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  #76 (permalink)  
Old 05-02-2013, 10:53 PM
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We got all the nice weather this weekend.
In Canada there are 3 seasons. Winter , Road Construction, and Patio !!

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  #77 (permalink)  
Old 05-03-2013, 07:15 AM
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Originally Posted by F-BIRD'88 View Post
We got all the nice weather this weekend.
In Canada there are 3 seasons. Winter , Road Construction, and Patio !!
We set a record today. Woke up to some or your Canadan weather down here. Bout .3 inch of snow, in MAY!
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  #78 (permalink)  
Old 05-06-2013, 04:17 PM
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Finally cleared up to where I could get back on it. Reversed the jetting as you suggested from the 95-98 to 98-95, 70x37 needles and 4" springs and reset idle. Been running a vacuum gauge for a while now. Idle vacuum is 9.5-10" and cruise is the same. Here's the latest LM2 logs for your perusal. lol
appreciate all your help and time.
Attached Files
File Type: txt 05061300-Session 1.txt (99.7 KB, 29 views)
File Type: txt 05061300-Session 2.txt (73.7 KB, 29 views)
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  #79 (permalink)  
Old 05-06-2013, 11:44 PM
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It did no like that jetting change at all,, WOT.
it is way too rich now @ WOT.
So try 98 primary jet 70x.042 pri rod and 95 secondary jet.

try that...

Overdrive.... This big cammed motor won't be very happy cruising at a low rpm.
Do not force the engine to run in overdrive.. it wants to rev. Let it rev.

Why is the idle AFR so lean... Are you setting the idle correctly for best idle quality using a vacuum gauge?
Are the header gaskets leaking?
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Old 05-07-2013, 06:24 AM
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Quote:
Originally Posted by F-BIRD'88 View Post
It did no like that jetting change at all,, WOT.
it is way too rich now @ WOT.
So try 98 primary jet 70x.042 pri rod and 95 secondary jet.

try that...

Overdrive.... This big cammed motor won't be very happy cruising at a low rpm.
Do not force the engine to run in overdrive.. it wants to rev. Let it rev.

Why is the idle AFR so lean... Are you setting the idle correctly for best idle quality using a vacuum gauge?
Are the header gaskets leaking?
I don't have a 70x42 rod. Got 2 tunning kits. 1 for a 1407 and 1 for a 1406 but no 70x42 rod. lol Go figure! LOL I'll do some math and see how close I can get between the 2 kits. Maybe I can get the rods from summit or ?

Was just checking OD. Usually run round 2500+ RPM when using OD on interstate.
Idle was set with a vacuum gauge to best vacuum 9.5-10". Any hints on setting idle with twin carbs? Have 2 vacuum gauges if needed. Been using one off manifold below carbs. Vacuum is same when using 2 gauges.
Header gaskets are pretty new and show no evidence of leaking. 1600 miles on them.
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Old 05-07-2013, 10:37 AM
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When the idle is set up correctly and set for best vac at idle,,, the resulting air fuel ratio should be in the 12.5 to 13.5:1 zone. 14.5 and leaner is too lean at idle Engines idle richer than 14.7:1 normally.

This indicates to me that there is a air leak somewhere on the exhaust system creating false lean O2 sensor reading which throws off all AFRs on a gauge.
Headers and gasket joints can be very pesky.

600carb jetting: well try what you thing will help for your next test.
maybe try stock default jetting as the WOT was very rich.

I have never been big on the 600cfm carbs. The 750's will work better overall in my experience.
One reason is the pri an and sec throttle s are near the same diameter. More even flow on a tunnel ram.
The fuel curve will be better too. No they are not too big.
It would be nice to get that 750cfm carb back in service.
But I guess for now you are stuck with working with the 600's.
Let me know how you next test works out.

tell me something: when setting up the idle mixture and adjsuting the idle screws while watching the vacuum gauge, tach rpm and AFR gauge are you able to shift the gauge AFR rich with the 4 mixture screws counterclockwise is "richer" or is it always leaner than 14.7:1 at idle, reguardless of mixture screw adjustment?
As you should end up in the 12 to 13.5:1 area at idle.

Possible intake manifold gasket leak....probable exhaust leak even at the O2 bung.

Last edited by F-BIRD'88; 05-07-2013 at 10:50 AM.
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  #82 (permalink)  
Old 05-08-2013, 06:48 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
When the idle is set up correctly and set for best vac at idle,,, the resulting air fuel ratio should be in the 12.5 to 13.5:1 zone. 14.5 and leaner is too lean at idle Engines idle richer than 14.7:1 normally.

This indicates to me that there is a air leak somewhere on the exhaust system creating false lean O2 sensor reading which throws off all AFRs on a gauge.
Headers and gasket joints can be very pesky.

600carb jetting: well try what you thing will help for your next test.
maybe try stock default jetting as the WOT was very rich.

I have never been big on the 600cfm carbs. The 750's will work better overall in my experience.
One reason is the pri an and sec throttle s are near the same diameter. More even flow on a tunnel ram.
The fuel curve will be better too. No they are not too big.
It would be nice to get that 750cfm carb back in service.
But I guess for now you are stuck with working with the 600's.
Let me know how you next test works out.

tell me something: when setting up the idle mixture and adjsuting the idle screws while watching the vacuum gauge, tach rpm and AFR gauge are you able to shift the gauge AFR rich with the 4 mixture screws counterclockwise is "richer" or is it always leaner than 14.7:1 at idle, reguardless of mixture screw adjustment?
As you should end up in the 12 to 13.5:1 area at idle.

Possible intake manifold gasket leak....probable exhaust leak even at the O2 bung.
Oh yes, always been able to shift the AFR at idle with the IMS screws. Poured marvel mestry oil down carbs at high idle to make smoke looking for an exhuast leak but didn't see any.
AFR looking better? Still looks rich to me at normal cruise and way rich at WOT. I did some math on the jetting and rods looking for as close to setting you suggested last: 95 & 70x37, 98 last log run, u suggested 98 70x42, 95 sec. not having a 70x42 I went with 101, 73x42 and 95 sec. Way i did the math was deduct the rod sizes from the main jet sizes:
95 - 70x37= 25x58 and 98 secondary
98 - 70x37=28x61 and 95 secondary
98 - 70x42=28x56 and 95 secondary
101 - 73x42=28x59 and 95 secondary
Hope this makes sense?
Bout what AFR differance would be in, say, a 3point differance in sizes as in
98 - 70x37=28x61 and 95 secondary (61)
98 - 70x42=28x56 and 95 secondary (56)

Just hit me! I was looking at the rods backasswards! Will try a 101, 73x52 and 95 sec tomorrow.

Last edited by Fang16; 05-08-2013 at 06:58 PM.
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  #83 (permalink)  
Old 05-08-2013, 07:00 PM
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Guess the logs would be nice.

Here's the logs I forgot in above post.
Attached Files
File Type: txt 05081300-Session 1.txt (121.2 KB, 22 views)
File Type: txt 05081300-Session 2.txt (124.2 KB, 19 views)
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  #84 (permalink)  
Old 05-08-2013, 10:23 PM
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fyi.there are 3 step rods available.something to consider when you get closer to tune.They work good on the street when you do a 2/3 throttle.(Brisk take off while just hazing the tires)
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  #85 (permalink)  
Old 05-08-2013, 10:35 PM
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fyi.there are 3 step rods available.something to consider when you get closer to tune.They work good on the street when you do a 2/3 throttle.(Brisk take off while just hazing the tires)
I have the tunning kit for the 1406 and also 1407 carbs.
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  #86 (permalink)  
Old 05-08-2013, 10:46 PM
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You cannot do that.... you have to calc the area of the jet and area of the rod.
Subtract rod area from jet area.... not diameter.
AREA..

set the idle for best vacuum and idle quality ... should be 12.5:1 to 13.5:1 ish... you got it too lean at idle.

area of a circle is Pi x (radius squared) Pi='s 3.1416 radius is diameter /2

You cannot find an exhaust leak by dumping junk down the carb and looking for smoke.
Get a grip.

Last edited by F-BIRD'88; 05-08-2013 at 11:00 PM.
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  #87 (permalink)  
Old 05-08-2013, 11:55 PM
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Fang.I get it.You like figuring out this.Yep-I get that.My question to you knowing this manifold was never designed to run at part throttle and no matter what there are trade-offs,is it really worth it??.

I mean how often are you going to buzz this from 5,500 to 7 grand where this tunnel ram comes alive??.

Do take a third party look and think long and hard about that.Guys respect you for the car alone.Ya know.Nothing like a long pleasurable cruise too.

Just think about it some.
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  #88 (permalink)  
Old 05-09-2013, 08:53 AM
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Quote:
Originally Posted by F-BIRD'88 View Post
You cannot do that.... you have to calc the area of the jet and area of the rod.
Subtract rod area from jet area.... not diameter.
AREA..

set the idle for best vacuum and idle quality ... should be 12.5:1 to 13.5:1 ish... you got it too lean at idle.

area of a circle is Pi x (radius squared) Pi='s 3.1416 radius is diameter /2

You cannot find an exhaust leak by dumping junk down the carb and looking for smoke.
Get a grip.
How do you find an exhaust leak if there are no visable signs of one?
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  #89 (permalink)  
Old 05-09-2013, 08:57 AM
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Fang.I get it.You like figuring out this.Yep-I get that.My question to you knowing this manifold was never designed to run at part throttle and no matter what there are trade-offs,is it really worth it??.

I mean how often are you going to buzz this from 5,500 to 7 grand where this tunnel ram comes alive??.

Do take a third party look and think long and hard about that.Guys respect you for the car alone.Ya know.Nothing like a long pleasurable cruise too.

Just think about it some.
Thanks Gary! Seems I lost site of the big picture. Hit the track 6-8 times a year and was just concentrating on that. We lives and we learn. Thanks again!!
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  #90 (permalink)  
Old 05-09-2013, 10:31 AM
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A exhaust leak can be found by listening . Stuff a shop rag in the tailpipe with the engine running. Follow the exhaust piping. It will increase the backpressure sos that you hear the leak better.
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