Carb tuners - help!
Thread Starter
Instructor
Joined: Jun 2003
Posts: 231
Likes: 0
From: Frisco TX
Carb tuners - help!
I've read several people's posts about tuning the carb and picking up unbelievable amounts of 'seat 'O da pants' power. My '75 is a dog... I really expected a Corvette to be smokin, even with the L48. I noticed that if I am cruising along at 20-30 mph and goose it, the car bogs, like it's getting too much fuel. Same thing from a dead stop. Any ideas on what this could be? Is it tuning, or does something need to be replaced? I'm no carb tuner, but I have no problem diving in with a couple of screwdrivers and learning the hard way if someone is willing to give a little direction. Thanks!
:smash:
[Modified by WPEDirect, 10:53 PM 7/20/2003]
:smash:
[Modified by WPEDirect, 10:53 PM 7/20/2003]
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Carb tuners - help! (WPEDirect)
75 wasnt a big year for performance but that can be fixed. A few questions for you first. Is it all stock now? Do you have to contend with emission laws or testing? How much money do you have to spend?
Thread Starter
Instructor
Joined: Jun 2003
Posts: 231
Likes: 0
From: Frisco TX
Re: Carb tuners - help! (Jvette73)
As far as I can tell, it's completely stock. The engine is numbers matching, but it sure feels like it has more than 165HP. I guess my comparison experience is not fair - my last road burner was a '96 LT1 T/A 6 speed 300HP(read: WOOHOO!!). I do not have to contend with emissions, at least that is what I am told by other Texas Vette owners. I have absolutely no money to spend right now, but can save some if a goal is in sight. I just need to know what to do...
Right now, my focus is on purchasing and installing a complete poly front suspension rebuild kit. Never done it before, but I can figure out most anything on a car. She looks like someone tried a couple of the 'Dukes of Hazzard' style jumps... and both front tires are worn out on the inside, but new on the outside. Very nervous on the road, walking all over the place and it gets worse the faster you go (I won't drive it on the highway, and I consider myself to be pretty ballsy as far as driving).
I really can't just start buying tons of new parts, but would like to correct the misuse and neglect previous owners have caused (ie. adjustment and tuning).
[Modified by WPEDirect, 11:09 PM 7/20/2003]
Right now, my focus is on purchasing and installing a complete poly front suspension rebuild kit. Never done it before, but I can figure out most anything on a car. She looks like someone tried a couple of the 'Dukes of Hazzard' style jumps... and both front tires are worn out on the inside, but new on the outside. Very nervous on the road, walking all over the place and it gets worse the faster you go (I won't drive it on the highway, and I consider myself to be pretty ballsy as far as driving).
I really can't just start buying tons of new parts, but would like to correct the misuse and neglect previous owners have caused (ie. adjustment and tuning).
[Modified by WPEDirect, 11:09 PM 7/20/2003]
Drifting
Joined: Nov 2002
Posts: 1,665
Likes: 1
From: Ontario
Re: Carb tuners - help! (WPEDirect)
I also expected more out of my 1977 stock L48 when I first bought it. According to what I have read here on the forum our stock engines are set up slightly lean and tuned to be more on the emissions friendly side. As for tuning your quadrajet it is not just a matter of turning a few screws. You have to actually change primary rods or jets to change the primary air/fuel mixture. Its not that hard to do...
You will learn a lot from a forum search on this topic. Also check out these links. Read anything written by a guy named "Lars". He is famous for his carb tuning knowledge.
http://www.corvettefaq.com/listing.asp?group=1&sub=11
http://www.buickpartsdirectory.com/carbs.htm
Another thing you could try is to recurve your distributor. I haven't tried it yet but I was talking with my mechanic on the weekend and he recommended that I buy a recurve kit and just try different weight/spring combos. Good luck!
You will learn a lot from a forum search on this topic. Also check out these links. Read anything written by a guy named "Lars". He is famous for his carb tuning knowledge.
http://www.corvettefaq.com/listing.asp?group=1&sub=11
http://www.buickpartsdirectory.com/carbs.htm
Another thing you could try is to recurve your distributor. I haven't tried it yet but I was talking with my mechanic on the weekend and he recommended that I buy a recurve kit and just try different weight/spring combos. Good luck!
Melting Slicks
Joined: Jul 2002
Posts: 3,128
Likes: 3
From: Deltona (son of Deland and DAYTONA) FL
Re: Carb tuners - help! (WPEDirect)
For a quick fix on that bog, your secondary air valve might be opening too soon. There is a windup screw that adjusts the tension on the spring on the left rear of the Qjet. To set it to factory initial settings, turn the screw (either direction, clockwise if too loose, opposite if too tight) until you just barely feel tension. Then tighten it 3/4 to 7/8 of a turn. There is a allen set screw under it that will need to be loosened before the adjustment and re-tightened once you set the tension.
My car had the same symptoms and I found that there was NO tension on that airvavle. This is all in Lars' tuning papers on the Corvettefaq. Check out these pics for the location of the screws.
this first one is the tension screw.
second one is about where the set screw that keeps the windup screw from backing out.
[Modified by isosceles, 3:25 PM 7/21/2003]
My car had the same symptoms and I found that there was NO tension on that airvavle. This is all in Lars' tuning papers on the Corvettefaq. Check out these pics for the location of the screws.
this first one is the tension screw.
second one is about where the set screw that keeps the windup screw from backing out.
[Modified by isosceles, 3:25 PM 7/21/2003]
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Carb tuners - help! (WPEDirect)
Maybe yur transmission kickdown isnt working which is causing a bog feeling. From a 30mph cruise in 3rd gear, with a TH400 which is what yur car should have, when you punch it, it should drop to first gear and throw you back in your seat. If its only dropping to 2nd from a 30mph roll then yur kickdown aint workin right. On the same token. if yur doin 60mph down the highway and punch it it should drop to 2nd. If the kickdown isnt working, from a 60mph roll it usually wont down shift. it will just hang in 3rd and seem boggy.
Team Owner
Joined: Oct 2001
Posts: 23,121
Likes: 301
From: Do or do not there is no try YODA
Re: Carb tuners - help! (WPEDirect)
First thing to check on a bog, is the accelerator pump. Depress the gas, while looking down the throat of the carb, while the engine is off. You should see two strong even squirts of fuel. If not, there is a problem. Remember, air moves faster than fuel, so the pump has to squirt the fuel, so it can catch up to the air rushing in at WOT. Also as someone touched on, the secondary butterflies operate off of vacuum, and spring tension. If the Choke vacuum pulloff does not work (note that it is attached to the secondary butterflies by a rod ) they will fly open too fast, thus creating the too much air scenario, and the car will bog. Just a couple of real easy things to check!
:cheers:
:cheers:
