440 six pack idle fluctuates

Pulling my hair out.Idle fluctuates from 800 to 1300 and back. Base timing is at 20. Power valve was changed to 3.5 ,float levels are good. Cam is purple 474 lift 280 duration. Carbs are new. Please help

Are you running vacuum advance?

If so, unplug and cap it then see what your idle speed does.

Yes I have it plugged off.I even replaced the intake gasket and pan,same thing.

Sounds like a vacuum leak somewhere. Block off power brake vacuum if you have it. Pull off one vacuum line at a time, carb base gasket area, etc. More carbs, the more areas to check.

That's what I thought too but I can't find anything.I have manual brakes and pcv valve is blocked off. At fast idle vacuum is 12 then idle at 800 vac drops to 5 then eventually dies.

Check your initial timing and verify that the mechanical advance is not set too loose,

When you had the manifold off, did you inspect it for any cracks, esp in the runners?

If you used intake gaskets, are they installed under the "turkey" pan or on top of it?

hi

look at gasket under hot idle compensater .

idle speed for six pack is 900 rpm !

Thanks to all for responses.I haven' checked mechanical advance yet. Intake is new and looked fine. Gaskets on both sides of valley pan. Guess I don't know what hot idle compensater is?? This is my first six pack set up and its whipping my butt.

Back off the base to manifold bolts slightly. I have had them tweak the base plates just enough to hang up the throttle blades slightly.

Any evidence of a mis-fitting intake when you took the valley pan off ?? Were the valley pan's port sealing rings compressed evenly ??? Any oil pull over into the ports ??? There used to be a small paper in the box with the new 6bbl intakes that pretty much stated you may need to machine the intake to have it fit properly..Not sure if they still include that anymore...

The paper gaskets will help to a point with sealing but I've had intakes that needed machined to fit properly...

When I took the valley pan off there were some places that didn't compress all the way. I did not install the papers initially but i did use them the second time and high tacked them to the valley pan.

You have a vacuum leak. Spray some carb or brake cleaner strategically around the intake, fittings etc. Idle will speed up where there is a leak.

Generally I avoid the gaskets on aluminum or iron B/RB 6 pak manifold installs, I run a thin bead of RTV around the ports on the head, then install the "turkey" pan, run a bead around the pan's ports and install the manifold, and let it set up...

I'd suggest you try and eliminate the manifold/gaskets for a vacuum leak by spraying down those areas with the engine running using a carb/choke spray cleaner to see if the idle is affected

Another possibility is your power valve, have you since adjusted the main metering block (center carb) fuel/air screws?, try running them in all the way, if there's no change in current idle or the engine doesn't stall then the valve is faulty/leaking or the PV's gasket was torn/distorted during install

You did install a plug in the back of the manifold?

Robert

There is a great guide for tuning six paks - I don't think you used it to set up your carbs. It's very difficult to get you the right answer if the carbs are not base-lined, but as you see guesses are being ventured forth without asking the most important question first.

My suggestion is you read the guide & set the carbs up per the guide. Please be sure to read the part about the importance of a 195 degree thermostat.

Was it running well before carbs were removed and replaced? Without that information, I will throw out about 10, well maybe 20 minutes worth of things to check out.

Did you also change intake manifold when putting these new carbs on,,,,meaning conversion from 4 barrel to six pac.

That smells intake manifold leak to me as first guess if all was well with 4 barrel intake, particularly if brand new intake on heads of uncertain lineage of whether having been cut or not.

How far out from bottomed out are idle mixture screws on each carb?

Can you keep it running by manipulating gas pedal,,,,or does it still want die.

What does exhaust smell like,,,burning your eyes?

have you pulled some spark plugs, if so how do they look?

Sometimes a squirt of starter fluid at suspected vacuum leak spots will provide a clue that carb spray may not. Keep Halon type fire extinguisher close at hand and do testing outdoors.

Are you certain that center carb power valve is properly seated. It is possible to think it is, when may not be.

Can you keep it running by place cupped hand over choke?

Jumper ignition switch and wiring by running jumper wire direct from battery positive to coil positive,,,thereby removing most doubt but not all on ignition related problem.

Points or electronic ignition? Possible condenser if points,,,coil wired correctly,,,minus to distributor?

Best guess as with others is vacumm leak,,,but at times when you hear hoofbeats and you think it is horses, it really might be zebras.

this may be a mile off but what I would try is see if I could introduce some starting fluid under the valley pan to potentially uncover a vac leak (& on the top side on both sides too) and take off the end carbs & cap the manifold flanges & run it off of the center carb only & possibly swap one of the end carbs onto the center manifold flange (if it is the carb they cant all be leaking vacuum you wouldn't think).

Yes the rear plug is in the manifold.I followed the set up procedure for baseline. Center idle mixture screws are out 1.5 - 2 turns and out boards are out 1/8 turn. This is a fresh engine and first time running. Yes the exhaust fumes were horrible so I changed the intake gasket,power valve and carb base gaskets which did seem to improve the situaton but not fix it. It will continue to run by feathering the gas or setting idle too high. Closing the choke kills it.I converted to electronic using factory distributor and orange ignition box. Also running 195 thermostat. I really appreciate all of your suggestions. Can someone explain phasing the distributor to me.?

Double check that one or both of the out board carbs aren't open.

You have a vacuum leak so you need to track that down.

I checked the outboards this morning and they are closed.I also sprayed around the intake and nothing changed.I am so frustrated with this. I agree that it seems like a vac leak but ??? Just doesn't make sense. I may have a super bee for sale

Dist phasing is the last thing you need to worry about, most of your issue seems to point to a vacuum condition or fuel surge, disconnect the end carbs linkage to confirm the throttle blades are indeed fully closed, leave the linkage off until you have the idle sorted out, confirm that your fuel level is proper height in each carb, timing wise I'd start with 10 degrees BTDC, attach a vacuum gauge to the manifold port, at idle, motor fully warmed, choke fully off, idle in the 800 range (try and keep idle as low as possible thru out the set up procedure), turn in (one at a time) the center carbs fuel/air idle screws, turning out one screw at a time to achieve the highest vacuum rating you can achieve under the your current conditions, after you've set up the center carb initially, move to the front carb, blocking the outer air bleed located in the carbs throat with your finger tip (there's an outer bleed port in each venturi/throat/barrel) see how that effects idle, if the idle picks up that end carb bleed is lean, if the idle drops, it's rich, turn the base screw in/out as needed until there's very little to no noticeable idle change, do each side one at a time on the front carb, even after setting the idle screws, be it on any of the carbs, go thru the idle/fuel/air adjusting ritual 2-3 times just to balance off your adjustments, after you've adjusted the front carb, if you don't have a tool for accessing the rear fuel/air idle screws, remove the carb and swap it with the front one, with the rear carb now on the front of the motor, set the air/fuel idle screws up using the air bleed block off method, the nonsense of "X" amount of turns out/in only applies to an initial start up, you need to tailor the air/fuel idle circuits to your engines characteristics, if this doesn't establish a better running/idle condition, and your in the same boat with an erratic idle, then you need to look for a vacuum leak, even to the extent of pulling the manifold, new or not it could have an undetectable crack.

I'll assume you tried running in both center carb fuel/air idle screws and the motor stalled/sputtered to confirm the freshly installed PV/gasket is not leaking


Mike

All good responses. I had a similar issue with mine. It would especially show a high idle after I opened the outboard carbs. I found my issue to be the butterflies in the outboard carbs were sticking, just before they were completely closed. I had to push on the throttle shaft of the outboards in order to get the idle where it needed to be. I fixed mine by gently filing the throttle blade into a knife so it would not hang up. It took a long time to find this, so don't cross it off your list until it's checked. I puppied the car home with a high idle, got out and pushed on the secondaries to find the issue. I was told (as mentioned earlier in this thread) that tightening the carbs to the intake too tightly can warp the carb body. I now use a screw driver/ratchet in order to put them on nice and loose. No problems since.

By all means, it could be a vacuum leak as well. When you installed the valley pan, did you use permatex or other gasket maker where the front of the valley pan meets the bottom...it is the area just after the outside bolt of the valley pan on all four sides. If not, it can leak on the bottom side. Good luck.

How do you have the floats set? Do you get a trickle or a stream of fuel out of them? Verify the linkage is not hanging up anywhere.

Pull the carbs off and ensure that your throttle blades are not hanging up on the gaskets or manifold. Make sure your air bleeds are clean and clear of contaminants. Check inside the float bowls for contaminants.

Pull the intake and use the Hughes Engines intake sealing wax string or equivelent to verify fitment.

Do you have MSD? Are you using a standard dial back timing light or an MSD timing light?

it might be leaking on the underside. what about punching a very small hole in the valley pan at each group of ports (4 holes) & shoot some starting fluid in there with the thin red straw. you could solder the holes closed later when done

Fresh engine,,,,,camshaft degree, at minimum camshaft and crankshaft marks lined up? Long shot just asking.

Converted to electronic ignition,,,,before problem or after problem raised its head? In other words was electronic ignitiin installed after to possibly fix problem. If before problem,,,,perhaps the issue lies with unit or its installation.

Spark plug wiring firing order all in order?

Extreme exhaust odor Indicates possible misfiring of cylinders,,,,or overly rich fuel mixture.

Fuel line system in order from tank all the way to carb?. Not 3 year old fuel from car sitting for long period of time awaiting new engine.

Which carb to intake gasket are you using ? If you are using the thin black gasket in this picture,pitch it and use the O.E.M gasket.Even if it is not the problem,use the O.E.M. gasket.

I just checked all float levels,just trickling out sight hole. I am using the thicker Holley base gaskets. Electronic ignition was installed prior to start up. Yes timing marks were lined up and firing order is correct. Linkage rods and butterflies are good.After checking all of this,problem still exists. Timing seems to best at 20 btdc using a standard dial back light. This is a complete resto fuel system is new. Running mixture screws in causes stall out.Covering vent tube causes stall out. Cupping my hand over air horn picks up rpm which leads me back to a vac leak as most of you said.Thanks again to everyone that is trying to help me on this. Looks like I'm pulling the intake off again and see what's going on. You guys are great. I'll let you know.

Not for the faint of heart. You are on your own whether to consider following suggestion. However I have successfully done this in the past.

Disconnect fan and alt belt.

Using garden hose with no nozzle on it and engine NOT hot, warm ok.

Place and hold end of hose on radiator end of turkey pan

Have your helper start the engine.

Run for a minute to allow to settle down as much as possible. Note engine rhythm.

Turn on water to a modest stream under and over intake and all possible vacuum leak possibilities. A couple of minutes should prove sufficient. Fan was disconnected so as not to spray water everywhere.

Engine rhythm change at all as it will if water is sucked into engine? Hopefully not enough to cause hydrolock.


Also as ignition change was added to the equation, consider installation of prior system to eliminate new ignition as cause of problem.

"This is a fresh engine and first time running."





Are the rings seated yet?

what kind of piston rings did you use?

plain iron rings seat quick but some of the other kinds take longer.

synthetic oil might slow down the wear in process as well. (low vacuum/low signal at carbs)

You sure you dont wanna get some starting fluid under there first? EDIT I'd lift the front/rear valley pan end(s) & shoot some starting fluid in that way & see if it changes (& cap the PCV port).

Your hand over the carb as the engine idle picked up tells me everything. It's sucking air from somewhere.

but will add, Or it may just be lean.

To the OP,
Have you verified that the mechanical advance is not coming in to early ??
You may have more than 1 issue contributing to the problem.

what year?

So is the issue resolved? What did you find?