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Hilborn stack idle problems

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PSweeney:
Running a Holborn stack set up on a 420 SBC. With the butterfly's closed to .002 thou and bv set to 20% it idles at 2500rpm in neutral and 1800 to 2000 in gear, any richer on the bv and its noticeably rich and milking oil. Timing is at 32 degrees all in. How can we get this thing to idle lower, it's pretty undefinable at low speed and getting through a lot of fuel. Can the holes in the throttle bodies above the butterfly's be tuned with bleeds to bring the idle down ?

Spud Miller:

 Sounds like you have an air leak. The intake gasket, in the injector...something like that. You didn't mention how big the butterflies are, but a motor that size shouldn't have a problem with the aspiration vents in the nozzles being too much air.

 Maybe your intake gasket shifted as you put the injector on and it's sucking air from the lifter valley.

 Is this the model Hilborn that has the banks of butterflies that bolt to a base? Maybe one of those is loose or not sealing.

 You could check the exhaust temps with a heat gun and see if you can narrow down the problem to one side of the motor, or a pair of cylinders or something like that. It may help you track it down.

 Spud

dreracecar:
Making the BV richer will not increase idle, more air or less fuel will raise idle rpm. Trans in gear puts a load on the engine and brings rpm down and is why you run a secondary idle bypass to lean the fuel system and bring the rpm's up.

PSweeney:
thanks guys.  Will look at a manifold leak.  We we're getting some oil out the left bank header but assumed that was due to the damaged valve stem seals we had to swap out.  It could also be a leak from the valley I guess.

PSweeney:
Just re-visiting this issue.

Firing the car at home, the idle in neutral was still 2500rpm, blip the throttle and it doesn't come back down on it's own and will sit at 2800rpm until you drop back into gear.  We looked for vacuum leaks, resealed the manifold, split the throttle bodies and used new gaskets.  Fired the motor and it's no different, 2500rpm in neutral, around 1800 -2000rpm in gear.

We ran the car again this weekend and managed to get 5 passes on it.  The converter is loose enough that it can be driven at low speed and staged but I just don't like it that high.  The BV is already set at 25% and is milking oil on each run.

This is a Hilborn 2 1/8" stack system on a 421cu in SBC, iron heads, 32 degrees timing locked out.  Running the quarter it ran 9.005 @ 148mph which is the best ET and MPH on the engine from when it last ran in an altered. 

I'm launching off idle, it revs well, no stumbling, pulls hard and stays lit in the shutdown, the xxxx thing will just not idle below 1800rpm.  Where do I go next ?

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