JD A spitting back through carb

Anonymous-0 · May 3, 2013

Need some advice. Have a 1952 A we pull. Had some motor work done. Striker crank, ground cam, and bored. Head work with bigger valves and stiffer springs. We just put together and timed everything up. We've timed many two cylinders in our time. Nothing else was changed on tractor. Went to start tractor for first time and she started right up. Problem was is that it us spitting air/fuel back through the carb. We checked all the timing again, it was all ok. Any ideas of what to try next? We are lost. Valve train seems to work accordingly, distributor is timed properly with flywheel LH impulse. Could it be ignition, valve??? We out of ideas.

Mike N Mo · May 3, 2013

What is the cam intake & exhaust durations, lobe seperation, and intake centerline specs? Did you use a degree wheel to time the cam? Too much intake duration, or a cam retarded too much could have the problem you describe.

Mike

bill finn · May 3, 2013

apply air pressure to cylinders through the plug holes, make sure valves are closed(easier to just close the vales by backing off adjustment screws). The piston will move to the bottom of the stroke, then listen for air escaping thru intake or exhaust or breather. If air is coming thru carb, you have a leaking intake valve.If its a simple miss fire, some plugs work better then others. Someone with more experience than me could probably make a suggestion.I would also pay close attention to float height, needle and seat and fuel quality.and last spray carb cleaner around intake manifold and listen for rpm changes.
Good luck

old · May 3, 2013

May sound funny but if you choke it some does that hurt or help??? If it helps then it is running lean. Also make sure the valves are set correctly and are seating as they should be. Been almost 40 years since I last ran an A but back then it out pulled a Ford 5000 since I pulled a hay wagon in half with the A and the ford would only sit there and spin its tires. Much longer story but a funny one

teddy52food · May 4, 2013

You have to keep the piston at TDC. if it goes to the bottom, the exaust valve will be open.

RandyB(MI) · May 4, 2013

Your post says "spitting air/fuel back through carb". It does not say backfiring through the carb or fuel running out of the carb. Given that description there has to be an intake valve that is still slightly open or not seating properly when the piston is comming back up on compression. Should be easy to tell with rocker cover off and turning. You can't turn a 2 cyl JD enough rpm to need that kind of cam timming that would have the intake still be open on the start of compression stroke. It's not an Indy car.

JD A spitting back through carb

Anonymous-0

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Mike N Mo

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bill finn

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old

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teddy52food

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RandyB(MI)

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