FE Experts need advise Help!!!!!!!!!!

[priobe]

Hello All,

I have been trying to tune my weber carbs and been using a Inovative LM1 anaylzer. I am noticing around 2000 - 3000 RPM my A/F mixture is shoots to 22 which is lean and I get a detonating ticking sound / backfire (which sould like it is not firing on all cylinders)

I have check / changed

rotor
cap
plugs
wires
firing order
ground / added extra ground
adjust valves

adjust carbs to run rich

and on the LM 1 everything looks good but at 2000 -2200 - 3000 all hell breaks loose.

I am stumped.

Can someone please advise?

[CHANMADD]

Check the power valve

[priobe]

Webers do not have power valves.

Also, you can see in the log that everything looks fine then all of a sudden you see it spike lean than back to normal. When it spikes lean you hear it detonate.

[CHANMADD]

OOOPs Sorry ...I do know that but a did'nt even look at that.. Would that be the wrong emulsion tubes??Maybe a sticking needle or float??

[CHANMADD]

Hey Mate ,Here is a nice link I found for you.Hope it helps .
http://www.aircooled.net/gnrlsite/re...idarebuild.htm

[68gt500]

There is a special Weber Tuning section here at Club Cobra. http://www.clubcobra.com/forums/weber-tuning/

Your post over there will yield much better responses.

What you have is a huge lean spot at the point where the carb transitions from the idle to the main circuit.

On the Webers all driving, basically up to 2500 rpm is done on the "idle" circuit.

You already have done one important step, getting the LM-1 - a great tool.

Read up on the topics in the Weber section - that will help you understand your Webers and tune them to perfection.

I was where you are now some months back - now I have great running carbs and the know how to tune them.

[dlampe]

You need to tell us exactly how your webers are jetted, then we can offer some advice. I had a similar problem but without knowing your setup I can't really help.

[Jac Mac]

Originally Posted by dlampe

You need to tell us exactly how your webers are jetted, then we can offer some advice. I had a similar problem but without knowing your setup I can't really help.

And if you have anything like a 'SWITCH' that can be used to change from locked to advance curve type ignition, or change from pump to race fuel, "NOW" would be a good time to inform us of those little issues as well, tends to cloud the issue if you suddenly remember after a couple of pages.

Jac Mac

[dlampe]

Who would ever do something so silly?

Seriously, you are the one to sort this stuff out. I really appreciate the help you've given me.

[priobe]

dlampe / 68gt500,

I have tried many different config to the carbs and yeild the same results

Here is config # 1

42 choke
120 idle holder
65 mains
210 air corrector
f-11 / F-16 / F-7 Etube
180 main
oo bleed

When you look at the LM1 everything looks great but all of a sudden you spikes that go to 22 on the LM (in and out / up and down like a mis fire

Next setup

60 holder
60 jet
f-7 / f-11 /f-16
210 air corrector
180 main
42 choke

Same result

I know most people with the webers run:

37 choke
60 idle
120 holder
F-7 e tube
210 corrector
160 main
50 bleed

My car ran pig rich.

Hmmm maybe I should try the 37 chokes again to see if the problem still exist.

I would love to send my data log to someone to see if that come up with the same results.

Any thoughts??????????????/

Standard setup other wise
Holley pump
msd dist
6al msd
return line
I am actually using the heavy springs in the dist to see if that would help


When I gradually easy into the throttle it is fine but drive normal and it happens.

[Jac Mac]

OK, so you have tried two jet combos in the car with same problem-------- Are you sure that it is not an ignition curve problem with all the advance arriving at that 2500 approx rpm point or perhaps a 'sticky' advance mechanism. Hook your timing light up & run the rpm up thru the range, the advance should be a gradual advance with RPM, not a sudden increase of say 10°/15° in 500rpm. You must try and have a reasonable curve plotted before attempting to rejet. Heat range , Rotor Phase , Incorrect MSD wiring and a possible cross-fire from plug leads are other things that might be worth looking at as well.

Detonation is going to kill it quick so try to nut the problem out with minimal engine use- look hard & re-examine everything you have done prior to the problem- lot easier to live with than the problem coming out to meet you.

Jac Mac

[68gt500]

Originally Posted by priobe

dlampe / 68gt500,

I have tried many different config to the carbs and yeild the same results

Here is config # 1

42 choke
120 idle holder
65 mains
210 air corrector
f-11 / F-16 / F-7 Etube
180 main
oo bleed

When you look at the LM1 everything looks great but all of a sudden you spikes that go to 22 on the LM (in and out / up and down like a mis fire

Next setup

60 holder
60 jet
f-7 / f-11 /f-16
210 air corrector
180 main
42 choke

Same result

I know most people with the webers run:

37 choke
60 idle
120 holder
F-7 e tube
210 corrector
160 main
50 bleed
.....
When I gradually easy into the throttle it is fine but drive normal and it happens.

Your problem sounds almost exactly like the one I was having.

A huge flat spot on transition.

The one change, that did the trick for me was to drill the 3rd transition hole.

Here is my setup:
idle 65
idle holder 110
Emulsion tube F7
3rd transition hole drilled
Main 140
Main air correction 120
Venturis 40 mm

As you can see my setup is way leaner than yours - still no flat spots.

[priobe]

68gt500

I sent the carbs out to peircemanifold to have them checked and the 3rd progession hole modified.

I have the same jets that you have listed but I will try to post the log of the LM 1 so you can see the eratic lean condition.

I think Jac Mac is correct. I also think it might be a ignition problem.

I have a 2nd mallory dist that I am thinking of changing. I would like to bypass the MSD 6AL to eliminate MSD from the problem.


JAC MAC,

I even installed the 2 Large springs for the advace curve and the problem still exist.
I am going to try locking out the dist to say 15 degrees and see if the problem still exist.

I recall that MSD 6 AL do not operate until 1500 - 3000 RPM. I am thinking it might be a problem with the 6AL


Has anyone heard the same about the operating range of the MSD.

[priobe]

68GT500,

Originally Posted by 68gt500

Your problem sounds almost exactly like the one I was having.

A huge flat spot on transition.

The one change, that did the trick for me was to drill the 3rd transition hole.

Here is my setup:
idle 65
idle holder 110
Emulsion tube F7
3rd transition hole drilled
Main 140
Main air correction 120
Venturis 40 mm

As you can see my setup is way leaner than yours - still no flat spots.

From what I could see, you setup is not leaner than mine.

idle 65
holder 110

In my setup I am running
65 idle
135 holder
with 42 chokes - my setup seems leaner

I am still leanering about this but correct me if I am wrong

you are running
F7 tube - which is a richer tube than the F-11 & F-16

Your 120 air corrector w/ 140 main

Mine 210 air corrector w/ 180 main

The air corrector is only used at 4000 rpm and above and even than yours is running richer.

Help me understand if I am understanding this correctly or if I am wrong.

[Jac Mac]

Originally Posted by priobe

68GT500,



From what I could see, you setup is not leaner than mine.

idle 65
holder 110

In my setup I am running
65 idle
135 holder
with 42 chokes - my setup seems leaner

I am still leanering about this but correct me if I am wrong

you are running
F7 tube - which is a richer tube than the F-11 & F-16

Your 120 air corrector w/ 140 main

Mine 210 air corrector w/ 180 main

The air corrector is only used at 4000 rpm and above and even than yours is running richer.

Help me understand if I am understanding this correctly or if I am wrong.

Priobe, I can see that your understanding of Weber fuel /air flow path's is somewhat flawed.

Take your Idle circuit for example; 65 jet(fuel)- 135 holder(air) is leaner than the setting of 68GT500--65jet(fuel)-110 holder(air). While both jets are the same size your 135 air allows more air to be introduced in the emulsification process.

On your main circuit, similar thing-you have:180jet(fuel)-210 corrector(air), Yes you have a large jet,but you also have a larger corrector @210 which will lean it out where 68GT500: 140 jet(fuel)-120 corrector (air) tends to pull more on the fuel due to the smaller air corrector. His system will start to flow fuel earlier due to the smaller AIR (RICH) while yours will be later due to the larger air (LEAN)- your larger 42mm choke size also gives a weaker signal to both air &fuel.

Now that was ONLY to give you a basic understanding of how & why. Every change you make affects another part of the system so one change at a time please!! I will need your: Bore-Stroke-Cam Specs-Comp Ratio to give a ballpark start point plus an HONEST idea of how you drive the car and RPM range you use.

Not sure what you mean with MSD not operating until 3000. Dist weights control advance curve-not MSD.

Jac Mac

[priobe]

Jac Mac,

I see that makes perfect sense.

Here are the bore and stroke info.
4.232" X 3.784"

Cam specs

Intake and Exhaust
Lobe Separation= 111.9 Cam Deg
Valve Overlap= 23.4 Crank Deg


Intake

valve open = 14.6 Cam Deg
Centerline 115.8
Valve Close= 50.2
Duration------> 244.7 Crank Deg
lobe lift ------> .37689 IN
Valve lift-----> .65956 IN
Lobe Area ----> 30.85 IN * DEG


Exhaust
Valve Open = 60.5
Centerline = 115.8 BTDC
valve close = 8.9 ATDC
Duration----> 249.3 Crank Deg
lobe lift ----> .3789 IN
valve lift ----> .66307 IN
Lobe Area ---> 31.83 IN

Compression Ratio = 9.5:1

My driving style is mostly street driving with sometimes aggressive manner.

Please let me know if anything else is needed.

My comment about the MSD was that I was thinking it might be a MSD 6AL problem. I was told that the 6AL does not operate above 3000 rpm with the multiple spark discharge. That may be the MSD might be bad. ( I dont know anymore I am throwing up my hands)


I was also thinking of returning the carbs back to the setup list below

37 mm choke
60 idle
120 holder
f-7 Etubes
210 air
160 mains
55 bleeds

Just to see if I still have the problem.

Suggestions ????????????

[RICK LAKE]

Priobe I have in the past had multi problems with Mallory distributors. The weights would stick and not advance at 2,400 rpm. The motor would fall flat on it's face. Mallory has had a problem with the pins the weights pivot on wearing. I would go with the MSD billet distributor and set the timing at 36 degrees at 2,700 rpm. Maybe there is a friend who would let you borrow his setup and try. I am not a weber tuner, but it sound like a idle to main curcuit transfer causing the leanout. I know you check the fuel pressure and the float levels. To go that lean on the LM-1 is more fuel than ignition problem. I have seen fuel pressure gauges not reading right. I have a manual and electric gauge setup in my car for the FI system. If you turn up the fuel pressure 2-3 psi is there a change in the lean condition?? This is a easy check. If change, go back to the carbs. If not go back to the pig running condition and work from there. Rick L.

[68gt500]

Priobe

while your displacement is about the same, your cam is much wilder (mine is a straight cam with about 225@.050 in/ex) and your compression lower (10:1)

Even whitout seeing your lm-1 data I would rule out ignition as the primary cause. Btw, the MSD stops beeing a multiple spark unit at about 3000. Its just single (long duration) spark from there on up.

Jac already pointed out why, both your Idle & Main are leaner than mine.

With the wilder cam and lower compression, it most probably will need a richer mixture that what I am running.

Depending on what parts you have on hand, I would start by reducing the Venturi size to 40. Don´t go to 37mm that is way to small even for my motor.

The stronger signal from the smaller Venturi will allow the transition circuit to kick in earlier.

As a next step I would reduce the air corrector, too big an air corrector will slow down the kick in of the transition ...

Just make sure to do one change at a time - I use an Excel table to keep track of the changes - at my age I tend to forget quickly

[priobe]

68gt500,

I am glad you posted that information. I was actually thinking of replacing my setup with the 37 choke setup to see if the problem persist.

If you feel that the 40 will work, I will try those first and work my way on down if needed.

I agree with you about forgetting. I have decided to create a diary on all my changes.

I will let you know.

[Jac Mac]

Priobe-
Idle fuel jet--------75
Idle jet holder -----110/120

Main fuel jet-------170
Main Air Correction-130/140

Pump or Bleed------55

Choke size---------42mm

Check your fuel pressure (running & as close to carbs as possible- remember webers dont like high pressures)

From the info you have given it looks like your main problem has been the air correction size- dont forget to check the advance curve out as well.

One other thing that helps is any form of anti-reversion cone in the exhaust primary pipes- really smooths out the idle on a setup like this.

Jac Mac