Big cam, stinky rich idle

[77cruiser]

Have you tried giving it more timing? Go as far as can while still getting improvement in the idle, you can always limit the mechanical after you've determined where it idles the best. You may not get it to work with manifold vac. as you know the vac. drops off too much when you put it gear.

[dave at hsp]

I finally got a chance to work on this thing again today.
I went from .140 to .150 on the main air bleeds in the base plate by the butterflies, went from .042 on the idle tubes to .051. The mixture screws are at 1 turn out. That's where it idles the best with the highest vacuum of just above 4". I changed the vacuum advance from full vacuum to ported. Didn't really see much difference except for a more steady idle as opposed to a slight up and down before due to the vacuum at idle being up and down. I'm gonna leave it there for now.
 My LM-2 is reading 13.0 at idle in gear at 550 to 600 rpm, and 12.5 in park at 650 to 700 rpm. It sat there and idled in gear for about 5 minutes with a nice chop. Never stalled or even acted like it wanted to stall. It still stinks rich at idle, not real bad, but it seems to run fine and revs right up. I'll go take it for a drive in a while and see how everything else runs. Sitting here in the shop at 3500 rpm the LM-2 reads 12.1 to 12. 5.
  I still would like a leaner idle, but right now, I'll take what I can get. Not bad for a way too big cam.

Dave

[77cruiser]

Try 2 more things the timing & try adjusting the mixture screws with it in gear to best idle.

[dave at hsp]

Well, I gave it a little more timing, and since it's a small cube engine, I'm sure it won't mind. I left the vacuum to the distributor on ported, not full, adjusted the mixture screws at idle in gear, (the way I always do) and they are still just a tad over 1 turn out.
 I ran it down the road about 5 miles and it runs really nice. The AFR is 14.5 at 3500 rpm cruising. I got back and let it set and idle in park for about 10 minutes. 750 rpm and 13.2 AFR. Dropped it in gear and sat there and idled at 600 rpm with 13.3 to 13.5 AFR for about 5 minutes. Nice chop to the idle. Sounds like a pro stock. Kinda cool and the kid that owns the car really likes it. When I drove it, from a stop, I smashed the pedal to the floor and it just kinda hazed the tires and went. Chirps the tires when it shifts and pulls hard up to about 80 mph when I let off. Pretty strong for a 305.
 Anyway, I let it go and the kid has driven it now for a couple days and has a BIG grin on his face. That's what we were after. After getting some miles on it now, the idle doesn't smell so rich anymore and will idle all day in gear, and no hesitation on acceleration.
 Thanks for all the help and advice guys!
Cliff now has another recipe for the next book.

Dave

[Cliff Ruggles]

I went from .140 to .150 on the main air bleeds in the base plate by the butterflies, went from .042 on the idle tubes to .051. The mixture screws are at 1 turn out

There are no "main airbleeds" in the baseplate, did you mean idle bypass air?

Having to go to .051" idle tubes indicate a lot of idle airbleed for the application.  In many cases it's easier and more effective to reduce or install smaller idle airbleeds so there isn't so much emulsion air at idle when the vacuum signal is really low.  Non-emission and Marine carbs are set-up like this, and put down a TON of idle fuel with pretty small idle tubes and down channel restrictions......Cliff

[dave at hsp]

Yep, idle bypass air, not main air bleeds, sorry.
I had reduced the idle air bleeds to .052. That's why I asked. I wasn't sure which direction to go, so, I just did some 'spearmentin.
  If I get the car back later in the summer, I'll reduce them a bit more and go smaller on the idle tubes.
That's why I ordered a couple extra from you the other day.
 Oh well, it runs pretty good now and you can't wipe the smile off the kids face with a crow bar.
I'll let you know when I get the car back.

Thanks!
Dave