B Carb

The tractor runs, but only with the choke mostly on? It also backfires when throttle is reduced. Any ideas?

~Though it probably wouldn't hurt to do the fuel flow test mentioned below.

~Then make sure the float top is parallel with the top float bowl gasket surface. [if the float is set too low it will effect metering]

~To answer your question...the main nozzle is the load & fuel metering system for off-idle through full load. There are holes in the side of the main nozzle that must be open & clean as that is what mixes the air with the fuel for the load fuel emulsification before it is fully mixed with the incoming air at the venturi.

~That main nozzle is just held up into it's bore with that spring & doesn't move when in operation. [it must stay sealed at the bottom to work correctly]

~You probably should pull the main nozzle out & verify the little side holes are clean. To pull it out just use a sheetmetal screw, or run a tap into the bottom of the nozzle [no more than 3/8"] then either clamp a pair of vice grips on the screw & rap down on it with a hammer, or, if the hole is threaded with a tap, run a piece of all-thread in the tapped hole then use a couple of washers & a nut to pull the nozzle out [CAUTION: don't push or pry on the top of the load nozzle or it won't work correctly]

~If you decide to pull the brass plugs & clean the idle & main passages [probably will have to for that carb to work correctly] you might have to heat those passage blocking brass plugs until dull red then let cool to get them out without damage. Once the plugs are out, run a wire or even a drill bit down those passage bores as blowing compressed air & carb clean down those passages won't help at all. There are many small holes & passages that could be blocked & they all have to be clean fro that carb to operate correctly. Roberts Carb [Phone: (712) 262-5311] should have the correct 6" drill bits to clean those passages. If you want to go through that carb let me know & I will send you a picture showing the correct passages & locations that need cleaning.

~Once the carb is cleaned out, start with the load needle backed out 1 turn from seated & the idle needle backed out 2 turns from seated & see how it runs, if it still doesn't run correctly post back or give me an E-Mail...

You should first try the standard fuel flow test cuz the nozzle may be okay. Open the carb bowls lower drain cock and with the gas on at the sediment bowl, gas should run out there continuous (try it at least for 2 or 3 mins) about the size of a lead pencil lead.

If not, remove the fuel line from the carb and gas should flow out strong and continuouas there the size of the lines ID. If there is good flow there (but not at bowl drain), the carbs side strainer and/or needle valve n seat may have dirt or a restriction a common problem. You might remove the side strainer top nut and cap and clean that all out (it gets crud accumulated in there which can clog/restrict the needle/seat), but if you dont have a new top gasket, she may leak there.

If not, (no good flow out the line) remove the sediment bowl and gas should run out the 2 lil side holes to try n fill the glass bowl strong and continuous.

If not, there may be crud up inside the tanks inlet pipe or screen if it has one left.

NEXT

Have you adjusted the carbs top load and idle needles????? try richening them a tad by turnign them out and see if she runs betetr then????? ??? Initial rough in settign is 1 out for load and 2 out for idle.

NEXT Do you suspect any vacuum leaks (air being sucked in leans the fuel/air mixture) like around the carbs throttle shaft bushigns or elsewhere around the manifold base??? A spray of carb cleaner or wd40 or an unlit propane torch when tractor is runnign would maker her speed up if theres a vacuum leak anywhere.

FLOAT SETTING; Do you have an idea as to where the float level is set??? I set them where the fuel is shut off when they are approximately level. If the float turns the fuel off way too low, it could cause the problem.

FINALLY BACK TO NOZZLE (if all tests above pass and theres good fuel flow at ALL places and adjustments dont help and float level is okay)

If you cant get it out (sounds like it may be clogged) you have to drill and tap threads inside its small center bore and then use a washer and nut(s) to pull/back it out. It may well have some of it small side holes clogged, be sure and clean ALL them out and I light wire brush and sand it all nice n clean n smooth and be sure all the lil side horizontal bore holes are open.

You might take a look at the air cleaners bottom bowl and also check to se if the choke butterfly plate is tight on the shaft and moves and stays properly in accordance with where the external settign is.

IGNITION Althouhg it sounds like fuel starvation, to be safe, clean and inspect the plugs or replace them and check the points gap and if gray oxide copated clean/polish them and replace if pitted or burned or carboned up bad.

Try this and let me know what you find.

John T Nordhoff in Indiana