Cub 1641 Backfire/Pop Through Carb

ggloob · Jul 11, 2015

Hi and thanks for reading,

I was mowing the lawn and the motor started to sound like it was missing, then stalled. I pushed it into the shed, removed the air cleaner, and the plate the air filter sits on was very wet with gas. It runs but misses, pops, backfires (but with no flames). It does not seem random. It has kind of a pattern to it. Any idea what would be causing this?

Thanks!!!

RandyT · Jul 11, 2015

You are running on one cylinder. Could be a spark plug wire shorting out, faulty plug, valve clearance issues. Just will need to start checking out things.

ggloob · Jul 11, 2015

Thanks for the quick reply! It says 16 Hp on the air cleaner but no brand of motor. Any idea who make it?

Thanks Again!

Leejohn · Jul 11, 2015

Don't overlook the flywheel keyway.

Bob_Bainbridge · Jul 12, 2015

ggloob said:
Thanks for the quick reply! It says 16 Hp on the air cleaner but no brand of motor. Any idea who make it?

Thanks Again!

It's probably a Briggs & Stratton engine. It could be a blown head gasket.

Bob B.

RandyT · Jul 12, 2015

From the short video I can confirm that it is the Briggs Vanguard engine. Model type and code will be either on a tag on the blower housing, or stamped into one of the valve covers. The vanguards will bend a pushrod now and again for no apparent reason, so that may be the issue.

ggloob · Jul 12, 2015

So...to close, and not to leave this post open and unfinished (I hate it when people do that).
RANDYT..You were right!!!
And here is the reason:
You can see the front rocker pivot was installed backwards.

And this was the result.

So I inspected the other cylinder, and both pivots were installed backwards! My neighbor bought this at a garage sale for a song and a dance. The seller said the top end was just rebuilt. I'm willing to bet that they just replaced the valve seals and screwed things up putting everything back together. I'm surprised he could even drive it off the trailer, let alone finish mowing half of his lawn. I think 4 new push rods and he will be back in business.
You folks are the best! Thanks for the guidance!!!

GG