# MTD Yard Machine tiller/cultivator



## Dale1 (Nov 13, 2013)

The engine on this front tine garden tiller is very hard to crank using the pull cord. It's a 2 cycle 31cc engine, Model 21A-121R900, revO1. I didn't see a tag with the manufacturer's name on it. The problem is that it takes a great deal of strength to pull the start rope to TRY to start the enigine.

When I remove the spark plug, the pull cord operates smoothly as would be expected. However, with the spark plug in place, the engine can be 'turned over' 
but with a 'not normal' great pulling force. It seems strange that the compression would be so high it takes a significant amount of pull force to get the engine to turn over. 

I removed the muffler and the spark screen thinking that if they were blocked it might have something to do with the 'hard pull' problem. The muffler and screen were quite clean so it appears they have nothing to do with the problem.

I'd appreciate any comments or suggestions as what else could be looked at to resolve this problem.


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## paulr44 (Oct 14, 2008)

First, that unit is an MTD (the engine originally designed by IDC/Ryan which became Ryobi, then MTD bought 'em). Using the model number you posted, you can go here for the IPL:

http://mtdparts.arinet.com/scripts/...=Empartweb&loginID=mtddealer&Loginpwd=6922941

There are a number of reasons a 2-stroke can be hard to pull over. Plugged exhaust doesn't usually 'em make unreasonably hard, but they'll sound extra-quiet when pulling if they are plugged up.

An ign. coil rubbing on the flywheel. Bad main bearings. Clutch frozen in the expanded position which in turn means you're turning over all drive components when cranking. Wrong screw in a shroud and the tip is grinding the flywheel down (we see that here and there). Scored piston and cylinder.

As it pulls freely with the spark plug out, I can only offer two explanations for it being hard to pull with the plug inserted. That is, unless you're finding the plug is wet and the engine is getting hydro-locked, which is next-to-impossible on a 2-stroke, and surely you'd have fuel coming out the intake and exhaust. If that were the case you'd probably have related that to us in your post.

So, my reasons would be:

One would be excessive carbon buildup in the combustion chamber, resulting in excessively high compression.

The other is you've gotten older, and it just seems harder to pull (sorry, but I do see this with some customers).

Paul


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## Dale1 (Nov 13, 2013)

Thanks for your response Paulr44. I hadn't thought of the carbon buildup possibility. I'll give that some more thought. I need some more fuel line ( have a bunch of 2 and 4 cycle pieces of lawn and yard equipment ) and I think I'll take the engine down to the shop when I get some more and see if anyone there has any other ideas. Course they may say they need to do a diagnostic which they usually charge about $50 for. If so, I'll just take the engine apart to see for myself. 

The reference to the MTD site is very helpful...and appreciated.

No question I've gotten older, but fortunately my health, and strength, is still good. My strength 'ain't' the problem. As a very senior citizen I can still manage the old creosoted railroad ties single handed for garden projects.


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## paulr44 (Oct 14, 2008)

There are a number of fuel line kits out there that'll fit many MTD, Troy-Bilt, Craftsman, Poulan, Ryobi and other mass-merchant units. I use one kit, that contains two sizes of lines, one for fuel feed, the other being smaller ID for primer lines. I'll try to remember to get the number from my work PC and post it.

The STIHL 4-mix motors are a good example of carbon buildup creating excessive compression. Usually it's the valve adj. being too large, making the deko ineffective. After adj. the valves some of them still are hard to pull over, and it's due to carbon buildup. Some 2-strokes when heavily carboned will actually have piston interference, and with the plug out will have a hard-spot when cranking at TDC. Kind of rare, but not uncommon.

Paul


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## paulr44 (Oct 14, 2008)

I finally remembered to get the numbers. I use the ...599 kit most often as it contains a smaller OD/ID line that'll fit the tiny primer nipples on some box-store units. The lines in the kit are more than enough to do any one repair, often enough to do two.

POULAN OEM 530069216 FUEL LINE KIT 3/16 OD X 3/32 ID (2 foot of 1 size)
POULAN OEM 530069599 FUEL LINE KIT W/ 2 LINE SIZES (with length of 3/16 x 3/32 + length of the smaller primer line)
"Micro" nipple fuel filter EHP 530095646

And if this helps you or anyone for some Echo lines or box-store units:
Most units will use 3/32 ID, 3/16 OD Stens 115-327	THICK wall
Some units will use 1/8 ID, 3/16 OD Stens 115-331	THIN wall

I keep this and a lot of carb. information handy at work, in computer files. It helps not having to re-research shit like this.


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