Garden Tractor Forums banner
1 - 20 of 25 Posts

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
Discussion Starter · #1 ·
Hello everyone, I finally got some time to try and figure out why my MF12G dies when I engage the cutting deck but have not come up with a reason. It drives around fine without the deck engaged. I pulled the deck and there isn't a bunch of debris wound around any of the blade hubs, the gearbox seems ok and turning the whole deal by hand, I'd say for what it is it turns pretty well.

The engine is a Tecumseh HH120 and may be original from 1975. I felt the spark plug color looked ok but I did a compression check anyway. Is 95 psi an indication that the engine is in need of an overhaul? Seems like kind of a low number to me, but I don't really know what is good on one of these.

Thanks in advance for any help!---DAC
 

Attachments

  • Like
Reactions: larryd

·
Electric Tractors
Joined
·
5,639 Posts
The first thing that comes to mind is too much resistance somewhere when the deck is engaged, could be 1 thing or several things causing a bit of drag that adds up.

2nd thing would be lean fuel mixture the plug looks good for sure it's not running rich but maybe 1/2 turn out on the high speed main jet might make a difference. ???
 

·
Tractorholic
Joined
·
3,097 Posts
  • Like
Reactions: larryd and MFDAC

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
The first thing that comes to mind is too much resistance somewhere when the deck is engaged, could be 1 thing or several things causing a bit of drag that adds up.

2nd thing would be lean fuel mixture the plug looks good for sure it's not running rich but maybe 1/2 turn out on the high speed main jet might make a difference. ???
That was my first thought too, DH1, I figured that a wad of wire or twine was wrapped around a hub but everything looks normal. Bearings and gearbox seem ok. It spins well, can't do it with a finger you know, but it don't take much manual effort. Next will be to try to tune the high speed jet better then.

95 would be good, even high-ish... there's a compression release on most of these

Really hard to find compression for sure.
Yeah I was wondering about that. I remember when I was racing B/S 5HP go-karts that we were told that a compression test wasn't very accurate as the cams had a compression release ground into them. I guess maybe an overhaul may not be what I need, hopefully!

My vote is also for too lean of a fuel mixture. When a load is applied such as engaging the deck - the governor slams the throttle open all at once and the engine just doesn't have ample fuel to run so it stalls out. ?????
Well Gtractor, that will be my next thing to try to get tuned. I do know the fuel flow to the carb is good, I had the carb off a couple weeks ago and it was clean as could be inside and I checked with the bowl off that good flow came from the tank. I did tweak the idle mixture and high speed screws then by ear but must have missed something.

Thanks guys!---Later---DAC
 
  • Like
Reactions: larryd

·
Super Moderator
Joined
·
14,167 Posts
Any safety switches on the PTO of those tractors. If all else fails it may be worth checking for a problem there.
 

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
Discussion Starter · #9 ·
The PTO idler pulley, the one on the pedal you use to engage the mower deck, can give you fits. I'd double check that. You could also have an issue with timing, that one gave me fits with my massey 12. Here is a link for that.
http://gardentractortalk.com/forums/topic/13926-tecumseh-engine-lacks-power/
I didn't get time to reply last night, you must have posted while I was typing. I did run a search before I posted but didn't see that one for some reason. I will read it tonite. I have just put a new belt on that idler pulley the same day I started having this dieing issue and broke the starter, if any of you remember that. It had done the dieing deal a couple of times before but then would work ok though.
I posted a couple pics of the new belt disengaged and engaged.

Any safety switches on the PTO of those tractors. If all else fails it may be worth checking for a problem there.
There is a a switch right there by that pto idler that doesnt seem to contact anything, and the wires are messed up. I unplugged and it still did the same thing.

Sounds like a voltage issue IMO

larryd
I will check on that too! It does feel like a car or truck running only on battery power till the battery dies, but it kinda feels like running outa fuel too--can I make this any more confusing??-LOL!
No noticable sputter or backfire to speak of it just starts losing rpm till it dies.

Thanks for all the help, folks! I better do some reading then try some of these helpful ideas. I may not get to really dig into it again till the weekend but I will try.

Later---DAC
 

Attachments

·
Tractorholic
Joined
·
3,097 Posts
Yes, that is the pulley. When the PTO is disengaged, the deck rotates fine. When you engage the PTO, you don't expect the deck to be able to turn the engine. But if the idler pulley is frozen, it will put a big load on the engine when you engage the deck. Hard to find without specifically trying to turn the pulley.
 
  • Like
Reactions: MFDAC

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
Yes, that is the pulley. When the PTO is disengaged, the deck rotates fine. When you engage the PTO, you don't expect the deck to be able to turn the engine. But if the idler pulley is frozen, it will put a big load on the engine when you engage the deck. Hard to find without specifically trying to turn the pulley.
The idler and the drive pully both spin real free so that isn't the problem. I re-tweaked the carb last night, put the cutting deck back on and installed a new spark plug. It started fine but it filled the shop with smoke, and was still dieing 15 seconds or so after engaging the blades. It sounds just like that thread you linked me to, but no knocking noise. It always would use a little oil everytime I mowed, having to top it off after 6-8 hours of operation. The smoke was pretty bad this time tho. Think I will pull the head and assess things there. Sure didn't think by the plug color that it was using an exessive amount of oil, but maybe it has just gotten worse. The battery voltage was 12-13 with the engine off and 14.4 with it running.

I did see the link to the parts supplier on that thread that has the parts for this engine too. Thanks again.

Later---DAC
 

·
Member
Joined
·
129 Posts
It might be worth checking the carb again - the idle circuit is not easy to clean. If the main jet needle is backed out anything more than 2 turns, it might be that the carb has been tuned to run without the idle circuit working (i.e. with the idle rpm stop opened up a bit and the main needle opened up a lot - that allows the engine to idle, but it will bog when it comes under load). It's fairly easy to check how far out the main needle is sitting and that might give you a clue, since the Walbro carbs seem to run well close to the recommended initial setting of about 1 1/2 turns out on the main needle when the idle circuit is working properly.
 

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
Discussion Starter · #13 ·
It might be worth checking the carb again - the idle circuit is not easy to clean. If the main jet needle is backed out anything more than 2 turns, it might be that the carb has been tuned to run without the idle circuit working (i.e. with the idle rpm stop opened up a bit and the main needle opened up a lot - that allows the engine to idle, but it will bog when it comes under load). It's fairly easy to check how far out the main needle is sitting and that might give you a clue, since the Walbro carbs seem to run well close to the recommended initial setting of about 1 1/2 turns out on the main needle when the idle circuit is working properly.
I took your advice and double checked the idle mixture screw and I had it at 1-1/4 turns out. I did pull the head and the aluminum is washed clean around the back of the piston and the corresponding area of the head. There were considerable crusty baked on deposits and areas wet with oil. The valves look great and have virtually no wiggle in the guides. The bore measures 3.48 before removing a slight ridge that appears to be mostly deposits and the bore is supposed to be 3.5 according to specs. I think I will roll the dice as for about 50 bucks I can get a rebuild kit that comes with the gaskets, seals, rings and a piston. Scroll down to HH120. If I had to go .020 over the piston is over $100!

http://www.psep.biz/store/tecumseh_rebuild_kit.htm

Thanks to DH1 for that link in the thread HowardsMF155 mentioned above.
Here are some more pics.

Later---DAC
 

Attachments

·
Electric Tractors
Joined
·
5,639 Posts
When you engage the mower deck do you do it abruptly or slowly? With the deck off the tractor have you removed the belt on the deck and tried to turn each spindle, pulley, gear box separately by hand?
 

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
Discussion Starter · #15 ·
When you engage the mower deck do you do it abruptly or slowly? With the deck off the tractor have you removed the belt on the deck and tried to turn each spindle, pulley, gear box separately by hand?
I just ease into it like lettin' out the clutch in my 58 year old pickup-LOL!
I did take the belt off the deck and turned and wiggled the spindles and gearbox. The bearing on the middle blade has just a touch of wiggle but everything spun freely.

I have been mowing with this tractor for 2 years so I think I had a pretty good feel for it.

Later---DAC
 
  • Like
Reactions: MH81

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
Discussion Starter · #16 ·
Hello everyone, time for an update. There were two problems with this engine so far and I have gotten the smoking situation solved and was able to mow long enough tonight to seat the rings on the new piston.
The old piston had about .020" of collapse in the skirt and it was slightly cocked in the cylinder. Fortunately the block honed out nicely with a minimum of metal removal.

GTractor and MFGray were right on in their thinking too, about the fuel mixture leaning out. The carb is clean but the throttle shaft has so much play that the choke needs to be 3/4 closed to run well. You can measure the play with a yardstick, not a dial indicator!-LOL The shaft is half cut thru and the bores in the carb are egg shaped. Gonna have to order a new carb, but they aren't as expensive as I expected. I mowed a half acre tonight with the choke 3/4 shut and the oil still looks fresh! No smoke in the shop when I was getting it going, except for a couple puffs from the assembly lube.

I got a pic of the piston damage. The scoring on the top ring land corresponds with the area where oil was washing the top of the piston and the combustion chamber. When I get a new carb I will show pics of how loose the throttle shaft is.

Later---DAC
 

Attachments

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
Discussion Starter · #17 ·
I re-torqued the head tonite and decided to do a compression test again with the new piston and rings. Maybe some of you remember before it was 95 psi. Now it is about 126. Now wether or not that means anything I don't know with the compression release potentially being a factor.

I decided to put a dial indicator on the carb throttle shaft too and it was .050". That's a pretty bad vacuum leak in my opinion. Got the new carb ordered tonite.

Here's pics.

Later---DAC
 

Attachments

·
Tractorholic
Joined
·
3,097 Posts
Thanks for the followup. I know I've compression tested two of mine and gotten right around 30. Whether that is due to compression release, or if the rings are just in that bad a shape, I don't know.
 
  • Like
Reactions: MFDAC

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
Discussion Starter · #19 ·
Thanks for the followup. I know I've compression tested two of mine and gotten right around 30. Whether that is due to compression release, or if the rings are just in that bad a shape, I don't know.
You're welcome Howard, from what I have read here, some of these engines have the compression release, and some don't. I guess if the 30 psi engines run, that's the main thing! If I remember correctly a lot of the B/S 5 HP engines we used to run on go-karts would test around 30 or 40 psi and they did have a compression release ground into the cams. Our rules required stock cams.

I have had a setback, Pat's Small Engines left a message on my phone that the carburetor I ordered is now discontinued. Probably going to have to hunt for a decent used one and that is a little scary price and condition wise I imagine.

Later---DAC
 

·
Only member from Western South Dakota!
Joined
·
1,771 Posts
Hey everyone, time for another update. I couldn't find a carb or any parts locally so I had to make something happen since having to run with the choke part closed wasn't going to hack it.

I decided I had to build some kind of bushing or shim to repair the throttle shaft and get the hole in the carb round again. The "speedy sleeve" kept entering my mind but far as I know they don't exist for this type of thing. To make a long story short, I measured a variety of pieces of tubing but everything that was close was around a quarter inch inside diameter, but I needed something a quarter inch outside diameter with pretty thin walls. What I finally found was a section of a broken car antenna from my daughters old Camry. I cut a little piece of the right size section with a tubing cutter, deburred it well and shoved it up the throttle shaft using some Locktite I had left from some automotive speedy sleeve installation, probably a vibration damper for the front main seal.

Then I drilled the carb bore out to 1/4 inch. Since the "speedy sleeve" was the same size a little clearance was accomplished by wrapping some 360 wet or dry sandpaper around a smaller drill bit and just taking a little time honing the bore till the shaft slid in tight but the spring on it would close it smoothly.

I put it on after lunch today, changed the break-in oil and went mowing! It ran great and I did the entire acre only stopping once when a twig tossed the belt on the cutting deck, in 95 degree heat.

So far so good, here's some pics of the carb work.

Later---DAC
 

Attachments

1 - 20 of 25 Posts
Top