General Category > Quadrajet Carb Talk and Tips

help with 17082224

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bruno:
so i re measured the cam again today, and can’t make sense of the numbers. i’ll post them here and maybe someone can decipher them or tell me what i’m doing wrong.
measurements are in this order- first movement of needle( very tough to catch),0.006”, and 0.050”
IO- 35btdc,20btdc,0(tdc)
IC- 105btdc,130btdc,156btdc
EO- 90atdc, 108atdc, 130atdc
EC- 50atdc, 25atdc, 15btdc
as far as i could measure, max lift occurred at 110atdc for intake, and 120btdc for the exhaust.
this is with a degree wheel on the crank, and a dial indicator on the pushrod, with just the spring pressure of the dial indicator pushing on the pushrod. it seemed like it was working correctly, i just can’t figure out the numbers. the lift numbers i posted above i actually measured off the cam, so they are correct. i didn’t know about the other measurements back then.
again, any suggestions or info about this cam would be appreciated!!

bruno:
well it turns out i can’t get a smooth enough rotation of the engine to measure exact enough.
pretty confident in the duration @.050” numbers, and the lift, but the LSA is not exact enough to be confident. dad always just said it was a “towing” cam.

for now i’m stuck with whatever cam this is, so hopefully it will work okay.

Cliff Ruggles:
If you are "stuck with the cam" then measuring to find out what it is really isn't important. 

Get the engine running and see what kind of vacuum it makes at idle speed with reasonable timing in it.  If it's idles well and makes good vacuum without running the timing clear off the scale you should be fine.

Timing is equally as important as idle fuel delivery when it comes to tuning.  Most well thought out engine builds will make good vacuum at idle and not need a lot of initial timing.  If that ends up being the case you will also find you don't have to bring in a lot of idle fuel either. 

I like to see at least 12" vacuum at 700-750rpm's with about 10-12 degrees initial timing.  Much below that and we start having to add both timing, idle fuel and idle bypass air to make things happy.

Your current carbs idle set-up is pretty lean so may need a bit more idle fuel if this engine/cam combo isn't making decent vacuum at idle speed......

bruno:
pretty sure vacuum was around 16”, but will double check that next time i get a chance. it developed a “pop” through the exhaust on high idle when i started it after trying to measure the cam. possibly i overtightened a valve, but don’t think so. i also turned the vacuum advance canister a bunch, and haven’t checked it yet, so thinking i have way to much timing right now. wait her one is easy fix, just have to find the time. i’ll post again when i am able to check those.
the manual calls for 2000rpm high idle, which seems high to me. i was thinking 1400ish? any suggestions there? no winter driving, and all the time in the world to let it warm up before driving it.

bruno:
so this is what i got today, car fired up great with single pump of pedal to engage choke.
high idle is 1470, with 18.5” vacuum.
mid idle is 1150, with 17.5” vacuum.
curb idle in park is 750, with 14” vacuum.
those were with vacuum advance disconnected

base timing is set @5 degrees.
VA adds 19” of vacuum, starting at 5”, and total at 10”(manual calls for 15 from VA) haven’t tried any adjustments there yet. idle timing seems pretty solid.
with VA connected, idle went to 1000, so adjusted it back to 750. idle timing with VA connected is 24 degrees.

then i tried adjusting the idle mixture screws, which were set at 3 turns out. right side seemed to make jo difference when seated. left side definitely had effect, regardless of where the right side was.

i covered the carb loosely with my hand and the idle speed climbed immediately, so i assume it wants more idle fuel?? also thinking due to right side not having any effect, possibly that side is got some crap in it? that would account for wanting more fuel too right?

looking for suggestions on what to do next. it has been a few years since i rebuilt this carb, so it has sat on the car for a while. idle tubes were new from cliff when rebuilt, so they “were” clean then, and all passages were clean then too. very possible the right side got some crap in it though.

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