Anyone had this problem
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
I think you should first change the filter and eliminate the cheapest and easiest and most likely problem first.
Then go into the harder more difficult stuff.
If you have a plugging fuel filter what is happening is your fuel level is dropping too much. WOT is sucking it dry and light throttle isn't.
A rebuilt carb don't mean it was set up for your car. It just had new gaskets put in it. Secondaries that open too soon or too late don't limit rpms though. Its only a bog or loss of potential acceleration. It should still wind up.
Then go into the harder more difficult stuff.
If you have a plugging fuel filter what is happening is your fuel level is dropping too much. WOT is sucking it dry and light throttle isn't.
A rebuilt carb don't mean it was set up for your car. It just had new gaskets put in it. Secondaries that open too soon or too late don't limit rpms though. Its only a bog or loss of potential acceleration. It should still wind up.
Burning Brakes
Joined: Jun 1999
Posts: 751
Likes: 0
From: Chandler AZ
St. Jude Contributor
Ok now I am wonder. I have posted here about my WOT detonation on a new rebuild. Are any of you detonating? If the carb is leaning out or droping fuel presure then would you for sure have to be detonating?
I have thought my fuel clunk sock could be cloged. I need to check my presure under load WOT and see it its the fuel. I will do this next week.
My Rochester 4MV carb was rebuilt as was the tack drive dist and was recurved. I AM RUNNING THE PERTRONIX AND NOW WONDER IF THIS COULD BE PROBLEMATIC TOO>.
The race guy down he street will not even look at the car unless he yanks the Rochester and the distributer to go with Edlbrock Performer and a better igniter. Like I said I want to keep it stock and the performer needs a square manifold which is out of the question.
What carbs are everyone running?
What distributer are you guys using? It needs tack drive.
Crap I rambled.....lol
I have thought my fuel clunk sock could be cloged. I need to check my presure under load WOT and see it its the fuel. I will do this next week.
My Rochester 4MV carb was rebuilt as was the tack drive dist and was recurved. I AM RUNNING THE PERTRONIX AND NOW WONDER IF THIS COULD BE PROBLEMATIC TOO>.
The race guy down he street will not even look at the car unless he yanks the Rochester and the distributer to go with Edlbrock Performer and a better igniter. Like I said I want to keep it stock and the performer needs a square manifold which is out of the question.
What carbs are everyone running?
What distributer are you guys using? It needs tack drive.
Crap I rambled.....lol
Safety Car
Joined: Aug 1999
Posts: 4,862
Likes: 118
From: Texas
Originally Posted by 71LS5
What carbs are everyone running?
What distributer are you guys using? It needs tack drive.
What distributer are you guys using? It needs tack drive.
I also use a Holley Blue pump with a modified fuel pressure regulator that gives me 5psi at idle and 8psi at wot.
Car runs strong to 6k rpm.
Last edited by RatRacer; Sep 3, 2005 at 12:53 AM.
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Melting Slicks
Joined: Jul 2005
Posts: 2,545
Likes: 3
From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM
Glad you sorted it out. I just bought a second Vette, 71 454 and it also would just fly when I nail it than sputter. I realized the 10 bucks worth of gas I just put in was gone 
Have fun with your ride...
Have fun with your ride...
Burning Brakes
Joined: Jun 1999
Posts: 751
Likes: 0
From: Chandler AZ
St. Jude Contributor
ok just checked my plugs (one) I am running a foweled Autolite 23 with a 0.035 gap. I assume they are all foweled. Must be rich at idle and lean at WOT. Anyone have a good place for me to start hunting down if its spark or fuel related?
Safety Car
Joined: Aug 1999
Posts: 4,862
Likes: 118
From: Texas
Originally Posted by 71LS5
Rat what Roch carb are you running? What the mods? What size metering rods etc?
I have richer jetting than stock on all circuits. I also have a large inlet valve. Idle circuits were drilled per Doug Roes book. It's been a few years since I built it so it's a little vague now. I'll let you know when I find my note book. I've been looking for it for a couple days.
Last edited by RatRacer; Sep 5, 2005 at 10:15 PM.
Burning Brakes
Joined: Jun 1999
Posts: 751
Likes: 0
From: Chandler AZ
St. Jude Contributor
Thanks RAT. I was thinking of getting a Jet Roch but not sure which one. I would be interested in your mods.
anyone else have a recomendations to divide my problem up? IFuel delivery vs spark)????
anyone else have a recomendations to divide my problem up? IFuel delivery vs spark)????
Safety Car
Joined: Aug 1999
Posts: 4,862
Likes: 118
From: Texas
Originally Posted by 71LS5
ok just checked my plugs (one) I am running a foweled Autolite 23 with a 0.035 gap. I assume they are all foweled. Must be rich at idle and lean at WOT. Anyone have a good place for me to start hunting down if its spark or fuel related?
It's also possible that the fuel wells in the bottom of the quad are leaking. It's always a good idea to epoxy over them when servicing the carb as they've been known to leak. The little rebuild kits usually come with a foam stuffer but epoxy is the way to go.
I never run anything but AC Delco R43TS plugs
Burning Brakes
Joined: Jun 1999
Posts: 751
Likes: 0
From: Chandler AZ
St. Jude Contributor
Hummmm no vac adv would that cause detonation at WOT? I assume it would not. It would run more rich right? I am not sure how long its been fowled or what the cause is yet.
Burning Brakes
Joined: Jun 1999
Posts: 751
Likes: 0
From: Chandler AZ
St. Jude Contributor
BTW just to be clear my advance might be ok its not been determined yet. I need some ones help put together a plan to debug this. Like what to look at first. Please keep in mind the carb was rebuilt with the engine and the distributer was recurved. I am using the Pertronix and thats why I jumped in here.....
Safety Car
Joined: Aug 1999
Posts: 4,862
Likes: 118
From: Texas
No vacuum advance will make the car idle slower and force you to increase idle speed which causes run-on. You'll also get poor throttle response. The exception is if you run only limited mechanical advance. I run a Mallory with no vacuum advance but it only has 22 degrees of mechanical advance. I have inital advance at 15 degrees BTDC and final is at 37 degrees BTDC.
A stock distributor has around 30-32 degrees mechanical so if your vacumm advance isn't working you could end up setting you timing too far advanced and end up with more than 38 degrees total timing. That would cause a high RPM knock.
The best way to set up a distributor is with a distributor machine but they are hard to find nowadays. You can do it with a good timing light and a timing mark sticker for you torsion damper, but it's time consuming.
A stock distributor has around 30-32 degrees mechanical so if your vacumm advance isn't working you could end up setting you timing too far advanced and end up with more than 38 degrees total timing. That would cause a high RPM knock.
The best way to set up a distributor is with a distributor machine but they are hard to find nowadays. You can do it with a good timing light and a timing mark sticker for you torsion damper, but it's time consuming.
Last edited by RatRacer; Sep 5, 2005 at 11:00 PM.
Racer
Joined: Aug 2005
Posts: 308
Likes: 0
From: Salem MA
its not a theory. its pretty common knowledge in the turbo world. but since you had other problems spark blowout may not apply in your case. and i dont know what causes it exactly. so i cant provide any supporting theory besides a larger gap creates a more fragile spark.
spark blow out is what occurs at WOT when your gaps are too big. its happened to me on other cars. the solution is to gap down to 0.030 or 0.028. i had blow out at 0.035 but not at 0.030. and the car ran kinda rough all the time at 0.028.
plugs are dirt cheap. change em. gap at 0.03. and see what happens.
spark blow out is what occurs at WOT when your gaps are too big. its happened to me on other cars. the solution is to gap down to 0.030 or 0.028. i had blow out at 0.035 but not at 0.030. and the car ran kinda rough all the time at 0.028.
plugs are dirt cheap. change em. gap at 0.03. and see what happens.