Best air-fuel ratio monitor?

[408 Nova]

Good idea Chris1.

[randy331]

No matter what jetting change I make on my carb, the ETs stay the same. I was at the drag strip the other day and was going to put an 88 in the secondaries. My son was helping me, and, unbeknownst to me, he handed me a 98 on accident. The speed and ET didn't change. I didn't notice the mistake until the next jet change.

I have seen this same thing caused by cylinder heads, or cylinder heads/cam combination.

Big valve/big throat/big overlap/big low lift flow ??

If fuel delivery was a problem, it should have ran out of fuel sooner after launch and caused at least a change in the incremental times.

Randy

[408 Nova]

No matter what jetting change I make on my carb, the ETs stay the same. I was at the drag strip the other day and was going to put an 88 in the secondaries. My son was helping me, and, unbeknownst to me, he handed me a 98 on accident. The speed and ET didn't change. I didn't notice the mistake until the next jet change.

I have seen this same thing caused by cylinder heads, or cylinder heads/cam combination.

Big valve/big throat/big overlap/big low lift flow ??

If fuel delivery was a problem, it should have ran out of fuel sooner after launch and caused at least a change in the incremental times.

Randy

Well shoot Randy, what do you suggest?

[randy331]

Well shoot Randy, what do you suggest?

You bought the o2 set-up so I'd suggest installing it and see if you can learn anything new about your set-up.

I'm just saying I've seen engines not respond to jetting for reasons other than the carb.

Also if you don't see a o2 difference when changing the jets, try 2-3 size different on air bleeds. I've seen a couple carbs not change fuel flow much with a couple jets sizes but, would show a considerable difference from 2 -3 bleed sizes.

Vacuum readings during a run would be good to have also.

Randy

[jmarkaudio]

Well shoot Randy, what do you suggest?

Also if you don't see a o2 difference when changing the jets, try 2-3 size different on air bleeds. I've seen a couple carbs not change fuel flow much with a couple jets sizes but, would show a considerable difference from 2 -3 bleed sizes.

Randy

Sounds like what happens when it has way too much emulsion to begin with...

[408 Nova]

Thanks Randy for the advice. The carburetor that's on the engine has adjustable everything. It's from Big's out of Wisconsin. I have a couple of other carbs I can try if this one continues to not be responsive.

[408 Nova]

Well shoot Randy, what do you suggest?

Also if you don't see a o2 difference when changing the jets, try 2-3 size different on air bleeds. I've seen a couple carbs not change fuel flow much with a couple jets sizes but, would show a considerable difference from 2 -3 bleed sizes.

Randy

Sounds like what happens when it has way too much emulsion to begin with...

I have never messed with the emulsion well jetting, and they are removable. I wouldn't have a clue where to start. I borrowed this carburetor from a buddy of mine who ordered it from Big's for his 434 project. It is very similar to my engine in that he has a big overlap cam and similar heads, compression, etc. Maybe a carb change is in order?

I run Turbo Blue also. Any special tuning requirements for this fuel?

[Orr89rocz]

Anyone use autometer wideband setups? My friend and tuner swears by them and wants me to get one. I already have an innovate lc1 which seems to work well enough but its got a few years on it.

[Chris1]

To be clear my post was one of many for instances... relevant point to the OP being if performance isn't responding to arguably significant changes you need to determine why. Is the carb flowing more fuel, or is it not? If so is the engine making more power, or is it not? Heck... maybe the engine made more power with the jet but it isn't getting to the tire... I didn't see anything about incremental times in the OP's comments. So many variables, but again my point is things should respond - they should do something. Gdlk!

[408 Nova]

Chris1, I installed an AFR monitor with data logging capabilities and discovered my carb is bad rich and increasingly richer with higher engine speeds. This weekend, I'm gonna do some carb tuning to see if I can get the AFR more inline with what is supposedly the best AFR for max power using the dragstrip clocks as a reference. Who knows if this thing is accurate or not, but I intend to find out. If anyone is interested, I'll post the results here.

[hrodgmc]

NTK was original wideband sensor. VW started putting the Bosch in the late 90's or early 2000's if I remember correctly. Caddy, Honda, and a few others use the Bosch now. It's a plug in OEM replacement for Innovate system. Most innovate will do ntk or Bosch, but the lm1 looks like a 3rd grader built it. LM2's are better.


If it's high dollar build go NTK and either test it before a run or calibrate it. The cross counts get too slow for good WOT read. The free air calibration is marketing hype. A lighter will give you an accurate idea if it's working well.

I've killed 6 or so Bosch's in the last 7 years and 1 NTK.

[Fordtechman]

I use an AEM 4900 because I have a blower, it makes recordings , is easy set up and I can tune my engine with it. It's cheap, has a great data logger and has a fail safe output. Use it with the MSD ignition and if the AFR goes above my preset limit it removes (X) degrees of timing. The system has so many options and it really is inexpensive . Good luck.

[408 Nova]

I love this WEGO III AFR and data logger. But, I am having a heck of a time calibrating this carb.

The engine started out bad rich across the rev range, with increasing richness at engine higher speeds. I went from a 33 high speed bleed to a 36. Still rich but leaner across the board with the 36s. No ET gain, because it's still really rich I guess.

Leaned out the jetting, went from 80s and 85s to 78s and 83s. 60 foot went from 1.38 to a 1.36, engine feels a lot better down low. At flash stall, the AFRs are about right, around 13.0. ETs drop those 2 hundreths as well. After stall RPM, the AFRs get increasingly rich, AFR 11.8, with a "hump" in the middle, around 12.3, then back down to 11.8 at 7000 RPM, and across the stripe (1/8th mile) at 7300 RPM with an AFR of 11.4.

Now, it seems to me that for a 950 carb, the jetting is going to be really small and unusual, once the AFRs are close.

The hump in the middle has to do with the emulsion jetting, doesn't it? Are the boosters really that active?

I have some 39 high speed bleeds I'm gonna try, too. However, this may lean it out too much on the bottom. I'll just have to try them and see.

I'm thinking about ditching that carb and trying a box stock Holley 830 I have just laying around for comparison, just to see if it's anywhere close to where it needs to be, AFR curve wise.

Any help is really appreciated.

[randy331]

Couple thoughts,

Being lean right off the starting line and getting richer after, would make me wonder if it has jet extensions in the back, and the right ones with a float that gives enough travel for the needle ?

Also a 5 jet spread from front to rear isn't normal assuming it has a power valve in the primary side. Most Holleys are 8-10 jet sizes different when one side has a power valve and the other doesn't. I'd look up your list number and see what it had from Holley.

Also, if the fuel curve was headed the right way with the bleed change, go that direction some more.

Also, If I remember right you have a narrow LSA cam in early? 100* ICL if my memory is right? That's one thing I'd change. Put it in at 104*-105* ICL. It may respond to jetting changes better then.

Just some thoughts that may or may not be right. LOL

Randy

[408 Nova]

Couple thoughts,

Being lean right off the starting line and getting richer after, would make me wonder if it has jet extensions in the back, and the right ones with a float that gives enough travel for the needle ?

Also a 5 jet spread from front to rear isn't normal assuming it has a power valve in the primary side. Most Holleys are 8-10 jet sizes different when one side has a power valve and the other doesn't. I'd look up your list number and see what it had from Holley.

Also, if the fuel curve was headed the right way with the bleed change, go that direction some more.

Also, If I remember right you have a narrow LSA cam in early? 100* ICL if my memory is right? That's one thing I'd change. Put it in at 104*-105* ICL. It may respond to jetting changes better then.

Just some thoughts that may or may not be right. LOL

Randy

Randy, it's a "custom carb" I borrowed from a buddy for his 434. It's a 950 with no choke tower, billet metering blocks and billet throttle plate. It's probably a chinese throttle body, but it does have tuneable high speed and idle bleeds.

It has jet extentions and a notched float in the back, plus a power valve in front, no power valve in the back. Float level is set exactly half way up on the sight glasses front and back at 7 PSI with a fully charged battery.

The cam is dot to dot. It is supposedly in at an ICL of 100 degrees. It may or may not be. It's a Competion Cams cam.

I still haven't found the time to move the cam around like you have suggested, but I would love to try it. This engine really wants to be shifted at 7000, which I thought was higher until I got that data logger. It crosses the stripe at 7300, and I think it might run a little better at an ICL of 104-105. Not to even mention that it might help carb tuning.

Thanks everybody for your help.