Interesting fix on M carb - stalling up hill

JRSutton · Sep 17, 2012

Interesting to me anyways.

My friends M has had a problem for a while dying under load or going up hill.

It'd run fine on flat ground, but when going up hill (or working hard) it'd run fine for a minute, then just sputter and die.

It was pretty obviously running out of fuel.

I assumed the carb was blocked somehow and did the usual everything you do to check and clean.

Then I thought maybe there was a float problem, but everything looked good there - though I couldn't measure the height accurately at the time.

Then it hit me - that it might be running too rich - and sucking in fuel faster than it could be replaced - not because it wasn't coming in fast enough, but because it was being drawn out too fast.

We had actually richened it up a bit to try to solve the problem at first - so I think that just aggravated it.

I leaned it out quite a bit and that did the trick - runs fine now.

SO my question is - does that sound right?

I just didn't expect a carb to be able to suck out more gas than is coming in - assuming the input side is operating as it should. I mean - that's a lot of gas.

Kind of a "it works so why mess with it" situation now... but I'm wondering if the floats don't need to be adjusted to let more gas in.

How do you tell if it's running too lean? Just watch the condition of the plugs?

Janicholson · Sep 17, 2012

With respect, I think it was not leaning it, but dislodging some flake of crud from the main jet, or it had some crud in the line or shutoff valve that was dislodged. The load screw will richen it to the point that it will make black carbony smoke, but under load that still pulls pretty well. If turned it to lean it. it can make it respond poorely to throttle opening, but most of the fuel goes through a different (main) jet to make power. Jim

JRSutton · Sep 17, 2012

maybe - but it was pulled and cleaned and still kept having the problem. Not that that proves anything.

I suppose I could check it easily enough be turning it back out to where it was and see what happens.

We certainly turned it a lot in and out in the process - but at the time it was counter intuitive (to me anyways) to go what seemed very lean - I kept thinking "needs more gas"... so I never tried it turned in as far as my final adjustment.

I'll test it tomorrow to see if I can repeat the problem.

I'll post back after I test it.

teddy52food · Sep 18, 2012

I would be looking for a restriction before the carb.

rustyfarmall · Sep 18, 2012

Set that screw at 3 turns out and leave it there. If the tractor will not pull itself up a hill at that setting, there is something else wrong.

DanR · Sep 18, 2012

(quoted from post at 14:14:31 09/18/12) I would be looking for a restriction before the carb.

Start looking inside the tank and work your way down one piece at a time. The carb is at the end of the line.

JRSutton · Sep 18, 2012

I did start with the tank, flow was anemic, but gas line had a bad kink - made up a new one. Flow's fine now.

Thing is - I'm less concerned with figuring out what the problem is at this point. It's more a question of IS there a problem?

Tractor's running perfectly fine now - but I've got a nagging suspicion that I found a lucky balance of leaning it enough to not bog with a slightly restricted gas flow.

So my main question is: CAN an M carb draw more gas than is coming in IF the gas is flowing properly.

With the main jet completely out - under moderately heavy load - would it be normal to drain the carb enough to starve the engine?

Forget about how I SHOULD set it - I'm just wondering if it's physically possible to drain it in a worst case scenario.

OR does its emptying automatically mean the gas flow IS restricted? OR float level is too low?

Anybody know for sure?

Also wondering if there's a way to quantify a properly flowing gas line - from the tank. X number of gallons per minute or X time to fill one gallon - something like that.

if not - it might be nice to establish one.

I see the question of restricted gas flow come up so often here. Might be nice to have a real test (other than "looks good") to be able to cross it off the list completely when diagnosing a problem. This one looks fine to me, but maybe I'm wrong.

JRSutton · Sep 18, 2012

sorry - turning meant to ask if it should bog turning the mixture screw all the way out.

- can't edit - not using modern view.

JRSutton · Sep 18, 2012

That's kinda what I thought when I started into this.

Didn't think these things were all that tempermental, and was surprised leaning it helped so much.

So - that helps to confirm that I'm not done fixing it.

Thanks

rustyfarmall · Sep 18, 2012

(quoted from post at 07:35:30 09/18/12) I did start with the tank, flow was anemic, but gas line had a bad kink - made up a new one. Flow's fine now.

Thing is - I'm less concerned with figuring out what the problem is at this point. It's more a question of IS there a problem?

Tractor's running perfectly fine now - but I've got a nagging suspicion that I found a lucky balance of leaning it enough to not bog with a slightly restricted gas flow.

So my main question is: CAN an M carb draw more gas than is coming in IF the gas is flowing properly.

With the main jet completely out - under moderately heavy load - would it be normal to drain the carb enough to starve the engine?

Forget about how I SHOULD set it - I'm just wondering if it's physically possible to drain it in a worst case scenario.

OR does its emptying automatically mean the gas flow IS restricted? OR float level is too low?

Anybody know for sure?

Also wondering if there's a way to quantify a properly flowing gas line - from the tank. X number of gallons per minute or X time to fill one gallon - something like that.

if not - it might be nice to establish one.

I see the question of restricted gas flow come up so often here. Might be nice to have a real test (other than "looks good") to be able to cross it off the list completely when diagnosing a problem. This one looks fine to me, but maybe I'm wrong.

The answer is no. It would take a very seriously modified engine to be able to use up the gasoline faster than it can come in.

A 560 and even a 706 use basically the same carburetor as an M and neither of those tractors have a problem with starving out.

Anonymous-0 · Sep 18, 2012

how full is the tank. the sediment bowl up front is a poor design . if lessthan 1/4 tank the gas lays in the back . we had this happen on a H one time.

JRSutton · Sep 18, 2012

definitely full enough - first thing I checked.

Interesting fix on M carb - stalling up hill

JRSutton

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Janicholson

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JRSutton

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teddy52food

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rustyfarmall

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DanR

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JRSutton

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JRSutton

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JRSutton

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rustyfarmall

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JRSutton

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