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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 25631
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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I have a 21 hrp briggs platinum engine , It wouldnt start

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I have a 21 hrp briggs platinum engine , It wouldn't start . the starter would only turn the fly wheel 1 revolution . so I stsrted with a new battery nothing changed , then went with a new starter ,nothing . so then a bought another battery 300amps instead of 230amps . same thing is going on ... took out the spark plug and it will turn all day long .. Too much compression im thinking ... what to do ? please help ..

Curtis B. :

Welcome to JUST ANSWER small engines, let me try to help you !!

Curtis B. :

Check compression, and if it is over 100 psi, the compression release is not working.

Customer: How do I do that , can I get a compression tester at auto zone .. Is there a pressure release button on the engine anywhere
Curtis B. :

What is the model number of the engine ? example(NNN) NNN-NNNNB1

Curtis B. :

There is no pressure release, if it is the engine I think it is , the release is on the camshaft gear. You can try adjusting the valves. Intake at .003 to .005 in. and .005 to .007 inch on exhaust.

Customer: 917.28852 that's the # XXXXX my owners manual
Curtis B. :

You can get compression gage at autozone, they may even rent them, Or harbor freight.

Customer: How do you adjust the valves , should even test for the psi or just adjust the valves
Curtis B. :

Try the valves first, remove the OHV cover, four bolts and the valves will be exposed.

Customer: I also seen online when I bought the new starter that a 18hrp motor on down should have a 14 tooth starter and 19 on up should have 16 tooth , my engine is 21 hrp with a14 tooth starter . Could that be the issue ?
Curtis B. :

No, starter is not going to be issue, you know the starter spins engine with spark plug out. So starter matches flywheel.

Customer: Ok trying the valves now , I have to go pick up a set of feeler Gage's , I left mine on a crane
Curtis B. :


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