i'd love to have one of those LM2s, what annoys me though uis that fact that the unit is mobile but the bungs aren't ;-)
would always have wanted to get one for the club.

 

LM2 is mobile...sort of. You can buy a bunch of bungs for different cars and just cap them when you are done tuning. What I have discovered is I like having it in the car. I am not a big fan of EFI in classics, but man this AFR meter has been AWESOME for tuning my carb. If you are a fantastic greasy wrench, you may can do this from feel, sound, and smell, but I am a computer engineer and need to see empirical data. I tell you it is amazing how much the weather and small tuning changes affect the performance, AFR, and the tune on my car. I will take the LM2 out eventually and loan it to my buddies (capping the bungs on my car), but not for a while yet.

I noticed something today on my cruise in that has be scratching my head again. At idle, I am a pretty steady 13.5, but at very low throttle, cruising in say second gear, I am running 15-15.5 or so. This is similar to what I see when I let go of the throttle (a lean out until the idle catches up). I think she is telling me to put her in the 12s at idle...which kinda follows what cprstreetmachines was saying.

cprstreetmachines, my racing buddy tells me regularly that if this was an HP or dominator carb, he could have it lined out in no time with air bleed valves. Unfortunately, from I know so far the 4150 double pumper does not have adjustable air bleeds. I could drill, I guess, but I am no where near that confident yet. I have also thought about drilling the butterflies, but I am seeing a need for that given the idle speed and transfer slot orientation. Before rolling up my sleeves this week, I was considering tossing this double pumper and choke setup and just going with an HP so I have some more control. The choke does not work well with this tune anyway. I will give it a little longer now that it seems I am getting closer, but adjustable air bleeds would be nice!

my77stang, I have a 5.5 PV on order have a 31 in my box. I will put those two on later this week. I am interested to see what affect they have. I plan to wait on re-jetting until I get the right PV in there and see when it opens. Right now, I think the PV is only opening under WOT given its low vacuum setting. I noticed while parked, if I just roll the throttle, the vacuum will climb from 11 to around 20 but when I quickly open the throttle, the vacuum will hit zero quickly then come back. I really need to get a vacuum gauge plumbed into the car to see what the vacuum is doing on the road.

I truly love tweaking on this thing and guess I will stop bothering everyone with my daily notes. I think what you gurus are saying is get the idle close, set WOT, and cruise will work it self out. Also high 12s is not too rich for idle. If I hit a wall, I will post back.

Thanks a bunch. I have learned tons recently on fine tuning carbs. Before it was a throw it in, get it close, and drive. Those engines did not know the difference anyway. This one amplifies everything so being off a little makes a big difference in power and responsiveness. Thanks again for the ideas and info.

 

DON'T. I'm interested. Here for learning. I only know the fundamentals of carb tuning. The more info the better

 

take the carb off and drill 'em. Most of the time the initial drill will pull out the bleeds. Just notch main body to fit the bleeds and tap, other wise you can crack the main body right where the bleed needs to go. Sounds scarier. I you are really against it, I have a used HP main body here. If the choke works better with the back closed, but you need more, than drilling the fronts blades is your only option. Just start SMALL. You can't drill holes smaller.
The vac gauge will help a lot. You want to put it at the about 2 in or so below cruising vac. That's generally where it goes. So you can ease and out of it to pass and such without it opening. horrible mpg it it opens every time you touch the pedal. Pretty much want to delay it as much as possible without a bog. Taking it to the track may prove differently. But for all intents now, try that. Not half of the idle vac.
Don't hesitate to post. Fun to help people that have done their own research and are stuck. Not the normal "This holley sucks, why ? Help me pick a good Edelbrock." Good luck

 

Haha. I hate the Holley sucks statement. I freaking love how adjustable they are! Drilling and tapping for Air Bleeds makes since. I hate that HP carbs don't have chokes and that 4150s don't have adjustable Air Bleeds. I will start reading on that. The PV range makes since too. I just read half the idle vacuum, so that is what I was basing my next move on. Thanks a bunch cprstreetmachines!

One more question. Assuming the primaries are showing slightly more transfer slot than the secondaries, should the primaries and secondaries idle adjustment mixture be the same number of turns off the seat? I have been working under the assumption that they should be the same or close to it, but should one or the other be richer?

 

Ah, you have 4 corner idle ? they will be very close. On the adjustments on those, they are VERY sensitive. They'll be pretty close. Usually do about 1/32 of a turn, all at once when you are close. then try the slight pedal movement I was describing. Sometimes you may find what the car likes, but need a smidgen more for off idle transition. Sticks usually run leaner than autos because they aren't under a constant load like autos. That's why you can't just assume a car will want 13.7. Same engine behind a stick might like it, but not for yours.
If you really like the choke,the only option I really see is close the backs until the choke works, and drill her out. I would leave it for last though. If you end up changing your LSAB's, it could effect the idle and offset what you did.

 

Daily update.

I noticed yesterday that the car would go crazy rich after sitting in traffic for a while. The idle AFR was fine, so something is screwy there. I need to jet down some anyway and put in a better fitting PV, so hopefully that will be fixed too. At very low throttle cruise, the AFR is basically the same as idle now. At more aggressive cruise, the AFR is in the mid to low 12s. This is strange b/c it was in the low 14s before I adjusted the butterflies and no jetting has been done since. I guess it was running in idle up front or something before...WOT is still low 12s so that has not changed. I tried Blue cam #1 up front and it hated that...Blue #2 up front totally takes out the off idle stumble.

I drove yesterday afternoon with a vacuum gauge hooked up and monitoring manifold vacuum. My vacuum currently is:
10-11" @ idle
16-17" @ cruise
0-5" @ quick throttle opening
20+ @ WOT

The idle vacuum was somewhat unstable, but the other vacuums were very stable. I have noticed that the AFR moves around a bunch since I opened the primary butterflies more and closed the secondary butterflies some. It may bounce around 1 whole point with seemingly no throttle or load change. The idle AFR moves around a 1/2 point or so, which is more what I am used to seeing.

Given these vacuum numbers, I am thinking I should put in a 9.5 or 8.5 PV since the vacuum never got below that point at idle or cruise unless I popped the throttle and it did not stay down there very long. I guess I am not working the engine much because under some load like in 4th gear going up hill, the vacuum still never got below 15" unless I popped the throttle. I also plan to jet down 2 point up front to start with. So that would mean putting in a 8.5 PV and a set of 66 jets (68 currently) up front. Hopefully that will put me in the mid 13s at heavy cruise.

Does that sound right?

 

yay for carb tinkering!!!!!

this whole thread is great information, i have a pretty damn good understanding about how a holley works but mine always kicks my butt in the end - i really need a a/f ratio gauge to get it right.

i will say i noticed a big power increase when i chopped my choke tower off, i know you have a aircleaner with a filter on the top so it may not be as noticable for you but the HP main bodies are supposed to add a good amount of horsepowwwa.

if you do wanna keep your choke and have a kickass carb, check this out

LINK

 

oh, your was an 850 right? have you considered going to a 750? it would probably be easier to tune anyways.

 

I have a 750 and wish I had gotten a 700. 750 on paper is about right, but it is a bear to tune.

I noticed a huge difference with the XTream lid, so dunno how much a no choke setup would help, but probably a little. I have been looking at the ProFrom main bodies b/c of the choke and adjustable air bleeds. Like I said, the electric choke is basically worthless on this engine as it opens too fast and the engine will not idle for nada until it hits operating temperature or at least 160*. If I did it over, I would just get an HP and be done, but I though at the time that a choke would be nice given the number of days I drive when it is below freezing in the mornings. Oh, well. But yeh, the ProForm bodies are super cool. Don't know why Holley makes a HP, which is basically a 4150 without choke with air bleeds, but they do not offer that in a regular 4150.