Timing or Carb??
Thread Starter
Melting Slicks
Joined: Feb 2004
Posts: 2,040
Likes: 105
From: State of Confusion!!!
2018 C2 of Year Winner
Timing or Carb??
This morning I was out and about. Car started fine, idled fine and ran fine at part throttle. My problem occoured when I was getting on the interstate pulling a hill on the on ramp. As i layed into it, I noticed it was not accelerating smoothly. Gave it more throttle and it got worse. Popping and backfiring and pretty much running like ****!!!
Let off and cruised up on the highway at part throttle and it ran fine.
Now we all know that there is no use in having a Corvette if you can't stand on the go pedal, so my search for the problem will begin tomorrow.
I am running a zz454 with a Holley 850/mech sec carb. My dist. is a HUI electronic tach drive dist. Not sure what I have for initial timing or what it advances to, but I know the vac advance is disconnected and always has been.
Any ideas where to start???
Let off and cruised up on the highway at part throttle and it ran fine.
Now we all know that there is no use in having a Corvette if you can't stand on the go pedal, so my search for the problem will begin tomorrow.I am running a zz454 with a Holley 850/mech sec carb. My dist. is a HUI electronic tach drive dist. Not sure what I have for initial timing or what it advances to, but I know the vac advance is disconnected and always has been.
Any ideas where to start???
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
Not to send You into a tail spin. Has this car been driven regularly? Has something just been recently changed? Even something as simple as a gas fill up could cause this. If nothing was changed I would question the distributor. But also check linkages on carb for binding or missing.
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
It sounds to me like fuel starvation. Is it only stumbling when you are asking for high fuel delivery, that is what I got from your post. How long since fuel filters were checked and screen in tank, how about the fuel pump?
Thread Starter
Melting Slicks
Joined: Feb 2004
Posts: 2,040
Likes: 105
From: State of Confusion!!!
2018 C2 of Year Winner
Nothing has been changed and it really hasn't been driven regularly yet this year. It does seem to be a WOT issue, but it starts to rear it's ugly head when I start laying into it. The filter and pump were new when the engine was installed about 6k miles ago.
I will check the hold down bracket first, as this is the easiest place to start and go from there.
I will check the hold down bracket first, as this is the easiest place to start and go from there.
Drifting
Joined: Mar 2011
Posts: 1,271
Likes: 1
From: PA
Yep, time for a shakedown after sitting. Look for loose connections, loose bolts, bad hoses, leaks, ect. Get some fresh gas in there and maybe even clean out the carb.....could even have varmits in your rigging....JMO
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Run a can of SeaFoam through it. You can get some accumulation of 'varnish', etc. over a 6K mile stretch. It will clean up the carb/engine. Also, if you still have a points ignition system, swap out the condenser. When that starts to go bad, performance 'sucks'.
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Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
Could be fuel starvation, but the back firing sound's more like a timing issue, and hopefully the timing chain didn't jump a few teeth. As for mentioning Lar's tune, last I heard he was in fine health. Believe there were some disagreement's on the forum, and no longer post's.
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
[QUOTE=Vette5.5;1577620872]Could be fuel starvation, but the back firing sound's more like a timing issue, and hopefully the timing chain didn't jump a few teeth. As for mentioning Lar's tune, last I heard he was in fine health. Believe there were some disagreement's on the forum, and no longer post's.[/QUOT
Lars is active in other areas, I also recommend trying seafoam, it's cheap and certainly won't hurt though I doubt it will cure this problem completely!
Lars is active in other areas, I also recommend trying seafoam, it's cheap and certainly won't hurt though I doubt it will cure this problem completely!
Last edited by BPHORSEGUY; May 15, 2011 at 12:54 PM.
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
My 70 camaro did the same thing a couple years ago. It was so bad it blew the valve cover gasket out. It turned out to be old gas. I ran through a couple of tanks and the problem went away.
Le Mans Master
Joined: Jun 2007
Posts: 7,666
Likes: 1
From: Where it's always hot as Hell-South Louisiana.
St. Jude Donor '07-'08-'09-'10-'11-'12-'13
also, check to see that the electric choke is working and opening the front baffles 100 % after 2 minutes of run time.
Advanced
Joined: Jan 2011
Posts: 77
Likes: 0
From: Winona Mo.
I sure like that Lars quote. I've seen lot's of guys spend money all the way up to buying a new carb and then finally admitting "well I did change the plug wires, but that couldn't be it".
I'm certainly not implying any of that with you, I just love the quote.
I'm certainly not implying any of that with you, I just love the quote.
Drifting
Joined: Mar 2006
Posts: 1,526
Likes: 2
From: Oak Ridge NC
This morning I was out and about. Car started fine, idled fine and ran fine at part throttle. My problem occoured when I was getting on the interstate pulling a hill on the on ramp. As i layed into it, I noticed it was not accelerating smoothly. Gave it more throttle and it got worse. Popping and backfiring and pretty much running like ****!!!
Let off and cruised up on the highway at part throttle and it ran fine. Now we all know that there is no use in having a Corvette if you can't stand on the go pedal, so my search for the problem will begin tomorrow.
I am running a zz454 with a Holley 850/mech sec carb. My dist. is a HUI electronic tach drive dist. Not sure what I have for initial timing or what it advances to, but I know the vac advance is disconnected and always has been.Any ideas where to start???
Let off and cruised up on the highway at part throttle and it ran fine.
Now we all know that there is no use in having a Corvette if you can't stand on the go pedal, so my search for the problem will begin tomorrow.I am running a zz454 with a Holley 850/mech sec carb. My dist. is a HUI electronic tach drive dist. Not sure what I have for initial timing or what it advances to, but I know the vac advance is disconnected and always has been.Any ideas where to start???
Drifting
Joined: Mar 2006
Posts: 1,526
Likes: 2
From: Oak Ridge NC
Thread Starter
Melting Slicks
Joined: Feb 2004
Posts: 2,040
Likes: 105
From: State of Confusion!!!
2018 C2 of Year Winner
so I no longer have his assitance, that is why I am looking for help here. I never messed with the technical stuff (carb or dist tuning), I was always the nuts and bolts guy. Never had any problems with removal or install of components, just never messed with the "finesse" stuff!!! I guess it is time to jump in feet first!!I am contemplating taking the dist. out and sending it to DUI and have them custom curve it for my application, with a functional vac can.
Has anyone had first hand experience dealing with DUI??
Drifting
Joined: Mar 2006
Posts: 1,526
Likes: 2
From: Oak Ridge NC
It always has been disconnected. When we installed the crate motor it was set up that way by a friend of mine. I have read all the flame posts that say you need it, but it was running fine last year. Sadly, he died this winter after a short battle with cancer, so I no longer have his assitance, that is why I am looking for help here. I never messed with the technical stuff (carb or dist tuning), I was always the nuts and bolts guy. Never had any problems with removal or install of components, just never messed with the "finesse" stuff!!! I guess it is time to jump in feet first!!
I am contemplating taking the dist. out and sending it to DUI and have them custom curve it for my application, with a functional vac can.
Has anyone had first hand experience dealing with DUI??
so I no longer have his assitance, that is why I am looking for help here. I never messed with the technical stuff (carb or dist tuning), I was always the nuts and bolts guy. Never had any problems with removal or install of components, just never messed with the "finesse" stuff!!! I guess it is time to jump in feet first!!I am contemplating taking the dist. out and sending it to DUI and have them custom curve it for my application, with a functional vac can.
Has anyone had first hand experience dealing with DUI??
So I gather that the specs are not on the dist? If you can get a mirror, look under the base. Another way to tell if it was custom is to look at the advance springs. They will paint the spring that goes with the accopanying advance weight.
Here is a link to a super Chevy article with the zz454 specs. They produced a nice 502hp with 34 degrees total mechanical timing(initial 12 plus 22 in the dist) and a 770CFM Holley and headers.
http://www.superchevy.com/technical/...t_results.html
You already know this, but if you are going to drive it mostly on the street, the most efficient set up will include the vacuum advance.
Good luck.
Last edited by SmokinBBC; May 19, 2011 at 06:46 PM.