Olds Q-jet?

[86-blk442]

Hi guys, new here but not new to Cliffs book.  I picked up a carb with a part # of 17054939.  I am having trouble breaking down the the number to really find out what it is.  I am gathering that it is a 1974 4MC carb but I thought the 170 series didn't start until 1975 and later?  I just put an order in to Cliff's for a new accelerator pump and power piston springs and I would like to find out what the factory jetting/rods would have been also?

The carb is being used in a 1986 442 with a 355 olds with 9.5:1 compression, xe262 cam, performer rpm intake, hei distributor, stock manifolds with 2.5" true duals with X pipe.  Transmission is an Auto Gear M22Z with 3.08 gears.

The carb currently has, 70 jets, 50C primary rods, AT secondary rods, and F hanger.  This is the way I got it.

When I first got it the idle mixtures were unresponsive and there was an off idle stumble, but I changed to a smaller cam (from 280H to xe262) and it seems now the idle mixtures work (I can stall the engine).  But when I go to take off from a stop the hesitation is still there.  As far as i know the accel pump was working but i ordered a new one anyway.  Could it be the power piston spring doing this? 

Any help in decoding this carb and solving the issue is greatly appreciated!

[Ethan1]

 Welcome to CHP!

 That carb is off a Marine application. 1974 Oldsmobile Inboard Marine, A/T, 455cid.

 Stock specs seem correct for your carb.

[86-blk442]

Thanks for the clarification on what this carb is originally from!

As far as my stumble goes, any thoughts on the power piston spring being incorrect? 

[Ethan1]

Thanks for the clarification on what this carb is originally from!

As far as my stumble goes, any thoughts on the power piston spring being incorrect?

 Cliff would be best to answer. Just give him the specs of your vehicle. 

[Cliff Ruggles]

The part number looks like a Service Replacement to me, as most of the 170549XX carbs were SR's. 

It may be for the Old's 455 Marine, no way to tell without seeing it.

Setting it up is still the same as any other q-jet, everything must be set-up exactly for the application.  If you lost control of idle fuel, make sure it has no "nozzle-drip" before proceeding.  It shouldn't, as the XE262 is a "tiny" cam even in a 355 engine build.  .070" jets and 50C rods would be pretty lean right off idle, and may be the root of your problems.

I have come to absolutely HATE those cams, not enough seat timing and LSA too tight.  They produce a "quirky" idle and nothing impressive for power production anyplace........Cliff

[Ethan1]

The part number looks like a Service Replacement to me, as most of the 170549XX carbs were SR's. 

It may be for the Old's 455 Marine, no way to tell without seeing it.

Setting it up is still the same as any other q-jet, everything must be set-up exactly for the application.  If you lost control of idle fuel, make sure it has no "nozzle-drip" before proceeding.  It shouldn't, as the XE262 is a "tiny" cam even in a 355 engine build.  .070" jets and 50C rods would be pretty lean right off idle, and may be the root of your problems.

I have come to absolutely HATE those cams, not enough seat timing and LSA too tight.  They produce a "quirky" idle and nothing impressive for power production anyplace........Cliff

 Could be, Cliff. I didn't find any reference for it being a SR, but of course, that doesn't mean anything. You know what you are talking about, so I will go with you. Unless this person posts a couple of photos of it.

[Cliff Ruggles]

Most of the 170529XX carb numbers will be Service Replacement.  We see a lot of those sent here for rebuilding, and not all the numbers are listed in our references......Cliff

[MG60]

Hi Cliff , on the front cover of your (How to rebuild and modify Rochester Quadrajet carburettors) book that I bought is a early 1970's (704 series) carb ; exactly what is it ?
Thanks , Tim .

[MG60]

I got it !  The carb is a 7029273 .   1969 Ram Air IV  400 "Judge"  for manual transmission .