Pop N Wood

iTrader: (1)

I would try going down a size on both the main jets and the high speed air bleed. Bleeds are suppose to keep the mixture flat as air flow increases, bigger bleeds lean it out on the top end while smaller keep it richer.

speedtigger

iTrader: (16)

The HSBs effect on the wide open throttle fuel curve is not that simple. The HSBs have an intricate relationship with the emulsion ports. Go too big with the HSBs and you could develop a lean condition at tip in. I am all for experimenting and measuring the results, but if you change the HSB-emulsion package you can have all kinds of strange and unexpected results. You may get what Pop says above or a completely different result.

krochus

iTrader: (1)

I don't think messing with the hsb is called for. The wot AF may start in the mid 11's but it cleans up REALLY QUICK into the ideal range as the engine pulls upwards in the rev band.

I chock that up to 3.27 gears

The ONLY time I'm missing the power valve is if I really dig into the throttle without downshifting.

speedtigger

iTrader: (16)

Unless you put the power valve back in and try to set up the carb the right way, I can't really be of any further help to you. If you like it the way it is now that is good enough for me.

krochus

iTrader: (1)

Well by all means tell me what you would do. It will have to lose a bunch of jet in order to use the PV though.

speedtigger

iTrader: (16)

First things first, do exactly that. Restore the carb back to the factory jetting and bleeds. Re-install a 6.5 power valve in the primary side metering block.

Then, since both your part throttle and your WOT are rich, start reducing the jet sizes equally on all 4 main jets. So, if you have 72s and 82s, go to 70s & 80s and go for a ride.

Measure the WOT and part throttle AFRs. If they are both still too rich, reduce the jet sizes all the way around and try again. Once you get the WOT between 12.5 - 13:1, make note of the part throttle A/F ratio. If it varies between 14 -15:1 great.

If part throttle is still too rich, follow this procedure: Make another WOT run. Make close note of the desired WOT A/F ratio that you have acheived. Then reduce only the primary side main jets size. Go for a ride and measure part throttle A/F ratio. Keep doing this until you get the desired part throttle A/F ratios. Don't worry about the upsetting the WOT A/F ratio.

Once you have achieved the desired part throttle A/F ratios, to restore the WOT A/F ratio, start increasing the size of the PVCRs until your WOT mixture returns to match the previously measured and desired WOT A/F ratio.

Once the above procedure is completed, then you are ready to evaluate if you need to change the power valve number, air bleeds or emulsion calibration.

krochus

iTrader: (1)

That make sense but is a daunting proposition as the carb is currently in essentially STOCK configuration sans power valve and is pulling really good part throttle and primary side numbers. If I go that route it will absolutely destroy not only the primary and secondary settings but the IAB and IFR relationships too.

I have changeable power valve discharge ports. Would there be any problems with using those to tune the powervalve enrichment around the carb's baseline tuning and compensate for the extra fuel on just the secondary jetting? Otherwize I'm starting over from scratch on EVERYTHING to tune it around the powervalve.

speedtigger

iTrader: (16)

You can do it any way you like. You may even be completely successful in achieving all of your performance and drivability goals doing it your way. It is just not the way that I learned how to tune, so I won't be able to help you much.

ZONES89RS

iTrader: (25)

Threw a wire in each side(folded in half like when in the wire brush handle) and for the cruise AFR where I wanted it. 15.5:1 at cruise. Had to back off the idle mix screws allot to get idle back.

When cruising in a high gear at low speed it will go dead lean nearly unless I anck off or give it throttle, not anything bad but it is obvious that you don't use 5th or 6th gear cruising 30 mph.

krochus

iTrader: (1)

That's good to hear.

I've not messed with mine much. I sorta came to the conclusion that it was time to drive and beat the pee out of it more and wrench on my junk less. And that's exactly what I've done.

I did pull all the plugs for an inspection the other day and the porcelain looks almost new. I took the car on a 70mile round trip through curvy mountain roads flogging the thing most of the way and netted 17 mpg for the entire trip which seems pretty satisfactory for a three speed trans and a heavy foot.

About the only carb tuning I've been doing is tweaking the secondary opening rate inching faster and faster searching for that bog that tells me I've got em opening too fast.

I have discovered that to get a satisfactory very light throttle low speed AF it's neccacary to run the idle mixture slightly fat (13) which is no biggie and isn't posing any issues I've yet found.

ZONES89RS

iTrader: (25)

Mine is 13.7:1 at idle, might throw some more at it, but I think the map sensor is fudging up my idle tuning. Lol

krochus

iTrader: (1)

I drove my car down the road with the laptop in the passangers seat so I could put my 10• map in at high vacuum light throttle level 45-55 cruise that way it pretty much drops out at the somewhat lower vacuum at idle

ZONES89RS

iTrader: (25)

Yea, I need to mess with that, at least it will only be lap top and idle mod adjustments for the most part. I was highly impressed my wire bush trick was spot on the first attempt.

TXsilverado

iTrader: (18)

since you guys are talking about idle tuning....

do you guys tune idle by afr or vacuum? my vacuum gauge says my idle needs to be around 12.3...when i idle to 14.5-15.0 i get cold start issues. i settled with 12.7-13.0 at idle in gear and it starts great cold with no choke.

my MPG is SUCKING

krochus

iTrader: (1)

I've not checked the two methods against one another but what you say makes sense having observed how shooting for "ideal" wideband idle AF ratio seems to introduce the issues you note.

Like I said above things seen to work much better if I leave the idle in gear ratio in the high 12 to low 13 range according to my aem wideband gauge

ZONES89RS

iTrader: (25)

Without a choke, cold starts will suck and even worse in winter with much above 13:1.

What's you cruise AFR Stewart?

TXsilverado

iTrader: (18)

once the converter locks it's in the 14 range. but light throttle tip in goes rich as hell. it dabbles in the 10.9 range for a half of a split second before it leans up.

ZONES89RS

iTrader: (25)

Start tuning fool.

speedtigger

iTrader: (16)

If your idle is set to run clean once the car is warm, it will be fussy when cold. That is life without a choke on a high performance car. If you richen it up so it runs good cold, it is too damn rich once it warms up.

Each car is different, but my set up is happiest at high 13s on the wide band when up to temperature and idling in gear.

For your part throttle a/f fuel mixture try going to the next step lower numbered powervalve. Take it out for a ride and see if that helps.

What is your WOT A/F ratio?

1 FMF

iTrader: (1)

this post was an interesting read. fwiw there is a systematic way of tuning carbs that can save you a lot of time and headache and get you to 90% of ideal pretty quick provided you have a good working engine and a good vacuum signal to carb.
one thing to remember- lean mixtures burn slower and require or can use more ignition timing. rich mixtues burn quicker and require less ignition timing. that's to say if you have your idle mixture rich, your ignition timing will be around 8-12°. if your idle mixture is leaner then you would run over 12° timing. and same principle applies under any load condition, if your electronic ignition constantly adjusts ignition timing then that will drive you crazy- you need to disable it and have fixed timing for a given load/rpm so you can observe the affect of carb adjustments. once you get the mixture dialed in close, then hook up a vacuum advance or enable variable ignition timing and make adjustments to spark timing.
the other big thing is intake vacuum and monitoring that to know what carb adjustments to make- i'm not saying adjust mixture to achieve a high vacuum reading, you observe the vacuum reading then you'll know what circuit of the carb that needs adjustment whether it's the transition circuit or the main jets. i'd be willing to bet you would have noticed a low vacuum signal which indicates your power valve was dumping fuel at light load cruise conditions, which is why running no power valve helped immensely. load/vacuum signal and airflow through the carb are 2 different things, you can have high load (no vacuum) under low rpms which means low airflow- the result the main jets don't come online everything is through the idle & transition circuits plus the power valve because of the low vacuum. so you would need a power valve with a smaller number, and possibly a 2-stage power valve. normally you don't run a power valve when the engine application is circle track where it's nearly wide open all the time and never less than half throttle- there's always high airflow through carb = main jets online so simply tune a/f by main jet size. other than that, the big thing to remember (step #1) is always set and recheck fuel level in the bowl first, everything runs off that. high float level = richer mixture everywhere, lower = leaner. simply adjusting float level sometimes can seem to fix nearly everything and prevent you from chasing your tail.