# Compression value for Tecumseh AH520 type 1574A



## skipper0802 (Dec 2, 2010)

Hello Folks,
After scrounging through the forum threads and through all the Toro service manuals that I've downloaded I still cannot find a reference value for compression. I'd like to quantify my old snowblowers "health" more than just pulling the plug and feeling the pressure squeak past my thumb.

Can anyone help with a number?

Thanks in advance,
-Eric


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## Basementgeek (Feb 7, 2005)

Hi and welcome to TSF :wave:

My book on Tecumseh does not show any either. (3-10 HP)

I guess if runs good, little to no oil use, I guess it is OK.

BG


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## skipper0802 (Dec 2, 2010)

Howdy! and Thanks


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## k2skier (Sep 30, 2008)

Is this a 2cycle engine? Roughly 75-85 if it is.


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## skipper0802 (Dec 2, 2010)

Thanks K2. Yes, it is a two-cycle engine. Would you mind telling me where you found that figure? I couldn't find a number anywhere so far.

-Eric


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## Basementgeek (Feb 7, 2005)

Very probably K2 knows from experience, as he has lot with small engines.

I never seen them published either.

BG


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## k2skier (Sep 30, 2008)

Tecumseh manual says nothing about compression or numbers. It's an 85cc engine with a 2.09" bore and 1.5" stroke. It has a compression release hole right about the exhaust ports; so depending on how hard you pull, whether or not the compression release hole is open and your compression gauge (they all differ slightly) you could get anywhere from 50-120 PSI. Most 2 cycles will run just fine in the 75-85 range as they have lower compression ratios than 4 strokes.


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## skipper0802 (Dec 2, 2010)

Definitive enough for me. Thanks k2.


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## skipper0802 (Dec 2, 2010)

New information:

Hope everyone's holidays were enjoyable. My compression gauge shows 70-75 after a few good pulls on the starter. These readings aren't too low I hope? I know the double reed type valve plays a part during start-up.

Here's this issue: my engine can't develop power/higher rpm. In testing, I bypassed the air vane governor with a rubber band; holding the throttle at the low idle position. The engine idles fine but as soon as I open the throttle the engine bogs down like it's fuel- starved. I've turned the main needle in and out but this doesn't seem to affect. Additionally, the engine will occasionally backfire through the carburetor when trying to open the throttle.

I suspect a fuel flow problem, i.e. debris at the main needle preventing fuel flow. I also suspect an improperly gapped spark plug?

Thoughts anyone?

Thanks,
-Eric


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## jrrdw (Jun 26, 2010)

Sounds like the carb needs a good cleaning, then re-adjust. The backfiring can come from out of adjustment, (carb). Contaminated fuel, partly sheared flywheel key. Your fuel/air adjustment needles have to be in good shape, no grooves, bent or broken tips, clean.


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## skipper0802 (Dec 2, 2010)

Thanks JR,
I'll check the carb again.

-Eric


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