine, held it to the floor when cranking first time, no difference still didn't start the first time but fired up on second cranking. It's almost as if it needs the first cranking to prime the carb when warm. Whats confusing to me is why it starts right away when cold if it's the carb or fuel clogging.

 

[Wolverine]

How about this theory(just thinking out load):

When you engine sits warm, it boils gas out of the carb. To get the car started you need to get the bowls filled.

Refutation of this is the car should still start after a little cranking, and shouldn't backfire out the exhaust. Also, why would it start cold if gas boiled out when warm.

I think this theory stinks. But, if motor is consistently not starting when warm, try the following to a warm motor:

1. What is the position of the choke plates when motor is warm?

2. Before attempting a start, put a 1/2 teaspoon of gas into the top of the carb.

If she fires right up, then it would seem NO GAS at warm start. Maybe floats are too low?

I am glad to here she is running great when warm. I intend on using that carb on my build.

How do you typically start the car? For example, do you give it one pump of the gas pedal, release the gas and then turn the key?

Does your distributor get it's vacuum from the manifold, or do you use a WARM TEMPERATURE VACUUM SOLENOID on your car? This is the vacuum tree typically at the front of the motor that would provide vacuum to your distributor.

Does your distributor have and advance and retard vacuum pod, meaning 2 vacuum lines on it?

Do you know if your builder installed the turkey pan under the manifold?

Also, this thread is a little long. Maybe you could summarize the suggestions, questions and your actions. This is going to be something simple. I feel for you.

 

[Jim and Jutta]

How about this theory(just thinking out load):

When you engine sits warm, it boils gas out of the carb. To get the car started you need to get the bowls filled.

Refutation of this is the car should still start after a little cranking, and shouldn't backfire out the exhaust. Also, why would it start cold if gas boiled out when warm.

I think this theory stinks. But, if motor is consistently not starting when warm, try the following to a warm motor:

1. What is the position of the choke plates when motor is warm?

2. Before attempting a start, put a 1/2 teaspoon of gas into the top of the carb.

If she fires right up, then it would seem NO GAS at warm start. Maybe floats are too low?

I am glad to here she is running great when warm. I intend on using that carb on my build.

How do you typically start the car? For example, do you give it one pump of the gas pedal, release the gas and then turn the key?

Does your distributor get it's vacuum from the manifold, or do you use a WARM TEMPERATURE VACUUM SOLENOID on your car? This is the vacuum tree typically at the front of the motor that would provide vacuum to your distributor.

Does your distributor have and advance and retard vacuum pod, meaning 2 vacuum lines on it?

Do you know if your builder installed the turkey pan under the manifold?

Also, this thread is a little long. Maybe you could summarize the suggestions, questions and your actions. This is going to be something simple. I feel for you.

- It could be the gas is boiling out of the carb when warm, it's a consideration.

- Yep the Edelbrock Thunder Series carb 650CFM really woke the engine up over the Autolite 4300D I had on it. Only issue was percolation issues I didn't have with the Autolite, I installed a heat insulator under it that appeared to take care of it. I have a a ram air filter that holds in more heat so it may not be an issue if you're not using one. When I was having percolation issues it just wouldn't start and take along time to start, never had back firing.

- When cold I start the car by turning the key to the on position, pump it slowly once then start it. When warm I just hold the pedal about 1/4 of the way down with no pumping...that's the way it always started best in the past.

- The builder left the turkey pan off he said it didn't need it.

- the distributor only has one vacuum line

Here's a few pictures, maybe someone will see something out of place I'm missing.

 

[guys72Mach1]

How about this theory(just thinking out load):

When you engine sits warm, it boils gas out of the carb. To get the car started you need to get the bowls filled.

Refutation of this is the car should still start after a little cranking, and shouldn't backfire out the exhaust. Also, why would it start cold if gas boiled out when warm.

I think this theory stinks. But, if motor is consistently not starting when warm, try the following to a warm motor:

1. What is the position of the choke plates when motor is warm?

2. Before attempting a start, put a 1/2 teaspoon of gas into the top of the carb.

If she fires right up, then it would seem NO GAS at warm start. Maybe floats are too low?

I am glad to here she is running great when warm. I intend on using that carb on my build.

How do you typically start the car? For example, do you give it one pump of the gas pedal, release the gas and then turn the key?

Does your distributor get it's vacuum from the manifold, or do you use a WARM TEMPERATURE VACUUM SOLENOID on your car? This is the vacuum tree typically at the front of the motor that would provide vacuum to your distributor.

Does your distributor have and advance and retard vacuum pod, meaning 2 vacuum lines on it?

Do you know if your builder installed the turkey pan under the manifold?

Also, this thread is a little long. Maybe you could summarize the suggestions, questions and your actions. This is going to be something simple. I feel for you.

- It could be the gas is boiling out of the carb when warm, it's a consideration.

- Yep the Edelbrock Thunder Series carb 650CFM really woke the engine up over the Autolite 4300D I had on it. Only issue was percolation issues I didn't have with the Autolite, I installed a heat insulator under it that appeared to take care of it. I have a a ram air filter that holds in more heat so it may not be an issue if you're not using one. When I was having percolation issues it just wouldn't start and take along time to start, never had back firing.

- When cold I start the car by turning the key to the on position, pump it slowly once then start it. When warm I just hold the pedal about 1/4 of the way down with no pumping...that's the way it always started best in the past.

- The builder left the turkey pan off he said it didn't need it.

- the distributor only has one vacuum line

Here's a few pictures, maybe someone will see something out of place I'm missing.

Wolv...Except if the floats were low, it wouldn't be getting enough fuel and would just fail to fire. The backfire would indicate too much fuel and excess fuel is sitting in the exhaust port.

Not a big Edelbrock carb fan myself. Reminds me too much of a Carter AFB. Consistant perfomance, but not does not have the peak performance I want and you a re limited on tunning the carb to fit your engine. Plus lots of parts inside...but that's just me. I digress..

Sooooo, what do the primary butterlys look like when it's hot? I am thinking that maybe when you shut the car off, they are closing. Then when you go to start, the choke is stuck closed and it's not getting enough air. Maybe the first crank and throttle jiggle loosens it up?? I dunno, hard to see without seeing!

Maybe, after it's warmed up and you shut it down, pull the air cleaner and look at the butterflys before you try and start it again.

They should be open. If they are closed, it's a choke issue.

Starting to get a headache!! Must.....have........beer.........stat!

 

[Jim and Jutta]

Sooooo, what do the primary butterlys look like when it's hot? I am thinking that maybe when you shut the car off, they are closing. Then when you go to start, the choke is stuck closed and it's not getting enough air. Maybe the first crank and throttle jiggle loosens it up?? I dunno, hard to see without seeing!

I won't have time to tinker with it until this weekend but did start it up and take a pic with the engine warm, the choke opens as it should when the engine is warm. Taking that picture what I did notice is the shop that installed it for me and also ran a new stainless steel fuel line to replace my old fuel line , didn't install the fuel filter I provided with Carb to be installed, in fact I can't find any kind of fuel filter on it. Maybe that's part of the problem???

 

[Qcode351mach]

Just for the heck of it when this happens again..try pulling a plug wire & see if you have spark during the first try when you crank.. At least this would rule out a possible electrical issue..

 

[Wolverine]

Just for the heck of it when this happens again..try pulling a plug wire & see if you have spark during the first try when you crank.. At least this would rule out a possible electrical issue..

Alternatively to pulling plugs, take a timing light to see if you are getting a spark at the plugs.

As bad as the motorcraft filter was, the aftermarket filters are a real pain. I have the Edelbrock filter on an XR7, but strictly because it looks better, not that it is better.

Don't forget to try a 1/2 teaspoon of gas into the butterfly prior to the first warm start.

And, I would devise a better return spring hook.

Good luck.

 

[Jim and Jutta]

Just for the heck of it when this happens again..try pulling a plug wire & see if you have spark during the first try when you crank.. At least this would rule out a possible electrical issue..

I'll see if I can get the wife to hold the wire while I crank it over, if she kicks my ass I'll know it's firing. On second thought I'd better let her do the cranking and I'll watch for the spark.

 

[Wolverine]

I'll see if I can get the wife to hold the wire while I crank it over, if she kicks my ass I'll know it's firing.

My wife usually kicks my ass when it isn't firing.

 

[TommyK]

With no fuel filter I expect you may have picked up some debris which has lodged itself somewhere in the idle circuit. The reason it starts when cold is with the choke closed it is providing a rich enough idle mixture to fire. When warm and with the choke open it is too lean and is lean miss firing out the exhaust. The reason it starts on the second try when warm is probably from the accelerator pump shot but back fires due to lean miss.

 

[Qcode351mach]

I'll see if I can get the wife to hold the wire while I crank it over, if she kicks my ass I'll know it's firing.

My wife usually kicks my ass when it isn't firing.

lollerz

 

[Jim and Jutta]

Just for the heck of it when this happens again..try pulling a plug wire & see if you have spark during the first try when you crank.. At least this would rule out a possible electrical issue..

Don't forget to try a 1/2 teaspoon of gas into the butterfly prior to the first warm start.

And, I would devise a better return spring hook.

Good luck.

I'll try the 1/2 teaspoon of gas next time I get it warmed up. I also questioned the return spring hook, looks flimsly but works, but that last thing I want it not return to idle when I let up on the gas. What would you recommend for a better return?

 

[Qcode351mach]

I also questioned the return spring hook, looks flimsly but works, but that last thing I want it not return to idle when I let up on the gas. What would you recommend for a better return?

http://www.summitracing.com/parts/AAF-ALL54200/?rtype=10

 

[Wolverine]

I also questioned the return spring hook, looks flimsly but works, but that last thing I want it not return to idle when I let up on the gas. What would you recommend for a better return?

http://www.summitracing.com/parts/AAF-ALL54200/?rtype=10

$43????? Are you kidding me? Didn't the carb cost like $250 and now $43 for to hold 2 springs?

Am I the only one that believe is Edelbrock sells you a carb "BUILT/TUNED" for your motor, that piece should come with the car?

Not that this pieces isn't nice, but $43????

I am going to start a new thread in this regard. I will post my solutions and perhaps others have theirs.... $43????? plus tax and shipping...

 

[Jim and Jutta]

With no fuel filter I expect you may have picked up some debris which has lodged itself somewhere in the idle circuit. The reason it starts when cold is with the choke closed it is providing a rich enough idle mixture to fire. When warm and with the choke open it is too lean and is lean miss firing out the exhaust. The reason it starts on the second try when warm is probably from the accelerator pump shot but back fires due to lean miss.

Sounds reasonable to me since it came on all of sudden with no recent changes to the engine. I've got some gumout I can spray into the carb while it's running to see if that clears any debris, it's not a durashine carb so the gumout shouldn't hurt anything (?)...worth a try, easy enough.

 

[73vertproject]

Update?

 

[Jim and Jutta]

Update?

Haven't been able to tinker with it much this week other than starting it a few times due to work (I know that sucks), taking it out tomorrow morning on a 60 mile Mustang club breakfast cruise, when I get back the engine will be nice and warmed up, going to first try the small amount of gas in the carb before trying to start it (as recommended by Wolverine), then go from there, gumout carb cleaner, timing check etc. Who knows the 60 mile cruise may clear it up if it's something clogging the carb (I have towing on my insurance AND I'm a AAA member so I have no fear).

Jim

Jim

 

[Totalled]

Where/when are they going?

 

[Jim and Jutta]

Where/when are they going?

We're meeting tomorrow at 9:45 at Top Foods parking lot in Olympia off of Black Lake Blvd, at 10:00 we're hitting 101 and cruising to Elma to have breakfast at the Rusty Tractor Inn. If you can make the cruise breakfast is on me!

Jim