15.5 hp B&S riding mower motor - backfiring and not wanting to start

[RobertC]

Hey Folks,

Thought this might should go in the B&S thread, but it has more than two wheels !

Went out today to try to blow some leaves around, and cut some tall weeds with my riding mower....

The 15.5 hp B&S motor on our Poulan riding mower - was turning over fine, but was backfiring and not wanting to start.

I believe it is getting gas, as i could smell it when i had it choked..

It did this in warm weather also. When trying to start this past summer/fall you could choke it, turn it over a few times, then to start it, you had to move the throttle to about 80 % of mowing power...and it would start, but would occasionally backfire while trying to start.... but it would eventually start.

Well today, it turned over fine, and backfired often :doah: , but would never start ?

Any ideas what could be causing this ?

Thank you for your help.

RobertC

 

[trailbronc]

possibly points depending on how old it is:shrug:

 

[gumpit]

Dirty carb? How about the air filter? Ever clean it?

 

[RobertC]

possibly points depending on how old it is:shrug:

Thanks trailbronc...I bought my mower used (another Craigslist find !), so i dont' know exact year, but it's probably less than 6 or 7 years old i'd say....(I can go out in daylight and find the model and s/n #'s if that helps to determine.)

Given that approx age would it have points, or some sort of 'electronic' ignition ?

 

[buckeye]

It's the valves needing adjustment. Mine does the same thing. About every third or 4th mow. Biatch will barely turn over and won't start. Pain in the butt.

 

[trailbronc]

nope...not old enough to have points:shrug: could be valves like buck said though...

 

[RobertC]

Dirty carb? How about the air filter? Ever clean it?

Hey Gumpit, thank you for the ideas..i'm just now trying to figure it out, and kinda was looking for some general possibilities to look at.

I know i'll for sure try cleaning the air filter first (it probably needs it anyway).

Then to either eliminate or implicate the carburetor.... I'll try to squirt some gas directly in the cylinder heads to see if it will fire correctly (I think this vertical shaft motor has horizontal cylynders, so have been wondering if i squirt gas in there how do i keep it from just pouring out before i put the plug in :shrug: or will enough of the gas lay low enough in the sides of the cylinder heads to fire ?

I'll see what happens w/ these two ideas, and the points / ingnition ideas trailbronc has, and any others that folks offer up...I am determined that with the advice i get here, i'll be able to get it figured out, and learn more while i'm at it.

Thanks again, and hey, how is your arm Gumpit ? I hope you are on the mend, and feeling better.

Robert

 

[RobertC]

It's the valves needing adjustment. Mine does the same thing. About every third or 4th mow. Biatch will barely turn over and won't start. Pain in the butt.

Thank you Buckeye...had a couple of other replies from some other nice folks too :thumbsup: , but the way you answered sounds like you know exactly what it's doing :hammer: .

Is that valve adjustment something an aspiring apprentice ( I aspire to be one :laugh: ) can do on my own...with some advice, and a few technical documents of course ?

Thanks,

Robert

 

[buckeye]

Pretty easy.
Take the valve cover off. Turn the engine by hand until the exhasut valve is open. Set the intake valve at .004-005.
Turn the engine by hand until the intake valve is open. Adjust the exhaust valve to about .006-.007.

Need a I think 10mm box wrench and the apprptiate star screwdriver.

Search utube for adjusting valves on briggs ohv engine. I've done it at least a hundred times.
I don't know why mine keeps coming out of adjustment but, they do.

The numbers a I gave you work for mine.18hp briggs intec.

 

[fiero377ci]

flywheel key is your prob. drop flywheel on then insert key, NOT key then flywheel.

 

[Bill Ellerby]

Briggs likes to use blue type lock tight on the adjustable valves to keep them tight. When I adjust mine and can't get it just right I usually remove the whole adjustment nut and use a propane torch to help lossen the lock screw. Then reinstall and set the valves and tighten the lock real good. Haven't had any issues yet, but if you do just use some blue lock tight. Good Luck Buy the way I use the blue type on all my rod end bolts and head bolts and never had any come lose.

 

[grandpa ray]

i go along with the flywheel key .they will partially sheer sometimes if the motor backfires .also a new sparkplug wouldn,t be a bad idea

 

[RobertC]

Thank you Trailbronc, Gumpit, Buckeye, fiero377ci, Bill Elerbe, and grandpa ray, and anyone i have missed.

I sure appreciate the suggestions. I was busy working yesterday, and at the gym, so did not have time to try any of these, but i definately have some good ideas of what to check thanks to you all.

It may be the weekend before i get to tear in to it, but i will let you all know what i find.

Thank you again :thumbsup: .

Robert C

 

[RobertC]

Hey Folks,

Just wanted to check back in regarding this issue.

Everything went dormant after my last post and I became less motivated to get the yard cut, I guess I went dormant too, regarding this issue anyway.

Recently got motivated on this issue, did some reading, and what was most helpful was watching two different videos on valve adjusting 15.5 ohv b and s motors, first was by smallenginemaster1, and the second by donyboy73..very helpful.

Watched each numerous times such that when I actually did the adjustment, I felt like I had an idea of what I was going...after listening do donyboy73 vid, even had a better idea of why they are to be set at which tolerance, and resisted the urge to overtighten them.

Got it to start finally, but would still like it to start up as fast as those guys did on the videos....gonna watch some other ones with related symptoms to see if i can get mine to be one of those motors that starts up right away though, as mine still turns a number of times before starting and will still backfire...but once started, it runs great.

Thanks for everyone's encouragement, and advice !

 

[buckeye]

Valves!

Thanks for getting back.:thumbsup:

 

[RobertC]

Valves!

Thanks for getting back.:thumbsup:

Hey Buckyeye,

For sure...it's alway's nice to know what happened when someone asked for advice.

The weather got cool here back in december, and I let that and the fact that I was initially intimidated by the 'sound' of the fix put me off for a while...you know the mentality.... I thought valve adjustment=rocket science :laugh: !

Your reply and encouragment (as well as that from the other folks) helped me to think it was something I could probably figure out...and I did...Thanks again :thumbsup: .

Robert

 

[buckeye]

:thumbsup:
That is exactly what mine did amd still does occasionally. Just pop the valve cover off and adjust them again. Takes me about five minutes now compared to the 2 hours it took the first time.
These things aren't as hard as we overthink them .

 

[Bill Ellerby]

When I adjust my Briggs Inteks it calls for backing it off top dead center by a 1/4". So I use a popsicle stick that I put two marks on. The first mark is TDC and the second mark is 1/4" from that one. When adjusting you can by mistake adjust it on the wrong stroke. So after adjusting I rotate it again to TDC and check the rocker arms. If they are real tight no slack the valves were adjusted on the correct stroke.

 

[RobertC]

:thumbsup:
That is exactly what mine did amd still does occasionally. Just pop the valve cover off and adjust them again. Takes me about five minutes now compared to the 2 hours it took the first time.
These things aren't as hard as we overthink them .

Hey Buckeye, yes, after the first couple times, it is something I can do much faster, and with more confidence.

And like i said earlier, thanks for the encouragement :thumbsup: .

The overthinking part though....it's got me again...I think...:doah:...I'm going to start a new thread about my (new to me) VT-8 and it's inconsistent spark....been reading Sticky by ThrownRod on big block tecumseh coil not firing, and i'm thinking that may be my issue, so i've reread the thread a number of times, and he's talking about flywheel removal, and flywheel magnet positioning, and :grind: on and :grind: on....:shrug:...i've just got to reread it, and then actually go through doing it one step at a time to see if this is my issue, but it scares me, as I feel i'll probably also need to rebuid the carb before it will run also. And thinking i'm opening a proverbial can of worms !....but i figure consistent spark first, fuel delivery second, and small engine repair shop as last resort :laugh: !

I'm goin' out there in a little bit to take the recoil shroud off, so i can see the flywheel keyway as step one, and if that's not it, you'll see my thread, I'll be needing your moral support :laugh: !!

 

[RobertC]

When I adjust my Briggs Inteks it calls for backing it off top dead center by a 1/4". So I use a popsicle stick that I put two marks on. The first mark is TDC and the second mark is 1/4" from that one. When adjusting you can by mistake adjust it on the wrong stroke. So after adjusting I rotate it again to TDC and check the rocker arms. If they are real tight no slack the valves were adjusted on the correct stroke.

Hey Bill,

I like this idea, and I thank you :thumbsup: !

I was using a small screwdriver to touch the piston head, and guestimating where tdc was...once there, i did do the 1/4" from there...but my measurement method was too crude.

I think next time, i'll get me a popsicle stick and do exactly as you described. After a few time's of turning the motor i'll be able to determine which stroke is highest, and can then mark the stick, and keep for future adjustments...that makes the setup part of getting to top dead center plus 1/4" a repeatable process !

Thanks again,

Robert