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Help with B&S IC 17.5 HP OHV engine

Posted by wmshay6 6 (My Page) on
Sun, Jul 20, 08 at 18:22

I just picked up a used (but apparently not abused) MTD lawn tractor with a B&S engine in it. The engine is an I/C engine with OHV 17.5 HP.

I cannot get the engine to start or fire. The engine cranks when connected to my jump starter. I am currently charging the dead battery in the thing. I have spark. I have (new) fuel. I replaced the plug with a brand new one and verified the spark.

Engine cranks just fine, but won't fire. In reading through some of the posts here, it seems my problems could be carb, valves, cam, or a number of things. I don't want to spend a ton of money on this, but am not opposed to buying some parts and doing some work. The mower was completely free so I really have nothing to lose tearing into it, but would like to get an idea of where to start.

Can someone give me some advice as to where to start and what to look for. Fuel is passing through the engine as when I crank and crank and crank, it putters sort of like an old 2-cylinder engine or like an old steam engine. And seems to backfire

I am wondering if that is caused by sticking valves, but not sure how to proceed. I am mechanically inclined, but never worked on much in the realm of small engines.

I have not changed the oil, but topped it off as it was a little low.


Follow-Up Postings:

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RE: Help with B&S IC 17.5 HP OHV engine

"it putters sort of like an old 2-cylinder engine or like an old steam engine. And seems to backfire"

Inspect the fly wheel key.


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RE: Help with B&S IC 17.5 HP OHV engine

fouled plugs ? why not pull the plugs out and see if you can crank it without the plugs in it ... if its flooded you will see excess moister (water / gas) being pushed out of the plugs.

you might want to swap the plug(s).

it sounds as if you could have a big dose of water in the carb bowl ... why not clean the plugs off - pull the air filter and and dump a little raw as down carb body ... see if you can get it to fire up.

if it fires nicely for the first few seconds then I suspect to have a fair amount of water in your carb bowl / fuel system.

get in their clean it out real good - and dont forget to replace the fuel filter - and add one if it doesnt have one.

good luck


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RE: Help with B&S IC 17.5 HP OHV engine

Not to be an idiot Bill- but how do I do that? Is the flywheel under the cowling? Or do I need to pull the head for that? Or is the flywheel on the bottom of the crank?

NJDPO- There is only one plug and it's brand new I did dump fuel in after pulling off the air filter. Engine demonstrated the symptoms I listed above.


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RE: Help with B&S IC 17.5 HP OHV engine

bad plug?
bad coil?
grounded coil?

pull the plug and se if it fires at all. if nto then change the plug. if the new one has no fire then the coil is likely bad or grounded. first see if it is grounded by disconnecting the kill wire to the coil and with the plug out turn the key, if the plug now fires find out why it is grounding the coil. if it still does not then the coil is bad.

could be a bad/missing magnet onthe flywheel, but that one is rare. i have not owned a briggs engine yet that did not have a coil go bad on it. the one on my generator eats coils at a rate of about one per 100 hours.


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RE: Help with B&S IC 17.5 HP OHV engine

The flywheel is under the shroud.
You can down load an IPL from the Briggs website to get an exploded parts view.
http://www.briggsandstratton.com/maint_repair/manual_and_more/


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RE: Help with B&S IC 17.5 HP OHV engine

"could be a bad/missing magnet onthe flywheel, but that one is rare. i have not owned a briggs engine yet that did not have a coil go bad on it. the one on my generator eats coils at a rate of about one per 100 hours"

First off, there is only one magnet on the flywheel that affects ignition.

Second, I have been working with small engines for about 60 years. The only B&s engine I have ever encountered that had regular ignition coil problems were the horizontal twins, 40, 42 and 46 series. Other B&S CDI coils very seldom fail and I would say are among the most reliable in the industry.

If you have one regularly going bad in 100 hours, you have some other problem causing it, probably getting a shot of juice from some extraneous source.

Walt Conner


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RE: Help with B&S IC 17.5 HP OHV engine

Thank you for the advice Bill. Now that I have a little time, I plan to take it apart and see what I can find. I downloaded the IPS from the Briggs site, so I will look at the flywheel in the next few days.


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RE: Help with B&S IC 17.5 HP OHV engine

Sorry Walt, but I had one of the coils fail on a 17.5. Same symptoms. I had a spark so I thought it was OK. Gave up and called a mobile repair guy. He took one look at the spark and said, yeah, you got a spark, but it is much too weak. Put in a new coil and it ran just fine. He showed me the new "spark" and it definitely was a lot brighter with the new coil. Ed


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RE: Help with B&S IC 17.5 HP OHV engine

"Sorry Walt, but I had one of the coils fail on a 17.5."

"Put in a new coil and it ran just fine. He showed me the new "spark" and it definitely was a lot brighter with the new coil. Ed"

Anything made can fail sometimes. The indication was that B&S had very unreliable CDI which is not so.

As for your having spark but weak, there is a good chance if you had just cleaned the contact areas where the coil mounted, you would have been OK. Removing and installing a new coil may very well have accomplished this but then, your tech wouldn't have had the sale of a new coil.

Walt Conner


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