Author Topic: Another Idle question  (Read 325 times)

Offline richie49

  • Newbie
  • *
  • Posts: 7
Another Idle question
« on: April 15, 2019, 07:11:14 PM »
I have a problem with the idle.I got parts for my carb from cliffs recommendations. Now I havent drove the car to see how the new jets and needles respond but (not the best cam for my needs ) the cam has a 108 lobe sep. and 296 duration so the idle is rough. The engine is a 1976 caddy 500 that has been rebuilt other wise stock .Iam trying to see how much I can do with this cam before I go thru the problems of replacing cam.The cam says 950 idle spec but when I get it to 950 in gear it is 1250 out of gear,any suggestions on what to look for that would make a 300 rpm change.Tryed manifold vacumn for advance and it didnt like it so went back to ported. ignitial timing is 19 degrees advanced.

 Richard richie49

Offline 77cruiser

  • Jet Head
  • ****
  • Posts: 466
Re: Another Idle question
« Reply #1 on: April 15, 2019, 08:11:31 PM »
How is the idle circuit set up? What didn't it like about manifold vac.? What size engine & comp. ratio?
Jim

Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 3927
Re: Another Idle question
« Reply #2 on: April 16, 2019, 03:14:05 AM »
Take a look at the timing to make sure it is ROCK SOLID in and out of gear. 

Look into the carb at idle speed and check for nozzle drip.  If you have nozzle drip you will need more bypass air and/or more idle fuel to the mixture screws.

No big secret here that I am NOT fond of tight LSA camshafts with a lot of seat timing for street engines. 

I get more complaints from folks who go that direction than any other.  The Thumper and Thump your Mutha stuff tops the list, followed by the Comp XE cams.  Hardly a day goes by someone doesn't call here bellyaching about rough idle, doesn't want to stay running when placed in gear, or the wife woln't ride in the car now that the new engine is in place because it stinks her hair up!

On a more serious note, I get involved in a LOT of big CID "stroker" engine builds, and FAST Class set-ups.  Over the years the wider we've gone with LSA the quicker the cars are at the track and milder and easier to manage on the street.

I attached a dyno sheet below showing how this works.  The first cam was purchased after the engine builder called Comp for a recommendation.  The XR276HR is a very popular hydraulic roller cam from their catalog. 

The ONLY change I recommended to our customer after everyone at the dyno shop right down to the janitor was blaming the Q-jet for the piss-poor power production of the fresh 455 engine build and some pinging when they tried to crank up the timing to make more power.

I told them to leave the carb alone and change the cam, and provided the specs.  The new cam idled better, improved throttle response, broader power curve and made more power as well.......Cliff

Offline richie49

  • Newbie
  • *
  • Posts: 7
Re: Another Idle question
« Reply #3 on: April 16, 2019, 08:17:41 AM »
Thanks Cliff
  I'll check for that   and repost the results ,probably be another week before I can do that.
    Richard richie49

Offline richie49

  • Newbie
  • *
  • Posts: 7
Re: Another Idle question
« Reply #4 on: April 29, 2019, 05:34:24 PM »
Cliff
    I havnt forgot about the post but the car is killing me.   I have been having starter problems. Cant tune anything till I get the starters behaving.I burned up 3 oem style and waiting on a gear reduction style .So I soon as I can get it to start and I'll reply with what I have to do with the tuneupand idle.
      Thanks
Richard richie49

Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 3927
Re: Another Idle question
« Reply #5 on: April 29, 2019, 08:01:24 PM »
Bummer, what's killing the starters?

Cheap reman's or the big motor just taking to much to crank it thru when it's hot?

I will say that I went to a mini-starter about 20 years ago for my engine(s) and I could literally drive the car to town with it if the batter held up long enough!

It's been one of the best purchases I've ever made for my set-up.........Cliff

Offline richie49

  • Newbie
  • *
  • Posts: 7
Re: Another Idle question
« Reply #6 on: May 01, 2019, 06:40:10 PM »
The starters are just bad.I was starting the engine,trying to get some tune and checking what you had said to try. The starters would just moan and go to smoking. I did put a hitachi gear reduction on it and the starter cranks it just fine at 19 degrees of advance, BUT the dang thing rattles the flywheel .I shimed the darn head with two shims and you can see clearance between the flywheel and gear drive but it still makes noise.I dont think I can put more shims in it. So aggravated I feel like grinding the gear back some more and rebeveling the ends..  Might have to try one off a mid 90's lt1 ,I think the oem's have more clearance from flywheel..
      Richard richie49

Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 3927
Re: Another Idle question
« Reply #7 on: May 02, 2019, 04:06:37 AM »
Bummer.  I had to shim mine a way away from the flywheel to get it to run quiet, been fine now for nearly 20 years......

Offline richie49

  • Newbie
  • *
  • Posts: 7
Re: Another Idle question
« Reply #8 on: May 03, 2019, 07:53:16 AM »
It seems I finally got the starter to behave.The engine starts fairly easy but still is rough.I checked the timing and its not rock steady but it doesn't move very much,just wiggles a little. I turned the idle screws and they dont seem to make much differance on the idle quality.Does rev up nicely. Do you think it needs more fuel? Pulled a vacumn hose off of carb and didn't seem to make a differance.
    Richard richie49

Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 3927
Re: Another Idle question
« Reply #9 on: May 04, 2019, 05:55:56 AM »
Take a look into the carb at idle speed and see if you have any nozzle-drip?

If so it's not completely on the idle system.

If you don't have any you should be able to turn the screws in and reduce engine speed or at least have some effect on the idle system as it goes lean.

Something else to try just to see how the engine can behave with that cam is to loosen up the distributor and turn it in both directions until it smoothes out or as smooth as possible.  Then take a gander at where the timing is at.  Also fine tune the mixture screws while at that setting to see if you can make it even better and have control from rich to lean.

If there is a point in the deal where you can get it to smooth out then there will be combinations of idle and fuel to achieve this with correct tuning......Cliff

Offline richie49

  • Newbie
  • *
  • Posts: 7
Re: Another Idle question
« Reply #10 on: May 12, 2019, 08:33:47 AM »
Cliff
  I finally got it to idle in gear.But it isn't going to work.The idle is 1000 in gear and is so rough that it would not be any fun to drive.So I'm pulling the engine and swapping out the cam as soon as I get the funds to buy new parts. After I get it back together I'll have to see if the carb will work with the larger idle tubes and down channel restictions. Always something. Is there any suggestions on general cam specs, looking for a new cam more suited for the engine.

      Richard richie49

Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 3927
Re: Another Idle question
« Reply #11 on: May 13, 2019, 03:25:14 AM »
The cam isn't really too big it's just ground on too tight for LSA, so too much overlap and without increasing the compression ratio to offset the lack of "squeeze" at low rpms the engine isn't happy about it.

I've never built an Cadillac engines so no direct experience but have done quite a few "strokers" at or near 500 CID using Pontiac blocks.  We've found that the big long stroke engines love 114LSA with the ICL around 109-110. 

Assuming your compression ratio is around 7.5-8.5 to 1 I'd want closet to 230 @ .050" and around 280-290 seat timing.  It will idle much smoother than the 108 LSA cam and make "locomotive" type power from right off idle to about 4800-5000rpms........Cliff

Offline richie49

  • Newbie
  • *
  • Posts: 7
Re: Another Idle question
« Reply #12 on: May 13, 2019, 07:31:06 AM »
Thanks Cliff
     I'm looking into different cams now but that suggestion would help idle which is what I'm looking for.Whenever I get one and get it together I 'll  reply on this thread .No telling how long this will be .

Richard richie49

Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 3927
Re: Another Idle question
« Reply #13 on: May 16, 2019, 05:39:24 AM »
I don't have any direct experience with Cadillac engines so wouldn't know any specific part numbers.

What are your goals for the project?

You mentioned pretty much a "stock" low rebuild with a cam change.  What is the application, drivetrain specs, etc?