51 G backfiring at low RPMs

Dan Davidson · Jan 11, 2009

When I idle down my G it pops loudly (backfires) at low RPM"s. Pulls nicely under a load, but I need to pull out the choke a little at idle...this seems to help it. Thinking I need to set the carb up better. Any ideas? Where is a good start point on those carb adjustments? Or could it be somthing else?

Anonymous-0 · Jan 11, 2009

Do you have a magneto or ditributor? With either one it needs to be statically timed so the flywheel plug fires at TDC and not later. If you have a ditributor be sure the centrifugal advance mechanism is not stuck in either the fully advanced or fully retarded position. Check for vacuum leaks where the carburetor bolts to the manifold and where the manifold bolts to the head. Does the carburetor respond to turning the idle screw? Screwing it in should kill the tractor and opening it up hould make it smoke at slow throttle(slow idle). If not responsive the carburetor needs to be taken apart, all the brass plugs removed and the passages(including the "secret" passage) cleaned with the appropriate drill bits. Let us know what happens.

Dan Davidson · Jan 11, 2009

It does not respond well to adjustment on the "idle" screw. I was running it tonight outside and I can see the gasket between the carb and manifold is missing a piece....probally blew it out when it backfired. It does not have a magneto. I will remove the carb and try to clean it all up. Still wondering where to start with on those external adjustment screws. Where is the "secret passage"?

johndeereman · Jan 11, 2009

if my memory serves me correctly its 1 1/2 turns on idle and 2 turns on load this is just a starting point all tractors are different this should be close enought to get it running also you might need new plugs after the gasket ordeal

jd b puller · Jan 11, 2009

(quoted from post at 16:08:05 01/11/09) When I idle down my G it pops loudly (backfires) at low RPM"s. Pulls nicely under a load, but I need to pull out the choke a little at idle...this seems to help it. Thinking I need to set the carb up better. Any ideas? Where is a good start point on those carb adjustments? Or could it be somthing else?

Set the carb where "johndeereman" told you to start. None of this will matter if you have an intake leak though....

Dan Davidson · Jan 11, 2009

I removed the carb tonight After loosening the bolts I discovered the actually body of the carb is cracked and broke. One "ear" and piece of casting has broken off the carb housing thus explaining the major air leak at the intake....I can't believe I couldn't see it but it was on the backside of the carb where it bolts to the intake........time for some JB weld or Devcon?

Duane Larson · Jan 11, 2009

Dan,
Well, that is tough luck. A broken flange casting really needs to be brazed (or welded) back to the carb. Once the air intake (and just basically vibration from the running engine) is connected, epoxies likely will not do the job. Whoever does it needs to have done this type work before - After beveling the carb castings to be brazed, I bolt the carb and broken ear down to a steel plate template with an access hole cut that allows brazing from both sides. Otherwise, as brazing cools the ear will warp - bolting prevents this problem. If done properly, it is hard to tell it has been repaired. I assume the broken ear is one of the manifold ears - if it is the one with the holes drilled for access to brass plugs, those holes have to remain after the repair job is done - and they are not perpendicular to the front face of the flange.

51 G backfiring at low RPMs

Dan Davidson

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Anonymous-0

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Dan Davidson

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johndeereman

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jd b puller

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Dan Davidson

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Duane Larson

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