idle hunt help

I have searched the archives and have tried several of the suggestions but still can't get the hunt out of my idle unless its 1800 rpms in gear and that's to hard to stage. Neutral is 2200 rpms.

Buckle up...I'll be as detailed as possible.

Gorr flowed my fuel system for 540 BBC big chief heads powerglide littlefield 1471 HHR top dragster and it has idled fine without a hunt for a couple of years as low as 1500 rpms. fuel system consisted of bird catcher with the dimples drilled to 3/16, k valve, 110 pump, hats and ports. Idle poppet set at 9#, port check at 26#

This winter I changed to a 526 BBC Brodix BB2 heads and a little newer littlefield 1471 HHR, same fuel system as above, everything else same.

Cars runs fine...actually qualified #1 and R/U this weekend in orlando first time out. But I had to idle it to 1800 in gear to get the hunt out. This made staging difficult.

So this week after discussing with Gorr I plugged the 3/16 holes, set BV at 25%, blades at .007. No change and actually has a dead spot right off idle. Only way to get the dead spot out is to set BV in the 30-35 range.

I have made sure blades are same top and bottom...adjusted BV from 25-40%, adjusted poppet from 9-5%. Nothing has worked. Even pulled everything off and resealed to make sure no vacuum leak.

I kind of understand the catch 22 once it starts hunting that's why I closed the blades down as much as possible and made sure that the blade gap is same and throttle adjustments on both sides are hitting the stops. Still hunting unless raise idle to 1800.

Looking for additional tips or suggestions. Thinking I need to try some type of needle valve adjustment using one of the extra nozzle holes and close the blades down to just before sticking in order to reduce blade flex. But really don't understand why I am having this problem when I didn't on the other engine.

With that said I put the other engine in another car and mimicked the fuel system exactly except used a buzzard catcher and it idles just as before...no hunt at 1500 rpms.

Something else that is odd is it will shoot flames out pretty regularly with BV set at 25. 35-40 only shots an occasional flame. So that seems kind of odd that it shots more flames with less fuel going to engine? Also understand this could be a timing issue. Timing set at 30. I do intend to move this...have to reread Cantors plug tuning based on where bluing line was during full pulls. Was down around weld.

Taking all suggestions/tips.

Thanks in advance

Casey

 

What ignition are you running? What degree Big Chief were you running?

What compression are/were both motors? Flames sounds retarded to start.

I ran 34-38 on my BBC conventional head, MSD 10 plus,

 

Sorry to confuse...old motor had big cheifs.

New motor is Brodix BB2Xtra. 30* timing. MSD 10 with grid. compression 11.5:1

 

First question I have is what are your idle temperatures with the BV valve set so low (25%)? Flames are probably caused by being to lean. I thought the BV valve should be set between 88-92% leak down. I once tried opening a bleed plug on each side of a buzzard hat and setting the butters to .005 and yes the motor hunted. This is a common problem with many BBC and should make for a good post. I'm interested in your solution.
Good luck, Joe

 

poppets

Mike
Thanks after reading farther back in the archives last night I was planing on blocking off ports tonight because when I am setting BV I think the port check is coming in (not sure if supposed to). When I set BV I block off everything but the hat and port outlets. I have tried the the idle poppet from the other motor to no avail. Gorr also suggested the throttle shaft adjustment and I checked it...will double check it as this is obviously important. Also I will try your suggestion about the other poppets.

thanks very much

 

BV setting percentage

I sometimes confuse the numbers on my leakdown gauge and the leakage percentage. So below is my description of what I am doing...please comment.

First I use a JEGS leakdown tester with dual 100 PSI gauges.

When checking popets, input pressure is 100 PSI and I start at 0 PSI and increase pressure until I hear air. I.E. idle poppet is 9#

For checking BV I block of idle, PR, HS on kvavle. Leave line to hats and ports connected. Input air at 100 PSI and set BV at 75 PSI. My rational is that is is 25% leak because when I open throttle the gauge goes all the way back to 0 PSI indicating 100% leak.

So am I setting the BV correctly?

Thanks

 

update

Ok after putting my procedure into words and then checking my gorr sheets again and they say 76% BV setting. Seems as if my BV setting is wrong?? I am indeed setting at 25% and should be 75%.

Confirmations?

 

The following is Mike's initial procedure to set up a Barrel Valve:

The true way to adjust the BV is to move the rod one flat at a time until either the motor goes rich and it blubbers when moving off or idle or going lean until it hesitates off of idle. The best way is to be on the rich side to keep the motor cool so go rich until it blubbers then go one or two flats lean until it is crisp. Then check the leak down at that point and record it so you can always return to it.

Leak Down Procedure:
1. Set the middle butterfly to .010 - .012 gap at the bottom.
2. Check that the BV arm is aligned with the engraved dot on the BV.
3. Remove the idle return fuel line from the idle poppet and cap the idle poppet.
4. Remove just one of the main output fuel lines from the BV and leave it open to the BV.
5. Hookup the leak-down tester and set the left gauge to 100 psi.
6. Read the value on the right gauge while maintaining 100 psi on the left gauge.
7. Now read the PSI off the second gauge The BV should be around 88 to 92%. You should be idling at 1800-2000 rpm on a blower motor.
8. Also, when you set your poppets at 2-3 lbs or 15-20 lbs we are talking cracking pressures NOT wide open pressures.

Hope this helps, Joe

 

idle

we ran roots 526/540 chevys with typical fuel system and 110 or 990 pumps and big chief or dart 360's. I always set the BV at 69%. it idled good and kept the oil clean.
If you can get it started adjust the BV while running and see if you can get it happier.

 

I'm watching this thread with great interest but check me if I'm wrong but isn't 88-92% off a bit. I thought the "sweet spot" was 78%. I set mine using the above procedure to .010" and 78% with a fresh build and my idle was perfect right off the hop. I fine tuned it a little but I could have hit the lanes and ran it just like that. No hunting or anything. 540BB chev/ conventional heads heads, 14-71hhr almost exactly what the op has.


Corey

 

Danger zone

Any need to be concerned about engine damage while running in the shop with the flames popping. Ran like 10 gal of fuel through it that way. But was mindful to let cool a little between adjustments.

 

I have a similar setup. Never put a leak gauge on it. It lopes a couple hundred at 1700 with the blades set at .010 (any less and it binds). I can get the lope out, but then it stumbles. If I really play with it, I can get the lope out and it comes up clean as long as I bump the pedal to get about 2k before I deck it. Last time out I had it this way, but if it ran for a long time, it would start loping. Pretty sure it was putting too much fuel in #2 at idle and started putting that cylinder out.

Are your egts all the same at idle?

 

got it

thanks...feel stupid but knowing the correct way to leak BV works wonders. both engines idle at 1600 easy now. set BV on one to 72% and the other to 78%.

thanks everyone for the advise.

 

I'm a little confused on item 4, I was taught that the leak down was set thru the nozzles, why disconnect and leave open an output line? Not arguing, just wanting to learn.

 

Not sure if one of Casey's question was fully answered. If you have a dual gauge setup and 1st gauge reads 100 psi and second gauge reads 75 psi, then that is only 25% leak in the motor. That would be really lean. You second gauge needs to read 25 psi for 75% leak. Only thing i'd add to Mike's procedure is on line 7, 88-92% means second gauge should say 8-12 psi.

Josh