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John Deere D110 with 19hp 540cc single cylinder B&G engine. MIA12859 Model Year 2015 Engine Family FBSXS.5402VL

240 hours on the run clock.
Head gasket replaced and valves adjusted at 100 hours.
Starts with no problem.
Idles perfectly.
Runs full throttle with the blades engaged with no problems.

Run it at full throttle without blades engaged, just driving around and the engine starts to stumble badly. No backfires. No smoke. Just periodic pulsing loss of power.

I've changed air filter, plug, fuel filter and oil/filter. Oil level is mid fill. No obstructions (or oil) in the vacuum line from the oil fill tube to the fuel pump.

Fuel pump is working (didn't measure volume pumped, but it was a good flow).

Carburetor solenoid tests good.

The little spring on the governor linkage is intact.

Fuel in tank is fresh (I've run 3 tankfuls of fresh fuel with no change in the situation).

I've now reached the point where I have to ask for help because I don't know what else I can try next to solve the problem. Any and all suggestions welcome. I really want to solve this myself rather than having to take it somewhere for service.

Ed

Recheck the valve adjustment.

Just to be sure,

they may be adjusted a little tight.

Thanks Fish - I'll give the valves a check. Looks like a rainy weekend here so that will give me something to do.

Some additional info. When I first start from a cold engine there is no problem. After it's been running a couple of minutes the stumbling starts at full throttle if there is no load on the engine. I've tried running with the gas tank cap off to see if it might be a venting problem, but that didn't make any difference.

Ed

spinningwood said:

Thanks Fish - I'll give the valves a check. Looks like a rainy weekend here so that will give me something to do.

Some additional info. When I first start from a cold engine there is no problem. After it's been running a couple of minutes the stumbling starts at full throttle if there is no load on the engine. I've tried running with the gas tank cap off to see if it might be a venting problem, but that didn't make any difference.

Ed

Click to expand...

Yeah, that would be the case with the valves being too tight.

at or near full load mixture issues will appear. That doesn't mean it is the mixture. First thing I do is think about fuel pump diaphragms, air filters fuel filters etc.. I also would check the valves again because the expand when hotter. Last - if the engine has a catalytic converter a partially plugged one will show up at full load. Good luck.

Fish said:

Yeah, that would be the case with the valves being too tight.

Click to expand...

Thanks for all the replies. As Fish first suggested, it appears it was the valve clearance. The specs I found for a B&G Model 33 R87 were

Intake 0.003" - 0.005" and exhaust 0.005" - 0.007"

I found the intake at 0.004" and opened it to 0.005". I found the exhaust at 0.006" and opened it to 0.007".

On my first test drive the problem appears to have been resolved. Woohoo!!!! I'll give it a real run later today and hope that it is all good.

I suppose I should just declare victory and move on, but I find myself wondering why this issue cropped up. I set the valve clearance at 100 hours about 18 months ago when I had to change a blown head gasket. It ran great for the next 120 hours after that. It started the stumbling at around 220 hours a month ago. Loosening the clearance seems to have solved the problem, but is the fact that they had to be loosened an indication of another problem lurking in the engine somewhere? Or am I just being paranoid and I should find something better to do than worry about problems that might not exist?

All thoughts welcome!

Ed

And again, thanks for helping me solve my problem.

I wouldn't worry too much, if it is running fine now.

Just keep the cooling fins clean, as well as the oil.

I always like to try the cheapest things first.....

Run it at full throttle too.

I had more time this afternoon and gave it a workout. The stumbling problem is still there. I had really hoped the valve adjustment had fixed it, but it seems not.

To review:

Engine starts right away.

Engine idles smoothly (whether it is standing still or driving sloooowly). It idles smoothly hot or cold.

Engine runs smooth up to half throttle (whether standing still or driving). It runs smooth up to half throttle hot or cold.

Above half throttle, within a couple of minutes of engine start, the engine starts to stumble. This happens whether it is sitting parked or whether I am driving around. I can stop the stumbling by engaging the mower blades. With the load from the blades engaged it runs as good as new.

Without the load from the engaged blades, I seem to be able to sometimes reduce the frequency of stumbling by slightly nudging the throttle past full into a slight choke position. But this doesn't always work, possibly because I can't reliably hit the throttle position that reduces the stumbling (or maybe it has nothing to do with it).

I spent 10 minutes driving up and down my driveway which is on an incline (5% grade). The stumbling would stop on the downhill part and resume on the uphill and level part.

There is no catalytic converter on the engine. I checked the fuel flow from the fuel pump and it seemed to be adequate, but maybe my visual identification of adequate is not what the engine considers adequate. Should I consider replacing the fuel pump or look elsewhere first?

I'm also going to check the valve clearance yet again. Just want to be sure that nothing changed since I set it this morning.

Ed

Now it starts to sound like a layer of dirty water in the bottom of your carb bowl.

Loosen the nut or solenoid on the bottom of the carb, with a small can, try to catch some of the fuel to look at.

Let it dribble a bit to get all of the water out.

Hi Fish - I had the solenoid out the other day to check and see if it was working. I caught most of the gas in a small cup and didn't notice any problems. I took the solenoid out again this afternoon and made sure I caught all the gas this time. The gas was clear and clean. No water, debris or anything.


Ed

Yeah, didn't cost any money to check it.

Water can sit in the bottom of the bowl, and it will run fine until you turn, stop, jiggle etc..,

Then a bit of water sloshes up and gets sucked into the engine.

So when it starts acting up, it will run better if you partially choke it?

This one doesn't have a separate choke control. It's integrated into the throttle control. If I gently start nudging up the throttle past full (into the choke zone) I seem to often be able to get to a point where it runs better. But it is really touchy. Not enough and it still runs rough. Too much and it starts to stall out. The difference between the two in throttle movement is tiny.


Ed

That tends to indicate a low float bowl fuel level a partially blocked main jet or partially blocked bowl vent.
In the top of the float bowl there should be a hole .
On most carbs it leads to another hole at the engine flange.
This is the hole that allows air to get into the float bowl so the fuel can get out.
When the throttle is open wider, the suction at the main jet is strong ( it gets called "signal " by wan#@$%" trying to sound superior ) .
Thus if the air vent is partially blocked it is strong enough to drag air in
When the "signal" is low there is not enough pressure to drag air through so the engine runs a bit lean
A stuck open reed valve on the breather can also divert a lot of air at lower speeds causing a stumble

When i get stuck I drag out the colortune ( a Gunsens product, Google it ) thus I can just watch what is happening in the combustion chamber

Problem solved.

I removed the carburetor. It was really clean inside. Almost looked new. I didn't see any debris or blockages, but I took everything apart and I blew everything out with compressed air. The main gasket was expanded, so I shrank it back down by boiling it for a couple of minutes and then putting it in the refrigerator for a couple of minutes.

Put everything back together. It started right away and ran great.

I never did identify the problem, but something I did in the process must have resolved it. Maybe some tiny bit of debris somewhere I couldn't see got blown out.

Just glad it's working again.


Ed