Bud2

Background. 383 full roller, MSD Ignition set at 20 initial, +16 mechanical, vacuum advance will add another 20 degrees (will fix the 16 later). AFR 195s. Cam is 290/239 In. @50 - 290/239 Ex. @50 with LCA 107. 2 inch through exhaust. Carb is a Proform 750 with vacuum secondaries.

When approaching a stop sign or real low RPM cruse the car will ‘buck’ until you push the clutch in and settle it down. A real pain in the ****.

Started with 76 primary jets and the log displayed way too ‘lean’ AFR. Went to 80s and it was off the scale lean. It never displayed black smoke but the plugs were sooty. Went back to 70s and you see what I’ve got. Isn’t that backwards???? It came with a pink cam and seemed to be drowning out under hard accelerator pump so went with a blue cam in the 2nd position. Feels much better. This combination is in this log.

The secondaries have been disabled for this test.

The car feels strong but I think there is a fair bit more to be finessed out.

Any comments re accelerator shot or others?

Bud.

bluedawg

I bleave when you step the jets up it started to miss fire from the fuel flooding, when you miss fire it shows a high o2 reading leading you to beleave that its lean. I could be wrong in your case, but i know that really high o2 readings are an indication of a miss fire.

MelWff

try 72 primary, 76 or 78 secondary

Matt Gruber

1st i'd check the vacuum on decel, get specs on vac. adv, try disconnecting vac adv to see if bucking improves.
.
also turn up idle up up UP in driveway and vary timing to correct surging, post results.

Bud2

Thanks for the replies. The engine has never backfired - at least not that I heard and/or felt. When I had the 76 and 80 jets in it, it was 'heavy' but didn't missfire. I've got a bushing on the vac. adv. to limit it but didn't check to see when it comes in. The engine idles fine at 1100 and I've got 11 inches of vacuum at that rpm. The power valve is 5.5 and the primary idle screw is almost 1/2 turn in.

Are you guys picking up that it seems the LM software seems to be up-side-down? The accelerater pump puts it in the lean, increasing jets puts it in the lean, at 5000rpm with no secondary to help the primary it indicates richer. Isn't that the opposite of what it should be?

If that is the case, what numbers do I aim for???

I'll try dis-connecting the vac adv to see what that does.

I can't see what trying 72 jets in the primary will achieve. Will try 74s in the secondary tho.

Bud.

Crepitus

misfire may read lean because the sensor reads O2 that was not burned.

Shark Racer

Agreed (third) on missfires showing up as lean spikes.

Your car is running quite rich, there's absolutely no reason to believe that the carb is causing the bucking from what I see in the charts.

What is a "real low RPM cruise", I think you may be experiencing cam surge?

MotorHead

The graph looks fine to me. What happens when you WOT, the throttle plates open wide letting a lot of air, it momentarily goes lean then back to where it's supposed to be you are talking about very little time. Take a look when you let off the gas after going WOT, what happens, the throttle blades close and you fat for a moment. There are ways to fix the lean part but really it is normal and not worth all the trouble.

If your cam bucks at 1600RPM in third gear, then you should be second JMHO

Bud2

I understand about the O2 result of a backfire but there wasn't any noticable backfiring or lean 'spikes', other than WOT. Just a constant VERY lean line. I think the 76 jets were averaging an AFR reading in the 20s. The 80 jets were off the scale. In fact, that is why I tried the 80s after the 76s, because I saw that it was indicating 'lean'. Then I saw the sooty plugs and started to get really confused.

What about the 5000rpm mark? It indicates a richer condition when it should be starving for fuel. Remember the secondaries had been disconnected.

I dunno, I'm confused.

Here's another question. Would the opening and/or closing of the power valve be seamless to the LM1?

The 'bucking' being caused by the cam is something to think about......

Bud.

Bud2

Hi Motorhead, right you are about the air but what about the 20cc accelerator pump shot? That must have some effect on the curve. Or is the fuel dropping out of the mix conteracting that?

Bud.

Shark Racer

Bud- if the secondaries are disconnected why would it starve for fuel? There's no air crossing the secondaries.

When you went WOT did you flatfoot it or roll into it? Judging from the plot I'd say you jumped on it.

Matt Gruber

a carb expert disagreed with me when i told him i 1st tuned the primary. he said his carbs go rich at high rpm on just the primary so he keeps everything hooked up. So i told him my 3 carbs did NOT go rich, but if i ran across any that did, i'd hook it all back up. Which is what BUD should try.

Matt Gruber

"if your cam bucks in 3rd gear at 1600, then try 2nd"
.
That is something a SINGLE PLANE user would do.
a fully divided dual plane user would not have that problem at 1600, not with the good vacuum bud has.
.
still could be too much advance, however. or erratic timing,like weights moving around a bit, making it surge. even a loose timing chain could do it.

chevymans 77

Need to see a log of steady cruise, starting from 2000 rpm in 200 increments up to 3000 rpm.

You are not on the primary jets until over 2600 to 2800 rpm, below that you are using the transition slots and idle circuit.

First show us the steady cruise logs and we may be able to help.

the lean spike upon throttle opening can be resolved in a couple ways but we really need to get the carb closer to dialed in before moving to that issue.

The second position on the pump cam may be some of the lean spike issue. That position was to be used when the throttle opening at idle or when staging is high. The second position is used to gain back some of the pump volume. If you use the second position on the cam and than go WOT from idle you will cause the lean spot due to pump shot delay.

Do you have a way to measure the air bleeds for both the idle and primary circuits?

I may be missing something but that log is of you coasting and of a short WOT pull. We need to get the cruise first and than move on.

Stay with tuning the primaries, leave the secondaries disconnected.

Neal

Bud2

I don't know about the rest of you less-mechanically-inclined blokes out there but I LOVE this stuff! Identifying the problem, the challenge of learning how to correct it and finally the satisfaction of achieving the results through your own hard work. Not just paying someone else to do the work for you. That is what this hobby is for me. Love it!

The LM1 could be a real asset in the tunning department but lack of information on how to interpert the log sessions is a bummer. I'm learning tho.....

I’ll post up the air bleeds, do a log of idle, then cruse @ 2000 to 3000rpm in 200 increments. I work during the day and then help out the wife in her restaurant at nights so I won’t be able to do this until Sat. arvo. We have a drag race meeting this Sunday. I’ll have to go. Even at this stage I need to work out a few other issues too. So I’ll post up again on our Monday.

Thanks everyone.

Bud.

MotorHead

Please voice your opinion and don't just dismiss mine as being wrong. I do no respect that kind of thinking, "your wrong here's what I think the problem is" is not the way to go about things here.

His problem could be any number of things, so if you say I am wrong then tell him what the problem is and then tell him how to fix it.

MotorHead

I have 50cc pumps front and rear with 40 shooter in front and 45 in the back of my 825 Drag Race Demon, no lean spike when I hit the throttle.

How long have you had your LM-1. There is a learning curve with it that takes some time, then you tinker with the carb parts and settings to see what effect they have on A/F readings. Good luck and have some fun the LM-1 is an excellent tuning tool

cv67

May be tough getiting an accurate low rpm reading with a lumpy cam on much below cruise rpm

Had a similar combo littel more cam. 76/84 worked great. I suspect your idle air bleed is lean not so much the jets. Are yours plugged or adjustable? Used to pull my hair out figuring that one then bought an AED (a holley hp is nice too) and man what an overall difference. Even without a choke). Running 20 deg more cam and barely surges when lugging it back to idle (you have to expect some with a large stick-downshift lol)

Numbers are good for reference but pay attention to how the motor feels..give it what it wants> numbers

Crepitus

Innovate used to have a great support forum but they shut it down...tards!

MotorHead

I agree dumbest thing they could have done, real carb tuners are a dying breed and there were a few there that forgot more than I know about them