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FE Power Forums => FE Technical Forum => Topic started by: Robin Hood on August 18, 2022, 07:18:55 AM

Title: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 18, 2022, 07:18:55 AM
I own a 1964 Thunderbolt Tribute car that I can’t get to run strong, pops through the carbs or starts to cut out when accelerating.
12.7 compression, 20 degrees initial timing, 110 octane. Installing fuel pressure gage to determine if I’m starving it for fuel?
It has glimpses of unreal power but then starts cutting out and sometimes popping through the carbs.
Any help would be appreciated
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: GerryP on August 18, 2022, 09:06:03 AM
Sort out the timing first.  Back your total down to around 35 total, which generally is going to put your initial at around 15.  Your symptoms point to timing too far advanced.  The popping would be out the exhaust.  Though that can be hard to distinguish from intake popping.  If you have access to an ignition oscilloscope, you want to use that and see how sturdy your ignition system is.  But the easiest thing to do is to dial back your timing since that is an instant A-B comparison and you can move on from there.

It's wise to also baseline your fuel system.

One other thing that causes what you're describing are failing valve springs.  Once the valves float, the engine seems as though it has a rev limiter on it.  Rule out the simple stuff first.  Again, start with the ignition. 
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Falcon67 on August 18, 2022, 09:59:16 AM
Typically - not always, but typically - backfire in the intake is a lean condition or some condition with valves/springs.  Hitting a "wall" at 3500 could be both a weak spring issue and/or fuel delivery problem. 110 is right on the edge for 12.7 IMHO and per VP.  Like Gerry says, check your max advance with the 20 initial.  You can run as much initial as you can stand, it's the max that causes issues. 

Exhaust pops are lean conditions in the exhaust - gasket leak, loose bolts, etc.  Especially if it pops on decell, like off the throttle in the traps.  If you lift off and it pops through the exhaust it's almost guaranteed that's an air leak in the exhaust, usually at the header flange.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 18, 2022, 10:25:47 AM
Thank you for your advice i do appreciate everyones input as i sort this out.
When I have the initial timing set to 16 it runs smoother at middle range but it still hits a wall around 4,000rpm, starts to cut out and backfire.
I am going to install two fuel pressure gages to see what the pressure is. Not sure what is recommended for this setup but at least i will have a base line to go from.
It almost seams as though it is starving for fuel during WOT. Any thoughts on what fuel pressure the feed rail should be set to?
Thanks for your help.
 
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: GerryP on August 18, 2022, 11:45:02 AM
For Holley carbs, limit your pressure to six PSI max.  Over that will blow the needle off the seat or push past the o-rings.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Stangman on August 18, 2022, 06:06:57 PM
Mechanical fuel pump or electric? I had a mechanical pump do a lot of what your saying. I could drive anywhere at normal operation but getting on it it would buck and fall on its face. Seemed like ignition and because it ran good around town I wasn’t thinking fuel pump.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 18, 2022, 09:09:03 PM
Thank you for the info on the fuel pressure, I will check is my once my new gage comes in the mail and let you know what it is.

Also, it is a mechanical fuel pump with an electric pump pushing to it from the tank. It is a factory fuel pump that runs into a large fuel filter canister. You can see it in the attached photo
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 20, 2022, 09:42:27 PM
Can someone tell me what the fuel
Pressure should be for my car? I installed an in-line fuel pressure gage between the fuel rail and the front carburetor and it is 3.5 psi. Seams like it should be higher for my car.
Thank you in advance
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Stangman on August 20, 2022, 11:33:46 PM
Between 5.5 and 6.5 psi is good
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: frnkeore on August 21, 2022, 01:22:19 AM
The spec, I grew up with, for Holley 4150/4160's, was always max 6lb, min 3 lb. At WOT, the pressure can drop but, shouldn't go below 3 lb.

But, that assumes a good needle & seat as well as float.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 21, 2022, 05:41:28 AM
What are you running for ignition?

Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 21, 2022, 07:40:18 AM
Thank you!
I am running OEM coil and cap and rotor I believe.
When the motor was built 20 years ago it was done to be factory for authentication.
I want the vehicle to represent the intention of factory however, I would like it to run like it should.
Driving it into a car show it acts just fine, but put your foot in it and it struggles to make any real power.
Dyno at the real wheels was 350hp at 4,000. Above 4,000 and it wants to cut out and falls on its self.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 21, 2022, 07:46:13 AM
I had a Pertonix 3 do that on a dyno. Regardless of the trigger I would look and see what the timing is doing when it breaks down, also consider unhooking the tach to see if it changes

Additionally, I have seen point pigtails go brittle, dist grounds straps fail or go missing and condensers fail, all of which could to what you are seeing

Last look very close at the underside of the cap for carbon tracking and keep plug gaps at .035 or so, wider makes it harder for the secondary ignition
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: rockhouse66 on August 21, 2022, 07:57:18 AM
It would be really handy to have another distributor to stick in there for testing purposes.  I have a Mallory dual point I use when I want to eliminate issues with whatever car I am having concerns about.  Do you have another or can borrow one nearby?  And also try another coil to eliminate a weak spark.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 21, 2022, 07:49:34 PM
So today I did the following.
New Holley Fuel Pump and Pressure Regulator- set at 5.5psi at the fuel supply line to front carburetor
New MSD Coil
New Autolite Spark Plugs gapped to .035
Set initial timing at 18-BTDC
Did not run well, popping through the exhaust on acceleration and same rev limiting
Reset initial timing to 26-BTDC, no popping on acceleration and shows glimpses of starting to get after it, pulls harder up to about 5,000 with some hesitation but does run better.
 It like the larger gap in the spark plugs and the advanced timing at 26. That just seams to far advanced though…..
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: 66FAIRLANE on August 21, 2022, 08:32:59 PM
Have you verified true TDC on the balancer?
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: e philpott on August 22, 2022, 02:26:24 PM
Cam wiping out ?
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 23, 2022, 11:07:37 AM
Here is what I would do

1 - Triple check firing order - even the best of us cross a wire now and then.  Changing timing can make a crossed wire or wires run better-ish
2 - Verify TDC - could be a slipped balancer or mismatched pointer/balancer - Seems likely due to advancing the timing helping. Your 26 could be really zero but indicated wrong.  Piston stop is really the only accurate way, but bringing it to TDC with a dowel, etc, and verifying that both #1 valves are closed can show gross mismatch of marks (although a stop is the way to do it)
3 - Put a light on it and see if timing hops around when it misfires
4 - Take a compression test, look for differences cylinder to cylinder.  Doesn't seem that way to me, but need to eliminate a tight or bad valve.
5 - Check to see if any of the rockers aren't moving much, could intake a wiped cam





Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 23, 2022, 12:39:19 PM
I will check TDC on Friday when I return to where my cars. Thank you both for suggesting it!
I will go through the firing order as well to make sure it is correct.
I did set the valve lash at .028 when the engine was cold because the local speed shop set them at .020 cold and from what i was reading online at the time it was mentioned that .028 was the best cold setting for the valves,
When I adjusted the valves it seamed as though all the rockers were moving well but I will recheck this weekend, along with the valve lash to make sure I did not make one to tight or to loose.
Is .028 a good cold lash for my valves?

Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 23, 2022, 02:05:59 PM
I woud consider .028 to be on the loosest side of good I would want, but it is good if done on the base circle correctly as it makes no doubt you don't have a valve too tight.

Valve lash is generally better to be slightly tight over loose to ensure it uses the lash ramp and doesn't slam at the end of it, but .028 with a 1.76 rocker should be fine.  I run many down to even .012-.014 with alum heads, iron block, you just can't have zero
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 23, 2022, 03:55:52 PM
I will recheck to be sure what they are at currently. Thanks for your advice, I appreciate it.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: machoneman on August 24, 2022, 06:42:21 AM
Also, be sure #7 and #8 plug wires do not run parallel. Route them to cross at say 90 degrees and keep them well apart to prevent spark jump.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 24, 2022, 08:54:07 AM
I will check TDC on Friday when I return to where my cars. Thank you both for suggesting it!


I don't want you to assume I think you don't know, but have seen some odd techniques, so offering one good, one sort of emergency room trauma that might send you back to the good one

1 - Best way is to use a piston stop, thread it in the plug hole, turn the engine with a wrench until it hits, mark the balancer at the timing mark.  Turn it the opposite direction until it hits again, mark the balancer.  Absolute true TDC will be exactly the middle when measured between those two points

2 - Battlefield check - plug out, bump the starter until you get very light pressure on your finger.  Slowly by hand, with a dowel or some other tool, have a buddy turn the motor by hand, same direction (clockwise from the front) and watch/feel the dowel raise.  When you feel it ever so slightly drop, go back to highest point  NOT exact, but it would show if your balancer ring slipped by a large amount or you had the wrong balancer/pointer combo

If that were the case, then you can get a piston stop.  If the balancer slipped you can get a new one, if the timing pointer doesn't match, you can remark your timing marks

The good thing is when you do this and check the firing order, 2 troubleshooting steps are done and behind you.  Best way to eat that elephant
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: SMA390 on August 24, 2022, 09:23:16 AM
What type of distributor ? Is it points or Msd...  I had the same problem once and turned out the magnetic pick up on the MSD dizzy was bad so I replaced the magnetic pick up. And I  installed it incorrectly, I had it in upside down, the car had the exact symptoms you described, Pulled it and installed it correctly and ran good then.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Falcon67 on August 24, 2022, 10:48:44 AM
Mag pickup wired with wrong polarity will cause all kinds f weird issues, especially when hooked to a good MSD box.  But I don't think OP has that setup.  All the above is good stuff to look into.  When you said your set the timing back to 26 initial and it ran better, that was a big red flag that timing, balance, timing chain, firing order, ignition trigger setup - something could be contributing to the problem. 
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 24, 2022, 12:34:57 PM
This forum is the best! I am printing all of these suggestions out and will go through them one by one to eliminate any of these possibilities.
I am a new 427 owner but i have owned a lot of small block stuff and newer modular stuff.
I havent worked on engines/cars since my father passed in the mid 90's so my knowledge is limited in actual execution but not from an understanding point. But please assume i'm an idiot as I tend to render things down to its simplest form of understanding:)
I have not heard of the dowel method for finding TDC but i understand the concept.
As for the distributor, when I removed the cap there was only an electronic module inside no points. I was expecting points and I know how to adjust them from years back but i have not worked with this system, thank you for the advise on how to check that out I will for sure Friday.
Thanks to everyone for sharing your knowledge i prefer to fix this on my own if possible as I feel like i have the ability but obviously all of your help is definitley going to give me the best shot. I dont want to have to ship the car to someone or remove the engine and send it to a professional if I can avoid that.
Also, I will report back on each suggestion and what if any impact it had on diagnosing/performance so everyone knows.
thanks again
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 24, 2022, 05:01:45 PM
Awesome, looking forward to your response

If you could, take a picture of the ignition module.  I had the same thing happen with a Pertronix 3 on the dyno.  Had us scratching our heads. We slipped a set of points in and made 608 HP instantly...I am not one for parts swapping, but after you check the foundational stuff, we'll all keep going
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: sixty9cobra on August 24, 2022, 07:34:44 PM
How old are the valve springs?
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: oldiron.fe on August 25, 2022, 11:18:47 AM
           all of above- if this is a older build make SURE the fuel system is cleaned /flushed very good !!  at that comp. ratio i would use my favorite snoco 112 while getting the tune right --also if spring pressure wasnt released on long storage you need to be sure of spring pressure-good luck john  ---                                      old iron                         
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Falcon67 on August 25, 2022, 11:43:51 AM
>As for the distributor, when I removed the cap there was only an electronic module inside no points.

As above - Identify / post a picture of the module in the distributor.  If the output it connected to a control box, then also a picture or some identification/mfg/model/etc will help us help you some more. 
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 25, 2022, 07:48:59 PM
Hey Guy's,
I have attached a picture of the module inside the cap. Getting the cap out from under the carburetor was a bit difficult! no clearance  :)
Here is what i have done/checked today:
1- There is no control box for the ignition.
2- I have drained the fuel and replaced with VP Racing 110, thanks for the tip John, Also to the valve train questions / suggestions, I cannot say if it set for long periods of time without running or if they were ever decompressed during storage. I believe longest without running may have been 6 months?
3- I bought a new Ignition Module to swap out the one in the photo
4- Double checked firing order and it was correct
5- Made sure #7 & #8 wires are not running close together or crossing over each other in parallel path
6- Purchased piston stop to check TDC accuracy of my balancer/pointer
Tomorrow:
1- Replace Ignition Module
2-Replace Cap & Rotor
3- Check TDC / Set if needed
4- Recheck Timing and set to 15 degrees BTDC
5- Check valve lash and set to .020 cold?
5- Test run/drive to see how it runs (I will report back to everyone tomorrow)
i have attached a couple photos of the car ( I like my license plate, although right now it doesn't really apply ;D)


Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: WConley on August 25, 2022, 11:27:50 PM
Have you verified that the distributor advance is working?  I remember years ago a friend had a small-block Ford in his boat that was doing the same thing as your car.  Turned out the centrifugal advance linkage was stuck from corrosion.

It should be easy enough to check with a timing light while blipping the throttle.  You should see that timing mark move up a lot with rpm.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 26, 2022, 05:24:41 AM
It does move with acceleration and with quick revs.
Thank you for your help
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 26, 2022, 06:23:24 AM
So that is an Ignitor 2, which is usually a decent module, but they can fail.  I don't see the small ground strap, it's not necessarily required, but I put them back to make sure it has another option to ground, especially if you have a good amount of the heat sink goop under the module.

If you could get it to misbehave with a timing light on it, it would be helpful to prove a bad module, but I think the TDC check should be the priority.

FYI - I have one act real unhappy and it was a burnt coil wire end too, couldn't see it, Ohmed OK, but couln't handle a heavy load high RPM.  Also would show up with a timing light if you can make it burble
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: GerryP on August 26, 2022, 06:36:05 AM
From you list, make one change at a time and test the result.  If you do all of it, you will never know where the problem was and if it comes back, you are back to square one.  Do the simplest and most likely thing first and work your way down the list.  Yes, it does take more time using a methodical approach to problem solving.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: rockhouse66 on August 26, 2022, 07:05:34 AM
It absolutely needs a ground wire between the breaker plate and Pertronix module.  Good eye Ross.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: machoneman on August 26, 2022, 07:27:53 AM

FYI - I have one act real unhappy and it was a burnt coil wire end too, couldn't see it, Ohmed OK, but couln't handle a heavy load high RPM. 

Had that happen as well but once at the race track in our towed-to-the-track racer. Started fine and ran up to about 3K and then no more. Found out after some frantic checking I'd left the coil-side wire less than 1/2 into the deep tower of my Accel coil  back home in the garage! Pushed it in all the way and voila!

Point is, the brass terminals on the coil wire can sometimes prevent one from pushing in the wire enough to make good contact. Separately, does the car have a well-grounded ground strap from a head or the intake to the firewall or frame rail?
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 27, 2022, 09:55:45 PM
Here is what I did today guy's.
1- checked TDC with new piston stop tool- was 1 degree different, I checked it again and was 1/2 degree so i called it good to go.
2- Replaced the Petronix
3- Replaced Cap & Rotor
4- Checked timing and was at about 18 but every few seconds the timing was moving 5-8 degrees. checked wires again all were tight and inserted into the can and plugs correctly, the car definitely ran better in the garage, so I took it for a drive and it ran much better, pulled hard with some spots of hesitation/misfiring but no back firing and the engine was definitely willing to run the RPM's up without falling on itself like it did the day before.
I was extremely happy with these results, however, I felt like there was something I was missing because it still had hesitation and a slight misfire.
So then I did the following:
5-Rest the timing to 15 BTDC, and I noticed out of the corner of my I a spark jumped from the number 5 spark plug connection on the cap to the front float bowl on the carburetor!so I took a small screw driver and touched the top of the wire at the cap and when I got close to the carb with the screw driver shaft it arced to the carb, I checked the #1 cylinder and same thing happen.
I checked all the wires and only #5 and #1 were arcing on occasion. so i attributed the misfiring to that.
6- I added a 1/16 rubber spacer between the cap and carburetor to help with insulation. I know they are most likely arcing to each other but I first wanted to try with a simple fix.
Started the car and it was definitely a different car, idle was more consistent, checked the timing still at 15 with an occasional blip but it was remarkably better.
Throttle response was considerably better.
Took it for a test drive and the normal acceleration was very good with a rare misfire but overall ran very well, turned around and heading back to the house i put my foot in it and it was unreal, don't even know what to say other than we taint in Kansas anymore!
It lost traction for about 30 feet and then pulled like a brute (with that rare misfire) all the way until i got out of it at about 4500 in 4th gear because I wouldn't have been able to slow the car down enough to make my driveway:)
there is still a small misfire that I think is the arcing between those two wires but it was very exciting to see my car
finally start to run very close to the way it should.
Today I bought a new set of wires and will install them tomorrow. hopefully that will fix the misfire issue, It is very tight between the top of the spark plug wires and the bottom of the carburetor, do they make a lower profile distributor ao i can gain some clearance? or should i add a small riser to the carburetors?
I want to thank each of you for all your input and direction to help me with my car! Everyone on this forum has been awesome and i really appreciate the help. It has also been very fun to work on the car with probably like 500 years of experience helping me.
thanks a lot gentlemen!
Also,I own a fishing tackle company and if anyone of you guys fish or has someone that is into fishing and need any lures send me a message and I will take care of you.
My web page is in my bio (acmetackle.com)
i will post the results after i replace the spark plug wires.
Than You!!
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: WConley on August 28, 2022, 12:27:50 AM
Glad to hear you're getting it it sorted!  If you had an MSD distributor you could run the low profile "crab cap", but I'm not aware of any that readily fit a stock-style FE distributor.

Swartz Racing makes a sweet offset distributor for dual four-barrel FE's, but I'm not sure how long it would take to get your hands on one.  That would be the hot ticket though!

http://www.swartzracingmanifolds.com/distributors/
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 28, 2022, 03:49:18 PM
Good methodical troubleshooting, well done!  Not only are you getting there but you know your foundation is solid!
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 28, 2022, 07:16:04 PM
Right on Guys! Thanks for the input.
So I do hear my rockers at idle, I’m wondering if I should reset the lash to .020 cold? As I mentioned I set them to .028 cold.
Also, I keep having a small leak on the bottom side of my water outlet connection to the pressure tank. The threads seam a bit sloppy when I replaced the gasket which didn’t help the leak. It looks like it’s coming out around the bolt hole.
Thanks for the help, it’s getting better everyday I make small adjustments.
 
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: 66FAIRLANE on August 28, 2022, 10:49:31 PM
What cam is it? 028 sounds rather large. Is this an all iron combo? My experience (not as much as many here) has been that with stock adjustables, iron heads and block the difference between hot and cold lash was zero. With iron block, alloy heads and Erson rockers they open up 007 when hot.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 29, 2022, 04:53:54 AM
I am unsure of the cam as the person who built the engine died 10 years ago and all the engine details were lost.
It has cast iron components with what looks to be original rockers (they are stamped steel).
From what I was told internally the engine was built to original specs. But again I would need to check it
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 29, 2022, 06:32:19 AM
Here are some rules of thumb

1 - On a solid roller or solid flat, the tightest lash you can run, without holding the valve off the seat at all operating temperatures is the best for parts longevity
2 - Lash is a tuning tool, less makes the cam act bigger, more makes it more mellow.

I would run them down to .018 cold, could even go tighter, but that's a good safe number.  I think .028 cold is crazy loose for alum heads and very loose for iron.  That leaves plenty of of lash ramp available to spin and accelerate the lifter

Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 29, 2022, 01:09:52 PM
Thanks Ross! I am going to adjust them tonight.
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 30, 2022, 08:58:12 PM
Today I adjusted the valve lash to .018 and rest the timing to 18 BTDC.
I adjusted the the carburetors to 1&1/4 turns out, this produced the highest vacuum 32hg.
Adjusted the idle to 850rpm.
The car performed without issue and pulled hard as far as I wanted to push it! What a difference on the top end performance.
Thank you very much. I feel much bettter about the car and have no concerns now for valve float or sticking. It really runs great now!!!
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: My427stang on August 30, 2022, 09:56:56 PM
Very glad to hear! Nice work!
Title: Re: 427 popping through the carburetors during acceleration and no power above 3500
Post by: Robin Hood on August 30, 2022, 10:19:26 PM
Thanks for the help