Carb tuning / Timing issues???
Melting Slicks
Joined: Jan 2005
Posts: 3,028
Likes: 0
From: Madison Ms
Hotwater.......read this.........Timing 101.... http://69.253.166.197/page1/page65/f...101Article.pdf
Kalway.......me and you both, but they said their were "signs" of detonation. Other circumstances also contributed, included higher that spec'd compression in two cylinders they tested. Other grey area's as well. That's why they covered it under warranty.
I still can't say with 100% certainty that I didn't detonate it, nor can they say I did.
Therefore, the new motor (which is supposed to be shipped today!!)
Kalway.......me and you both, but they said their were "signs" of detonation. Other circumstances also contributed, included higher that spec'd compression in two cylinders they tested. Other grey area's as well. That's why they covered it under warranty.
I still can't say with 100% certainty that I didn't detonate it, nor can they say I did.
Therefore, the new motor (which is supposed to be shipped today!!)
Thread Starter
Instructor
Joined: Mar 2006
Posts: 181
Likes: 0
From: Ft Hood TEXAS
Well, I got the timing advanced like you said. I have it set to 12 degrees BTDC at idle with the vacuum advance disconnected. I took it out for a test drive and everything seemed better. It did seem to loose a little of the "off the line" acceleration though. Any way, when I got home and went to pull into the driveway, POP!. It backfired again and died. I'm ready to grenade the engine and start over. LOL.
Thread Starter
Instructor
Joined: Mar 2006
Posts: 181
Likes: 0
From: Ft Hood TEXAS
What kind of symptoms would I have if I had some bad plugs or wires? I know that it would hinder performance but what about driveability? I recently replaced the plugs and wires but before I replaced my carb. Could the poor tuning or the new carb setup had caused the plugs to go bad? I would just go out there and pull them but I can't get to them right now. At the hospital with the spouse. 
Thanks again to all.
Also, due to budget restraints, I had to go with stock style wires. Could this hurt as well?
Thanks again to all.Also, due to budget restraints, I had to go with stock style wires. Could this hurt as well?
Instructor
Joined: Sep 2001
Posts: 208
Likes: 8
From: Grand Ledge MI
My neighbor has a really nice BB in his 70 4x4 chevy and suffered the same symptoms you describe after the install of his new Holley. Sent it back to Jegs and put his rebuilt Q-jet back on and has run great for 2 years running now 
Melting Slicks
Joined: Jan 2005
Posts: 3,028
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From: Madison Ms
You did hook the vac advance back up, right? And.....put the light on it again and check and see how much advance you are getting b4 3000 rpm.
Just trying to rule out a timing issue first.....then, maybe someone can help you with that carb, as I no nothing about those.
Just trying to rule out a timing issue first.....then, maybe someone can help you with that carb, as I no nothing about those.
Last edited by MsVetteMan; Apr 4, 2006 at 10:33 PM.
Thread Starter
Instructor
Joined: Mar 2006
Posts: 181
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From: Ft Hood TEXAS
Originally Posted by MsVetteMan
You did hook the vac advance back up, right? And.....put the light on it again and check and see how much advance you are getting b4 3000 rpm.
Just trying to rule out a timing issue first.....then, maybe someone can help you with that carb, as I no nothing about those.
Just trying to rule out a timing issue first.....then, maybe someone can help you with that carb, as I no nothing about those.
Melting Slicks
Joined: Jan 2005
Posts: 3,028
Likes: 0
From: Madison Ms
Originally Posted by hotwater
Yeah, I hooked the vac advance back up. My timing light doesn't measure advance. So now I guess I need a new timing light.
What you want is to be very close to 36 or more at that rpm. This is also done with vac unhooked. If you aren't even close, then add some softer springs, and try again.
Next check and see if you are advancing beyond 36.......have the same party hold steady at 3000 rpm, while you reset the light to 0, then have him get on it to raise rpm's.....if you continue to advance, you have gone to far. You need stiffer springs.
Read Lars paper, i'm not to good at explaining this.
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Pro
Joined: Jan 2002
Posts: 624
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From: Marietta ga
Originally Posted by MsVetteMan
Lars, or Chilton? Trust us.......
Chilton is for a stock setup and strictly for economy, and is very conservative. You won't hurt anything, just start a 10 if that makes you feel better, and then work your way up.
Chilton is for a stock setup and strictly for economy, and is very conservative. You won't hurt anything, just start a 10 if that makes you feel better, and then work your way up.
I am have about 11:1 on pump gas and I get away with 14 no problem
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
this sounds like you have fuel delivery problem to me....perhaps your fuel pump is dying....those are exactly the symptons....
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
the timing we use most for a mild cam engine is 12 deg initial, 24 degrees mechanical and 10 degrees from the vacuum advance
the carburetor hesitation could be a weak spring on the pump arm, a cure would be the old Barry Grant trick of putting a couple of flat washers on top of the duration spring. be sure the carb has a .031 squirter and a "pink" pump cam #330
some of the holley avenger carbs need a lot of jetting work to get them right
good luck
the carburetor hesitation could be a weak spring on the pump arm, a cure would be the old Barry Grant trick of putting a couple of flat washers on top of the duration spring. be sure the carb has a .031 squirter and a "pink" pump cam #330
some of the holley avenger carbs need a lot of jetting work to get them right
good luck
Thread Starter
Instructor
Joined: Mar 2006
Posts: 181
Likes: 0
From: Ft Hood TEXAS
Fuel Pump is brand new. Thought the same thing so I replaced the pump. Got a new timing light a few minutes ago and I am gonna try to check the advance. Thanks to everyone so far for all of your help.
Racer
Joined: Jun 2005
Posts: 409
Likes: 13
From: Lavonia Georgia
Originally Posted by MsVetteMan
Hotwater.......read this.........Timing 101.... http://69.253.166.197/page1/page65/f...101Article.pdf
Kalway.......me and you both, but they said their were "signs" of detonation. Other circumstances also contributed, included higher that spec'd compression in two cylinders they tested. Other grey area's as well. That's why they covered it under warranty.
I still can't say with 100% certainty that I didn't detonate it, nor can they say I did.
Therefore, the new motor (which is supposed to be shipped today!!)
Kalway.......me and you both, but they said their were "signs" of detonation. Other circumstances also contributed, included higher that spec'd compression in two cylinders they tested. Other grey area's as well. That's why they covered it under warranty.
I still can't say with 100% certainty that I didn't detonate it, nor can they say I did.
Therefore, the new motor (which is supposed to be shipped today!!)
In there is a very well written article on setting up your Holley carb. Lars takes a very methodical approach to setting up the systems. He stresses that they must be done in a specific order since setting up most of them is dependent on getting prior adjustments correct. Start at the beginning of the adjustment procedure and work your way through. When you're done, you should not only have a properly adjusted Holley, but you will probably have a much greater understanding of your carb and how it work. Good luck!
Burning Brakes
Joined: Mar 2006
Posts: 750
Likes: 82
From: Bedford IN
If it is back firing i would think that it needs more timing. Everyengine is different. I have 10 to 1 compression pistons in mine and i am at 18 initial timing. I also put 202 intake and 160 exahst valves in the heads. Try bumping it up a little and as you are looking at the mark, raise the engine RPM's withthe other hand. You should be able to see the timing go up then top out at probly somewhere around 3000 or less, depending on the springs. You can raise you timing as long as it does not go over 35 total timing when it tops out.
