kalli

somethign I was thinking about some time ago. But before I am even go and attempt it I thought I throw it in here to see if it's a bad idea.
Carb is a 650 speed demon. double pumper with 4 corner idle.
To adjust (that's what I did) the manual states to open both just so far that transfer slot is square. bolt it on and set idle speed with the ez-idle (basically a vacuum leak, replacement for throttle plate holes). but I had to go down on the idle speed screws to bring the rpm down. However I went so far that i nearly disabled the idle mixture system.

the idle speed is where I want it (850ish) but I have a light bog off idle and the idle AFR jumps all over the place (can't get a proper reading. goes ok for a while then a few seconds lean (ever so slight change in engine rythm and AFR goes lean). then comes back again

if open primary and secondary buterflies (both only by a quarter turn) (this is with the ezidle fully closed) I can get the idle mixture to run perfect. all 4 screws are effective. However the idle speed is over 950-1000. works great but it's crap for cruising and parking. sometimes I park using clutch pedal only ... :-( like half presse dto pick up a bit of speed and press the pedal again etc

so what I was thinking is to close the secondary butterfly fully and only work of the primary butterfly position and regulate idlespeed with 4corner idle and set mixture only in front.

Is that a bad idea? I know I'm downgrading my carb from 4corner idle system to 2. But my engine doesn't seem to need both during idle. Would it have bad affect when secondaries open? lean spots?

001mustang

one thing i do w/ long dur cam is to use manual choke fast idle cam to control idle speed. in certain situations it's nice to pop clutch w/ foot off accelerator.

other times its nice to have a low rpm idle.

from a splash lubrication point of view you don't want idle too low.

did you already adjust your pump shots.

got better tool to tune than I.

wide band AFR still on my wish list.

frdnut

What if you adjusted your accelerator pump cams to come in a bit quicker to give you a bit more shot to get you through the lean spot?

kalli

originall I was thinking to modify around the acc pump but there'2 the reasons why not:
a) compared to my old 570 street avenger those are now a waterfall. you can drown a rat in carb when flooring it. and it's adjusted with no play on bottom. comes straight in
b) when idle is a bit higher and AFR stable there's no problem with the bog.

I believe it really is just down to not getting much of a signal when down low.
so it's either increase idle. no problem is perfect, but on a top sign it sounds like a race car instead of a cruiser. this constant ...wahahhhhhhhhhh.... instead of a subtle rab-ta-babbaapppabbb :-)

anyway I'll just do it and see what happens. Hell it's sunday and I've nothing better to do :-)

kalli

well this is the result. If I go any lower the AFR either jumps all over the place or it just goes lean (20+ AFR).
the AFR is gerat tool for tuning. But during idle I'm not so sure how good it actually picks up in the back with the venturi. works great during drive.

Anyway, I think I'm gonna leave it like this. Tuned how it is supposed to be, just a tad high ???


http://www.youtube.com/watch?v=KoeKYgDUkeI

001mustang

nice afr.

if you have a generous cam duration w/ minimal idle vac signal then u may have to work up to a generous rpm b4 dropping the hammer.

kalli

Ya. No rpm gauge but engine is going bananas from about 3000+ to 6500 ish

001mustang

unless u've got a pretty good calibrated ear i hope u put a rev limit, rev light, tach or something b4 she blows.

guess u don't have a ralley pack..one came w/ my 64.5. i took it out cuz no need w/ oem engine and C4. not to mention it was never wired up. i never checked if it works or not.

what's your red line estimate?

musnicki

I don't think that it was answered yet but I thought that you wanted some idle coming from the secondaries that way the fuel in the secondary bowl is cycled through in case you don't drive hard enough to open them.

James

kalli

001: yes. a bent a few pushrods the last time and then a rev limiter went in. All good sicne. I have it set to 6500 and I haven't hit the limiter in quite a while (plenty at the time I put it in). So that's currently my redline. what it's capable above that I don't know but I have a strong feeling that I woun't gain anythign revving it any higher
I have a rally pac, but I have no idea how to wire that with an MSD box. the rally pack is inline the ignition and 'lives' of the voltage drop at coil when firing. this of course is not there anymore with an MSD ignition. I think I might go with one of those additional boxes. Ultimately the goal was to put in a JME cluster. But I have no money for the car anymore (doing sensible things and saving for buying a house)

musnicki: thx. I have given up on it. I'm revving a bit higher now but I'm using both. front and back. its what the carb is designed for so I thought I better go with it. Good point