|02-24-2012 12:58 PM|
Get the mechanical spark advance curve corrected first. I guarantee it ain't right.
You cannot get the required curve by just throwing in a curve kit.
You must set up the mechanical curve stop limit to allow the increased base idle timing and correct curve and max advance.
vac adv is a separate issue.
Then work on the idle and low speed- part throttle jetting.
re read post #15
|02-24-2012 12:15 PM|
I don't remember what the timing is set on, but the guy that installed the curve kit set the vacuum advance and the timing when he done the heads and cam swap. I haven't messed with it because I don't seem to be very good with the ignition system. As soon as I get a chance I'll check to see what it's set on.
What about the WOT, is it pretty much safe to say it needs leaned down, or should I double check the ignition first?
|02-22-2012 05:22 AM|
Rich idle and just off idle:
is the PCV installed and functional?
If not , get one.
No PCV creates a rich idle.
What is the idle base timing and max mechanical advance?
May have to slow the motor down to read the base timing. (no vacuum advance)
|02-21-2012 09:52 PM|
|chevydragster83||I took it out today and drove about 12 miles at different speeds and the gauge showed to be in the 11s at idle and just off idle. It staid in the 12s until I got up to about 55 and it leaned down a little. It seemed to be staying right on 14 to low 15 between a quarter and half throttle, like pulling a small hill. At WOT it dropped into the high 10s for a second and then staid in the mid 11s. From what I could tell it was showing rich everywhere but at moderate throttle.|
|02-20-2012 06:17 PM|
It takes a good half hour of driving to get the motor completely warmed up to operating temp. The AFR reading will be all over the place so do be too concerned.
Be sure to get the dist setup correctly first. By all means use a vac adv if you want good mpg.
Download the Logworks program and make some runs to establish a base line. Make sure you note what you did on each log.
You will need a set of number drills from about 40-80 to measure the restriction and bleeds and jets.
Mark all of these down so you have a base line here too. Make sure you do not have any exhaust leaks before the o-2 sensor.
Also make sure yo
|02-20-2012 05:39 PM|
The guy that installed the heads and cam for me installed a curve kit in the distributor when he done the swap.
I calibrated the gauge as the instructions explained to do. I ran a ground directly to the battery to avoid any noise.
I have a manifold vacuum gauge also.
I'll update after I do some test driving.
|02-20-2012 01:20 AM|
|F-BIRD'88||Initial "free air" calibration of that innovate gauge is critical. Tell me how that wide band gauge works for you. electrical Grounding is critical too. Watch for false - funky readings.|
|02-19-2012 10:28 PM|
Ya at idle it is richer than it needs to be. You need to get the ignition curve in order first, before you dig into th4e carb.
Is the PCV hooked up and functional.?
What is the AFR at different part throttle cruise conditions say 30mph, 45mph, 60mph steady driving.
Once you have recurved the distributo as I outlined earler, the carb will want readjustment Idle speed and idle mixture screws. This itself will be a big clean up.
Use a manifold vaccuum gauge. THE ENGINE MUST BE FULLY WARMED UP before any real meaningfull assesment and adjustments.
Best to take it out and drive it around to get it all warmed up, then set the carb
idle up using the vac gauge and AFR meter ( the vac gauge is the priority at idle.) .
Next is to get the part throttle cruise dialed in. ( primary jet and rod choice.)
Then tune the step up spring tension ( start with the 4# spring)
Take it one step at a time.
The idle spark advance is critical. 24ish+/- BTDC base timing at idle is required
This does not include vacuum advance (yet)
This distributor curve needs modification first. You cannot get the desired curve by just swappping advance springs.
Get a manifold vacuum gauge.
|02-19-2012 05:45 PM|
|chevydragster83||I got an Innovate MTX-L wide band AFR gauge. I installed it yesterday and let the engine warm up. It was staying in the low 12s then it dropped as low as 11.3 at idle after it had gotten warmed up. Looks like I have a pretty major rich condition. I am going to change the oil and take it out and see what it does at different driving styles this week before I do anything to the carb. That probably explains the terrible MPG and low power wouldn't you think?|
|02-03-2012 03:03 PM|
|02-03-2012 12:54 PM|
|ap72||just tune the carb you have. Edelbrocks deliver some of the best mileage you can get from a carb, and are dirt simple. Even with it in perfect tune at best you're only going to se about 9 mpg's with your combo.|
|02-03-2012 12:04 PM|
the edelbrock #1407 750 only requires a pri metering rod and or pri jet swap to improve the fuel mileage.
Its factory calibrated a bit rich for power.
lean it down on the primary cruise. The secondary jetting is fine and does not effect mileage.
Its not too big and its very tunable.
You don;t need a new carb. Just tune the 750.
A AFR gauge will help you dial in the jetting.
A cheaper narrow band type (with heated 02sensor) is good enough for this.
Its a real eye opener.
The 230° cam has to go if you want mileage.
The duration and LSA(overlap) is too high for mileage.
A cam with 208 to 214° @.050" intake duration and a wider 112+ LSA will help a lot. A single or a dual pattern cam is fine.
it will still go like hell.
I've used the 214-224 .442 .465 112 cam with good results.
* summit, crane blue racer etc*
Recurve the distributer mechanical and vacuum advance curves.
They both need optimizing.
The 230 cam will need lots of initial base timing at idle 24-26deg at idle
vacuum advance also needs to be dialed in.
The stock-default distributor curve will be all wrong.
The jetting and distributor curves make a huge difference.
The high stall converter is not as bad as you think as long as you can keep your foot out of it.
If you are heavy on the foot you are going to burn gas.
How you drive has more to do with it.
I used a 214-224 cam and a 3500stall converter and 4.10's and it was reasonably good on gas. Again, if you rug it a lot, you are going to use fuel.
get the jetting and timing curve sorted out and see where you are at.
then find a milder cam.
This is what your 230° cam needs:
start with 24-26deg initial 10-12deg mechanical (34-36 total advance)
shorten limit the mechanical advance travel limit stop.
+ 10-12deg vacuum advance that comes in at hiway cruise.
Ported or full manifold vacuum source no rules, don't care, use what works.
swap the primary jet to a .110" pri metering rod .075"x.047"
4" power piston springs yellow
This will lean down the part throttle cruise and insure the power piston stays down-lean at idle.
This and the ignition recurve will really clean up the idle and low speed and mileage. Get new plugs with the correct heat range.
A smaller voodoo cam will help #60100 or 60101
Lunati #301A2LUN or 301A4LUN are other good choices.
Anything mild like this is good.
|02-03-2012 02:28 AM|
IMO, the things that are killin your MPG are:
* the 230 deg cam
* the tq converter
* the 315's wide tires on the rear
* the 750 carb
I would start with the cam. Get something with around 220* at .050, and 112 LS. This may wake up the motor because you will have a compression increase. When you do the cam, also install a 2 piece timing cover (much easier to swap out the cam later on)
Next I would replace that TQ converter to match your new cam. Get something with a low stall. As much as I like that Gear Vendors Unit, I could never pay that much. Maybe one day I'll find a cheap one on ebay.
You will need at least a 31" to 33" rear tire to offset the 4.11's. Just keep it around 11" wide
I would sell that 750 carb and get a rebuilt 625-650 cfm carb. The smaller carb will "work" better with the air velocity increase & the new cam. You can find great used carb deals all day long on line. The good news is that your 750 carb has a good resale factor, so you might make out good on that
The o2 meter kit is a good idea. If you cant afford to get one now, at least order an O2 bung & cap from Summit when you get the cam - like 7 bucks
With the cam & torque converter change, you are looking at around $450.
You can also find a good used vac advance dist on-line (vac advance = MPG)
Not counting the tires, the changes above should give you about 12-13 MPG
|02-03-2012 12:20 AM|
In order to make the AFR work or better yet to use it properly, you must have a very good understanding of how the carb works. You need to know how the idle circuit, transition power and cruise circuits affect the AFR.
Best bet is to get the Holley book with the cut away view of a 4500 on the cover. I don't have mine handy but just check Amazon.
Above all don't get "drill happy" before you understand what you are doing.
The AFR gage simply tells you what is going on. It can be misleading if you don't understand the carb. It's not hard learning you just have to put your mind to it.
|02-02-2012 05:59 PM|
[QUOTE=bentwings]I thinkthe best thing would be to install an Ait Fuel gage (AFR gage) These run a couple hundred bucks. Innovative motorsports is very popular and they have an active forum. This will help you with the tuning. I get 15-16 mpg with the blower so you should be able to get the same or better....this is on 87 gas too. Also install a vacuum gage. These are a great load sensor....low vac means low mpg.
I'm sorry it has taken me so long to reply. I have been looking at some air/fuel ratio gauges. That sounds like that would be great for tuning. It would definitely help for calibrating the carb wouldn't it? I would think it would be pretty easy to do just basic tuning with one wouldn't it? Is the gauge and the sending unit all I would need?
|This thread has more than 15 replies. Click here to review the whole thread.|