NAA carburetor adjustment

joe201

Member
I'm trying to get tractor running it will start but runs rough. PO put new carburetor on tractor but I suspect the adjustment screws have been turn. How many turns out should the screws be turned when the carburetor was new.
Thanks Joe
 
1.5 turns from the stop is a good general rule of thumb if you don't have a manual with explicit recommendations -

ignition system in good shape? air cleaner serviced? good fuel flow thru the carb? (remove the drain plug and see that there's a steady stream) no vacuum leaks? get it running and check the dwell and timing - fussing with the carb is done last -
 
I've got running but had fuel leak and had to order new fuel shut off assy and a few other parts from this site parts should be here today.Tractor belongs to a friends son and he is still in school and going to bushog for summer job. Its good to see a young man getting interested in tractors and actually work, so I'm trying to get him going.Thanks for you input and advice Joe
 
How many turns out should the screws be turned when the carburetor was new.

Pomester gave you excellent advice on troubleshooting the run problems. All I can add are a few steps on how to adjust as was your original question:

Initial setting should be 1½ turn out on idle mixture screw, and 1½ turns out for the main fuel needle. Start at idle speed (450-500 RPM) and let the engine warm to operating temp then, adjust the idle mixture for the highest, smooth idle 1/8th turn at a time. Ensure idle speed remains below 500 RPM while setting the idle mixture. After you make the idle mixture adjustment, then you can set the main jet for fuel requirements when running under load at WOT.

Keep in mind, the idle jet needle is an [u:c32d27e576]air control needle[/u:c32d27e576] so turning it in enriches the idle mixture whereas the power jet needle controls [u:c32d27e576]fuel delivery[/u:c32d27e576] and turning it in leans the mixture.

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A rough running engine may not be due to a bad carburetor. Having bad/wrong wiring for instance -got the firing order right? The original FORD NAA Tractor used the Marvel-Schebler TSX-428 Carburetor. The TSX-428 initial carb spec settings are MAIN = 1-1/4 Turns; Idle Air (side pointing) set at 1- turn out from IN seated position when cold; Idle Speed position is set when choke plate just begins to open. Carb adjustments need to be made at 450-500 RPM idle speed (observe Proofmeter) when engine is at normal up to temp heat range and often times performed a few times in order to get right. What type of 'new' carb is on it now? The original parts were designed to be rebuilt over and over and chances are the original carb simply just needs good cleaning and rebuild. This is another reason why one should avoid buying 'new' major parts sold today -most are junk from Cheena. A leaking Sediment Bulb Assembly should be addressed first. The usual culprit is the valve stem -p/n APN-9194, a $6 part and no need to replace the entire bulb. There is a rubber seal on the valve stem that eventually gets chewed up and thus causes the leaking. The next root cause of leaks is cross threaded fuel line ports and fittings. A special thread is used on fuel lines -7/16-24 UNS. Always start and tighten by hand before using a wrench and never force. Leaking gas is a huge SAFETY issue and needs to be corrected before anything else is pursued. Only use the correct steel fuel line and never copper, plastic, nylon, or aluminum. These N's DO NOT need an additional non-original fuel filter -they already have three in the system. If you still have the original M/S TSX-428 carb and you don't want it, I'll buy it -my email is open.

FORD N-SERIES TRACTOR FUEL SEDIMENT BULB VALVE STEM:
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Tim *PloughNman* Daley(MI)
 
What brand and model of "new carb"? Is it a Zenith, an
aftermarket Marvel Schebler look-alike or something else?
A picture would probably help.
 
Yeah, like Royse said pictures would help. Marvel-Schebler, later bought and owned by Borg-Warner Corp, was the original supplier to Ford, but they are no longer in business so no new ones are made/sold today. ZENITH (Holly too) was a Ford supplier going back to the Model A's and Early V8's, but I don't like them on my Ford Tractors. There are a few aftermarket companies that repop them today and I try to avoid those as well. They usually have aluminum bodies so they are easy to spot. M/S carbs have the name/logo cast on the bodies. Like I said earlier, problem may not a fuel/carb issue. Rough running can be an electrical problem. Have you verified the spark plug to cap wiring is right? If the timing is off, engine will run rough too.

TPD
 

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