172 gas Lugging under light load

Im working through one small maintenance and
repair after another in this 1959 871.

Tractor starts. Ensured good fuel flow. Have not
cleaned carb but opened drain plugs an ms carb.
Spark Plugs are about 13 years old.

While working on the FEL when lifting forks with no
weight the motor lugs and knocks and almost shuts
down.

It was doing this in shifting gears too. Its an SOS.

Advice? Is it timing? Or should i pull spark plugs
and put new ones in? Pertronix on it too.
 
Those motors run so smooth an engine can be missing on one or even two cylinders and you won't know it until you put it under load.

Using insulated pliers made for this purpose, pull the plug leads off one at a time and verify the idle speed drops for each one.
 
Copy. Just dropped in 5 quarts of oil and now need another trip to the supply store to get an oil filter wrench that fits. Aaargh! 4 trips today for one small part after another. Just checked wires on spark plugs plugs and cap. No. 4 cylinder wire on cap clicked in. That could be the culprit. Will start tomorrow with new oil filter on!
 

A slightly too tight first band in the SOS will do that. Try going through the adjustment procedure in your manual. It is not difficult.
 
Yes. Question: would that transmission band have
an effect when just using the hydraulic pump for the
FEL? And in neutral?
 
(quoted from post at 16:44:24 05/06/19) Yes. Question: would that transmission band have
an effect when just using the hydraulic pump for the
FEL? And in neutral?

YES IT WOULD. When I had that problem it would run good for a few minutes then the load would come on very strongly.
 
Sounds about right. Thanks for your help and to everyone else who has responded. Will dig into the manual and see if I can make adjustments.
 
(quoted from post at 05:06:07 05/07/19) Sounds about right. Thanks for your help and to everyone else who has responded. Will dig into the manual and see if I can make adjustments.

Murray, I believe that when I did the bands that it called for tightening to a specific torque value then backing off so much. At the time I got to the torque value, but then got called away, and when I came back I had forgotten about the back off part. It took me a few hours screwing around to correct it, because like you I wanted to blame it on the motor rather than the transmission.
 
Hi. I read the manual. It wasn't clear about Band 1 adjustment in detail and I need to ask:

To adjust Band 1 to loosen the band (and load on the motor) is the set screw turned counter clockwise? And what would you recommend for starters? 1 revolution? 1/2 turn? etc?
 
might be super lean, and / or running on reduced cylinders. Lean could be a fuel flow issue.. and may be why it is stalling under hydraulic load.

Does some level of choke help it during these tests?
 
I'll get back to you on these questions. I opened the drains on the carb, cleaned the sediment bowl, and adjusted the set screw on the top pf the carb by closing it down then backing it off 1.25 turns. Now it starts better without full choke and runs better without holding the choke lever out.

I checked the wires on the cap and plugs and the cylinder closest to the radiator (no. 1 or 4?) clicked in on the cap. Restarted the motor but it continues to operate with what seems like a loss of initial power - as if a cylinder is not firing. But I won't know until I test the spark by pulling each wire.

I haven't pulled the plugs yet to see their condition as well. Will have to do this after work today (and check gap).

Question: The brass drain on the bottom of the carb? Has a screw or needle valve on it. Does that help with fuel flow into the carb? There is another drain plug too. I opened both. THe brass plug with set screw or needle valve had good but not great flow.

thanks for asking....
 
1.25 turns out on the main will, IMHO, always be lean.. open it more.

do a test and see if any plugs affect rpm more than others.
 
Runs fine without choking. Shuts down and slows with choke pulled. Saw a drip under tank. Noted perhaps a rubber fuel line connected to fuel valve. Its soft and kinked. This nay be the culprit. Need to pull tank and solve drip and replace line or rubber fuel line connector.
May be cause for lean symptoms.
 
To get back to you after working more on the tractor yesterday. Yes. Some choke helps the RPM's. I opened the main needle valve two plus turns too. But with the choke slightly pulled there is a sweet spot where the motor RPMs increase and seems to have more power.

I'm assuming that some choke is needed with a lean fuel mixture. Correct? and with a kink in the rubber fuel line just past the fuel shutoff valve I'm thinking that may be the issue. I ordered a correct fuel line and shutoff valve for the 871. Will replace as soon as it comes in the mail and keep my fingers crossed.
 

Murray, while getting your tractor to run well is good, it will not make the load that the SOS is putting on it go away. Here is the band one adjusting procedure, slightly condensed: It is on the left, approx. three inches below steering pedestal. First, with the engine off, and traction disconnect uncoupled, hold the screw with a screwdriver and back the lock nut off two full turns. Then with a screw diver in your torque wrench, (I bought a set of ratchet screwdrivers for this job), tighten the screw to ten foot lbs. Next, back the screw out one full turn. Now, start the motor, and move the selector to 3rd speed, hold the screw and tighten the lock nut to 20-25 lbs.

When I was adjusting mine, and got distracted, I skipped the back off one full turn step. I spent at least a day tying to correct a problem with the motor before I went back to the transmission. It would start up and run OK for a minute or two the first time, then it would suddenly lug way down and stall. Once it had done this, on successive starts it would lug down much sooner.

Replacing that old soft fuel line is good. You may not be able to see the gold plating on a new one though, LOL. I replaced just the rubber part of mine with some rubber gas line. The drip does not affect your tractors ability to run well even under full load.
 
kinked line sure could be causing a fuel stoppage. choke just makes the carb try harder to get fuel.
 
This helps a lot. Thanks for helping me on this. By the way, I live in Shelburne, NH just east of Gorham, NH and near the Maine line.
 
(quoted from post at 09:16:19 05/09/19) This helps a lot. Thanks for helping me on this. By the way, I live in Shelburne, NH just east of Gorham, NH and near the Maine line.

Murray, I was borne and raised in Lancaster and my younger brother lives in Gorham.
 
Finally was able to spend part of the morning replacing the fuel line, plugs, and tranny adjustment.
Thank you for posting this condensed version of the Band 1 adjustment. Tractor is running better
under load - some minor tweaking is needed, but i made a lot of progress on the performance of
the loader and transmission. Thank you.
 

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