Here is one for you guys, CSU carb 351W with an 85 HO cam, I've got the LM1 plugged in and it shows a 14 to 1 idle reading, thats cool but when I get cruising, very light throttle, it runs really lean like 18.5 and starts surging, I have to richen my idle up to 11 to 1 to get rid of it and the off idle stumble that comes with it, it then cruises at 15.5 still lean but no surging. I want my cake and I want a bite! how do I run a reasonable afr at idle and not run lean at part throttle cruise? I have done some research but I would like some input guys. THANX!

 

My engine is doing the same thing, nice idle and good at WOT. Have you tried opening up the IFR's in the metering block? I have not tested it yet, still needing to install new gas tank, but I went up from 0.028" to 0.031". This is what give the fuel at idle and during the transition/off idle of the carb. Some else have anything to add, am I on the right track?

Kirk

 

Try smaller idle air bleeds before you drill anything unless the idle jets are threaded too. Smaller IAB will make it richer in the T-slot and the mixture screw but you can adjust the screw. How much of the T-slot is showing below the butterfly at the idle speed you want? Adjust it to the best idle and take the carb off and look.

 

I have the same problem, but only gets to about 16.5. My slots look square. I read somewhere that is good, but cracked the secondaries to get them there. I am going to try closing the secondaries to get a little more slot to show. That may be where Tuner is going, not sure.

 

You want to keep minimum t-slot showing so it doesn't waste fuel when you're coasting and the vacuum goes high. It's OK to adjust the secondary to get whatever makes it run the way you want, but minimum t-slot and tuning the IJ and IAB for the right AFR's is the way to get the best mileage. If you have sporty valve timing that drops the idling manifold vacuum much below 14" using a T-slot jet will allow using a big enough idle jet to get the curb idle mixture screws to behave and still get the correct AFR in the off-idle T-slot area. Using a vacuum advance or some other timing device to get the light load timing up to 45 or 50 will help if you are using locked timing set to the safe amount for under boost. That will cool the exhaust temps, too. Smoothest idle will probably be with about 13/1 unless the valve timing is really radical, in which case 12.5 or richer may be necessary unless you use a high idle speed. Do this idle and low load tuning as much by ear as by watching numbers on a gauge. The O2 sensors get tricked a little sometimes by the air passing through on overlap and small exhaust leaks are proportionally larger at the small air flow of low HP loads. Run it as lean as it won't stumble at level road load and light acceleration.

The links and the attachment here give a graphic representation of AFR vs. LOAD (not RPM).
http://www.innovatemotorsports.com/forums/showpost.php?p=34750&postcount=17

 

Tuner thanks for your advice. I have been researching here and over at your other sight "innovative" and will try the t-slot bleeds that you have advised. I have this holley just about conquered, maybe.

On the t-slots I have about 20% showing at the current idle (@ 800rpms), and I have the quickfuel metering block w/ removable bleeds and I did tap the IAB's for bleeds also. Have experimented w/ both (IAB's & IFR's) and still get that lean off-idle either direction. I am back at stock, 0.070" on the IAB's and at 0.003" over on the IFR's (stock 0.028"). We will see what happens...

Oh by the way this site is GREAT! I would not have been anywhere close in this turbo project, until the info I have learned here, Thanks Everyone.

Kirk

Kirk

 

Check to see if the top E-hole (not the kill-bleed in the angle channel, the top hole in the vertical well) is at or above float level. Some of the billet blocks have the topmost E-hole above float level and it acts to double the kill-bleed area, delaying the main nozzle start. Bummer is, along with that the second hole is too low. If it is one of the high-holers you could try raising the float level but then the float gets too close to the vent baffle. Stock metering block will fix it if that's your problem. For blow-through, only the top E-hole should be used anyway, I think.

 

I talked to Dennis at CSU and he said that I should close the secondaries off a bit and open the primaries a little more which he said will pull fuel from the boosters at light cruise and fix the problem. It makes sense to me and I will post my results in the next 48 hours.

 

Any updates yet?

 

It seems to have helped a bit, just by the seat of my pants, I'll have to put the LM1 back on to see what it says.

 

How did closing the secondaries work out?