Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

M4ME 17085580 primary circuit

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tayto:
The only fuel in western canada that doesn't have ethanol in it is Shell 91 and Chevron 94, FWIW.

theraymondguy:


--- Quote from: old cars on October 06, 2021, 03:31:33 AM ---Ontario, Canada gasoline is 10% ethanol in regular fuel (approximate) Premium is ethanol free.

--- End quote ---

I am in Ontario Canada.  I run Costco premium which I'm told by the attendants is ethanol free (I try to ask a different attendant every time I go, always the same answer).

Thank you all for your help.   I'll be trying the idle mixture mod first and report back with results.

theraymondguy:
Okay, it's been a while but here are the measurements of my m4me 17085580 carb.
I have now installed the 204/214 cam.

I have purchased Cliffs book, still somewhat unclear about certain component locations

Idle tubes 0.033"
Idle down channel 0.047" - restricted port beside idle tube port
Upper idle air bleed 0.070" - on 45 degree angle, above idle down channel and into primary bore
Lower idle air bleed 0.070" - into bottom of primary bore
Idle bypass air 0.070" into throttle plate
Mixture screw holes 0.070" I have opened these u to 0.093" the closest I could get to 0.090".
Holes in primary plates - none

I have purchased a micro drill kit and numbered drill set. I have a new rebuild kit (using for gaskets only),

Some of you may recognize the camshaft specs there is an example for this cam in Cliffs book.  However that example carb has no Idle bypass air ports.

Cliff Ruggles:
It takes 5 (five) full turns out on the adjustment screws to achieve this, which seems out of line.

No, that's actually pretty "normal" for a later model carburetor with the metric pitch idle mixture screws and small holes typically found under them.  Most come in around 5-7 turns vs 2.5-3.5 turns with the early units that have #10-32 pitch threads.

Your "blue" pump seal will fail in ethanol unless you bought one of mine.  They are dubbed as "ethanol resistant" but are offshore production and swell up in this new fuel.

Idle tuning should be based on CID, compression ratio and cam being used.  When you install an aftermarket cam with more seat timing, tighter LSA or both this reduces the "signal" to the carburetor and may require larger idle tubes, DCR's, smaller idle bleeds and idle bypass air to make things happy. 

The "recipes" in my book work very well, but one still has to custom tune at times as it's pretty rare for any two engines to behave in exactly the same fashion.  The little 305 9.5 to 1 compression with a 204/214 cam would behave about like a 350 with 8.5 to 1 compression (same cam) as far as idle fuel requirements, for example.

Initial timing is a big player with these things.  When you install a larger cam and make the engine less efficient at idle they will want more timing as well.  I do NOT like to run more than about 10-12 degrees initial timing in one of these engines.  When you find yourself having to increase initial timing pretty far and open up idle system passages quite a bit you just missed the cam choice some.......Cliff

tayto:
Cliff, by "miss the cam choice some" do you mean too big of a cam was installed? I found my 355 with TBI heads liked more timing at idle around 14-16*. This is under what the factory TBIs ran (usually high zzzzz, low 20s @ idle). It woild run fine at 10 or less, but made 1 to 2 in-hg less @ idle.

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