Will Not Idle

[mtuck]

I need some help. I am trying to get my car running and i am having trouble. I have a chevy 350 that i have rebuilt. The car will start up and run as long as i give it gas and keep it above 1500rpm. It is very rough running. But as soon as i take my foot off the gas pedal and the rpms come down the car dies. I can not keep it running. I can not keep it running long enough to set the timing. Any suggestions that i might look at? I have a new holley 750. I checked the floats and they seem alright. I also have noticed that while it is running, i am having some gas "pop" back up through the carburetor.

Any ideas i might try?

Thanks in advance for all your help
Matthew

[CAMAROBOY69]

Vacuum leak.

[mtuck]

I checked all the vacuum lines last night and it still will not idle. Anymore ideas on what it might be?

[CAMAROBOY69]

Did you check the line in the back that goes to your brake booster? If you have power brakes.

[slowcamaro]

timing issue? crossed plug wires?

[mtuck]

I do not have power brakes on this car. I have that vacuum line going to a PVC valve. Is that not right?

As for the timing, i can not keep it running long enough to get it timed.

I was also wondering why gas is coming back up through the carburetor. I was talking with some people i work with and one of them suggested that i might have my rocker arms tightened to much. Could that be causing it not to idle also?


I am just so close to getting it on the road. This is driving me crazy...:confused:

[Travis B]

Yes to tight of valve lash will keep it from idleing! what stlye of cam is it(hydrualic,solid-roller,flat tappet)? Popping back through the carb sounds like timing....... is it hard to start? Does it die even after it gets warm? Are you positive it is on the right tooth??

[mtuck]

I can not thank you all enough for the help.

I am running a hydraulic cam. And it is not hard to start. It turns over a couple of times and starts right up. I can give it gas to keep it running at a higher rpm. But as soon as i take my foot off the gas pedal and the idle comes down it coughs and shuts right off.

As for the right tooth. Are you meaning the distributor on the right tooth?

[toofun]

I had a similiar problem a while ago when I rebuilt my motor. I heard everything from vaccuum leaks to too tight valves. A local motor head came over and in about 40 minutes had the car started on the first try.

Here is what he did. It was a little unorthodox but it worked.

First make sure the valves are not too tight. Use the EOIC method and remember that if they are hydraulic, it is better to have them TOO loose than a little tight. The hydraulics will make up for any slack there may be and you can adjust any slack out of it after it is running. Then recheck all of your vacuum hoses just for piece of mind. This is where it was a little weird but like I said, it worked. Pull the distributer out of the engine and remove Just the number one cylinder spark plug. Then stuff the spark plug hole with a piece of paper towel(I know many of you will say that this is not the right way and that you will not get true top dead center but believe me it works to get you where you need to be and you will be able to adjust the timing afterwards) ....Bump the motor over until the paper towel blows clear out of the hole. DONT BUMP THE MOTOR OVER ANY MORE LEAVE IT WHERE IT LIES. Then place the distributer back in place making sure that the pointer of the distributer is pointing directly at the FRONT INSIDE CORNER lip of the driver side cylinder head where the valve cover would go on (front meaning towards the RADIATOR SUPPORT NOT FIREWALL) you can use a screw driver to line it up by laying it at the corner towards the distributer. Now put the distributor cover on and clinch it down.

Many of you may disagree with this but it worked dead on for me on the first turn of the key. The car started and stayed started. I was able to time it and it sounded and ran great!! Dont know if this method works for all engines but know for sure it works for SMALL BLOCK CHEVYS. I had four other guys try it after me and they raved about it. May not be the optimal way but it will get your motor started and able to idle so that you can time, tune and take it from there.

HOPE THIS HELPS

Mark
TOOFUN

[CAMAROBOY69]

Yeah rocker adjustment was my reply in I think every single one of those threads so I started out small on this one. I would have eventually got to rocker adjustment again. :lmao:

[mtuck]

toofun, I will try your trick this weekend. I will keep you informed on how it goes.

I was also wondering about the valves. Can i just take off the valve covers and just loosen all the nuts on the rockers? Or is there a sequence i need to follow. And how much should i back off the rockers if i can?

[Travis B]

I can not thank you all enough for the help.

I am running a hydraulic cam. And it is not hard to start. It turns over a couple of times and starts right up. I can give it gas to keep it running at a higher rpm. But as soon as i take my foot off the gas pedal and the idle comes down it coughs and shuts right off.

As for the right tooth. Are you meaning the distributor on the right tooth?

Ya I meant timing sorry! When I get stuck that is where I start....Put it back on TDC recheck all vacuum lines, relash the valves set them loose....let us know

[toofun]

OK,

Here is what I did. You may have a ton of different ways to do it but this I found is the best to get you started without fear of overtightening them . I am assuming that you are working with hydraulic lifters so this is a good thing.

Back off all of the rocker nuts a few turns and make sure they are loose. Then start with the first cylinder in the row. Make sure you are looking at the right valve whether it is the intake or exhaust. It is easy to get confused so take your time and make sure of the one you are working on. Bump the motor over and watch the exhaust valve. when it just starts to move(compressing the valve spring) adjust the INTAKE VALVE ON THE SAME CYLINDER. Tighten the nut gently until the pushrod can no longer move up and down. DONT CRANK IT DOWN just do it easy until you just start to feel it no being able to move up or down. Most people will tell you to do a quarter turn more but I DO NOT. Like I said better loose then too tight. It is easy to over tighten them and the hydraulics will get it close enough to pump up the slack until you get the motor going and can readjust if necessary. Besides the motor will be cold so expansion will help as well. TRUST ME DONT DO THE QUARTER TURN.

Rotate the engine over again and watch the intake valve this time. Let it compress the valve spring all the way and watch it as it starts to decompress it. Once it is almost all the way back from its travel THEN ADJUST THE EXHAUST VALVE ON THE SAME CYLINDER the same way. After that go to the next set of valves on the next cylinder. BE SURE TO DOUBLE CHECK WHICH VALVE IS WHICH WHILE WORKING ON IT. IT IS EASY TO GET CONFUSED. This is time consuming and there are quicker ways to do it, but I believe it is better to take more time and do it this way. It is a fool proof way to set the valves. Just remember that you dont want to over tighten them.Just enough so that the push rod cant go up and down. It takes a light touch. Some of the valves are going to look like they are flopping at rest but dont worry, when the engine starts and the hydraulics pump up the lifters and the engine heat expands them, youll be fine. This should get you going if you have any questions or this doesnt make sense, give me a call at 978-479-8319. I can try to explain it different.

After you get the motor up and running, if you hear any ticking sounds and think the valves are too loose there is a very simple fix for this while adjusting them. Best way Ive found yet..


GOODLUCK.

MARK
TOOFUN

[toofun]

hEY mtuck, How did it work?

Mark
TOOFUN

[Steve Chryssos]

New carburetor or not, it just sounds like a stuck needle & seat to me.

[cad]

Check this before you go thru the valves.
Gas spitting out the top of the carb could be timing, but is also caused by the floats stuck or needle and seat is stuck.
If the timing were that far off, it probably wouldnt idle even to 1500, let alone start.
Take a wooden hammer handle or medium screw driver handle and tap gently on the top of the float adjustment screws while the engine is off and again while running. I had the floats hang up one time recently after a quick jet change.
Gently=about twice as hard as you would tap on a pop can that was shook up.

Vacuum leaks could be from the large rear hose attachment port, generally used for PCV, or the top, righthand side where the vacuum advance should be connected(ported vacuum), or at the base of the carb in the front where the transmission vacuum is sometimes connected to(full manifold vacuum).

[Steve Chryssos]

Yeah, the old hammer trick is nice, but frankly, it's not that hard to pull a needle & seat and check it. Even on a new carb, a tiny piece of gasket material could get trapped between the needle & seat and the hammer tap might not help. I'd hate to think that the needle & seat assembly might be ruled out as a potential problem just because the hammer tap didn't solve the issue.

Also you should be able to see fuel pouring out of the vent tube and into the engine. But be super careful while checking since fuel can spit back at you.