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Diagnose good or bad carb

S

sald

Member
I have been through my Farmall A Zenith Carb 9749A/48616DC three times now, and I am finding that idle screw settings have very little effect on the way the tractor runs. Additionally no matter what I do with the main jet, it only makes a difference when almost completely turned in. I would expect air fuel mixtures would be more sensitive (I have a lot of experience with carbs from outboards to lawnmower to V8s) I am almost tempted to buy a new carb slap it on and if it behaves the same way then return it. What would be a litmus test for a "bad" carburetor?
 
One of us is likely to have a carb that works. Ask. A broken off load screw, or modified load screw seat are possible issues with your description. An Idle air adjust screw that fails could be due to a throttle plate not centered in the throttle bore, and thus not correctly aligned with the Idle port. Jim
 
When one cleans theses carbs on tractor one has to do so with carb cleaner to soak them in plus spray carb cleaner plus a small piece of wire or as I use a torch tip cleaner tool to poke out the passageways. Idle screw has very little effect and in is rich out for lean at idle only. Main jet if adjustable one should be able to shut ti down by screwing it in and get black smoke if you open it up to far if and only if all the passageways are as clean as they should be
 
I went thru it in detail, removed everything that could be removed. Used torch cleaning wires blew air and soaked. I don't believe it is clogged but will look at the plate to see if it is center.
 
(quoted from post at 00:08:50 07/23/19) I went thru it in detail, removed everything that could be removed. Used torch cleaning wires blew air and soaked. I don't believe it is clogged but will look at the plate to see if it is center.
Click to expand...

We rebuild them and send them all over the country. Always guaranteed to run great and you wont have to do anything but bolt it on and go. Our carbs are machined and fixed in everyway possible. New bushings, threads fixed, tops flattened, new high quality kit, etc. They are tested and adjusted before they leave too. As long as your tank is clean, you're good. If you're tired of fooling with it and interested in sending yours in as a core exchange, give me a shout. [email protected]
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So... I am getting smoke with the needle out 3 turns. If I go in more I start to get a little rough (at idle) I get the smoke for an instance just as I push up the throttle but never any smoke at any other time really. Because I don't put the tractor under a load I try to keep it as lean as possible because this carb seems to be on the rich side. I guess Zenith believes in "fat is where it at"?
 
(quoted from post at 00:57:07 07/23/19) So... I am getting smoke with the needle out 3 turns. If I go in more I start to get a little rough (at idle) I get the smoke for an instance just as I push up the throttle but never any smoke at any other time really. Because I don't put the tractor under a load I try to keep it as lean as possible because this carb seems to be on the rich side. I guess Zenith believes in "fat is where it at"?
Click to expand...

We always set the load needles at 2 1/4 turns out.
 
Idle jet you set at about one turn out and leave it. Main jet you have it at a work stage and adjust it NEVER adjust the main at idle
 
Can you elaborate on this? "Work Stage" How do you adjust?. I have found documentation online but would like to hear how you suggest.
 
(quoted from post at 11:08:51 07/22/19) I have been through my Farmall A Zenith Carb 9749A/48616DC three times now, and I am finding that idle screw settings have very little effect on the way the tractor runs. Additionally no matter what I do with the main jet, it only makes a difference when almost completely turned in. I would expect air fuel mixtures would be more sensitive (I have a lot of experience with carbs from outboards to lawnmower to V8s) I am almost tempted to buy a new carb slap it on and if it behaves the same way then return it. What would be a litmus test for a "bad" carburetor?
Click to expand...

When the adjustment screws have very little effect, or NO effect, the carburetor is NOT clean. Get a can of aerosol carb and choke cleaner. Stick the nozzle into a hole and spray. The spray SHOULD come out of another hole somewhere. Every hole has an opening somewhere else.
 
(quoted from post at 02:16:42 07/23/19)
(quoted from post at 11:08:51 07/22/19) I have been through my Farmall A Zenith Carb 9749A/48616DC three times now, and I am finding that idle screw settings have very little effect on the way the tractor runs. Additionally no matter what I do with the main jet, it only makes a difference when almost completely turned in. I would expect air fuel mixtures would be more sensitive (I have a lot of experience with carbs from outboards to lawnmower to V8s) I am almost tempted to buy a new carb slap it on and if it behaves the same way then return it. What would be a litmus test for a "bad" carburetor?
Click to expand...

When the adjustment screws have very little effect, or NO effect, the carburetor is NOT clean. Get a can of aerosol carb and choke cleaner. Stick the nozzle into a hole and spray. The spray SHOULD come out of another hole somewhere. Every hole has an opening somewhere else.
Click to expand...


Rusty is correct.
 
Work stage as in you have the RPM up where you would have it if your going to work it. Then adjust the main so you do not have black smoke but you still have good power
 
Where would the place to be to "ask"? Chase offers a great service but I do not wish to get another carb and find out it performs the same especially when we are talking a nice chunk of change. If I buy a new one online that has a return policy I can determine by comparison if there is in fact something wrong with my carb. I can then make an educated decision.
 
Start a new Thread here asking to borrow a spare carb. I do not have one, so I can't do it. Pay the shipping both ways. Jim
 
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