help with 17082224

[bruno]

i’m looking for some guidance in getting this carb and my ignition set up correctly.
carb-17082224, rebuilt by me with cliffs kit, about 7-8 years ago. finally getting time to fire it up. idle tubes are .036, DCR .055, discharge holes are .086, UIAB=.068, LIAB=.077. primary jets are 73 with 51M rods.
engine is ‘68, 396(325hp) with stock pistons and 215 heads. engine has been freshened up with new rings and bearings, and fel pro head gaskets that came in the kit. also an unknown cam, which i attempted to measure today, and came up with 205/215@.050”and 274/293 lift. i’m not entirely sure of the ICL or lobe separation, but i do have the opening and closing point of both valves if that helps. i just not sure how to interpret the numbers.

Th400, with 3.31 gears. just want to be able to cruise, no racing or daily driver.
distributor is 1111196, dwell is at 30,
just working on the vacuum advance, as i was only getting 5 degrees. then i discovered it was adjustable, but haven’t got to fit it back up yet. haven’t checked centrifugal yet. base timing calls for 4, i had it set at 8. seemed to work okay.
questions:
looking for timing recommendations, high idle rpm’s and then i can start trying to tune carb. i have cliffs book, and will read it again, but want to get distributor set up first.
i haven’t tried driving yet, just running in garage.
any more info that will help, let me know.

[bruno]

possibly an XE 250 cam? only thing i know is it was bought from performance auto warehouse in the 80s. the bill just lists it as CHE 396.

[Cliff Ruggles]

Not sure if they made XE cams that far back.  Most of the Comp stuff used to be single pattern and nearly if not all of it on 110LSA's.  Far from ideal but they did that to put enough overlap in the deal so your engine had some "attitude" at idle when you went to a car show or cruise in.

The XE256 specifically would be a very poor choice for a 396 unless is was very low compression.  a cam like that wouldn't even come close to taking advantage of good flowing heads used on most big block Chevy engines from that period.

My cam of choice for most of those builds is the GM Marine cam or Melling 22216.  It's pretty much identical to the original 396 and 427 cams from the late 1960's used in the lower performance engines.  Ground on a 115LSA it idles well and produces a very broad/smooth/flat power curve which really helps manage pump fuel at the higher compression ratios many of those engines used.....

[bruno]

well i must have measured something wrong, cause i’m getting an LSA of 133 degrees. will look at my numbers again, but i came up with an ICL of 104, and an exhaust ICL of 237 degrees.
keep in mind i was using a dial indicator on the end of a pushrod, so definitely could have gotten skewed!

[bruno]

and i should mention i’m running the factory iron manifolds.

[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.

[bruno]

placed an order for a new carb kit from you, with some extra gaskets incase i rip one of them while figuring this out. i also put a note about distributor springs for the centrifugal advance. haven’t got there yet, but i assume these are original. but not knowing for sure, i’d rather get some good new ones to be sure. i will try to figure out the centrifugal advance numbers tomorrow, and i’ll post them here if i can.

[bruno]

pulled carb today, luckily the gaskets came apart easily!! used a .030” mig wire to poke through the idle tubes, and blew out the passage as best as possible. i didn’t pull the tubes, hoping the poke and air would dislodge anything in there. i removed the idle screws while doing this.
float height is set at 9/32”, not sure where it should be, as i no longer have the rebuild instructions. i’ll leave it there for now. throttle plates look good, a tiny bit of light around the primaries, but i think it’s okay? secondaries are excellent, no light. will put it back together and see what happens.
cliff, i’ll still take that kit i ordered just to have the gaskets for future use. thx.

[bruno]

fired right back up after putting carb back on. think i misread vacuum gauge last test, as i’ve got 16.5” of vacuum know. think i was thinking the needle moved the other way!!

i also just checked the pcv valve, and it is sucking air at idle. just for clarification, that should not be the case right? it should only be operational at part throttle? it it hooked to manifold vacuum on front of carb.

still have almost no effect with mixture screws, and can’t see any nozzle drip.

[bruno]

 can’t seem to upload pics from my iphone. says it won’t accept that file type, and i don’t know how to change it!!

[bruno]

pics