Technical > Spud Miller's Cave

Hilborn Help Needed

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dusterdave173:
OK Let me lay a little ground work first--got my dragster finished and went to the track--darn thing fires up, idled, burnout great and ran fantastic first run--went 5.68 120 mph like a champ.
355 sbc , roller good compression, alky with 80A-0 in good shape--Hilborn 2 3/16ths unit older but good--new nozzles sized for my 355 CI, 75 main pill  etc
I would have never touched it but one bank a little hotter than the other at idle--best I can tell at the header crook with a cheapo temp gun somthing like 430 on one bank and 260 on the other give or take
I was told again and again to fix that
well..yesterday I went through all the alky I had on hand and finally got them close at 360-380 range each  OK...that was with about .002 on one bank and the other bank a tad more--OK...but to get it to idle down to reasonable RPM I have the idle mixture way fat--like maybe if you leaked it maybe 30-40 % range
What to do?? It runs fantatsic like it is but should I close the blades and start over??
And with it like it is now it sort of over centers the lever on the barrel valve when wide open
ROOKIE here that needs help
Thanks!!!!!!!

dreracecar:
Did you set the blades first by
1) backing off the throttle stop screw and remove ty-bar
2) loosening the blade screws on the shaft
3) while holding slight pressure on shaft, tap with the end of the screwdriver the blades to get them centered
4) retighten screws
5) adjust blade clearence with throttle stop screw
6) re-attach ty-bar

Spud Miller:

 Give my tech article on this topic a read:
 http://www.fuelinjectionent.com/butterflies.php

 Let me know if you still have trouble.

 Spud

dusterdave173:
So... If I had known then what I know now I would have left it alone and kept going.

Spud, I had read and used your instructions way back when I built the unit--long time back--when I first fired it up--I fattened the idle and away I went--everything AOK to me and it Ran Great!! Then in the pits folks smarter than me noticed my banks were at different temps--hey you have to fix that--well..
I got so far out in the field I could not see the porch light.
OK went back to your instructions--started from scratch --now I am back to about where I was--I have a better understanding of it all as I have been all over it for a week now. I was being faked out by one cool front tube--took that nozzle out--blew through it and that cylinder cam back to life--had another way hotter and I fussed over that blade until I finally relized the butterfly itself was in need of special attention--I took that one blade out--cleaned a bur off the edge--pounded it flater than it was and that cylinder is better but the blade still has less drag on the feeler gauge no matter what I do to it and that header pipe is always hotter than the others
So..after a couple of jugs of alky she is back and doing OK
It still pops just a little out the pipes at idle--still need to rich it up a little you think??
 Or open blades a fraction more then go back to mixture???  I mean--it sounds better with more blade opening but then idles too high--I am at about .002 on blades give or take-- Throttle response is amazing--not too warm too fast but overall I just get the feeling it is a little lean at idle---I started with BV leaked at 25% and turned it a couple of flats to rich after start up.
Whew!!!
Driving it is way easier than this :)

Spud Miller:

 I generally start with the barrel valve setting at 7% of the engine size to start with (a 355 motor would be 25%). If your main check valve is set correctly (1-3 PSI) that is usually very close and then it can adjusted from there.

 Depending on where your idle stops, return spring and pull are located, you may always have some shaft twist that will make 1 or 2 cylinders richer or leaner than the rest. Placing all of these things on the same segment of shaft is the best situation but also really tough to do on most cars. There are other band-aids that can be employed like blocking one or more of the air bleed holes in a nozzle for a lean cylinder or drilling a small hole in the butterfly on a rich one.

 Everyone is usually a fanatic about all the linkage rod ends being very tight and precision. I've found the best combination however is to use a super-sloppy couple of rod ends on the cross link so it's just loose as a goose. Put an idle stop on BOTH banks so they can be adjusted and set individually. Adjust the connecting cross link so it's in the middle of the slop. Now, changes in temperature won't be tugging things around and changing your side-to-side balance.

 I've gone to using an actual slotted rod end on one end of my cross link. The slot gives .030+" slop. I can set the perfect idle balance and it stays put all the time. Since I leave from an idle it really makes a big difference. At WOT, there isn't even a perceptible difference in opening from one side to another. Works great.

 It's normal for things to pop and crackle a bit at idle...I wouldn't worry about an occasional pop. If you're making good temps and throttle response is good, I'd quit fiddling with it and go have fun.

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