68 427 435 hp tri power idle issues

[Ed P.]

Have new set of holey 3660 tri power carbs installed and will not idle below 1300 rpm. Starts fine runs on choke till warmed up but will not idle below 1300 rpm. Removed outer carbs and installed blank plates. Vacuum advanced disconnected. Engine vacuum system isolated from car. No vacuum leaks. I turn down idle speed to about 1100 rpm with idle mixture needles closed or open 4 turns makes no difference. Idles there for 30 sec. then just dies. Restarts fine. I have center carb apart now and i dont see any blockage. Idle circuit orifice is .029 .

[Danny P.]

Re: 68 427 435 hp tri power idle issues

Have new set of holey 3660 tri power carbs installed and will not idle below 1300 rpm. Starts fine runs on choke till warmed up but will not idle below 1300 rpm. Removed outer carbs and installed blank plates. Vacuum advanced disconnected. Engine vacuum system isolated from car. No vacuum leaks. I turn down idle speed to about 1100 rpm with idle mixture needles closed or open 4 turns makes no difference. Idles there for 30 sec. then just dies. Restarts fine. I have center carb apart now and i dont see any blockage. Idle circuit orifice is .029 .

Ed , check your metering plate for warpage could be sucking vacuum there and if there's a proper meter gasket was install, Danny

[Ed P.]

Re: 68 427 435 hp tri power idle issues

metering plate good. Did find loose power valve was only hand tight. Will install new one and try again.

[Ed P.]

Re: 68 427 435 hp tri power idle issues

update: rebuilt center carb and installed with power valve blanked off. I had idle at 700 for a few minutes then lost it . Went back to same problem. At 1500 afr is 14.5 1300 afr is 16.5 when i get to 1100 afr goes to 21 and shuts off. I have looked for vacuum leaks and even put smoke in vacuum system with no leaks. Main jets are at 66 idle fuel orifice is .029. I had idle mixture screws out 4 turns with no change.

[Timothy B.]

Re: 68 427 435 hp tri power idle issues

Hi ED,

Are the idle air bleeds in place, and did you double check the gaskets match the holes in the main body. Is it possible the idle feed restrictions are clogged with old gas residue, did you blow through them with air.

[Danny P.]

Re: 68 427 435 hp tri power idle issues

metering plate good. Did find loose power valve was only hand tight. Will install new one and try again.

Whether the throttle housing is warp or the meter plate , did you check for vaccum leaks on the base of the center Carb. and intake for vaccum

[Ed P.]

Re: 68 427 435 hp tri power idle issues

Carb cleaned and all passages blown out with compressed air. I have checked and double checked for a vacuum leak with map gas. Also injected smoke into engine vacuum system with no leakage found. All gaskets installed correctly. Will check idle air bleed size when i get my larger pin gauge set. Idle fuel restriction is .029 which seems small to me.

[Timothy B.]

Re: 68 427 435 hp tri power idle issues

Ed, .029 is not that small considering the outer carbs also have an idle circuit and probably have the small constant feed holes just under the transfer slot. These holes keep a small flow of fuel so gas does not get stale in the secondary bowls.

The idle air bleeds should be around .070 in diameter. If you close the choke by hand can you keep the engine running?

I remember something years ago about the manifold/carburetor gasket being different causing a vacuum leak. Also, if the base gasket (throttle body to main body) is somehow incorrect covering the curb idle holes into the throttle body that would block fuel flow at idle.

[Ed P.]

Re: 68 427 435 hp tri power idle issues

yes if I hold choke plate closed engine will idle at 800

[Chris H.]

[Timothy B.]

Re: 68 427 435 hp tri power idle issues

yes if I hold choke plate closed engine will idle at 800

Tell me about the carbs, have they ever run right or is this a new install.

If they have never been on the car before don't rule out the possibility that there is something not drilled or amiss inside the Holley. Quality control is certainly not what is was in the past.

[Ed P.]

Re: 68 427 435 hp tri power idle issues

Yes new carbs and new install they have never run right. Remember I have outer carbs blanked off right now.

[Ken A.]

Re: 68 427 435 hp tri power idle issues

Ed,

what I would do
1 Hook up all carbs correctly, as they all influence idle
2 Get a new #65 power valve and a blow out preventer kit. With out the kit, then each backfire will damage the PV
3 Remove the metering block and enlarge the 2 plugs next to the jets by 2 drill sizes (You will need a pin vise & a
set of #60 to #80 drill bits.
4 Increase the jet size to #66 as the 64'sare too lean.
Your engine will idle rich but will idle at 600-700 RPM's
This will also eliminate the problem of exposed idle transfer slots.

[Timothy B.]

Re: 68 427 435 hp tri power idle issues

If all the suggestions don't make any difference then my guess is that there is a incorrect gasket blocking the curb idle circuit holes or a passage that may not have been drilled, you may need to get another set of eyes on it.

If you can close the throttle blades to a very small transfer slot showing below the blades and turn the emulsion screws in/out four turns as you mentioned then something's not allowing fuel to the engine at idle. You can finger the idle air bleeds at idle to see if it makes the engine change speed and richen up. This may at least tell you fuel is flowing through the idle circuit. Idle air bleeds are the small brass restrictions outboard looking from the carburetor top.

Did you verify that the vacuum advance control is not leaking.

[Danny P.]

Re: 68 427 435 hp tri power idle issues

Yes new carbs and new install they have never run right. Remember I have outer carbs blanked off right now.

There new or rebuild carbs. someone rebuild , if new and you did the check up like float level and air mixture , then it your intake leaking somewhere , how you checking the intake for any vacuum leak ?