Engine sputtering on heavy acceleration

[JIMOCO]

I need your help in diagnosing an acceleration problem. It has happened two times recently. The first time I was traveling about 50 mph in a two lane 55 mph zone. I had an opening and got on the gas to pass. As I got along side the car I was passing my car started to sputter as though I was hitting the rev limiter. I can't remember if I was in third or fourth gear but either way, I was below 4,000 rpms. I thought it might be a fuel problem and changed the filter. A couple of weeks ago, I was entering the highway and got on it in a spirited way. I was winding out the gears and shifting at about 4500 rpms. I shifted to forth at about 80 mph and could not accelerate any further. The engine was sputtering and acceleration stopped but I was maintaining 80 mph. Based on gear ratios, 3.27 rear, 1-1 fourth and tire size, rpms at 80 are about 3500. I did not look at the actual as I backed off shortly after the sputtering started. It seems like a fuel problem but I am not experiencing any issues (rev limiter) as I wind out the gears to 4500 rpms. Any thoughts will be appreciated.

[hineas]

Do you have the EFI or a carb?

EFI needs higher fuel pressures, have you checked that? I had a friend who didn't install the return line for the gas and had similar issues as well (but more pronounced)

[JIMOCO]

I should have noted that I am carbed. Edelbrock thunder series 650 cfm. Mechanical fuel pump, RPM air gap intake and edelbrock performer heads.

[Al_C]

Sounds like fuel. Is it all the time, or intermittent? Everything check out on the ignition system? Based on my own experience (of course with a different engine and pump setup...), I'd check the fuel pump first. To my little brain, it sounds like you are getting *some* fuel, but not always enough. But if it were the fuel pump, I'd suspect it would happen all of the time.

[GoDadGo]

Question:..Did the issue continue to happen over and over or was it a one-time occurrence?

The strange thing about the AVS and Performer Series carbs is if you have not used the secondary jets in a while, the first time you really goose it your car will stumble.
Basically, the fuel needs to be drawn through the secondaries if they haven't been used in a while so it's a common problem often misdiagnosed.
If the issue continues after the first hard acceleration, you may have crap in the rear jets or gooed-up secondary circut passages.
Pop the top off and take look to see if you've got stuff in there.
You may need to do a rebuild to clean things up.

I Hope This Helps You & I Hope You Find Your Issue Sooner Than Later!

Good Luck!

I'm running an 800 AVS so I'm familiar with this carb.

Rebuild Video:
https://youtu.be/mNz1DLcocWc

[Rdone585]

You could take a quick look at your distributor cap and rotor, but I suspect it's fuel related. Are you able to monitor fuel pressure at or near the carb? I've also been told that many carbs have an inline filter at the carb inlet. So if your filter didn't catch everything there may be crud in one or more of the (internal) carb filters. I have a very fine mesh inline filter just before the regulator. That filter has clogged more than a few times, and results in similar issues you're describing.

[JIMOCO]

The problem has happened on the two occasions noted. The only filter I have on the fuel line is the cannister filter that came with the kit that I installed near the gas tank. I replaced that after the first time I had the issue.

I did note that I did not feel the secondaries open. I will look at that but I think it would have begun to loose fuel at the higher RPMs at the top of each gear. It does not and only sputters after the shift into 4th. It is almost like there is a governor preventing me from exceeding 80mph.

I will try again but I am loosing the good weather here in central PA. I do not want to push the limits with summer tires. If anything comes to light I will post. Thanks for the thoughts.

[Jeff Kleiner]

... Mechanical fuel pump...


...The only filter I have on the fuel line is the cannister filter that came with the kit that I installed near the gas tank...

Jim,
Filter should be AFTER the pump, on the pressure side, not the suction side. That canister filter is intended to be used with an in-tank electric pump. It does sound like you're running out of fuel under load and although I can't say that it's a certainty there is the possibility that if the pump has weakened it is having difficulty pulling through the filter on the suction side.

Jeff

[J R Jones]

By design, tank (electric) pumps push well but do not suck well. Mechanical (diaphragm) pumps suck harder. Nonetheless as Jeff states you protect the carb most effectively after the mechanical pump. That is how OEMs do it.
Your problem sounds like a lean condition due to secondaries with inadequate fuel. The secondaries open without fuel and the primary fuel flow is not enough.
You can test my theory by blocking the secondaries closed so you can accelerate on primaries only. That is easier with vacuum actuated secondaries, mechanical secondaries might be more difficult.
If that test stops the stumble, you need to clean the secondary fuel circuit. Good season for that.
jim

[NAZ]

Just a note: you are not supposed to "feel" the secondaries open -- hear them, maybe.

If it's a fuel issue it will typically be repeatable under the same conditions. Ignition, not so much. GoDadGo, Jeff, and Jim have given you some good things to change & check while troubleshooting this issue.

Is this a new out of the box carb or did you buy a used bargain carb?

[Hellion]

I should have noted that I am carbed. Edelbrock thunder series 650 cfm. Mechanical fuel pump, RPM air gap intake and edelbrock performer heads.

I'm not a fan of the Edelbrock Thunder Series carbs - never got mine to tune correctly on an old '65 Mustang of mine several years back - replaced it with a model #1411 750 cfm and never had an issue thereafter.

[JIMOCO]

I have heard of tuning issues with the Edelbrock carbs. I had it tuned spring of 2020 and it has been running great until this recent issue. The carb was purchased new in 2014 and has about 17k miles on it.

I think the first step I'll try will be to remove the fuel filter by the tank and install a filter at the carb. If that is not helping I will clean the carb. Last step will be to check the pump pressure and possibly replace the pump. If the weather gets nice I will test and relay my results. Thank you for the great comments.

[Rdone585]

I'll try will be to remove the fuel filter by the tank and install a filter at the carb.
Adding the filter at the car is a good idea. You don't have to remove the one by the tank. The one by the tank can be a regular 100 micron filter. The one by the carb can be a 10 micron mesh filter (tons of these available in many different configurations). This is the setup I have used with success.

[NAZ]

The carb has been in service since 2014? With the oxygenated fuels today, that's a long time to be exposed to the corrosive affects of alcohol. Pop the top of that carb and look for aluminum oxide or other contaminates. Here's what oxygenated fuel corrosion looks like, these are extreame examples and it doesn't take this level of corrosion to cause issues. https://www.google.com/search?source=univ&tbm=isch&q=photos+of+oxygenated+gas+corrosion+in+carburetor&client=firefox-b-1-d&fir=yUr2Sdhnnux4iM%252CzRyykn18-__4DM%252C_%253BxuhVEC-1PRKAXM%252CxFIF3xg1xqMeGM%252C_%253BCIN7XS1htfrqR M%252CQRX3XEKQ39gqAM%252C_%253BlhGdaITMpx8pqM%252C zRyykn18-__4DM%252C_%253BKwA55vY23lc7hM%252ChaH_qH-rM0c35M%252C_%253BKemB_IO60eb7SM%252CzRyykn18-__4DM%252C_%253BZUIGztJzxS910M%252C_qNbXBBTJIWQKM% 252C_%253BHHOSOoRVML47oM%252CcxIPqi_JsyDhUM%252C_% 253Bpa7ALSWi7OetxM%252CVE6qvR5ctFpV9M%252C_%253BIW IlhhZoefxqcM%252CzRyykn18-__4DM%252C_&usg=AI4_-kTOuzCqK9_0ekXLE7ht06cy2yP2Qw&sa=X&ved=2ahUKEwinm4eWtOn0AhXQHzQIHfOkA1YQjJkEegQIGBAC&biw=1600&bih=775#imgrc=CIN7XS1htfrqRM

[JIMOCO]

Thanks NAZ. I will take a look. It has only been two running seasons since I had the carb cleaned and tuned. Additionally, I use Sta-Bil 360 with almost every fill-up. It supposedly eliminates/reduces the effect of ethanol gas. There is some literature that Sta-bil can cause deposits that were in the system to be freed and gunk up the carp. This could be the situation and is worth checking.

[Rickysnickers]

I have limited experience with Edelbrock carbs. With that said, they don't like a lot of pressure. I know you said the issue just started recently, but what is the fuel pressure at the carb? They don't like much more than 5psi. Do you have a regulator and/or pressure gauge in the fuel line? It may be worth checking what the fuel pressure is at idle.

[Railroad]

Not to change the subject too much, but...
One of the TV shows that test effects of bolt on changes to an engines output, tested the Edel, Summit and Holley carbs for apples to apples on HP output.
The Edel needed to go in the trash, the Summit made comparable HP to the Holley and was the cheapest carb in cost.
It does sound like the secondaries are not feeding the needed gasoline. Good news the Edel is easy to work on. Let us know what you find.

[NAZ]

The Edelbrock AVS seems to be a modern version of the Carter AVS (Air Valve Secondary), a carb that in my younger days was coveted by gearheads as an improvement over the AFB (Aluminum Four Barrel). And one that I never liked to tune on. I've tuned a lot of different carbs, of all of the designs out there I prefer the Holley 4150 over everything else. Vacuum secondaries have their place but in the light cars like FFR offers, I prefer the good old Double Pumper. It's the ideal carburetor ever made for an American V-8 performance engine. It has more adjustment potential than most folks realize, and probably the most popular performance carb ever.

[J R Jones]

Richard, I agree with you on the Holley 4150 and mechanical secondaries leave control up to the driver, WOT is not arbitrary and succeeds as long as the carb is not too big.
I had a negative experience running a GT40 MK IV with a 427 side oiler. We vintage raced it and the owner may not have been a good developer.
When I drove it in practice the throttle was too responsive with two four barrel double pumpers linked in synchronicity. Acceleration was explosive and running close to other cars was hazardous. I could not set-up passes from a drafting position, I had to keep distance to get out of the draft while accelerating, or modulating speed to be in a position to pass. A progressive linkage was my solution to running in traffic and controlling wheel spin coming off corners. I used the Holley kit with acceleration pump jets extended to the rear veturies to make a 715 carb a double pumper on my GT350.
jim

158763

[JIMOCO]

I have heard lots of comments about the edelbrock carb and its performance/tuning limitations. Had I been aware when I bought the engine package (first time builder) I would have opted for a different carb. It is what it is for now. I just want to make the best of what I have. The tune done a couple of years ago took an underperforming engine to an incredibly responsive machine with strong performance. I was happy until this new problem developed.

The traveling builder was ready to replace my Edelbrock with a Quick Fuel double pumper 650 cfm carb. I am beginning to regret the decision to try to make the Edelbrock work. I am researching a fuel pressure gauge and inline filter and will try this as a start. I will also take a look inside to see if there is a gunk problem.

Are carb cleaning fuel additives effective?

[RoadRacer]

Sorry to pile on, but I had an Edelbrock (came free with motor) and I could never get it running reliably. I bought a new 650cfm Brawler (https://www.jegs.com/i/Quick-Fuel/793/BR-67212/10002/-1?trk_msg=0T0QTD5238MKF33E6C70O4HR8S&trk_contact=G8JTM1UU6T1IVBBP0CQNRLJRDS&trk_module=tra&trk_sid=J039MPKOIEM8OTBDD7HUBHIAFO&utm_source=listrak&utm_medium=email&utm_term=Product&utm_campaign=Transactional&utm_content=Order+Confirmation) and it was night and day.. in every way. More responsive, more reliable, worked out of the box. Haven't touched it in 7,000 miles.

[Railroad]

I have used some carb cleaner to clear up some small engines. I pull the fuel line loose and fill it and the carb with straight fuel cleaner. I let it run till empty, refill and let sit for an exact time of a couple of days, joking.
Repeat a few times and hit the gas tank with a heavy load of cleaner and start running it regularly. It cleaned up my Honda 4 wheeler, which would not take full throttle, but will now. I do buy non ethanol now.

[NAZ]

One thing you can do that will help prevent carb corrosion with today's pump gas is to drain the bowls of fuel when parking the car for more than a few days. That's an effective way to limit exposure time if the car doesn't get driven except on weekends or only during the warmer months. Easy on a Holley, maybe not so much on the Edelbrock carb.

[J R Jones]

Richard, I was waiting for that wisdom to come-out. Draining motorcycle carbs is SOP for the astute; with bowl drain valve (screws) and hoses to below the engine, I would take another step and blow them dry through the needle valves and leave everything open for the winter. EFI makes that less of an issue.
jim

[NAZ]

You're right Jim, us old motorcycle racers drained the carb after every race and back in the olden days we had good gas without the alcohol. I still drain my drag car carb.

[J R Jones]

You're right Jim, us old motorcycle racers drained the carb after every race and back in the olden days we had good gas without the alcohol. I still drain my drag car carb.

Speaking of olden days and motorcycle racers, Carroll Resweber and I worked for Harley, him in racing and me in development. Carroll was from Port Arthur TX and was the four time National Champion on flat track in the fifties and sixties. https://www.dirtbikes.com/carroll-resweber-1936-2015/
Carroll was a gracious mentor
Carroll told me of running the mile clay in Indiana at ~120MPH. As an independent, he and the (Factory Team) leader had gapped the field but Carroll could not pass. Three laps from the end Carroll reached down and opened the mixture screws on his carbs, counting the turns while tucking in and maintaining the draft. The rich mixture cooled the heads and cylinders. On the last back straight Carroll leaned-out the carbs to where tuner Ralph Berndt had set them. When they slid out of the last turn Carroll pulled out of the draft and accelerated past the leader to win.
BTW Ralph Berndt also joined Harley and I saw him TIG a steel fill-neck to an aluminum fuel tank. No, I can not do that.
jim