347 idle rpm

[gick70]

I acquired this motor and was wondering what is the average idle rpm ??

 

[Broncobowsher]

500-1500

No idea how the engine was built. How wild the cam is. You are dealing with an unknown amount of aftermarket stuff. Just have to wing it.

 

[gick70]

With the carb not set,I can't get it under 1000,but it sounds good,I'm not use to a cammed engine and their preferred idle.

 

[Tiko433]

Isn’t a high idle a sign of vacuum leak? Maybe spay carb clean around and listen for change...

 

[spap]

So when you turn down the idle screws it stalls under 1000 rpm
Is the idle lumpy or smooth

 

[EPB72]

Also have you checked timing ,and how /is vacuum advance set up manifold/ported ?? What carb you running?? No vaccum leaks?? It will take some trial and error

 

[gick70]

I think it's the nature of the beast,15 mechanical,Lopey cam,seems like ported works best.I had a 670 truck avenger laying around,that's on it.

 

[SHX669]

Does your 347 have aluminum heads or cast Iron ; is your intake a " higher performance " one - air gap or single plane ? That would give a better indicator of how wild or mild the build is.

 

[T-7ToNewOldB]

I have a blueprint 347 with a proflo4. It idles fine from 700 up but I keep it at 850. It does have IAC though. So may not be a useful comparison.

 

[gick70]

Cast heads,dual plane intake

 

[gick70]

Dual plane air gap

 

[Broncobowsher]

All heads are cast, unless you are doing top fuel in which cast they are carved out of billet.

You really should be able to get the idle under 1000.

670 Holley. check the float level front and rear. I've had fresh installs get a piece of gunk (fuel line sliver) get caught in the needle and seat causing the fuel bowl to overfill and dribble down the boosters. It would run, but could never get a good idle. the first time took a lot of trying to figure what was wrong, the second time it was 7 years later and took longer to get the air cleaner off to inspect than anything else. and only a couple minutes to actually fix.

 

[gick70]

Cast iron,not aluminum

 

[xltboy]

If you cant adjust the idle RPM below 1000rpm then I think you have something wrong. My blue print 347 once warmed up can be adjusted to any rpm desired down to the point where it wont run. To me there is something not letting the throttle plates close when the idle speed screw is adjusted. Is the linkage keeping the throttle from completely closing? Is the choke not coming off and overriding the idle speed?
Xltboy

 

[73azbronco]

With my cam it starts first time and idles cold at 1150. Warmed up 650-720 w/19 in/vacuum. I can get it to idle at 450 but vacuum drops off, idles gets really rough.

Like they said, if it won't idle lower, you have a really hot cam more than likely.

 

[gick70]

Update,my idle transfer slots were showing too much,all is good now,idling around 800rpm,thanks all!! Adjustied to total timing spec. I had,set idle after that!!

 

[68ford]

What are the cam specs? If it happens to have a cam with tight lobe separation(under 110) and especially if in conjunction with more lift than average, it may never idle below a 1000. I run a isky mega 270 cam. Lift is right at .500 and 270 duration. Both not super aggressive at all. But it is on a 108 lobe separation cause a lot of overlap. I can dial it in to idle at 850-900 but it will stall if the wind blows hahaha

 

[gick70]

Yeah,like I said I didn't know specs, so I am good with idle now...