Srobinsonx2 Carb Tuning

[bobl]

Made some progress on the LM-2. Got the software installed without issue. I have only issue yet to resolve. I can't get the LM-2 handheld to connect to my computer. I keep getting a USB device error. It is either a bad driver or bad hardware (something with the LM-2 as I checked the cable and USB port on my computer). This ins't a show stopper since I won't be using the LM Programming software. Here are some other learnings so far:

The system is easy to turn on/calibrate and I got the wideband O2 sensor up and running right away (via power in my daily driver). When doing this calibrations I just held the O2 sensor in my hand, let it warm up and then calibrated. When done the O2 sensor reads 20.9. This is not an air fuel ratio but is the oxygen concentration in air. Any AFR above 100, the handheld displays and records the concentration of oxygen and not a true AFR. This can be recorded as such and played back on the handheld. When the log is imported into Logworks 3, the software can only display AFR's between 7.35 and 22.38. Anything above or below this range, the software trends will only display the max or min and not the same value as the display (in my case something near 20.9).

An SD card reader works great to import the logs and pretty cheap.

I got the analog cable hooked up to the tach to measure RPM. Since I am using an MSD ignition box, this system requires I connect to that wire. On my MSD-6AL the tach signal is a gray wire. Found it and made a tie if for it and a ground. Also ran the wire for the O2 sensor and got it installed in the exhaust. I tried to power this all up but ran into an issue. On my car, I installed a USB power supply for charging my phone. The LM-2 has a cigarette lighter plug for power. I bought a USB to cigarette lighter adapter off amazon for a few bucks. It would power up the unit but apparently won't provide enough power to warm up and run the O2 sensor. To verify, I checked this USB to cigarette lighter system in my daily driver and had the same issue. The LM-2 and sensor works great in the daily driver when connected directly to the cigarette lighter. So I am going to pick up a cigarette lighter power outlet tomorrow and replace my USB power outlet. Should be easy and that will allow me to get my tuning system up and running.

I am very hopeful that the LM-2 system will provide good data and allow me to properly tune my carb. But be aware that it appears the LM-2 does have a learning curve and a few idiosyncrasies that one must navigate to use the system proficiently.

Yes they need a good power supply. I use a cigarette lighter adapter with clip leads to connect directly to the battery.

Once you get to testing don't be surprised if you end up around 13:1 A/F for best idle. I've never had much luck getting them to idle really lean and still start well and have good throttle response.

[CraigS]

....
Once you get to testing don't be surprised if you end up around 13:1 A/F for best idle. I've never had much luck getting them to idle really lean and still start well and have good throttle response.

I don't pay attention to the idle afr except as a curiosity. I set idle mixture via 'lean best idle' method on a warm engine and that's it. My QF650 was real lean at cruise of 13-1400 and a QF tech recommended, as an easily done and removed test, to open the idle mix screws 1 turn from best idle and drive it and try 1 more turn if needed. Doing that told me the idle system was lean so then I started replacing jets. I was surprised how far up the rpm range the idle system is affecting the engine. At the low throttle openings our cars use at cruise the idle system is effective up to about 1800.

[Avalanche325]

OK. I am probably being anal about the whole thing. You likely could smack on a spacer and tune away. But that kind of stuff bugs me.

Is the carb new or used? If used, I wonder if it didn't have a throttle stop and was romped on. That can bend the primary shaft, or wear the holes in the base plate.

I was poking at the Quickfuel (Holley - *sigh*) site to see if I could get a good shot of the secondary T-slots. I saw the primaries in a couple pictures and they were identical. I didn't see a secondary shot

Keep in mind, I have not had your situation, so I am saying what pops into my head and what I would do. Again, if someone like Gordon or Craig calls me an idiot, laugh at me and move on.

For tweaking, here is what I am thinking.

Check the base plate first, of course.

Always, least aggressive first. No need to come out of the gate like a silverback gorilla. You are just looking for a few thousandths.
I would take the butterflies off of the shaft, and see if any of those are noticeably bent. Check the shaft and butterflies for any flashing or burrs that could be making one sit funny .
Swap the butterflies around, flip them over, etc. See if it gets better.
I would then consider seeing if I could twist the shaft, without bending it. The amount you would need would most likely be imperceptible to make a difference at the edge of the plates. A new one is <$30 if it goes horribly wrong. Heck, you might just want to try a new one. You could leave it in the base plate to hold the ends and center and make use of the butterfly mounting holes to mount in some handles to get a little leverage on (just a bump, then check).
The cheesier way would be to bend the plates themselves. Again, almost imperceptible would get you enough at the edge and not affect the rest of the range. Butterflies aren't exactly a precision device.

[srobinsonx2]

OK. I am probably being anal about the whole thing. You likely could smack on a spacer and tune away. But that kind of stuff bugs me.

Is the carb new or used? If used, I wonder if it didn't have a throttle stop and was romped on. That can bend the primary shaft, or wear the holes in the base plate.

I was poking at the Quickfuel (Holley - *sigh*) site to see if I could get a good shot of the secondary T-slots. I saw the primaries in a couple pictures and they were identical. I didn't see a secondary shot

Keep in mind, I have not had your situation, so I am saying what pops into my head and what I would do. Again, if someone like Gordon or Craig calls me an idiot, laugh at me and move on.

For tweaking, here is what I am thinking.

Check the base plate first, of course.

Always, least aggressive first. No need to come out of the gate like a silverback gorilla. You are just looking for a few thousandths.
I would take the butterflies off of the shaft, and see if any of those are noticeably bent. Check the shaft and butterflies for any flashing or burrs that could be making one sit funny .
Swap the butterflies around, flip them over, etc. See if it gets better.
I would then consider seeing if I could twist the shaft, without bending it. The amount you would need would most likely be imperceptible to make a difference at the edge of the plates. A new one is <$30 if it goes horribly wrong. Heck, you might just want to try a new one. You could leave it in the base plate to hold the ends and center and make use of the butterfly mounting holes to mount in some handles to get a little leverage on (just a bump, then check).
The cheesier way would be to bend the plates themselves. Again, almost imperceptible would get you enough at the edge and not affect the rest of the range. Butterflies aren't exactly a precision device.

Avalanche325.

I hear ya brother. It bothers me too. But it doesn't bother me $600 worth. At least not right now. If I can get it to tune and run well then I can live with it. If I can't get it to tune or there is a risk of engine damage I will spring for a new carb. I know. I have come this far and spent this much but at some point you gotta stop the bleeding. The wife keeps seeing boxes delivered and finally asked, "So how much has this car really cost?" I immediately suggested a nice Italian dinner, a glass of wine, and trip to the mall. These are dangerous times. I need to camouflage, adapt, blend in, and avoid eye contact. Answer no question. Name and rank only. WHAT WAS THAT???.

Sssshhh. I gotta go.

[srobinsonx2]

LM-2 update. I got the 12v power plug (cigarette lighter) installed. Plugged everything in (analog cable, O2 sensor, SD card) including the power cable and powered it up. With the cigarette lighter hooked up directly, the LM-2 powered up as expected and the O2 sensor warmed up (about 15-30 seconds). I cranked the engine and the O2 sensor immediately went from 20.9 (oxygen concentration) to 12-14 as the AFR. I was pleased. The rpm was displaying about 7000. Turns out I didn't have the rpms configured correctly. I followed the instructions and got that lined out.

I then recorded a little bit via the LM-2. I then imported the log into the Logworks3 software. Here is screen shot of the trend.



I haven't done any tuning so there are probably some things I need to work out. This was just a test of the LM-2. I had some idle, revs and hold at 3000, then some short stabs. I am excited to get to tuning. Now the rain needs to stop.

Here is a short video. Sorry the video is so poor.

https://www.youtube.com/watch?v=gPCqRddH6JQ

[srobinsonx2]

FYI, I have found 1/2" open spacer on that really helps the upper mid range and top end

That's what I got headed my way. I will install it this weekend and report back. Thanks Gordon.

[CraigS]

Once the rain stops take a note pad w/ you to keep track of your recordings. IE #1 = from a stop 1st, 2nd, 3rd about 1/3 throttle, #2 = full throttle 3rd gear, etc. I find this helps cause I have gotten lost some times when I come back to the house and have 5-6 recordings. Especially for the full throttle stuff where I needed to drive 5 miles to get to a spot I could do that w/o pi$$ing someone off. Good luck and have fun!

[bobl]

Shannon, I was under the impression the carb came with the engine from Gordon. I'm now realizing that you must have acquired it elsewhere, which clears a few things up in my mind. Was it new?

[srobinsonx2]

It came with the engine. But I haven't asked Gordon to help in any way. Sure don't want folks to think he dropped the ball. Honestly, I don't feel right asking him to replace it or anything like that. I am an amateur and can not rule out this being something I did.

I did take the carb off and think I found the issue. I will post am update a little later.

[srobinsonx2]

After some consideration I came to the conclusion that Avalanche325 was probably right and the misaligned T-slots should get fixed. So with a little trepidation, I decided to take a stab at "fixing" the problem. Upon careful inspection, it was clear that the driver side butterfly valve was slightly tweaked. I used a pair of needle nose pliers and a screw driver to ever so carefully realign that butterfly. Took me a few minutes but I managed to straighten it out without disassembling the carb. I tried to get some pictures but they turned out blurry and you could not tell much. The carb is back on so, during the next removal, I will try and get a better picture. Once reinstalled, I set the idle circuit again. I used my LM-2 and a vacuum gauge. My second vacuum gauge came in this week so I took the opportunity to verify the one I had was accurate. I confirmed that they both read the same. So onto the tuning. I started from scratch on the idle circuit. Primary T slots set to at square, the secondary T-slots closed, and the idle mix screws out 1 1/2 turns. That gave me a rich idle (11.5-12 AFR), 800 rpm, and a vacuum of 8.5. I turned the idle mix screws in until I got the highest vacuum and the highest idle. That ended up being 950 rpm and a vacuum of 10" of Hg. The AFR ratio at this point was right around 13 (between 13-13.4). So I felt good about my idle set up.

With the new vacuum reading, the power valve needed to be changed. I removed the primary side. It was very easy. I used a 5/16" socket to remove the four bolts on the front corners of the bowl. I tapped on the top of the bowl with my hand and the bowl came right off. I then tapped on the metering block with the end of my socket driver and it came right off as well. Here are the parts disassembled.



I then took the power valve (PV) out of the metering block. The PV installed was a 6.5. I replaced it with a 5.0 Quick Fuel 5.0 "four door" PV. A 1" wrench fit the PV perfectly. It was not very tight so I reinstalled the 5.0 to the same tightness. Here is the PV and o ring.



I reassembled the primary side and reinstalled the carb. I also made a vent tube extender that should help with my hard braking. This is only a temporary prototype. If this works well, I will make something that looks nice.



I used two spark plug wire boots and a short piece of 3/8" fuel line. I cut the vent holes in the top with a razor knife. Not pretty I know but this is just for testing purposes.

Finally, I took the car down the road in my neighborhood to test the idle circuit. I will have to redo this run. I accidently got on the gas towards the end of the run and got out of the transition slot and into the main a little ( I think). I started the run at 1500 rpm and ramped up to 3000 rpm in second gear. I did this by applying just a little throttle with the intent of only exposing the T-slot. Here is the log.



Magenta is AFR and black is the rpm. It is not bad for the first half but gets a little rich towards the end. Per the experts, the entire run should give an AFR of 13.5-14. I won't change anything at this point. I will wait until I get another run from 1500-3000 rpm but in third gear and staying in the T slot.

[NAZ]

What we do with off-road vehicles is loop fuel hose in a inverted catenary connected from vent tube to vent tube. We then take a long slice out of the center of the hose just shy of half-way through the hose and a couple inches long (linear with the hose so the hose is still one-piece). This all fits under the air cleaner and is about as neat as you can make a home made extended vent. However, I've never had to do this on a street or even a track car that runs on a smooth track (stadium racing is the exception). But if you feel you need to extend the vents, this is a common low-cost way to do it.

But an even neater way is to purchase Holley vent whistles (Holley #59-10). It looks as you carb came without them. The vent whistles fit inside the bowl. There are also anti-spill valves out there but I've never used them so can't comment on them other than I know of them.

[srobinsonx2]

Thanks Naz. I do have the vent whistles. They are the black push in style. I lowered the bowl level in the secondary a little. Hopefully that solves my problem.

Thanks for the home made vent advice. I like that idea.

[NAZ]

Another thing to consider, especially if you run a lower level in the secondaries is fuel starvation during hard acceleration. With these light cars even a moderately powered car can accelerate in excess of 1.6 G's which can slosh fuel in the bowl >50-degrees potentially uncovering the secondary main jets. If you experience this I recommend you get main jet extenders on the secondary side. The kit includes a new float with clearance cutouts for the extenders. This puts the jets farther to the rear so they are not as likely to become uncovered when the fuel sloshes to the rear. Of course that's not a problem on the primary side and not an issue when hard on the brakes as you are off the gas during braking.

Just another tool for your tuner's tool kit.

[srobinsonx2]

That is funny. I have those too. Thanks though and keep 'em coming.

[srobinsonx2]

Here is my idle circuit.



I ramped from 1500 to 3000 rpm and took about a minute. The blue line is 13 AFR and the red line is 14 AFR. As you can see my AFR was well below 13 the entire run. It does slope a little bit to become more rich as the rpms increase. I also have a funny lean-rich-lean bump at the beginning of the run right at 1500 rpms. I am not sure what this is. So, here is my plan of action:

- Put in smaller idle feed restictors. I will start with 2 sizes smaller. I don't know what size I have so I will have to disassemble and inspect.
- I will hold out on adjusting the idle air bleeds. I think I might need a little smaller IAB to flatten out the slope but I will only change one thing at a time.

What do you guys think about the initial lean-rich-lean condition at 1500 rpm? Any advice. I don't really know what to do there. Maybe I got a little aggressive and the power valve came open to cause the rich condition but I don't know about the lean spikes. Any advice would be much appreciated.

[Gordon Levy]

Change the pump cam position from position 1 to position 2

[srobinsonx2]

I had to order some restrictors/bleeds. They came in today. Summit is great and I usually get items in about 2 -3 days. Here is what I got.



Based on my previous post, I had determined I needed smaller idle feed restrictors (IFR). The IFRs that came stock on the 750 SS appeared to be 0.031. There were no markings and used some small drill bits to gauge the size. Based on some additional research, others had confirmed the same. So, I had ordered a number of IFR sizes. One larger and two smaller. I decided to put in new IFRs that were two sized smaller so put in 0.029 in on the primary and secondary idle circuits. Here is where the IFR is located on the inside of the metering block. My screwdriver is pointing to the IFR.



Here is a picture comparing the stock IFR to the new one. The one on the left is the larger stock 0.031 and the right is the smaller 0.029.



Once I get everything back together, I will go for a drive again and test the idle/cruise circuit like I did before. I will then see if a small change in the idle air bleeds are needed. I won't get a chance to do that until this weekend (work is getting in the way of my hobby).

Finally, I think I see a potential issue that might be contributing to my stall on hard braking. The bowl vent baffle does not completely "plug" the vent opening. I have the black push in style. Here is a picture where you can see around the outside of the baffle.



I will think about potential solutions to this. Something that might help seal that up? Any thoughts here?

As always thanks for the input and let me know if I am headed in the wrong direction.

[srobinsonx2]

Got the chance to do some more tuning. Based on my previous post, I thought I needed to reduce the IFR down to 0.029. Didn't change much so I reduced them to 0.025. Here is what I ended up with. The AFR started off pretty good but around 2300 rpm the AFR dropped down to around 11.




I stewed over this a while and came to the conclusion I must have a vacuum leak somewhere that was allowing the PV to open. I had recently put in a chrome PCV on the valve cover. I replaced it with the one that came with my engine and that little dip went away. The smaller IFR didn't do much and it kind of seemed to make the AFR richer which didn't make sense. I decided to start over and put back in the stock 0.031 IFR. I also reduced the IABs on the primary side from 70 to 68. Got the following and felt pretty good. It still has a tendency to go from lean to rich but really close to my target AFR of 13.





This was done in 3rd gear. I got this funny little spot where the AFR went a little lean at 2600-2700 rpm. I think I let off the gas at this point so I went for another short run in the neighborhood. I got the following data log in 2nd gear. I think it looks pretty good. Interesting that the AFR stays around 14 in 2nd instead of an AFR of 13 I got in 3rd gear.





With the light cruise circuit dialed in about as good I think I can get, I moved onto the main circuit on the primary side. Here is what I got.





I could use some advice here. The overall AFR looks good except for the short rich period early in the rpm range. What do you guys think? Should I adjust this?

Once I get the primary side lined out, I will move on to tuning the secondaries with some WOT runs. Any help would be much appreciated.

[bobl]

You're getting pretty deep into this deal. What you are missing is load data. I would hook up a map sensor and log that to know exactly what the vacuum is. Also if the throttle is moving at all during these runs you've got accelerator pump discharge messing with the numbers. If you come to a slight incline the PV may start dumping and conversely you go a little down hill and it closes. You need that map data if you're trying to tune that close.

[CraigS]

You went from 2000 to 4600 in 7 seconds so I guess a 1/3 to 1/2 throttle application. That rich spot at 17 to 18.5 seconds is most likely pump shot. Or possibly it is the PV opening. Either way, I think I would ignore it and move on. You can always come back to this if you find you have a hesitation that might coincide w/ it. As you start w/ full throttle runs, one test I use is to disconnect the linkage so the secondaries don't open. This helps to decide whether you need to adjust primaries or secondaries. I remember someone, Wayne maybe, said that you will end up the primaries on the rich (I think) side if you try to get them perfect by themselves so just use this as an indicator.

[srobinsonx2]

Sorry for leaving this unfinished. I kind of stopped tuning much past the primaries. I don't have a good spot for WOT so tuning the secondary side will habe to wait.

I have been working on my hard braking issue. I tried a number of things without much luck. I will post that later (no computer right now so pics are hard). I ended up lowering my secondary fuel level to the bottom of the sight glass. Seemed to have worked. If it doesn't rain this weekend, I might test it at my first autocross.

[CraigS]

I understand. WOT in 2nd happens so fast it's hard to use. WOT in 3rd gets you up to maybe 80mph and makes a lot of noise for a longer time. I had the same problem. Had to drive 10 min to get to a spot where I could do WOT in 3rd. I ended up leaving the LM1 connected for months at a time so I could use it when the opportunity presented itself. Found I could do air bleed jets on the side of the road but any other changes I needed to get home.