The Stovebolt Site Forums The Shop Area Engine Shop Carb piston hole - what goes here? (picture)

Hey, anyone know what goes in this hole on the carb? I know the carb piston moves in and out due to vacuum but I don't know what what to do with it. When I bought the engine, there was a piece of rubber stuffed in there, but it fell out. When I plug the hole, the truck won't run. I can't find pictures or explanation for this.

Carb

That's a "vacuum break" piston bore, and the hole is supposed to have a flat steel plug pressed into the stepped end of the bore. Vacuum against the piston pulls against the automatic choke spring and helps open the choke slightly as the engine starts. If it won't run with the hole plugged, turn the idle speed screw clockwise to raise the airflow past the throttle plates.
Jerry

the missing peice looks like a silver convex lens you put it in the hole and hit it with a punch to lock it in place try the auto parts store in the help section they usualy have an assortment pack

Thats a car carb. Trucks with I 6 to 59 anyway all had a manual choke.

Where can I get the plug? I don't get the "auto parts store in the help section."

Anyone help me with this?
Cheers

What Dude means by the Help section. There is a line of auto parts called Help. They supply various popular replacement parts that otherwise are hard to find. Most parts stores handle them although they only keep a small amount of the items in the store. There is a catalog with a large amount of items. Theb store can look it up for you or I have the catalog at the shop & can look it up tomorrow. I know Carquest stores have this line & I have seen them in Advance stores. It seems you could cut a disc out of a piece of metal & super glue it in there staking it around the edges.

Thanks

I found part #s in the Dorman line. What is the diameter of it?

I got a plug and it fits perfect. Unfortunately, now my tuck doesn't run as well. 8 times out of 10 it will idle fine at a stop light. The other two, I'll push in the clutch, motor will come down to idle; then out of no where, the RPM's will drop. You can hear the advance try to catch it and it quits. Touch the starter and she fires up again.

I was at a car show today and during the idling drive through the park to my spot, it would do the same thing.

All because of the plug? There is no rhyme or reason.
Vacuum leak somewhere else maybe?

I would think you need to re-adjust your carbs idle and mixture screws now to compensate for the extra air that you've taken away by plugging that leak. You should be able to get it back running like it was before without too much trouble, if this is all that's going on.

I reset the throttle and mixture screws to no avail. It will run perfect, then the idle just falls out of it. When I pulled into my driveway the throttle pulsed and wanted to quit. I floored it and it sorted itself out.

The hard part is everything works perfect, set properly, then for now reason, the idle just crashes.

Like I said previously, its a 1 in 5 chance it happens, not consistent.

Hi, Lode51, one thing to check is the play in the distributor bushings. To check, set the point rubbing block on the highest part of the cam and then push with finger the cam away from the block and check clearance, then pull the cam towards block and recheck clearance and that will tell you how worn the bushings are. Maybe Hotrod will step in and say what is a usable difference is. I found this out with a 1950 ARIEL SQU. 4. When I would come to a stop it would idle between 0 and 2000 rpm. It had a point gap of .016" but I could change it by .022 with the above method. I had new bushings installed and then had normal idle speed.

Distributer bushings... hmm... never thought of that. I don't know why that would become an issue, the same day I put the plug in the carb.
Thanks