Carburetor issues??!? Or something else?

[30aadoodlebug]

So the title of the post says it all. I went out to start my truck the other day, and the strangest thing happened: it wouldn't idle. In order to make the truck continue to run, I have to pull the throttle level down to bring the engine up to around 4000 rpm. The truck was running fine last week when I put it away, and now I have this issue out of the blue. I have done the basic troubleshooting: closed the mix adjust valve via the choke rod and opened it to where it should be on a Zenith; putzed with the needle valve a bit to see if that might be the issue; and lastly sprayed crab cleaner into the carburetor to see if it was just dirty. Les Andrews book says that it could be the float being to low, but where it was running perfectly last week, I don't think this is the issue. I put this carb on this past June, and it is a fresh rebuild from a well-known reliable shop.

Any thoughts would be much appreciated!

Jon

[Ron in Quincy]

Jon,

Sounds like the idle circuit my be plugged; the compensator jet in the bowl provides fuel to the secondary well which provides gas to the idle jet; if the idle jet is plugged, which only has a .021 opening, or the comp jet is plugged the idle circuit will not function. The fact that you can make the engine run at higher RPM indicates you are , at that time, running on the cap and or the main jet.

Ron Rude

[Brentwood Bob]

To see if you have fuel to the carb open the drain plug at the bottom of the fuel bowl of the carb. put a can under the carb to catch the gas. open the shutoff valve there should be a strong flow assuming the gas tank has fuel in it.
If that fails next try the gas line at the inlet to the carb. If you have good floe then the carb is plugged up and you need to clean the carb. tom endy has a good method available on the santa anita model a ford club web site under his technical articles.
Let us know what you have found and we can proceed.
Bob

[Brentwood Bob]

Or go with Ron's suggestion since the truck would run, but not idle.

[Tom Wesenberg]

Start the engine and since it only runs fast slap your hand over the carb inlet, and remove it before the engine dies. Let the engine rev again and repeat. Maybe repeat 4 or 5 times to see if you can clear the junk out. This worked well on Omni's in the 80's.

I usually say to snap the throttle open, then slap your hand over the intake, but your engine is already at full speed.

[30aadoodlebug]

Sponsored Links (Register now to hide all advertisements)

So I tried what both Ron and Tom suggested and there are a few developments. With Tom's suggestion, the engine evens out for about five seconds and then goes back to running rough. I will pull the carb off tonight and slap one of my tilly's on and take a look at the carb in my workshop. Concerning what you recommended Bob, I pulled the whole fuel system apart and cleaned it out before I wrote the post as this was my initial thought towards the problem. Also, when I bring the truck up the higher speed idle, the carb begins to "fart" with a popping sound every so often. Thoughts???

[Mitch//pa]

you mention it runs better briefly when blocking the air at the carb throat.. try metering the air with your hand allow some but not much and see what happens...
if it runs better that way you could be pulling air from somewheres else like an intake gasket etc

[SeaSlugs]

Originally Posted by Tom Wesenberg

Start the engine and since it only runs fast slap your hand over the carb inlet, and remove it before the engine dies. Let the engine rev again and repeat. Maybe repeat 4 or 5 times to see if you can clear the junk out. This worked well on Omni's in the 80's.

I usually say to snap the throttle open, then slap your hand over the intake, but your engine is already at full speed.

Works well on pushmowers with the air filter removed that are cantankerous and will only run with a bump of the primerbulb too!

[SeaSlugs]

Originally Posted by Mitch//pa

you mention it runs better briefly when blocking the air at the carb throat.. try metering the air with your hand allow some but not much and see what happens...
if it runs better that way you could be pulling air from somewheres else like an intake gasket etc

thats what im wondering too, sounds like a vacuum leak (dont have vac wipers do you?)

[30aadoodlebug]

Originally Posted by SeaSlugs

thats what im wondering too, sounds like a vacuum leak (dont have vac wipers do you?)

SeaSlugs,

No, I do not have any wipers (open cab, no windshield). The thing is, I inherited the truck from my father who had owned it since the 70s, and the vacuum connection off the intake mani has been open since then. This was also a consideration, but when I threw a piece of electrical tape over the connection, there was no change in the engine's actions.

[Brentwood Bob]

See what the takedown of the zenith shows. sounds like debris in the carb. Since you have gone thru the fuel supply side, next is the carb passages.
the popping could be carb, or intake manifold. See if the tillitson runs better.

[30aadoodlebug]

Sorry for stepping away from the thread for a few days, I'm in the middle of moving back into school for the coming semester. I pulled the Zenith off last night, and put the Tilly on: what a difference. The truck ran great at both an idle and also driving around back roads for about 20 minutes. I plan on breaking the zenith down tonight, and I will post what I find during the process.

Thanks to all of you who posted answers to my question!

[hangarb7]

I had this exact same thing on my car a few weeks ago. It was a plugged idle jet.

However, it was NOT plugged all the way and you could spray carb cleaner through it. But looking through it with a 10X jewelers loupe and there is something lodged in there that could not be blown out.

Replace with an off the shelf, brand new (unflow tested) idle jet from Snyders and the car runs great.

JackD

[30aadoodlebug]

Thanks Jack, upon inspection, the idle jet is clogged to beat the band. My plan is to refurbish the original because i just really dont want to put a repop in.