VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 1946 won't idle

I would try either Gene's or Bob1951chevy's ideas before changing the manifold gaskets. You need to identify the problem before you can fix it. If it does not suck in the oil or propane then look for another cause. Have you done a compression test?

Thank you. I will double check idle mixture and speed screws.......I believe they are ok. Thanks for advice on gaskets...my next project ! LOL Do I need to put any sealant, etc. on this ? Want to make sure I do it right the 1st time.

Thanks m006840.....just saw your comments.....ok...yes, you are right.....and have not done a compression test yet......will do that also. Thanks again. Update next week as I work on it.

Chipper,

Did by chance did you get that post about the pump rod backwards? The rectangular and round part?

Charlie


BTW: Always enjoy and am enlightened by your comments that give us the scientific low-down whenever a chemical question comes up. Thank you for your knowledge and willingness to share it.

OK...did a compression test according to the shop manual directions Sunday , Jan 21st. Readings : Cylinder # 1 90 ; # 2 75 ; # 3 95 ; # 4 75 ; # 5 70 ; # 6 70. According to shop manual..supposed to be 110 or better. This does not sound good. Of course...this didn't happen overnight. The engine ran fine until I had issues starting a few months ago. ( always started right up and purred like a kitten ) For those just joining in the original coil went bad, then the replacement coil went bad, now the 3rd coil...which seemed to be fine. New electrical components installed...( plugs, points, plug wires, condensor, points, dist. cap ) Just installed a rebuilt carburetor. But doing the same darn thing...it will start, run, but NOT idle. I just don't understand all this. As soon as I push the choke all the way in it just dies. Another question....when the motor is at correct idle, how wide does the bottom flapper valve in carburetor have to be open ? ( the small brass flapper that lets in the fuel/air mixture into the manifold ). It was suggested I must have a major vacuum leak. I tightened all the manifold bolts. Good grief !!!!!

While the compression is low on some cylinders it should still run at an idle but will be a rough idle. Also the compression has been low and it came on slowly as it has been low for some time.
How much should the throttle plate be open at idle. That depends and several things but the opening is determined by the idle speed adjusting screw on the throttle linkage. If idleing too slow turn screw clockwise to increase idle speed.
BUT the fact that it will run better with the choke out suggests that there is another problem. The choke makes the fuel/air mixture richer and the problem is it is too lean for some reason.
Note that when first starting engine in cold weather the choke must be partly out and the throttle pulled out to a fast idle speed.

I am also assuming that the valves are not sticking as that could cause rough or no idle and low compression and could come on suddenlty

Thanks. I understand your comment about the idle speed screw. If it is running too lean then that sounds like there is a problem with the carburetor ? Or does that just mean I have to keep playing with the air mixture screw adjustment ? Or the choke ? As far as I can tell the choke is operating correctly as far as flapper operation when choke open and closed. The running too lean is a new problem.

Did you try either of the suggestions on checking for a vacuum leak? Check the rotor for correct length. I had a similar situation and an incorrect rotor was causing the coil to max out and fail. Did the same with the new coil. Put the old rotor in and it started and ran fine. The rotor arm was too short giving a huge air gap for the spark to jump to the cap terminal. Also I would do another compression test with oil in the cylinders to determine if your low compression is due to rings or a valve problem.

Have not done their tests for vacuum leaks yet. Interesting about the rotor.....Will check but I doubt that's it. It seems correct. The whole situation is crazy. I just want to get it running correctly. It has given me nothing but problems. I am not that worried about the compression...it purred like a kitten when I 1st got it. Then it is one problem after another. I just need to get vacuum leaks fixed ( if there are any ) and get it to idle properly. Thanks.

vacuum advance canister? jim

Welcome to the wonderful world of old cars.

Sooo....I tried Chevgene's trick of squirting oil and it did what he said. I took off the manifolds today...glad I did.....the intake to exhaust manifold gasket needs replaced, the exhaust to tailpipe gasket was completely deteriorated , and yes the gaskets from block to manifold need replaced. Chuckle for all of you...the manifold heat flapper is installed correctly and moves properly....the counterweight was installed "upside down" ( flat part on top ) , and there is an excess glob of welding metal on it, ( where counterweight was welded onto the shaft ) preventing it from complete/correct movement. People do funny things !! Going to correct that, take both manifolds to a place I know and have them dunked , cleaned, primed, painted. Yay. Question....are we supposed to use any gasket cement on manifold to block, or intake to exhaust ? Or if not, just a little dab here and there just to hold it in place while manifolds are re installed and bolted on ?

No gasket cement or sealers are used. Are the manifold to head alignmsnt rings their. They go in the intake (round holes" AND MAKE SURE THE MANIFOLD HOLE IS IN PERFECT ALIGNMENT IS LINED UP WITH THE HOLES IN THE HEAD.THEY ARE A ROUND SPRINGY METAL RING ABOUT 31/4" WIDE AND SPLIT AND FIT IN THE RECESS AT THE ROUND OPENINGS IN THE HEAD and IN THE MANIFOLD.

Also, you might want to have the surfaces on both manifolds where they mate with the cylinder head machined flat....or at least have them checked to make sure that the surfaces are flat and not warped.

Ok. Yes rings are there. Will check flatness. Thank you both !! Will keep you all updated .

Clem,

MOM,

Is right on about the flatness of the mating elements of the head to manifolds. Only thing I would suggest is to not check them but merely take them on down to the machine shop and have them ground flat. They will more than likely need it.

Best,
Charlie

Clem,

For the sake of keeping the forum afloat and it from being augmented by the 1941 and 1942, If you ever get that old 46 idle, you may want to keep it to yourself. Such a post as your initial one helps the forum from becoming even more of a dead zone. This forum, most times can be sescribed as zzzzzzz. No one awake, sober, lucid, talkative, or anything else to counter the belief by the rest of us that the forum has either tanked or gone belly up. :)

41s and 42s should be included to the mix. I have wrote about many times but to no avail. No openmindness at the upper reaches of the club may be the reason. Who knows. :)

The 46-48a need help. Anyone should be able to see that.

Charlie

If you understand that one you are better than I am

Gene,

It's rather simple. 41s and 42s have more in common with the 46-48 than they do with the 37-40.

The 46-48 forum is so narrow that most questions posed are answered by in the 37-42 forum.

Accordingly, the narrow scope of the 46-48 forum tends to limit the traffic thereon. See easy.

Best,
Charlie

Ah ha ok ! thx.