RPM idle problems

[1953]

Ok recently installed new head gasket and engine gasket set, I m getting ready to time the engine, problem is I can not get the rpms to drop it sounds like somone is holding the pedal half down in neutral, when I turn the idle screw on the carb it does nothing, I've found TDC on the flywheel and distributor and checked the rockers with feeler gauges to the specs I n the manual, the rpms just won't drop at all, is it possible the carb has issues?

[mr48chev]

Could be internal or it could be a vacuum leak but I'd think it is probably a linkage issue.

On the side of the carb there is a cam setup that pivots on the throttle shaft or on a shaft next to it that the idle speed screw makes contact with. It is the fast idle cam for when the choke is on and may be stuck in a position where it keeps the idle speed up. Or the idle speed screw may be turned in too far. Also the linkage may be hanging up or a return spring may be in the wrong spot.

[1953]

I will definitely look into that I rebuilt the carb as well so maybe I did something wrong I doubt that tho because I took my time and didn't overlook anything the linkage may be the issue I was looking into that earlier

[dsraven]

if you don't have a fast idle cam issue (try that first) then try disconncting the throttle linkage so it is just the carb with no linkage attached. maybe the linkage is holding open some or the choke cable isn't set up quite right, is too tight or binding so it can't release all the way, so the choke is held on enough to keep the fast idle cam in play. then check for a leaky base gasket, lean idle mix like the needle is turned in to far, low fuel bowl level, low fuel delivery, partially plugged filter etc. sometimes what works is to rev it up, with the air cleaner off, then let it return to idle and as it is doing that cover the carb inlet with your shop towel for a sec and quickly remove the rag before it dies. if there is a small blockage in the idle circuit the added vacuum will sometimes clear it. hey, dirt happens. when the carb is taken apart sometimes even the most carefull guys get a spec in there.

[mr48chev]

Most of us start with the idle mixture screw (s) backed out 1-1/2 turns on these carbs. Then fine tune it when everything else is working right. The idle circuit on this one is probably out of play because the throttle plate is open far enough that all the fuel is coming from the main nozzle.

[my56chevytruck]

Just as dsraven had mentioned (those Canadians are sharp), check the fast idle adjustment. what carb are you running and have you checked your choke as well? Like as said, disconnect your linkage and run it by hand and see if that solves your high idle problem.

[1953]

Well guys I tried to disconnect the linkage and stuff mentioned still nothing, I haven't checked the fuel filter but thats my next step and also to re do the carb again and clean and tripple check everything, still running at high rpms

[dsraven]

so,
-throttle linkage is NOT on the fast idle cam?
-carb base gasket is good?
-fuel pump flow is acceptable? take line off at carb, place end of line into a gallon jug, disconnect power wire at coil, have someone crank engine while you hold the jug and fuel line so you can see what the flow is like
-accel pump disharge is aimed correctly? should shoot a jet of fuel at the edge of the throttle plate so when the accel is opened there is a flow to the same area where the air is also entering the engine. down the middle in't gonna cut it
-float bowl level is good? take the top off the carb while it is still on the engine and check what you have for level in there.also can see what, if anything, may be in the bottom of the float bowl. sometimes a bit of crud can be in the fuel line or carb fitting and moves into the carb after assembly.
exhaust system not plugged? check with a vacuum guage connected to the engine. when running the vac guage will slowly drop off if the exhaust is plugged up. may have to rev the engine up and hold it there, like fast idle or a bit more.
after that, if all good but still running lean, maybe bust it apart. check for a broken or wrong gasket between the halves. maybe a passage is covered up. I have had to use a small flexible wire, like one found on a paper label tag back in the day, to "rod out" the passageways on carbs that have sat for a long time. I also have used plastic dental tooth pics or small dental brushes to clean the small parts. a metal screen tea thingy, the kind people use for loose tea leaves, also works good for cleaning small parts. they can't get lost easy if they are trapped inside the tea thing. a cake pan is also good for dissassembly because the carb is trapped inside the pan, so any extra fuel leakage is contained, plus the parts removed can be dropped in the pan for cleaning. carb cleaner spray doesn't hurt the metal pan either. make sure to remove the mixture needle and ensure the passageway is clean and clear. also the inlet needle passageway and all the rest of the passageways that lead out to the area near the throttle plate in the venturi area.
good luck. hope it wasn't too boring, just a few thoughts that work for me over the years.

[1953]

Thank you. I will take all of that into consideration.

[Hover]

Is your vacuum advance hooked to ported or unported? It made a big diffference on mine.

[dsraven]

that was another item I forgot to mention. good catch there hover. check the vacuum and centrifugal advance. sometimes hey stick. pop the dist cap off, grab the rotor and see if it turns easily against spring pressure and then snaps back after. if not it is sticking or worn out. apply vacuum to the vac advance pot, even with a spare piece of hose and your mouth, and see if the points plate moves and then easily goes back to the stop again after.