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Working on MPG

You know as well as I do with carbs there are many ways to skin the cat.. everyone has their "way"... here is my 2 cents.
put a switch in to manually lock the tc, at this point just for testing purposes.. just to see what the motor will handle at the low load/rpm lean cruise.. I have run my stock headed 355 into the 18:1 range without it pinging.. I ran like crap there but it didnt ping.. (who cares)

I would look at the Hi and low speed air bleeds and see if you can figure out what they are, I found in my vac sec carbs they are offset, so when I went and leaned out the front it actually started to pull more from the rear! talk about a nightmare to chase down.. I only found it because it was whistling..
The other area I would look at is teh PVCR, you might be chasing your butt on the richness when the PV comes in because its literally dumping the fuel. moving the PV drop in point only does that. moves it.. its not going to make it any less or more rich, obviuosly the engine being at higher load will change that but I digress.
I really enjoy tuning these but as I started to mod mine (3 circuit) drilling out the Air bleeds and basically changing the entire curve.. ended up being a pita without a carb like a quickfuel or something with all the areas pre drilled so I can make the changes I needed.. having the metering plate and removeable emulsion tubes would be awesome.. Im going to do that or go FI megasquirt or similiar.. Boost is in my future..
 
Oh I feel like I hardly know a thing. I am a little scared to go much past 15 but I could go to the next step. You are right the difficulty in working with a carb with fixed jets is a pain. The other fact is that this truck avenger either doesn't have high speed air bleeds or they are moved to some odd place. I mostly use the visard Holley book to check and be sure I am understanding what is going on. So far with the leaner setting the top of the wot right before the power valve opens is 13.6 and the pv opening is changing it one point to 12.6. If I go leaner I may need to drill the power valve or drill and tap it for a 6-32 to allow it to be changed easier. I think before I change the mixture more I need to buy a ignition box. It doesn't really detonate because it is lean but more one specific spot where just before the TV cable is tight enough it will keep the od and tcc at about 1500 lugging the engine. If I try to maintain speed (like if pulling a slight grade) it will rattle as I open the Throttle and gets worse as it opens farther. It has always done this making me wish I had went 4.56s. I have an adjustable vac switch now and 2 vacuum delays and it helps. The other thing I remember Ed is these heads have no crossover so the only intake heating is from conduction from the heads coolant and oil. I have a 195 thermostat I was going to swap in but it drives noticible better after a hour trip because the intake is warmer helping to vaporize those little rivers of fuel in the intake. Still working on the accelerator pump, blue cam now but should try it in the second hole since the "hole" seems to be later. If the doesn't fix it I will need a green can which I don't have in my Holley box.
 
They're there just not in the normal spot. I haven't worked on a truck avenger in a few years, the thing to think about it sperating the circuits, cruise is generally a pretty steady state affair, if you go a muck with the other parts of the enrichment side of things you really start effecting performance, 12:6-1 is pretty close to where you wanna be, if the motor can take a leaner range then run it, I just think at this point you may see diminishing returns. I personally like 12.5:1-12.8:1 for power to wot, the. Cruise can be as lean as 17:1 but must make sure to have enrichment to cover lean conditions. And during tip in disregard AF until airflow stabilizes, you will want to kind of ball park this. I got mine to 10:1 - 11:1 until the rpm comes up 2k rpm but if you think about it most any motor doesn't really like wot at anything below that anyway and a carb is a compromise anyway, not saying it can't be better just for me it wasn't worth tuning around it. When my stock ish 355 comes online you really hear and know it.. Off the secondaries you would have not idea.. Put it this way, in 2 low on dry pavement it blows the tires off in all 3 gears. 4:10s 36x14.50x16.5s. Welded 14 bolt.. I know it's low but it does it with authority.. All I did was swap carbs and tune it.. The qjet would never ever do that.. Not with bolt in parts anyway.
 
So I am more than likely going to buy a street fire today and work on leaning it out a tad more. The transition circuit to booster transition, is around the 2000 rpm mark because a change in either makes a difference at cruising at 65-70mph 1900-2100. The intermediate circuit is still pretty fat and decell has a very rich pull over. I am kind of a pussy because I am doing the old wire trick in the ifr rather than drill the iab. I thought about it but does the secondary ifr effect anything more than secondary tip in? I calculated if I want to lean the transition circuit another 2.6% (should be 15.5-16) I need about a .008 wire. It is still pretty fat at low speeds even with a 15-15.5 idle a/f. I guess I was scared to go much more because it would push the cruising into the 16s but the worst I can do is try it then go back if it is angry.
 
So if I was going to drill the iab it will not only lean out the mixture but extend the rpm range the engine is on the transition circuit during crusing? Bought a MSD street fire yesterday, will install it Saturday then attempt to lean out the low speed a/f a bit more. The box should allow a leaner mixture to be fired with out surge or at least delay surging into leaner ranges.
 
Added the street fire box and now I may have to back track a bit. Detonation has shown up at wot that wasn't there before. I think the HEI wasn't getting the job done. I bought a better advance set from Moroso that comes next week that should get the curve controlled better. Otherwise it seems to run better and idle better.
 
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The jury is still out. This is the $150 box so it is far from the best but it seems to have made it run a little better.
 
In regards to your comment yes if you enlarge the Iab it does extend the range some, remember the carb is always working off vacuum so it's load dependent still. You just use the circuit longer before the mains come on or your enrichment (Pv) etc start to work.. Be careful there is a too far and that creates a lean surge. I made screw in jets for mine.. Works awesome.
 
So after I said he'll with the day I installed a new advance kit from moroso. Just as a side note this should be the only kit you ever buy for your HEI. It will actually do that they are suppose to and not advance at idle but is all in by 2500 or 3200 in my case with on light one medium spring. So before another test drive I mapped the spark idle is 11, 2000 is 27-28, 2500 is 30, 3000 is 32, 3500 is 34. Vac advance is 8 deg at 5 inhg, 22 deg is 10 inhg and 24 at 15 inhg. So at 65-70 timing is 49-51. Seems to run good and finally the tcc low speed od detonation is minimized. Runs good, feels very strong. Only wierd thing is the vac on the highway was 18 and now it is more like 12. I am assuming this means it wants more timing.
 
I do not have a choke.. and the vacuum reading is weird.. what does the afr look like? I am going to order that advance kit for mine, glad you found a good one.
 
Fuel looks very similar, 15-16 at cruise 13s at low speed. Ithink I had advance at idle before. Thinking I may try the faster advance to see if it rattles.
 
Oh and mine is lean enough it needs a choke when it is 24 outside.
 
I hooked the vac advance back up to port vac. Idles better.
 
Been a week or 2. Today I changed the ifr wire to .012, changed the blue acc pump cam to the second hole and changed the advance springs to the lightest springs. Has a dead spot when cold but as soon as it gets warm it runs fine. I drive to school everyday 60 miles each way. Give me a good chance see how it is working.
 
After all this work, wouldn't it have just been easier to swap in a 6.2? Or switch to a commuter car? 120 miles is a long way to go each day, and a 40MPG car could pay for itself really quickly... :dunno:

(Aside from the practical considerations listed above, keep up the good work. I'm enjoying this thread a bunch.)
 
I have a park ave I drive most of the time but once in a while I drive this for fun. Plus I use this as a hunting rig.
 
My plan for "some day" is to swap in a new LS based 4.3 v6 with a 6l80e and a hair drier.
 
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