another carb question
Thread Starter
Racer
Joined: Jul 2009
Posts: 336
Likes: 1
From: Asheville N.C.
another carb question
Stock 79 350 L-48 Quadrajet 17059216 still a little sluggish on take off with lite throttle.
1. #71 jets
2. 40K type B (double tappered) primary rods
After useing Lars paper suggestions on setting the stop height for the power piston, I took the jet out and laid the rod beside it as shown. In laymen terms it measured 1-15/16". Then the APT was screwed up (or out) approx 1 1/2 turns and from the top of jet to the top of the rod the measurment is 1 15/16". This rebuild had the APT turned out 2-3/4 turns but was worse than now. Is this 1-15/16" sound right or close?
Thanks ED
1. #71 jets
2. 40K type B (double tappered) primary rods
After useing Lars paper suggestions on setting the stop height for the power piston, I took the jet out and laid the rod beside it as shown. In laymen terms it measured 1-15/16". Then the APT was screwed up (or out) approx 1 1/2 turns and from the top of jet to the top of the rod the measurment is 1 15/16". This rebuild had the APT turned out 2-3/4 turns but was worse than now. Is this 1-15/16" sound right or close?
Thanks ED
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
screw makes the difference
In my (limited) experience, set the ATP 3 turns up and drive. If it surges lean on the highway at cruise, increase it a quarter turn at a time (CCW). If not, close it down until you get best econonmy / cruise. You have to be sure the screw has full range of motion to know where the bottom is. It tends to stick. First, use WD40 to make sure you have about 8.5 tuns from bottom to top of the stop travel.
Thread Starter
Racer
Joined: Jul 2009
Posts: 336
Likes: 1
From: Asheville N.C.
In my (limited) experience, set the ATP 3 turns up and drive. If it surges lean on the highway at cruise, increase it a quarter turn at a time (CCW). If not, close it down until you get best econonmy / cruise. You have to be sure the screw has full range of motion to know where the bottom is. It tends to stick. First, use WD40 to make sure you have about 8.5 tuns from bottom to top of the stop travel.
ED
Le Mans Master
Joined: Jul 2009
Posts: 6,647
Likes: 1
From: East Aurora N.Y.
St. Jude Donor '10
I have the exact same numbered carb in my '79...I'm about to have it re-built next week but i'm having 2nd thoughts because when the car is fully warmed up and I go WOT from like 20mph and up, I have instant response.....Like you though, from a stand still, i'll get the "quad delay"....I've been tweaking my choke and it's starting like a champ, cold and hot.....It is running smooth as silk, and at WOT like this morning at 115 mph, just a pleasure to drive..........I wonder if I should get it re-built now or what ? The gaskets are wet and the smell of gas from the carb after shut down can be quite strong........Oh what to do ?...
Thread Starter
Racer
Joined: Jul 2009
Posts: 336
Likes: 1
From: Asheville N.C.
I have the exact same numbered carb in my '79...I'm about to have it re-built next week but i'm having 2nd thoughts because when the car is fully warmed up and I go WOT from like 20mph and up, I have instant response.....Like you though, from a stand still, i'll get the "quad delay"....I've been tweaking my choke and it's starting like a champ, cold and hot.....It is running smooth as silk, and at WOT like this morning at 115 mph, just a pleasure to drive..........I wonder if I should get it re-built now or what ? The gaskets are wet and the smell of gas from the carb after shut down can be quite strong........Oh what to do ?...As far as the wet gaskets, is the float too high? Set mine around 12/32" to 13/32"= approx 3/8" and yes the smell can still be there. Well there's plenty of nice days left go for the rebuild. LOL ED
Le Mans Master
Joined: Jul 2009
Posts: 6,647
Likes: 1
From: East Aurora N.Y.
St. Jude Donor '10
Hey Jeff, I rebuilt mine this past Winter and continue to tweak it here and there based on all the forum imput. My WOT is also dead on with response, choke is great, just that little lull and some hot starts.
As far as the wet gaskets, is the float too high? Set mine around 12/32" to 13/32"= approx 3/8" and yes the smell can still be there. Well there's plenty of nice days left go for the rebuild. LOL ED
As far as the wet gaskets, is the float too high? Set mine around 12/32" to 13/32"= approx 3/8" and yes the smell can still be there. Well there's plenty of nice days left go for the rebuild. LOL ED
....BTW...top speed was 120mph today....I ran out of room.Not bad for a stock '79 I must say...
Last edited by jeff79'; Aug 22, 2009 at 10:55 AM.
Thread Starter
Racer
Joined: Jul 2009
Posts: 336
Likes: 1
From: Asheville N.C.
That little lull.....I wonder if that's a timing thing now....Maybe a little advance would do the trick......I'm used to my perfect 525i , so maybe perfection will never be achieved.....Keep on tweakin' !.......BTW...top speed was 120mph today....I ran out of room.Not bad for a stock '79 I must say...
....BTW...top speed was 120mph today....I ran out of room.Not bad for a stock '79 I must say...
just keep her between the ditches and pin the ears back!!!!!!!! ED
Le Mans Master
Joined: Jul 2009
Posts: 6,647
Likes: 1
From: East Aurora N.Y.
St. Jude Donor '10
Could be, yesterday I went through the timing (sticky) process and it adjusted from 8 to 12 BTDC then did air adjustments, ended being out 3 1/2 turns w/19 1/2 vacuum @800 rpm, felt better but the rain stopped a road test, only time will tell. 120 yea!! not bad at all just keep her between the ditches and pin the ears back!!!!!!!! ED
just keep her between the ditches and pin the ears back!!!!!!!! EDCorvette Stories
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Le Mans Master
Joined: Jul 2009
Posts: 6,647
Likes: 1
From: East Aurora N.Y.
St. Jude Donor '10
Ed...I think I hit the jackpot !......I bumped up to 12 bdc from 10 @ 600 rpm, and it's almost perfect....42k miles on it, and it's like a brand new car....I'm going to run it for a couple of days and then MAYBE bump it up 1 more degree.....It starts perfectly hot now and off the line is almost instant.....I say almost because it's a VERY minimal pause....Hardly discernible now......What the hell am I going to do now.......I have to fix something....Hmmm...cam, heads, headers..........My wife will KILL me , but I've been killed before....
.......No carb rebuild for me , me thinks !......Keep me posted on your gig...
...I bumped up to 12 bdc from 10 @ 600 rpm, and it's almost perfect....42k miles on it, and it's like a brand new car....I'm going to run it for a couple of days and then MAYBE bump it up 1 more degree.....It starts perfectly hot now and off the line is almost instant.....I say almost because it's a VERY minimal pause....Hardly discernible now......What the hell am I going to do now.......I have to fix something....Hmmm...cam, heads, headers..........My wife will KILL me , but I've been killed before...........No carb rebuild for me , me thinks !......Keep me posted on your gig...
Last edited by jeff79'; Aug 22, 2009 at 07:26 PM.
Thread Starter
Racer
Joined: Jul 2009
Posts: 336
Likes: 1
From: Asheville N.C.
Ed...I think I hit the jackpot !......I bumped up to 12 bdc from 10 @ 600 rpm, and it's almost perfect....42k miles on it, and it's like a brand new car....I'm going to run it for a couple of days and then MAYBE bump it up 1 more degree.....It starts perfectly hot now and off the line is almost instant.....I say almost because it's a VERY minimal pause....Hardly discernible now......What the hell am I going to do now.......I have to fix something....Hmmm...cam, heads, headers..........My wife will KILL me , but I've been killed before...........No carb rebuild for me , me thinks !......Keep me posted on your gig...
...I bumped up to 12 bdc from 10 @ 600 rpm, and it's almost perfect....42k miles on it, and it's like a brand new car....I'm going to run it for a couple of days and then MAYBE bump it up 1 more degree.....It starts perfectly hot now and off the line is almost instant.....I say almost because it's a VERY minimal pause....Hardly discernible now......What the hell am I going to do now.......I have to fix something....Hmmm...cam, heads, headers..........My wife will KILL me , but I've been killed before...........No carb rebuild for me , me thinks !......Keep me posted on your gig...
wonder if bigger jets would help? I think I could go as big as 75 or 77 with my primary rods. Are yours still # 71? Yea, cleaned the bottom side and painted this week to determine locations of a couple oil leaks, new valve covers and gaskets helped but now it be the old rear main seal. ED
Le Mans Master
Joined: Jul 2009
Posts: 6,647
Likes: 1
From: East Aurora N.Y.
St. Jude Donor '10
Jeff, tried mine yesterday, still had the lull....response and wot is great. wonder if bigger jets would help? I think I could go as big as 75 or 77 with my primary rods. Are yours still # 71?
Yea, cleaned the bottom side and painted this week to determine locations of a couple oil leaks, new valve covers and gaskets helped but now it be the old rear main seal. ED
wonder if bigger jets would help? I think I could go as big as 75 or 77 with my primary rods. Are yours still # 71? Yea, cleaned the bottom side and painted this week to determine locations of a couple oil leaks, new valve covers and gaskets helped but now it be the old rear main seal. ED
Le Mans Master
Joined: Jul 2009
Posts: 6,647
Likes: 1
From: East Aurora N.Y.
St. Jude Donor '10
Jeff, tried mine yesterday, still had the lull....response and wot is great. wonder if bigger jets would help? I think I could go as big as 75 or 77 with my primary rods. Are yours still # 71?
Yea, cleaned the bottom side and painted this week to determine locations of a couple oil leaks, new valve covers and gaskets helped but now it be the old rear main seal. ED
wonder if bigger jets would help? I think I could go as big as 75 or 77 with my primary rods. Are yours still # 71? Yea, cleaned the bottom side and painted this week to determine locations of a couple oil leaks, new valve covers and gaskets helped but now it be the old rear main seal. ED
Thread Starter
Racer
Joined: Jul 2009
Posts: 336
Likes: 1
From: Asheville N.C.
ED !...I'm there !...I bumped the timing up to 13 btdc last night and tested it today......1 foot maash, and a turn of the key and no start....2nd try , right away.....I got it good and warmed up , stopped on an empty country road, and floored it....It was PERFECT ! It immediately hunkered down and screamed.I did it 5 different times because I just couldn't believe it....Same thing every time....I adjusted the fast idle with the car in gear (with the brake on of course), to 600rpm...It now lays at 7-800 rpm in park.....There is no pinging or detonation .The car shut right off and started hot like never before....It really flys !...It's funny that the shop manual says 6* btdc is the correct timing but 13 is the charm.....How is yours coming along ?
With all the above previous adjustments, that after Sundays drive, my tailpipes are showing alot less black sooting. Will keep an eye on it..........then maybe richen up some.????
Le Mans Master
Joined: Jul 2009
Posts: 6,647
Likes: 1
From: East Aurora N.Y.
St. Jude Donor '10
Hey Jeff sounds like you had a good day, when I did my timing per (sticky) mine was 18*BTDC. It felt good in the garage but........without a road test I brought it down to 12BTDC to be safe for now but the lull is still there between 1200 to 1500 RPM. Yes WOT from stop is great here also and the 6* thing I beleive was conservative.
With all the above previous adjustments, that after Sundays drive, my tailpipes are showing alot less black sooting. Will keep an eye on it..........then maybe richen up some.????
With all the above previous adjustments, that after Sundays drive, my tailpipes are showing alot less black sooting. Will keep an eye on it..........then maybe richen up some.????
.......I also think that my thermal vacuum switch is shot, so if someone answers that question, that will be the last piece to a 2 summer puzzle....
Le Mans Master
Joined: Jul 2009
Posts: 6,647
Likes: 1
From: East Aurora N.Y.
St. Jude Donor '10
YES...Definetly !...Like I said, when it's all warmed up, from a stop, if i floor it she immediately hunkers down and goes, in a screaming kind of way, that we all want and love......It's all better.....@12btdc there was just a little , hardly discernible lull left, but at @13.....NONE....I may go 12 1/2 just to see if it cold starts better and feel how warm take offs are....I think 13*btdc is the setting I like though.....Totally stock carb, same #'s as yours, never rebuilt.
Le Mans Master
Joined: Jul 2009
Posts: 6,647
Likes: 1
From: East Aurora N.Y.
St. Jude Donor '10
I really don't care about that range though. If I'm in that range, I'm just cruising, like in a neighborhood with stop signs and it really doesn't matter.Take off and general pedal response is my concern and I got it man !.......Cold Starts: So far I've found that just a touch of the gas pedal to engage the choke is all I need to start the car now...No more 1 full pedal mash needed....A few more days of testing and 13*btdc may be the ticket forever.....I'm really liking it as she sits ...
