Author Topic: 17054939 off idle stumble.  (Read 2222 times)

Offline 86-blk442

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17054939 off idle stumble.
« on: June 16, 2015, 05:48:53 PM »
As the title says I have a 17054939 that has an off idle stumble. This carb was supposedly rebuilt and freshened up before I got it. When I first bolted it onto the engine it seemed to run very rich, the idle mixture screws were unresponsive, and it had a bad off idle stumble.  At that point I had a 280H cam in a 355 Olds engine with a th350 2800 stall and 3.73 gears. Some time went by and I have since made some large changes to the drive train and I would like to try and get this carb to work. It still has the off idle stumble, but now the mixture screws seem to be working (I can stall the engine if I turn them in).

The current setup I am looking to use this carb on is a 1986 Olds 442.  It has a 355 Olds with 9.5:1 compression, #5 heads milled .038" with 1.995 intake/1.625 exhaust valves, some bowl porting, and stock manifolds with 2.5" duals with X pipe.  Intake is a performer RPM, cam is an XE262, HEI distributor with MSD module and coil.  Transmission is an Auto Gear M22Z 4 speed (ratios: 2.98,2.25,1.47,1) with a 3.08 posi rear. 

Inside the carb I found ,70 jets, 50C primary rods, AT secondary rods, and F hanger.  This is the way I got it. I know the accel pump is working but I am going to replace it anyway.

I was thinking maybe the power piston spring might be causing my stumbling issue? So I ordered power piston springs and a new accelerator pump from Cliff. Any thoughts are greatly appreciated!

Offline Cliff Ruggles

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Re: 17054939 off idle stumble.
« Reply #1 on: June 23, 2015, 04:27:57 AM »
It's going to be pretty lean with 50C primary rods in it, especially if you aren't using the APT system in the baseplate.

The tiny XE cam on a 110LSA isn't helping either.  Those cams create a "quirky" idle quality and degrade off idle response some.  Pretty small cam for what you are doing, 262 degrees seat timing is probably 20 degrees smaller than a factory cam in one of those engines.....Cliff