The Stovebolt Site Forums The Shop Area Engine Shop Idle Speed/mix Adjustments, Dies on deceleration

Hi, I've tried to adjust my rebuilt Rochester on my 216 to spec @ 450-500 RPM, but it seemed to want to die at this speed. In an effort to get it going I set it about 600RPM so I could take a drive around the block.

The truck died on me twice at stop signs... Is the a result of the "altered" idle setting, or should I be looking elsewhere? Fuel delivery/flooding...

It never did this before I got the carb and fuel pump rebuilt, so I'm at a bit of a loss.

Also, how much torque should I have on the carb to intake nuts? I was careful to use very little torque, maybe 1/2 a turn past finger tight. Didn't see a spec in the shop manual.

Thanks a lot!

Lee

The two nuts that hold the carburetor to the manifold take more torque than that. Use reasonable torque for that size of bolt.

If it is flooding, it will die at idle. Look to see if gas is running out at the bottom. It usually can tolerate more excess gas when the motor is cold. Also an incorrect idle mixture can cause it to die at idle.

Thanks a lot. Before I tightened the mounting nuts I worked the throttle and noticed that the bottom gasket was getting wet with gas. Is that flooding or just a result of insufficient torque? Probably a dumb question, sorry.

I proceded to tighten the mounting nuts and tried to start it up. The motor would fire but not run unless I gave it some gas and had the choke out a bit. After a few min it would only idle with the choke out. I turned the idle speed way up so I could get it to idle and then attempted to reset the speed and mix. Not sure if this is correct but it was all I could do at the time...


I bought a vac gauge and was able to get the hot idle speed down to 600 rpm with 18-20 in/hg. Any lower rpms than that it seemed really unstable at idle. Will the faster idle hurt anything? Or am I overthinking things?

Lee

So how does the mixture screw affect things? Usually the best idle mixture appears around 1 1/2 to 2 turns out from all the way in. Turning it in will at some point cause it to start to falter and then turning it out 1/2 a turn or so causes it to even out. One thing that will make the idle unstable is a worn throttle bushing. If you can wiggle the throttle plate so that the shaft moves around in the bore, then it is loose.

I'm about there I'd say. I had the gauge in my hand while I was turning the idle screw, like you said too far in and it would start to falter and the vac would start dropping. If I was fast enough, I could keep it running by backing the screw out. I just turned to the spot that looked the best on the gauge and ran well.

Not sure what that part is. Do you have to take the bowl off to check that?

Just went outside to see if I made a difference earlier today. After 2 attempts she fired up and idled well. I didn't have to choke it for it to run so I guess I didn't something right.

Lol I think I'm in over my head, but I'm trying.

Thanks again

nice truck, if it is running good now, dont mess with it any more..

That is a nice truck. I like the shot of it sitting in the field. I can see that on a calendar!

Agreed! Yeah, we were plowing food plots for deer last year when I took that picture. It definitely looked at home out there.

Lee

The mixture screw is what you were turning while holding the gauge. This adjusts the fuel to air ratio during idle and just off idle right before the main metering circuit takes over. As you went in with the screw you leaned out the mixture enough the engine couldn't run. Backing it back out the mixture became richer. As stated above, you should be in the 1 1/2 to 2 turns out from the seated position of the screw.

If its starting with out touching the throttle you are very close, a 1/4 turn either way should effect its starting, better out, worse in.

The throttle shaft is where the linkage hooks to, if it can be wiggles around a lot, then the bushings are worn out. No need to remove anything to check it.

Joe

Excellent info. Ill recheck this soon. Not sure if this makes a huge difference, but I noticed last night that my manifold doesn't have the thermostatic spring, must have rotted/fell off somewhere along the line.

Lee

The spring closes the heat valve in the exhaust manifold to direct exhaust heat right up under the carb for faster and more efficient cold starts. As the engine warms, the spring relaxes and backs off the valve. You still get some heat to the carb base with it not working, and in some warmer climates, you can get away with that all year long. If you are in colder climates, you should see about getting it fixed or replaced. Start by working the valve in the exhaust manifold. Use lots of solvent and slowly work it each day till it becomes free enough to rotate. Some of the venders in the LINKS above sell new springs.

Joe

Thanks. That's what I read when doing a search. I'm going to try and free it up over the next week or so. Hopefully I can get it free and a new spring installed.