B&S V twin 25hp starting issue

There is a early 2000's Poulan mower at the farm. Only gets used maybe 10hrs a year when I am there the past several since my Dad passed and Mom has someone come and mow.

Couple of years ago it was not wanting to turn over vigorously on a cold start and I'd have to open the hood and give it a little help to get rolling.

Took it home with me last summer to diagnose. Plus cable was not too great looking so I replaced that with some 4WAG welding cable I had available (original starter cables on this look like 6AWG). Seemed to help so it went back to the farm.

Used it at the farm and the problem was back. Battery at that time was 2yrs old and barely used.

2 weekends ago I tried to get it running and brought a 2nd battery with me. Tried both and with the booster charger on the battery too. No go. It turns and when it hits the compression the starter does not have enough torque to pull it through. This time I felt the cable from the solenoid to the starter and it was warm after a few attempts (another 6AWG cable).

So, for this weekend trip down there, I got a new battery and a 4AWG cable to go from the solenoid to the starter.

Same exact symptoms. It does not have enough torque to pull through the compression stroke. Giving it some manual help by just twisting the top of the flywheel it got past and when turning was spinning fast enough to fire up. Warm restarts were no issue.

The next day, cold start same problem.

3 different batteries (1 brand new) behave the same. Plus cable from battery to solenoid and from solenoid to starter replaced with heavier ones.

All that is left here is the negative cable to the frame, the solenoid, and the starter. When it would not pass through the compression on several attempts in a row, I felt the solenoid and not warm.

Negative cable looks clean, not corroded. Maybe the attachment at the frame is bad, but cannot see in there.

Any ideas? Do these B&S starters go bad?

As an aside, this engine is leaking oil on the bottom seal, I think the deck clutch under there slips under load from the oil.

Adjust the valves.
The engine has compression release during starting. A mechanism cracks a valve open just enough to release compression during starting.
Had same problem. Been there done that. After adjusting the valves, now spins right over and starts easily.

adjust the valves

Just add that on my single cylinder Briggs the compression release is built into the cam so you may not see it.

Find TDC on #1 cylinder then move past TDC 1/4-3/8 of an inch more in the direction of travel and adjust valves to .004 on intake and .006 on exhaust. Then do the same for #2 cylinder also. This
was a common problem on the greens mowers with the 25 hp V-twin Briggs engines at golf course where I worked. When the valve clearance is not correct the compression release doesn't work and the starter can't handle the cylinder under compression load.

Thanks all... Never thought about valve adj and compression release. My small engine experience is all with much smaller ones. I will have to check into this.

This reminds me that Dad once had this engine worked on. I think he ran some E85 in it (a no-no from what I have read) and that caused some valve damage. The shop did some work on those valves and maybe they never got it adj quite right and/or the clearances have worn since then.

Was at the farm this weekend. One task to check/adj the valves on this mower. Watched about 1/2 dozen u-tube vids on doing it with this series of engines.

Some internet lore was I needed a T30 torx to turn the adj screw and a 13mm for the lock nut.

At least on this example, the screws take a T40. A 30 works but sloppy when trying to hold the screw from turning while tightening the nut.

I brought my usual feeler gauge with but turned out it didn't have anything thinner than a .009. Fortunately, there was one at the farm that had the right sizes.

These adj are sure touchy!!! The thread pitch on those screws is pretty fast so its hard to get the clearances right w/o several attempts.

BUT, this sure fixed the issue. Turns over nice and fast now!

Its been really dry there the past few weeks so it was hard to find any grass worth mowing to test the mower.

Thanks all again.